CA1201199A - Dielectric rod feed for reflector antennas - Google Patents
Dielectric rod feed for reflector antennasInfo
- Publication number
- CA1201199A CA1201199A CA000429125A CA429125A CA1201199A CA 1201199 A CA1201199 A CA 1201199A CA 000429125 A CA000429125 A CA 000429125A CA 429125 A CA429125 A CA 429125A CA 1201199 A CA1201199 A CA 1201199A
- Authority
- CA
- Canada
- Prior art keywords
- feed
- lambda
- dielectric rod
- waveguide
- ghz
- 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
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- Aerials With Secondary Devices (AREA)
- Waveguide Aerials (AREA)
Abstract
TITLE
A DIELECTRIC ROD FEED FOR REFLECTOR ANTENNAS
INVENTORS
Lotfollah Shafai Apisak Ittipiboon Ernest Bridges ABSTRACT OF THE DISCLOSURE
The feed which may be designed for operation in a single or dual bandwidth within a broad frequency range extending from a fraction of a GHz to many GHz, up to and including the range of 8 to 13 GHz. The feed includes a circular waveguide wherein one end is fitted with an electrical coupler and the other end acts as the radiator. A cylindrical dielectric rod is located within the radiating end of the waveguide and extends out of the guide to a length L which is less than .lambda.c/2 where .lambda.
is the wavelength at the midband of the operating frequency. The diame-ter D of the dielectric rod may be equal to the inside of the waveguide, and is less than .lambda.o/.epsilon.r , where .lambda.o is the wavelength of the highest op-erating frequency of the feed and .epsilon.r is the relative dielectric constant of the dielectric rod.
A DIELECTRIC ROD FEED FOR REFLECTOR ANTENNAS
INVENTORS
Lotfollah Shafai Apisak Ittipiboon Ernest Bridges ABSTRACT OF THE DISCLOSURE
The feed which may be designed for operation in a single or dual bandwidth within a broad frequency range extending from a fraction of a GHz to many GHz, up to and including the range of 8 to 13 GHz. The feed includes a circular waveguide wherein one end is fitted with an electrical coupler and the other end acts as the radiator. A cylindrical dielectric rod is located within the radiating end of the waveguide and extends out of the guide to a length L which is less than .lambda.c/2 where .lambda.
is the wavelength at the midband of the operating frequency. The diame-ter D of the dielectric rod may be equal to the inside of the waveguide, and is less than .lambda.o/.epsilon.r , where .lambda.o is the wavelength of the highest op-erating frequency of the feed and .epsilon.r is the relative dielectric constant of the dielectric rod.
Description
Background of the Invention Thiæ invention is directed to reflector antennas, and in partlcular, to dielectrlc rod feeds for these antennas The prime focus fed paraboloid antenna is one of the most com-mon high gain antenna systems. It has a simple geometry consisting of areflecting paraboloid surface with a feed system at its focus. The wide-spread use of paraboloidal reflectors in satelllte communication and radio astronomy has stimulated consfderable interest in the design and development of optimum feeds, 80 that the antenna system can be ut~ ed ef~iciently. This can be achieved by designing feeds to have rotation-ally symmetric radiation patterns, low side and back lobes, low level of cross-polarization and a well defined phase centreO It is also required that they have broadband performance and a low return 108s . A rotation-ally symmetric radiation by the feed illuminates the reflector uniformly in the azimuthal direction and thus improves the reflector efficiency.
It also ensures a low level of cross-polar radiation.
This latter property9 apart from improving the antenna effici-ency, is important In polarization measurements of the celestial ob~ects in radio astronomy applications and ln the frequency re-use application, whereby two separate data channels within the same frequency band can be transmitted (or received). This is normally achieved by utilizing two or~hogonal polarizations at ~he same frequency to double the channel capacity. A low side and back radiatlon level is desirable to elimlnate interference from other radiation sources and, in particular, to reduce the antenna nolse temperature.
Historically, many types of feed systems have been used to illuminate microwave reflector antennas~ The most common type feed ls the horn antenna because of its design simplicity and its excellent impedance, polarization and power handling capabilities. The simplest ~ ¦
form of horn feed comprises a conventional waveguide supporting the domlnant mode of propagation and a horn. For these feeds, the radiatlon patterns are generally asymmetric, causing a loss in efficiency, an increased cross-polar radiation and an increased spillover power. These shortcomings have resulted in the development of several new types of high performance horns. The most useful of these are the multimode, the dielectric loaded and the corrugated horn antennas. The multimode horn "
I
. .
~3~
utilizing TEll and TM11 modes have been shown to produce a nearly circu-larly symmetr~c radiation pattern, as described in the publication by P.D. Potter, "~ New Horn Antenna with Suppressed Sidelobes and Equal Beamwidths", Microwave Journal, Vol. 6, pp 71-78, June 1963. Horns with higher order modes have also been designed, in which an aperture efEiciency of about 85% has been predicted. ~owever, for these higher order mode horns the operating bandwidth becomes increasingly limited, since each mode propagates with different velocity as it travels from its point of mode generatlon to the horn aper~ure and will arrive in a correct phase relationship at one only frequency.
A dielectric loaded horn using a conical low permittivity material to support the sub-reflector has been used in a Cassegrain-type system. Such a system is described by H~E. Bartlett and R.E. Moseley, "Dielguides-Highly Efficient Low Noise ~ntenna Feeds"9 Microwave Journal, Vol~ 9, pp 53-58, Dec. 19660 The dielectric cone was used initially to replace a strut support structure and the corresponding aperture block-age. The low permi~tivity dielectric cone is inserted into the feed horn and extends all the way to the sub-reflector. It was found that the structure has a symmetrical radiation pattern and also reduces the spill-over power. This resulted in an increase of the Cassegrain antenna efficiency up to 75 to 80%. A dlsadvantage of such a dielectric loaded horn seems to lie in the effect of the atmospheric moisture upon the dielectric, which results in the deterioration of the antenna performance over a long time period (when it is in an all weather environmentj.
The final type, a corrugated horn supporting balanced hybrid modes, has been shown to possess many of the desirable characteristics required of an ideal feed for a paraboloidal reflector. One such design is described in United States Patent 3,553,707, which issued on Jan. 5, -1971 to R.F.H. Yang et al. The drawback of this horn lies, not in i~s electrical performance, but in its massive shape, the complexity of its design and its high cos~ of fabrication. However, when considering the three high performance horns9 the corrugated horn is the one best sui~ed to serve as a feed for a paraboloidal reflector.
3~
Summary of the Invention I~ is therefore an ob~ect of this lnvention to provide an efficient paraboloidal reflector feed which is relatively inexpensive to fabricate.
This and other objects are achieved in a paraboloidal antenna feed which lncludes a circular waveguide with a first end fitted with an electrical coupler and a second radiating end. A cylindrical dielecttic rod ls loca~ed within the radiating end of the waveguide and extends out-ward therefrom to a length L which is less than ~c/2, where ~c i5 the wavelength at the midband of the operating frequency of the antenna. The diameter D of the dielectric rod may be equal to the inside diameter of the waveguide, and i6 less than ~o/~r ~ where ~0 is the wavelength of the highest operating frequency of the antenna and Er is the relative dielectric constant of the dielectric rod.
lS The operating frequency o a high frequency feed may be in the range of 3-13 Gllzo In a feed to be opera~ed in a frequency band of 11.5-12.3 GHz, the dielectric constant Er f approximately 2.54 may be select-ed, with a diameter D of approximately 1.5 cm and a length L of approxi-mately 1.0 cm.
Msny other ob~ects and aspects of the invention will be clear from the detailed de~cription of the drawings.
Brief Description of the Dr~
In the drawings:
The sole figure 1 illustrates a cro~s-section of the feed in accordance with the present lnvention.
Detailed Description The antenna feed 1, as illustrated in figure 1, consists of a circular waveguide 2 of thickness t and a diameter D ln which is located a circular dielectric rod 4 whose diameter is also essentially D and - -which extends to a length L out of the radia~ing end 3 of t~e waveguide
It also ensures a low level of cross-polar radiation.
This latter property9 apart from improving the antenna effici-ency, is important In polarization measurements of the celestial ob~ects in radio astronomy applications and ln the frequency re-use application, whereby two separate data channels within the same frequency band can be transmitted (or received). This is normally achieved by utilizing two or~hogonal polarizations at ~he same frequency to double the channel capacity. A low side and back radiatlon level is desirable to elimlnate interference from other radiation sources and, in particular, to reduce the antenna nolse temperature.
Historically, many types of feed systems have been used to illuminate microwave reflector antennas~ The most common type feed ls the horn antenna because of its design simplicity and its excellent impedance, polarization and power handling capabilities. The simplest ~ ¦
form of horn feed comprises a conventional waveguide supporting the domlnant mode of propagation and a horn. For these feeds, the radiatlon patterns are generally asymmetric, causing a loss in efficiency, an increased cross-polar radiation and an increased spillover power. These shortcomings have resulted in the development of several new types of high performance horns. The most useful of these are the multimode, the dielectric loaded and the corrugated horn antennas. The multimode horn "
I
. .
~3~
utilizing TEll and TM11 modes have been shown to produce a nearly circu-larly symmetr~c radiation pattern, as described in the publication by P.D. Potter, "~ New Horn Antenna with Suppressed Sidelobes and Equal Beamwidths", Microwave Journal, Vol. 6, pp 71-78, June 1963. Horns with higher order modes have also been designed, in which an aperture efEiciency of about 85% has been predicted. ~owever, for these higher order mode horns the operating bandwidth becomes increasingly limited, since each mode propagates with different velocity as it travels from its point of mode generatlon to the horn aper~ure and will arrive in a correct phase relationship at one only frequency.
A dielectric loaded horn using a conical low permittivity material to support the sub-reflector has been used in a Cassegrain-type system. Such a system is described by H~E. Bartlett and R.E. Moseley, "Dielguides-Highly Efficient Low Noise ~ntenna Feeds"9 Microwave Journal, Vol~ 9, pp 53-58, Dec. 19660 The dielectric cone was used initially to replace a strut support structure and the corresponding aperture block-age. The low permi~tivity dielectric cone is inserted into the feed horn and extends all the way to the sub-reflector. It was found that the structure has a symmetrical radiation pattern and also reduces the spill-over power. This resulted in an increase of the Cassegrain antenna efficiency up to 75 to 80%. A dlsadvantage of such a dielectric loaded horn seems to lie in the effect of the atmospheric moisture upon the dielectric, which results in the deterioration of the antenna performance over a long time period (when it is in an all weather environmentj.
The final type, a corrugated horn supporting balanced hybrid modes, has been shown to possess many of the desirable characteristics required of an ideal feed for a paraboloidal reflector. One such design is described in United States Patent 3,553,707, which issued on Jan. 5, -1971 to R.F.H. Yang et al. The drawback of this horn lies, not in i~s electrical performance, but in its massive shape, the complexity of its design and its high cos~ of fabrication. However, when considering the three high performance horns9 the corrugated horn is the one best sui~ed to serve as a feed for a paraboloidal reflector.
3~
Summary of the Invention I~ is therefore an ob~ect of this lnvention to provide an efficient paraboloidal reflector feed which is relatively inexpensive to fabricate.
This and other objects are achieved in a paraboloidal antenna feed which lncludes a circular waveguide with a first end fitted with an electrical coupler and a second radiating end. A cylindrical dielecttic rod ls loca~ed within the radiating end of the waveguide and extends out-ward therefrom to a length L which is less than ~c/2, where ~c i5 the wavelength at the midband of the operating frequency of the antenna. The diameter D of the dielectric rod may be equal to the inside diameter of the waveguide, and i6 less than ~o/~r ~ where ~0 is the wavelength of the highest operating frequency of the antenna and Er is the relative dielectric constant of the dielectric rod.
lS The operating frequency o a high frequency feed may be in the range of 3-13 Gllzo In a feed to be opera~ed in a frequency band of 11.5-12.3 GHz, the dielectric constant Er f approximately 2.54 may be select-ed, with a diameter D of approximately 1.5 cm and a length L of approxi-mately 1.0 cm.
Msny other ob~ects and aspects of the invention will be clear from the detailed de~cription of the drawings.
Brief Description of the Dr~
In the drawings:
The sole figure 1 illustrates a cro~s-section of the feed in accordance with the present lnvention.
Detailed Description The antenna feed 1, as illustrated in figure 1, consists of a circular waveguide 2 of thickness t and a diameter D ln which is located a circular dielectric rod 4 whose diameter is also essentially D and - -which extends to a length L out of the radia~ing end 3 of t~e waveguide
2. The dielectric rod 4 is thus excited through thè waveguide 2. The other end 5 of the waveguide 2 includes a coupler 6 for electrically con-necting the antenna feed 1 to a line so that it can functlon either as a transmitter or receiverq The antenna feed 1 can be designed to operate in a single or f ., ~L~f~
dual bandwidth within a broad frequency range extending from a fraction of a GHz to many GHz up to and lncluding the range 8-13 GHz. It has been found that the contribution of the waveguide 2 to the radiation results in only a small deviation of the patterns from a rotationally symmetric character. In addition, increasing the extension length L tends to re-duce the beam-width and, at the same time, increases the level of side and back lobe radiations. By llmiting the extension L, the size of the antenna f~ed will also be kept a8 small as possible which is advanta-geous. The dlameter D of that portion of the rod extending beyond the waveguide can be ad~usted to give an optlmum radiation pattern, to ad~ust the gain and to decrease the cross-polar radiation of the reflector antenna. In normal practice, D is selected to be equal to the inside diameter of the waveguide, whlch simplifies the feed fabrication.
When used as a feed for a prime focus reflector antenna, it has been determlned that the diameter D will be less than ~O/~ r ~ where ~ O
is the wavelength of the highest operating frequency and ~r is the rela-tive dielectric constant of the dielectric rod 4. In such a feed, the propagating mode are confined to TEl1 and TMol. The radiatlon patterns on E and H planes can be controlled by the dielectric constant ~r and the ext~nsion length L. For each value of ~r~ there is a corresponding opti-mum value of L which has been found to be less than half ~c' the wave-length at the midband of the operating frequenciesO
As an example, an antenna feed for a prime focus reflector antenna to be operated in a bandwidth of 11.5 ~o 12.3 GHz has ~he follow-ing parameters: the waveguide has an internal dlameter D ; 1.5 cm, and a : wall thickness t = 0.2 cm, the dielectric rod is made of plexiglass'with Er = 2.54 and is extended a length L ~ 1.0 cm. In this feed, the E and H
plane patterns remain relatively equal and nearly independent of fre-quency ranging from 134 to 127 for the E plane, and from 135 to 130 ~0 for the H-plane over the frequency bandwidth. Also, wlthin the frequency bandwidth of 800 MHz, the side lobe levels are always below -20 dB. The measurement of the cross-polar radiation lndicated 8 ma~imum cross-polar-ization level of -16 dB at the lower end of the frequency bandwidth, with the level reduced to -18 dB at 11.9 GHz and to -22 dB at 12.3 GHz~
-Many modifications in the above described embodiments of the invention can be carried out without departing from the scope thereof and, therefore, the scope of the present invention is lntended to be limited only by the appended claims.
` !
!
~,~
. . , ~, . . .
dual bandwidth within a broad frequency range extending from a fraction of a GHz to many GHz up to and lncluding the range 8-13 GHz. It has been found that the contribution of the waveguide 2 to the radiation results in only a small deviation of the patterns from a rotationally symmetric character. In addition, increasing the extension length L tends to re-duce the beam-width and, at the same time, increases the level of side and back lobe radiations. By llmiting the extension L, the size of the antenna f~ed will also be kept a8 small as possible which is advanta-geous. The dlameter D of that portion of the rod extending beyond the waveguide can be ad~usted to give an optlmum radiation pattern, to ad~ust the gain and to decrease the cross-polar radiation of the reflector antenna. In normal practice, D is selected to be equal to the inside diameter of the waveguide, whlch simplifies the feed fabrication.
When used as a feed for a prime focus reflector antenna, it has been determlned that the diameter D will be less than ~O/~ r ~ where ~ O
is the wavelength of the highest operating frequency and ~r is the rela-tive dielectric constant of the dielectric rod 4. In such a feed, the propagating mode are confined to TEl1 and TMol. The radiatlon patterns on E and H planes can be controlled by the dielectric constant ~r and the ext~nsion length L. For each value of ~r~ there is a corresponding opti-mum value of L which has been found to be less than half ~c' the wave-length at the midband of the operating frequenciesO
As an example, an antenna feed for a prime focus reflector antenna to be operated in a bandwidth of 11.5 ~o 12.3 GHz has ~he follow-ing parameters: the waveguide has an internal dlameter D ; 1.5 cm, and a : wall thickness t = 0.2 cm, the dielectric rod is made of plexiglass'with Er = 2.54 and is extended a length L ~ 1.0 cm. In this feed, the E and H
plane patterns remain relatively equal and nearly independent of fre-quency ranging from 134 to 127 for the E plane, and from 135 to 130 ~0 for the H-plane over the frequency bandwidth. Also, wlthin the frequency bandwidth of 800 MHz, the side lobe levels are always below -20 dB. The measurement of the cross-polar radiation lndicated 8 ma~imum cross-polar-ization level of -16 dB at the lower end of the frequency bandwidth, with the level reduced to -18 dB at 11.9 GHz and to -22 dB at 12.3 GHz~
-Many modifications in the above described embodiments of the invention can be carried out without departing from the scope thereof and, therefore, the scope of the present invention is lntended to be limited only by the appended claims.
` !
!
~,~
. . , ~, . . .
Claims (3)
1. A feed for a paraboloid antenna for operation at one frequency with substantially equal E and H
plane patterns comprising:
- a circular waveguide with a first end having an electrical coupler, a second radiating end; and an inner diameter D; and - a cylindrical dielectric rod located within the radiating end of the waveguide and extending outward thereof to a length L, L being less than .lambda.c/2 where .lambda.c is the wavelength at the midband of the operating frequency, the dielectric rod having a diameter substantially equal to D, D being less than .lambda.o/.epsilon.r, where .lambda.o is the wavelength of the highest operating frequency and .epsilon.r is the relative dielectric constant of the dielectric rod.
plane patterns comprising:
- a circular waveguide with a first end having an electrical coupler, a second radiating end; and an inner diameter D; and - a cylindrical dielectric rod located within the radiating end of the waveguide and extending outward thereof to a length L, L being less than .lambda.c/2 where .lambda.c is the wavelength at the midband of the operating frequency, the dielectric rod having a diameter substantially equal to D, D being less than .lambda.o/.epsilon.r, where .lambda.o is the wavelength of the highest operating frequency and .epsilon.r is the relative dielectric constant of the dielectric rod.
2. A feed as claimed in claim 1 wherein the operating frequency is in the range of 8-13 GHz.
3. A feed as claimed in claim 1 or 2 wherein the dielectric constant .epsilon.r is approximately 2.54, the diameter D of the dielectric rod is approximately 1.5 cm and the length L is approximately 1.0 cm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US41950382A | 1982-09-17 | 1982-09-17 | |
| US419,503 | 1982-09-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1201199A true CA1201199A (en) | 1986-02-25 |
Family
ID=23662559
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000429125A Expired CA1201199A (en) | 1982-09-17 | 1983-05-26 | Dielectric rod feed for reflector antennas |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1201199A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5109232A (en) * | 1990-02-20 | 1992-04-28 | Andrew Corporation | Dual frequency antenna feed with apertured channel |
| US5684495A (en) * | 1995-08-30 | 1997-11-04 | Andrew Corporation | Microwave transition using dielectric waveguides |
| CN106602225A (en) * | 2016-12-02 | 2017-04-26 | 上海无线电设备研究所 | Circularly-polarized data link antenna resistant to ablation of engine flame |
-
1983
- 1983-05-26 CA CA000429125A patent/CA1201199A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5109232A (en) * | 1990-02-20 | 1992-04-28 | Andrew Corporation | Dual frequency antenna feed with apertured channel |
| US5684495A (en) * | 1995-08-30 | 1997-11-04 | Andrew Corporation | Microwave transition using dielectric waveguides |
| CN106602225A (en) * | 2016-12-02 | 2017-04-26 | 上海无线电设备研究所 | Circularly-polarized data link antenna resistant to ablation of engine flame |
| CN106602225B (en) * | 2016-12-02 | 2020-04-17 | 上海无线电设备研究所 | Circular polarization data chain antenna resistant to flame ablation of engine |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |