CA1082801A - Fog clearing by microwave power - Google Patents
Fog clearing by microwave powerInfo
- Publication number
- CA1082801A CA1082801A CA274,000A CA274000A CA1082801A CA 1082801 A CA1082801 A CA 1082801A CA 274000 A CA274000 A CA 274000A CA 1082801 A CA1082801 A CA 1082801A
- Authority
- CA
- Canada
- Prior art keywords
- fog
- energy
- parasitic element
- antenna
- aperture
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- E—FIXED CONSTRUCTIONS
- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01H—STREET CLEANING; CLEANING OF PERMANENT WAYS; CLEANING BEACHES; DISPERSING OR PREVENTING FOG IN GENERAL CLEANING STREET OR RAILWAY FURNITURE OR TUNNEL WALLS
- E01H13/00—Dispersing or preventing fog in general, e.g. on roads, on airfields
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
- H01Q19/06—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using refracting or diffracting devices, e.g. lens
- H01Q19/08—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using refracting or diffracting devices, e.g. lens for modifying the radiation pattern of a radiating horn in which it is located
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
- H05B6/72—Radiators or antennas
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Atmospheric Sciences (AREA)
- Engineering & Computer Science (AREA)
- Architecture (AREA)
- Civil Engineering (AREA)
- Structural Engineering (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Aerials With Secondary Devices (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A horn antenna for transmitting electromagnetic energy is combined with a parasitic element in coaxial, spaced relation-ship to define an annular aperture through which the energy is propagated. Radiation patterns occurring in the E and H planes of the antenna combination vary in response to both frequency of the energy and size of the parasitic element and combine to produce predetermined fields of radiation. Embodiments are disclosed which develop an outwardly diverging conical radiation pattern that is useful in fog clearing operations using a minimum of effective radiated power. Similar embodiments may be operated under swept frequency conditions to produce a continually changing radiation pattern that finds utility in radar systems.
A horn antenna for transmitting electromagnetic energy is combined with a parasitic element in coaxial, spaced relation-ship to define an annular aperture through which the energy is propagated. Radiation patterns occurring in the E and H planes of the antenna combination vary in response to both frequency of the energy and size of the parasitic element and combine to produce predetermined fields of radiation. Embodiments are disclosed which develop an outwardly diverging conical radiation pattern that is useful in fog clearing operations using a minimum of effective radiated power. Similar embodiments may be operated under swept frequency conditions to produce a continually changing radiation pattern that finds utility in radar systems.
Description
10~2~0~
This invention relates to a horn antenna, applications therefor and more particularly to a horn antenna having adjustable direct:ional characteristics.
~lorn antennas are commonly used in microwave applica-tions because they provide a convenient and simple way in which to direct and propagate electrical energy at high frequencies.
Common examples may be seen in radar systems, microwave communi-cation links, and dielectric heating systems to name but a few applications. In each of these cases, microwave energy may be transmitted from a horn antenna and propagated through a predeter-mined medium in a particular pattern that is selected to suit the application. In radar and communications link applications, the horn antenna forms part of a greater antenna system and is often used to direct energy from a focus to the surface of a parabolic reflecting surface in order that the energy be radiated substantially as a parallel beam. On the other hand, a horn antenna may be used in dielectric heating applications to form a diverging beam which is required to cover a maximum volume, preferably with a simple energy radiating apparatus.
Fog conditions generally constitute a serious threat to safe navigation. Various attempts have therefore been made in the past in an effort to solve the problem of fog dispersal.
These attempts include evaporation by heating the fog with the exhaust from jet engines, microwave energy and chemical reagents.
Other methods include enlargement of drops for precipitation by chemical, electrical and acoustic means, mechanical impaction, mechanical air circulation, e.g. by helicopters, exposure to lasers and infrared radiation, seeding with hygroscopic agents and ultrasonic techniques. All of these methods have been applied to warm (radiation and advection), cold and ice fogs.
The foregoing attemps have met with only limited success ~3~
1~)8280~
due to low efficiency, complexity, high cost or excessive time delay in dispersing the fog to obtain adequate visibility.
In particular, a microwave heating technique described in U.S. patent no. 3,606,153, which issued on September 20, 1971, to R.M.G. Boucher, has several drawbacks. Firstly, the technique applies only to very low density fog, i.e., of the order of 7 gms of water per 100 cubic m. Also, with regard to passenger ex-posure to microwave energy and its attendant health hazard, Boucher indicates that an energy output of 10 mw/cm is acceptable and, moreover, that the aircraft will act as a shield so that the passengers will not even be subjected to this radiation level.
According to latest criteria, radiation exposure to humans should not exceed 1 mw/cm2. Unless the aircraft had no windows to admit radiation, it is believed that radiation exposure using Boucher's proposal would exceed the aforementioned currently acceptable level.
Apart from radiation hazards, it would appear that the greatest drawback of Boucher's proposal is the very large number of radiators and reflectors which are required. Not only does the system become expensive to construct, but it becomes more technically complicated in view of the extensive transmission system required to couple the microwave energy from a source to each radiating element.
A provision of the present invention is an embodiment thereof and a method of operation which substantially overcomes the difficulties inherent in known fog clearing systems.
The invention also provides an embodiment having an adjustable aperture and which exhibits utility in radar surveil-lance and guidance systems.
The disadvantages and problems of the prior art may be substantially overcome and the foregoing provisions achieved by - :. ;:.
10~01 recourse to the invention which relates to a horn antenna. The antenna comprises a radiating element having an input end adapted to be coupled to a source of microwave energy and conductive sidewalls diverging longitudinally therefrom and terminating in an output aperture. A parasitic element is provided which has an apex and conductive sidewalls diverging longitudinally therefrom and terminating in a base. The parasitic element is coaxially aligned with the radiating element and is spaced therefrom to define an annular aperture through which the energy is propagated. , The invention also relates to a method for clearing fog which comprises the step of downwardly circulating the fog over an area to be cleared so that the lower layers of the fog are warmed by friction, compression and downwardly moving fog to a condition where the relative humidity drops below 100 percent and the fog is sufficiently dissipated.
The invention will now be more particularly described with reference to embodiments thereof shown, by way of example, in the accompanying drawings wherein:
Fig. 1 is a diagrammatic perspective view of one embodi-ment of the invention;
Fig. 2 is a side elevation view of another embodimentof the invention;
Fig. 3 is a sectional view taken along the lines 3-3 of Fig. 2; and Figs. 4(a), (b) and (c), are graphs indicating energy radiation patterns of E and H planes in the embodiment illustrated in Fig. 2.
It is well-known that condensation always occurs in natural air whose dew point (Td) even slightly exceeds the temper-ature (T). Two processes act to prevent supersaturation and fogformation. First, in the case of a cold surface, the turbulent ~()8Z~01 eddies which transfer heat downward may also transfer water vapour downward. Second, the hygroscopic nature of the earth's surfac,e results in a decrease in the dew point below the temper-ature even at the surface. In spite of these factors, several processes help to bring about supersaturation and fog formation such as mixing of saturated air at different temperatures and vapour densities, radiative flux divergence might cause T to drop below Td, adiabatic cooling associated with upward motion or falling pressure, condensation on hygroscopic nuclei below 100% humidities (e.g. smog), etc.
The apparatus and method of the present invention are most applicable to a radiation fog where the humidity may remain at 100~ up to a typical height of 1000 feet and beyond that drops below 100% (i.e. a knee in the curve is at 1000 feet above the ground). The corresponding values of Td and T may typically remain at 40F and then drop around the knee to typically 37F
and 38F, respectively (see standard tephigrams). For such type of fog it would be desirable to create a downward circulation of the fog above the runway so that the lower layers of the fog are warmed by friction, compression and downward moving fog to the point where the humidity drops to say 99~. The method therefore is to heat the fog in a pattern defining an upwardly diverging conical surface about the airport so that the upward circulation of fog along the conical surface results in a downward flow of fog from the upper layers towards the tip of the cone. For most radiation fogs, a mere evaporation of 1 gm/m3 of water droplets along the conical surface would be sufficient to create the desirable fog circulation. Although the total power required for this fog density by Boucher's method is 14 megawatts at 2.45 GHz, it is estimated that 0.5 megawatts with a single antenna would be adequate by the present method due to the nature of fog circulation 108Zl~01 created. Two embodiments of a horn antenna suitable for the method of the present invention are shown in Figs. 1 and 2.
The embodiment in Fig. 1 is a horn antenna 10 which is illustrated in a diagrammatic perspective view in order to show its pr:incipal structural features as well as a radiation pattern 12 of microwave energy which is important to the operation of the invention. It will be seen that the antenna 10 comprises a pair of concentric cones that are coaxially aligned with an inner cone fitting inside the outer cone. The outer cone comprises a radi-ating element 13 having an input end that is adapted to be coupled to a source of microwave energy (not shown) via a rectangular-to-circ~lar waveguide adapter 14 of which only a portion is shown.
The inner cone is a parasitic element 15 which is coaxially a-ligned with the element 13 and is spaced therefrom to provide the configuration shown. Both elements are defined by conductive sidewalls which may be constructed of either solid sheet stock or open stock such as wire mesh screens. The angle ~ of the elements 13 and 15 is the same so that the sidewalls are always substantially parallel.
The cone angle B of the elements 13and 15 is shown fixed in the illustration of Fig. 1. It is, however, to be understood that the angle may be variable, with adjustment being effected to any desired angle using the umbrella principle. The cone angle ~ is determined by means of a fog density sensor (not shown) which is located at the end of a directional coupler in a feed waveguide (not shown) so as to monitor reflected power which controls servo equipment (not shown) that is designed to position the surfaces of the antenna elements in real time. In all cases, the cone angle ~ increases during the defogging process.
For supersaturated fogs,the parallel conical surfaces of the elements 13 and 15 may be driven from a source of radio 1~)821~01 frequency energy operating at a suitable frequency depending on the actual situation. In this case, the length of each of the elements 13 and 15 must be an appreciable fraction of the wave length. For example, at 13 MHz this would be approximately 10 m.
Microwave energy is transmitted from an annular output aperture 18 of the antenna 10 in the outwardly di-verging conical radiation pattern 12. The energy heats the fog laden air dielectrically and causes it to rise upwardly between the elements 13 and 15 in the direction of the arrows and into the atmosphere along an extension of their surfaces which comprises the pattern 12. This results in a downward axial flow of fog laden air towards the apex of the element 15.
The power output of the antenna is maintained at a low value in order to minimize the danger of exposure to humans.
In airport applications, a single antenna of the type illustrated in Fig. 1 may be located off the centre of a runway and will be sufficient to dissipate fog dispersed within the pattern 12.
Since the antenna need only be erected as required, the hazard of collisions with aircraft is minimized. The hazard is removed altogether if the antenna 10 is mounted with its output aperture end flush with the ground. In this event, the antenna may be raised when required or maintained flush with the ground by containing the antenna in a pit and closing the opening of the pit with a cover that is substantially transparent to the microwave energy. In this connection, it will be noted that a base 19 of the element 15 is in a plane defined by the output aperture of the element 13 which facilitates a flushmounting arrangement.
Another embodiment of the invention is shown as a horn : . : - -~ .. . . .
108Z80~
antenna 11 in Fig. 2. It will be noted that the structure of the ant:enna 11 is generally similar to that of the antenna 10, a principal difference being the manner in which the parasitic element: 15 is mounted. Unlike the antenna 10 wherein the element 15 is contained wholly within the element 13, a corresponding parasitic element 16 in Eig. 2 extends outwardly of a radiating element 17. It will be observed that the element 16 is coaxially aligned with the element 17. Furthermore, the apex of the ele-ment 16 extends in the direction of energy propagation and a base 19' thereof is disposed substantially in a plane defined by the output aperture of the element 17. It should be understood that whereas the base 19 of the element 15 in Fig. 1 may be either open or closed, the corresponding base 19' of the element 16 in Fig. 2 is open.
The spacing arrangement of the elements 16 and 17 is such that an annular aperture is defined through which the micro-wave energy is propagated. This is similar for the antenna 10 even though the position of the parasitic element 15 differs from its counterpart in the antenna 11. A common feature, however, is to be noted in this regard, that the base of each parasitic element is disposed substantially in a plane defined by the output aperture of the radiating element.
The antenna 11 has been operated in the x-band for experimental purposes (i.e. 8.4-12 GHz) and was excited in the TEll mode, since it was fed from a rectangular waveguide 20 operating in the TElo mode followed by a rectangular-to-circular waveguide adapter 21. The waveguide 20 is thus coupled to an input end of the adapter 21 and is mechanically connected thereto by means of a flange assembly 22. The output end of the adapter 21 is mechanically connected via a flange assembly 23 to the input end of the conical horn 17.
~0~
The angle ~ in both elements 16 and 17 may be adjusted as described for the antenna 10. However, in the embodiment il-lustrated, the angle is fixed at 30.
Means for mounting the element 16 in the manner illus-trated is provided by way of a support 24, a cross-sectional view of which is illustrated in Fig. 3. The support 24 in the embodiments of Figs. 2 and 3 is fabricated of acrylic plastic, but any other suitable material may be used provided that it is substantially transparent to the microwave energy.
An enlarged sectional view of the support 24 is shown in Fig. 3 in order to more accurately depict its mountir.g features.
For example, it will be noted that the support 24 includes an annular recess 25 having one tapered sidewall 25' that corresponds to the angle of the sidewalls of the element 17. The recess 25 thus fits over the peripheral edge of the element 17 which defines the output aperture and is held in place by mechanical friction. In a similar fashion, a passage 26 is formed coaxially with the support 24 and is provided with tapered sidewalls 27 that correspond to the angle of the sidewalls of the element 16.
The aforenoted structure of the support 24 is partic-ularly convenient since it not only serves to mount the parasitic element but also acts as a cover to prevent entry of foreign objects into the antenna 11. Although shown only for the antenna 11, the same principles of construction apply to a corresponding support for the antenna 10.
In tests conducted using the antenna 11, two different sizes of the parasitic element 16 were employed. Each parasitic element was cone shaped as illustrated with an open base 19' disposed substantially in the plane defined by the output aper-ture of the element 17. A small size element 16 was used having a base diameter of 1.25 inches and an overall length of 2.48 1()8Z801 inches. The larger element 16 had a base diameter of 1.75 inches and an overall length of 3.38 inches. The element 17 was used with both elementq 16 and had an aperture diameter of 2.75 inches to which was fitted a separate support 24 for each of the small and large elements 16.
It was previously described that the antenna 11 was excited in the TEll mode. Since this mode is not symmetrical in the azimuth and elevation planes, different radiation patterns were noted in both E and H planes for different frequencies and sizes of the parasitic element.
The salient feature of the antenna 11 is that at a certain frequency within the passband, a main lobe observed along the axis in the absence of the element 16 (i.e. for a conical horn antenna) practically disappears or is significantly reduced in intensity allowing at the same time the first side lobe (one on each side of the main lobe) to significantly increase in both the azimuth and elevation planes. This leads to the radiation pattern 12 as described for the antenna 10 which is desirable in fog clearing operations.
At other frequencies, an opposite condition occurs, i.e., the main lobe is revived to even a slightly higher value than for the conical horn antenna, thus increasing antenna gain, while the side lobe practically disappears. Since frequency switching or sweeping is known in the art, the appearance and disappearance of the main lobe with frequency variations (with the opposite behaviour for the first side lobe) is a feature of significant interest in radar surveillance and guidance systems.
The graphs shown in Figs. 4(a), (b) and (c) are plots of radiation patterns recorded in both E and H planes at differ-ent frequencies and sizes of the element 16. It will be observed . .
~0~2~0~
that each graph includes four curves. Each one of the curves characterizes the forward gain of the antenna 11 with respect to an angular distribution of radiated energy expressed in degrees of azirnuth angle.
The four curves of each graph are shown in pairs of two, one pair having an apparent greater amplitude than the other.
The greater amplitude curves represent radiation in the H plane, whereas the lower amplitude curves represent radiation in the E
plane. It is to be understood that there is no intention to convey a relationship between the H and E plane curves, the graphs being depicted in this manner merely as a matter of con-venience. Accordinsly, the greater peak amplitude value for each pair of curves represents substantially the same power output in all cases.
The plots in Fig. 4(a) were taken at a frequency of 9.6 GHz with and without the element 17. The curves 30 and 31 were plotted in the H plane, the curve 31 resulting when the element 16 was placed in cooperative relationship with the ele-ment 17 as indicated in Fig. 2. Curves 32 and 33 on the other hand represent plots in the E plane. Some change in azimuth angle was noted with and without the element 17. The curve 33 resulted when using the element 17.
In Fig. 4(b), the plots were taken with and without a large element 17, having dimensions as previously noted, and at a frequency of 11.51 G~z. Curves 34 and 35 are H plane curves, curve 35 being obtained when the element 16 was used in cooperative relationship with the element 17. The curves 36 and 37 are E
plane curves, the curve 37 obtaining with the element 16 in position as noted.
The plots of Fig. 4(c) were obtained with and without a large element 16 while operating the antenna 11 at a frequency .
~IU8Z~01 of 8.26 GHz. An improvement in antenna gain is noted in this figure by the H curves 38 and 39, the curve 38 being obtained when the element 16 was used. A corresponding increase in gain may be! seen in the E plane curves 40 and 41, the curve 40 resulting when the element 16 was used.
In view of the plots shown in Fig. 4, it is apparent that in some applications it would be desirable to vary not only the frequency but also the size of the parasitic element, but with the base of the parasitic element always remaining in the plane of the output aperture of the element 17. With regard to the latter variable, two possibilities are proposed for its achievement but are not illustrated.
The first is to use a pre-formed rubber cone coated with conducting material for the parasitic element 16 and to vary its size by inflating or deflating it from a gas bottle.
The base 19' of the element 16 is maintained coaxially with the aperture of the element 17 by means of thin radial rubber lines under tension which may be employed to join the base to the peripheral edge defining the output aperture. The second approach relies on the aforementioned umbrella principle. In this case, the cone is also made of rubber coated with conducting paint and is held by spokes which are opened or folded by a crank connected to mechanical elements similar to those of an umbrella.
Although the antennas 10 and 11 have been described as generally conical structures, it should be noted that tetrahedral structures may also be used to obtain similar results.
It willbe apparent to those killed in the art that the preceding description of the embodiments of the invention may be substantially varied to meet specialized requirements without departing from the spirit and scope of the invention disclosed. The foregoing embodiments are therefore not to be ~08Z~01 taken as limiting but rather as exemplary structures of the invention which is defined by the claims.
..
This invention relates to a horn antenna, applications therefor and more particularly to a horn antenna having adjustable direct:ional characteristics.
~lorn antennas are commonly used in microwave applica-tions because they provide a convenient and simple way in which to direct and propagate electrical energy at high frequencies.
Common examples may be seen in radar systems, microwave communi-cation links, and dielectric heating systems to name but a few applications. In each of these cases, microwave energy may be transmitted from a horn antenna and propagated through a predeter-mined medium in a particular pattern that is selected to suit the application. In radar and communications link applications, the horn antenna forms part of a greater antenna system and is often used to direct energy from a focus to the surface of a parabolic reflecting surface in order that the energy be radiated substantially as a parallel beam. On the other hand, a horn antenna may be used in dielectric heating applications to form a diverging beam which is required to cover a maximum volume, preferably with a simple energy radiating apparatus.
Fog conditions generally constitute a serious threat to safe navigation. Various attempts have therefore been made in the past in an effort to solve the problem of fog dispersal.
These attempts include evaporation by heating the fog with the exhaust from jet engines, microwave energy and chemical reagents.
Other methods include enlargement of drops for precipitation by chemical, electrical and acoustic means, mechanical impaction, mechanical air circulation, e.g. by helicopters, exposure to lasers and infrared radiation, seeding with hygroscopic agents and ultrasonic techniques. All of these methods have been applied to warm (radiation and advection), cold and ice fogs.
The foregoing attemps have met with only limited success ~3~
1~)8280~
due to low efficiency, complexity, high cost or excessive time delay in dispersing the fog to obtain adequate visibility.
In particular, a microwave heating technique described in U.S. patent no. 3,606,153, which issued on September 20, 1971, to R.M.G. Boucher, has several drawbacks. Firstly, the technique applies only to very low density fog, i.e., of the order of 7 gms of water per 100 cubic m. Also, with regard to passenger ex-posure to microwave energy and its attendant health hazard, Boucher indicates that an energy output of 10 mw/cm is acceptable and, moreover, that the aircraft will act as a shield so that the passengers will not even be subjected to this radiation level.
According to latest criteria, radiation exposure to humans should not exceed 1 mw/cm2. Unless the aircraft had no windows to admit radiation, it is believed that radiation exposure using Boucher's proposal would exceed the aforementioned currently acceptable level.
Apart from radiation hazards, it would appear that the greatest drawback of Boucher's proposal is the very large number of radiators and reflectors which are required. Not only does the system become expensive to construct, but it becomes more technically complicated in view of the extensive transmission system required to couple the microwave energy from a source to each radiating element.
A provision of the present invention is an embodiment thereof and a method of operation which substantially overcomes the difficulties inherent in known fog clearing systems.
The invention also provides an embodiment having an adjustable aperture and which exhibits utility in radar surveil-lance and guidance systems.
The disadvantages and problems of the prior art may be substantially overcome and the foregoing provisions achieved by - :. ;:.
10~01 recourse to the invention which relates to a horn antenna. The antenna comprises a radiating element having an input end adapted to be coupled to a source of microwave energy and conductive sidewalls diverging longitudinally therefrom and terminating in an output aperture. A parasitic element is provided which has an apex and conductive sidewalls diverging longitudinally therefrom and terminating in a base. The parasitic element is coaxially aligned with the radiating element and is spaced therefrom to define an annular aperture through which the energy is propagated. , The invention also relates to a method for clearing fog which comprises the step of downwardly circulating the fog over an area to be cleared so that the lower layers of the fog are warmed by friction, compression and downwardly moving fog to a condition where the relative humidity drops below 100 percent and the fog is sufficiently dissipated.
The invention will now be more particularly described with reference to embodiments thereof shown, by way of example, in the accompanying drawings wherein:
Fig. 1 is a diagrammatic perspective view of one embodi-ment of the invention;
Fig. 2 is a side elevation view of another embodimentof the invention;
Fig. 3 is a sectional view taken along the lines 3-3 of Fig. 2; and Figs. 4(a), (b) and (c), are graphs indicating energy radiation patterns of E and H planes in the embodiment illustrated in Fig. 2.
It is well-known that condensation always occurs in natural air whose dew point (Td) even slightly exceeds the temper-ature (T). Two processes act to prevent supersaturation and fogformation. First, in the case of a cold surface, the turbulent ~()8Z~01 eddies which transfer heat downward may also transfer water vapour downward. Second, the hygroscopic nature of the earth's surfac,e results in a decrease in the dew point below the temper-ature even at the surface. In spite of these factors, several processes help to bring about supersaturation and fog formation such as mixing of saturated air at different temperatures and vapour densities, radiative flux divergence might cause T to drop below Td, adiabatic cooling associated with upward motion or falling pressure, condensation on hygroscopic nuclei below 100% humidities (e.g. smog), etc.
The apparatus and method of the present invention are most applicable to a radiation fog where the humidity may remain at 100~ up to a typical height of 1000 feet and beyond that drops below 100% (i.e. a knee in the curve is at 1000 feet above the ground). The corresponding values of Td and T may typically remain at 40F and then drop around the knee to typically 37F
and 38F, respectively (see standard tephigrams). For such type of fog it would be desirable to create a downward circulation of the fog above the runway so that the lower layers of the fog are warmed by friction, compression and downward moving fog to the point where the humidity drops to say 99~. The method therefore is to heat the fog in a pattern defining an upwardly diverging conical surface about the airport so that the upward circulation of fog along the conical surface results in a downward flow of fog from the upper layers towards the tip of the cone. For most radiation fogs, a mere evaporation of 1 gm/m3 of water droplets along the conical surface would be sufficient to create the desirable fog circulation. Although the total power required for this fog density by Boucher's method is 14 megawatts at 2.45 GHz, it is estimated that 0.5 megawatts with a single antenna would be adequate by the present method due to the nature of fog circulation 108Zl~01 created. Two embodiments of a horn antenna suitable for the method of the present invention are shown in Figs. 1 and 2.
The embodiment in Fig. 1 is a horn antenna 10 which is illustrated in a diagrammatic perspective view in order to show its pr:incipal structural features as well as a radiation pattern 12 of microwave energy which is important to the operation of the invention. It will be seen that the antenna 10 comprises a pair of concentric cones that are coaxially aligned with an inner cone fitting inside the outer cone. The outer cone comprises a radi-ating element 13 having an input end that is adapted to be coupled to a source of microwave energy (not shown) via a rectangular-to-circ~lar waveguide adapter 14 of which only a portion is shown.
The inner cone is a parasitic element 15 which is coaxially a-ligned with the element 13 and is spaced therefrom to provide the configuration shown. Both elements are defined by conductive sidewalls which may be constructed of either solid sheet stock or open stock such as wire mesh screens. The angle ~ of the elements 13 and 15 is the same so that the sidewalls are always substantially parallel.
The cone angle B of the elements 13and 15 is shown fixed in the illustration of Fig. 1. It is, however, to be understood that the angle may be variable, with adjustment being effected to any desired angle using the umbrella principle. The cone angle ~ is determined by means of a fog density sensor (not shown) which is located at the end of a directional coupler in a feed waveguide (not shown) so as to monitor reflected power which controls servo equipment (not shown) that is designed to position the surfaces of the antenna elements in real time. In all cases, the cone angle ~ increases during the defogging process.
For supersaturated fogs,the parallel conical surfaces of the elements 13 and 15 may be driven from a source of radio 1~)821~01 frequency energy operating at a suitable frequency depending on the actual situation. In this case, the length of each of the elements 13 and 15 must be an appreciable fraction of the wave length. For example, at 13 MHz this would be approximately 10 m.
Microwave energy is transmitted from an annular output aperture 18 of the antenna 10 in the outwardly di-verging conical radiation pattern 12. The energy heats the fog laden air dielectrically and causes it to rise upwardly between the elements 13 and 15 in the direction of the arrows and into the atmosphere along an extension of their surfaces which comprises the pattern 12. This results in a downward axial flow of fog laden air towards the apex of the element 15.
The power output of the antenna is maintained at a low value in order to minimize the danger of exposure to humans.
In airport applications, a single antenna of the type illustrated in Fig. 1 may be located off the centre of a runway and will be sufficient to dissipate fog dispersed within the pattern 12.
Since the antenna need only be erected as required, the hazard of collisions with aircraft is minimized. The hazard is removed altogether if the antenna 10 is mounted with its output aperture end flush with the ground. In this event, the antenna may be raised when required or maintained flush with the ground by containing the antenna in a pit and closing the opening of the pit with a cover that is substantially transparent to the microwave energy. In this connection, it will be noted that a base 19 of the element 15 is in a plane defined by the output aperture of the element 13 which facilitates a flushmounting arrangement.
Another embodiment of the invention is shown as a horn : . : - -~ .. . . .
108Z80~
antenna 11 in Fig. 2. It will be noted that the structure of the ant:enna 11 is generally similar to that of the antenna 10, a principal difference being the manner in which the parasitic element: 15 is mounted. Unlike the antenna 10 wherein the element 15 is contained wholly within the element 13, a corresponding parasitic element 16 in Eig. 2 extends outwardly of a radiating element 17. It will be observed that the element 16 is coaxially aligned with the element 17. Furthermore, the apex of the ele-ment 16 extends in the direction of energy propagation and a base 19' thereof is disposed substantially in a plane defined by the output aperture of the element 17. It should be understood that whereas the base 19 of the element 15 in Fig. 1 may be either open or closed, the corresponding base 19' of the element 16 in Fig. 2 is open.
The spacing arrangement of the elements 16 and 17 is such that an annular aperture is defined through which the micro-wave energy is propagated. This is similar for the antenna 10 even though the position of the parasitic element 15 differs from its counterpart in the antenna 11. A common feature, however, is to be noted in this regard, that the base of each parasitic element is disposed substantially in a plane defined by the output aperture of the radiating element.
The antenna 11 has been operated in the x-band for experimental purposes (i.e. 8.4-12 GHz) and was excited in the TEll mode, since it was fed from a rectangular waveguide 20 operating in the TElo mode followed by a rectangular-to-circular waveguide adapter 21. The waveguide 20 is thus coupled to an input end of the adapter 21 and is mechanically connected thereto by means of a flange assembly 22. The output end of the adapter 21 is mechanically connected via a flange assembly 23 to the input end of the conical horn 17.
~0~
The angle ~ in both elements 16 and 17 may be adjusted as described for the antenna 10. However, in the embodiment il-lustrated, the angle is fixed at 30.
Means for mounting the element 16 in the manner illus-trated is provided by way of a support 24, a cross-sectional view of which is illustrated in Fig. 3. The support 24 in the embodiments of Figs. 2 and 3 is fabricated of acrylic plastic, but any other suitable material may be used provided that it is substantially transparent to the microwave energy.
An enlarged sectional view of the support 24 is shown in Fig. 3 in order to more accurately depict its mountir.g features.
For example, it will be noted that the support 24 includes an annular recess 25 having one tapered sidewall 25' that corresponds to the angle of the sidewalls of the element 17. The recess 25 thus fits over the peripheral edge of the element 17 which defines the output aperture and is held in place by mechanical friction. In a similar fashion, a passage 26 is formed coaxially with the support 24 and is provided with tapered sidewalls 27 that correspond to the angle of the sidewalls of the element 16.
The aforenoted structure of the support 24 is partic-ularly convenient since it not only serves to mount the parasitic element but also acts as a cover to prevent entry of foreign objects into the antenna 11. Although shown only for the antenna 11, the same principles of construction apply to a corresponding support for the antenna 10.
In tests conducted using the antenna 11, two different sizes of the parasitic element 16 were employed. Each parasitic element was cone shaped as illustrated with an open base 19' disposed substantially in the plane defined by the output aper-ture of the element 17. A small size element 16 was used having a base diameter of 1.25 inches and an overall length of 2.48 1()8Z801 inches. The larger element 16 had a base diameter of 1.75 inches and an overall length of 3.38 inches. The element 17 was used with both elementq 16 and had an aperture diameter of 2.75 inches to which was fitted a separate support 24 for each of the small and large elements 16.
It was previously described that the antenna 11 was excited in the TEll mode. Since this mode is not symmetrical in the azimuth and elevation planes, different radiation patterns were noted in both E and H planes for different frequencies and sizes of the parasitic element.
The salient feature of the antenna 11 is that at a certain frequency within the passband, a main lobe observed along the axis in the absence of the element 16 (i.e. for a conical horn antenna) practically disappears or is significantly reduced in intensity allowing at the same time the first side lobe (one on each side of the main lobe) to significantly increase in both the azimuth and elevation planes. This leads to the radiation pattern 12 as described for the antenna 10 which is desirable in fog clearing operations.
At other frequencies, an opposite condition occurs, i.e., the main lobe is revived to even a slightly higher value than for the conical horn antenna, thus increasing antenna gain, while the side lobe practically disappears. Since frequency switching or sweeping is known in the art, the appearance and disappearance of the main lobe with frequency variations (with the opposite behaviour for the first side lobe) is a feature of significant interest in radar surveillance and guidance systems.
The graphs shown in Figs. 4(a), (b) and (c) are plots of radiation patterns recorded in both E and H planes at differ-ent frequencies and sizes of the element 16. It will be observed . .
~0~2~0~
that each graph includes four curves. Each one of the curves characterizes the forward gain of the antenna 11 with respect to an angular distribution of radiated energy expressed in degrees of azirnuth angle.
The four curves of each graph are shown in pairs of two, one pair having an apparent greater amplitude than the other.
The greater amplitude curves represent radiation in the H plane, whereas the lower amplitude curves represent radiation in the E
plane. It is to be understood that there is no intention to convey a relationship between the H and E plane curves, the graphs being depicted in this manner merely as a matter of con-venience. Accordinsly, the greater peak amplitude value for each pair of curves represents substantially the same power output in all cases.
The plots in Fig. 4(a) were taken at a frequency of 9.6 GHz with and without the element 17. The curves 30 and 31 were plotted in the H plane, the curve 31 resulting when the element 16 was placed in cooperative relationship with the ele-ment 17 as indicated in Fig. 2. Curves 32 and 33 on the other hand represent plots in the E plane. Some change in azimuth angle was noted with and without the element 17. The curve 33 resulted when using the element 17.
In Fig. 4(b), the plots were taken with and without a large element 17, having dimensions as previously noted, and at a frequency of 11.51 G~z. Curves 34 and 35 are H plane curves, curve 35 being obtained when the element 16 was used in cooperative relationship with the element 17. The curves 36 and 37 are E
plane curves, the curve 37 obtaining with the element 16 in position as noted.
The plots of Fig. 4(c) were obtained with and without a large element 16 while operating the antenna 11 at a frequency .
~IU8Z~01 of 8.26 GHz. An improvement in antenna gain is noted in this figure by the H curves 38 and 39, the curve 38 being obtained when the element 16 was used. A corresponding increase in gain may be! seen in the E plane curves 40 and 41, the curve 40 resulting when the element 16 was used.
In view of the plots shown in Fig. 4, it is apparent that in some applications it would be desirable to vary not only the frequency but also the size of the parasitic element, but with the base of the parasitic element always remaining in the plane of the output aperture of the element 17. With regard to the latter variable, two possibilities are proposed for its achievement but are not illustrated.
The first is to use a pre-formed rubber cone coated with conducting material for the parasitic element 16 and to vary its size by inflating or deflating it from a gas bottle.
The base 19' of the element 16 is maintained coaxially with the aperture of the element 17 by means of thin radial rubber lines under tension which may be employed to join the base to the peripheral edge defining the output aperture. The second approach relies on the aforementioned umbrella principle. In this case, the cone is also made of rubber coated with conducting paint and is held by spokes which are opened or folded by a crank connected to mechanical elements similar to those of an umbrella.
Although the antennas 10 and 11 have been described as generally conical structures, it should be noted that tetrahedral structures may also be used to obtain similar results.
It willbe apparent to those killed in the art that the preceding description of the embodiments of the invention may be substantially varied to meet specialized requirements without departing from the spirit and scope of the invention disclosed. The foregoing embodiments are therefore not to be ~08Z~01 taken as limiting but rather as exemplary structures of the invention which is defined by the claims.
..
Claims (4)
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:
1. A horn antenna, comprising:
a radiating element having an input end adapted to be coupled to a source of microwave energy and conductive conical sidewalls diverging longitudinally therefrom and terminating in an output aperture;
a parasitic element having an apex with conductive conical sidewalls diverging longitudinally therefrom and terminating in a base, the parasitic element being coaxially aligned with the radiating element, contained therewithin and spaced therefrom to define an annular aperture through which the energy is propagated, the base of the parasitic element being disposed substantially in a plane defined by said out-put aperture and the sidewalls of both elements being adjus-table to vary the cone angle and to maintain adjacent sidewalls in parallel relation; and means disposed in the output aperture of the radiating element for securing the parasitic element in pre-determined relation therewith, said means being substantially transparent to the microwave energy and completely closing the annular aperture through which the energy is propagated.
a radiating element having an input end adapted to be coupled to a source of microwave energy and conductive conical sidewalls diverging longitudinally therefrom and terminating in an output aperture;
a parasitic element having an apex with conductive conical sidewalls diverging longitudinally therefrom and terminating in a base, the parasitic element being coaxially aligned with the radiating element, contained therewithin and spaced therefrom to define an annular aperture through which the energy is propagated, the base of the parasitic element being disposed substantially in a plane defined by said out-put aperture and the sidewalls of both elements being adjus-table to vary the cone angle and to maintain adjacent sidewalls in parallel relation; and means disposed in the output aperture of the radiating element for securing the parasitic element in pre-determined relation therewith, said means being substantially transparent to the microwave energy and completely closing the annular aperture through which the energy is propagated.
2. A horn antenna comprising:
a radiating element having an input end adapted to be coupled to a source of microwave energy and fixed conductive conical sidewalls diverging longitudinally therefrom and terminating in an output aperture;
a parasitic element having an apex with conductive conical sidewalls diverging longitudinally therefrom and terminating in a base, the parasitic element being coaxially aligned with the radiating element and spaced therefrom to define an annular aperture through which the energy is propagated, the apex of the parasitic element extending in the direction of energy propagation, the base thereof being open and disposed substantially in a plane defined by the output aperture of the radiating element and the sidewalls of the parasitic element being adjustable to vary the size thereof; and means disposed in the output aperture of the radiating element for securing the parasitic element in pre-determined relation therewith, said means being substantially transparent to the microwave energy and completely closing the annular aperture through which the energy is propagated.
a radiating element having an input end adapted to be coupled to a source of microwave energy and fixed conductive conical sidewalls diverging longitudinally therefrom and terminating in an output aperture;
a parasitic element having an apex with conductive conical sidewalls diverging longitudinally therefrom and terminating in a base, the parasitic element being coaxially aligned with the radiating element and spaced therefrom to define an annular aperture through which the energy is propagated, the apex of the parasitic element extending in the direction of energy propagation, the base thereof being open and disposed substantially in a plane defined by the output aperture of the radiating element and the sidewalls of the parasitic element being adjustable to vary the size thereof; and means disposed in the output aperture of the radiating element for securing the parasitic element in pre-determined relation therewith, said means being substantially transparent to the microwave energy and completely closing the annular aperture through which the energy is propagated.
3. A method for clearing fog with a horn antenna as claimed in Claim 1, comprising the steps of:
transmitting microwave energy through the annular output aperture of the antenna in an outwardly diverging conical radiation pattern extending from the conical surface of the radiating element; and dielectrically heating fog laden air with said energy to produce an upward circulation of fog along the radiation pattern and a subsequent downward axial circulation of fog towards the said apex, whereby the lower layers of the fog in the area to be cleared are warmed by friction, com-pression and the downwardly moving fog to a condition where the relative humidity drops below 100% and the fog is dissipated.
transmitting microwave energy through the annular output aperture of the antenna in an outwardly diverging conical radiation pattern extending from the conical surface of the radiating element; and dielectrically heating fog laden air with said energy to produce an upward circulation of fog along the radiation pattern and a subsequent downward axial circulation of fog towards the said apex, whereby the lower layers of the fog in the area to be cleared are warmed by friction, com-pression and the downwardly moving fog to a condition where the relative humidity drops below 100% and the fog is dissipated.
4. A method for clearing fog with a horn antenna as claimed in Claim 2, comprising the steps of:
transmitting microwave energy through the annular output aperture of the antenna in an outwardly diverging conical radiation pattern extending from the conical surface of the radiating element; and dielectrically heating fog laden air with said energy to produce an upward circulation of fog along the radiation pattern and a subsequent downward axial circulation of fog towards said apex, whereby the lower layers of the fog in the area to be cleared are warmed by friction, compression and the downwardly moving fog to a condition where the relative humidity drops below 100% and the fog is dissipated.
transmitting microwave energy through the annular output aperture of the antenna in an outwardly diverging conical radiation pattern extending from the conical surface of the radiating element; and dielectrically heating fog laden air with said energy to produce an upward circulation of fog along the radiation pattern and a subsequent downward axial circulation of fog towards said apex, whereby the lower layers of the fog in the area to be cleared are warmed by friction, compression and the downwardly moving fog to a condition where the relative humidity drops below 100% and the fog is dissipated.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA274,000A CA1082801A (en) | 1977-03-08 | 1977-03-08 | Fog clearing by microwave power |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA274,000A CA1082801A (en) | 1977-03-08 | 1977-03-08 | Fog clearing by microwave power |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1082801A true CA1082801A (en) | 1980-07-29 |
Family
ID=4108164
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA274,000A Expired CA1082801A (en) | 1977-03-08 | 1977-03-08 | Fog clearing by microwave power |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1082801A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1996010115A1 (en) * | 1994-09-26 | 1996-04-04 | Dimitris Moulianitakis | A method for dissolving fog and/or for melting ice or snow in a limited area |
| EP0967841A3 (en) * | 1998-06-25 | 2000-05-03 | Elmatec Oy | Portable microwave drying apparatus |
| WO2005079116A2 (en) * | 2004-02-11 | 2005-08-25 | Micro Heat Limited | Mehod and apparatus for heating a fluidic load using radio frequency energy |
| CN109708723A (en) * | 2018-11-21 | 2019-05-03 | 北京古大仪表有限公司 | A kind of radar levelmeter |
-
1977
- 1977-03-08 CA CA274,000A patent/CA1082801A/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1996010115A1 (en) * | 1994-09-26 | 1996-04-04 | Dimitris Moulianitakis | A method for dissolving fog and/or for melting ice or snow in a limited area |
| EP0967841A3 (en) * | 1998-06-25 | 2000-05-03 | Elmatec Oy | Portable microwave drying apparatus |
| WO2005079116A2 (en) * | 2004-02-11 | 2005-08-25 | Micro Heat Limited | Mehod and apparatus for heating a fluidic load using radio frequency energy |
| WO2005079116A3 (en) * | 2004-02-11 | 2005-10-27 | Micro Heat Ltd | Mehod and apparatus for heating a fluidic load using radio frequency energy |
| CN109708723A (en) * | 2018-11-21 | 2019-05-03 | 北京古大仪表有限公司 | A kind of radar levelmeter |
| CN109708723B (en) * | 2018-11-21 | 2020-11-10 | 北京古大仪表有限公司 | Radar level meter |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US6097343A (en) | Conformal load-bearing antenna system that excites aircraft structure | |
| US2415807A (en) | Directive electromagnetic radiator | |
| US4743916A (en) | Method and apparatus for proportional RF radiation from surface wave transmission line | |
| US7212147B2 (en) | Method of agile reduction of radar cross section using electromagnetic channelization | |
| Baum et al. | Impulse radiating antennas | |
| US8830112B1 (en) | Airborne radar jamming system | |
| EP2109184B1 (en) | Antenna system for a micro air vehicle | |
| EP3012912B1 (en) | Antenna electromagnetic radiation steering system | |
| CA1082801A (en) | Fog clearing by microwave power | |
| US4196346A (en) | Laser guided blind landing system for aircraft | |
| JP3985195B2 (en) | Method and apparatus for deicing an airplane by infrared radiation | |
| US6559807B2 (en) | Compact, lightweight, steerable, high-power microwave antenna | |
| US20070229382A1 (en) | Radiating element for radar array | |
| US4405925A (en) | Microwave transceiver, particularly for a doppler radar system | |
| US5006857A (en) | Asymmetrical triangular patch antenna element | |
| US2573401A (en) | Louver antenna | |
| US3261018A (en) | Miniature horn antenna | |
| JPH10150316A (en) | Plane antenna system | |
| CA2632220C (en) | Method of agile reduction of radar cross section using electromagnetic channelization | |
| US7154430B1 (en) | Ventriloqual jamming using a towed transmission line | |
| Kutinlahti | Antenna for Directive Energy Device Against Drones | |
| JP2002030632A (en) | Defogging device and defogging method | |
| US2756419A (en) | Antenna | |
| RU2168818C1 (en) | Combined radio and acoustic antenna | |
| RU2215669C1 (en) | Combined method of reduction of notability of flying vehicle power plant in radar, infra-red and acoustic ranges of waves at change of thrust vector |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |