US2860341A - Ultra high frequency television antenna - Google Patents

Description

Nov. 11, 1958 A. c3. KANDOIAN ET AL 2,360,341

ULTRA HIGH FREQUENCY TELEVISION ANTENNA Filed 001;. 7, 1953 SOL/0 o/aecm/c mam-s 2/ OF EQUAL STRENGTH United States Patent ULTRA HIGH FREQU NCY TELEVISION ANTENNA Armig G. Kandoian, Glen Rock, and Robert A. Felsenheld, East Orange, N. J., assignors to International Telephone and Telegraph Corporation, Nutley, N. J., a corporation of Maryland Application October 7, 1953, Serial No. 384,576

4 Claims. (Cl. 343-843) This invention relates to antennas and more particularly to ultra high frequency television transmitting antennas adapted for eflicient operation over a relatively broad frequency band. Various antenna structures have been devised for use as television transmitting antennas. In general, these antennas consist of a series of radiation members which are disposed around a common center and connected to a transmission line in such relative phase that the instantaneous current flow through all the members, considered as a continuous loop, is in the same direction. In ultra high frequency television transmitting antennas it is desirable that the antenna array have a high gain and an omnidirectional radiation pattern in the horizontal plane with a low standing wave ratio (SWR) in the operating frequency band. In order to provide the desirable high gain it has been found necessary to utilize a plurality of antenna radiating units for concentrating the emitted energy in the vertical plane. It has been found that horizontally polarized loop antennas have been found to be most satisfactory as radiating units. The present invention relates to this general type of antenna but provides an assembly which is rendered structu'rally rigid Without the use of complicated or expensive fastening members, and which can be fabricated from a small number of parts that can be readily and relatively inexpensively manufactured.

One of the objects of this invention therefore is to provide a loop antenna structure for operating over a relatively wide frequency band which lends itself to economical manufacture and ease of assembly.

Another object of this invention is to provide an ultra high frequency television loop antenna which lends itself readily for use in a stacked array to form an antenna system of high gain and omnidirectional characteristics.

It is a further object of this invention to provide an antenna array system wherein the branch leads coupled to the radiating members of the system are properly re lated to effect a substantial matching of impedances over a relatively wide frequency band.

According to one of the features of our invention we provide an antenna system of the loop type in which the radiant acting members comprise a pair of substantially planar radiating areas disposed in spaced edgewise relation to each other. A metal strip having each of its ends connected to one of radiating areas functions as a transformer section. A source of energy is coupled between the transformer section and the midpoint of the radiant member.

The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

Fig. l is a view in perspective of a radiating loop antenna in accordance with the principles of this invention;

Fig. 2 is a view in cross-section taken along the lines 2-4 of Fig. l of one of the radiating members; and

I 2,860,341 Patented Nov. 11, 1958 Fig. 3 is a schematic illustration of an antenna array utilizing the loop antenna of Fig. 1.

Referring to Figs. 1 and 2 of the drawing one embodiment of the radiating loop antenna of this invention is shown therein to comprise a plurality of radiating members 1, 2 and 3 disposed around a common center 4. Each of the radiating members 1, .2 and 3 comprises a pair of substantially rectangular planar radiating areas 5 and 6 having their inner edges disposed in spaced edgewise relation to present a substantially fiat conductor surface. Rearward of and spaced from the: radiating areas 5 and 6 is a conductive metal strip 7 which has one end 8 angled and connected to the outer edge of radiating area 5 and the other end 9 angled and connected to the radiating area 6 thus mechanically supporting the conductor surface of the radiating member. A rigid spoke 10 composed of a conductive material and disposed radially of the loop antenna is connected to the metal strip 7 and a center support structure 11. The support structure 11 may be supported by any wellknown antenna tower structure. A transmission line 12 couples energy to the loop feed point 4 where feed line branches 13, 14- and 15 join. Each radiating member feed line 13, 14and 15 comprises two leads, the first an inner conductor 16 surrounded by a jacket 17 of insulating material. The inner conductor 16 of each radiating member branch is coupled to the inner edge of area 5. A second lead return path or ground conductor is provided via the metallicstrip 7, the spoke 1t), support structure 11 and then either through a tower structure or a transmission line which has its outer conductor coupled to the support 11 or spokes 10. A metallic clamp 18 adjustable lengthwise of each spoke It) acts as an additional impedance matching device.

Preferably, the effective electrical length L of radiating members 1, 2 and 3 should be substantially equal to one-half wavelength at the mean operating frequency of the antenna system. The effective electrical width W of the areas 5 and 6 should preferably be equal to substantially one-half wavelength of the lowest operating frequency of the antenna system. It is obvious to those skilled in the art that if the width W of the: radiating areas 5 and 6 is increased the end effect is increased, thereby decreasing the optimum operating frequency. The spacing between the areas 5 and 6 should be adjusted to obtain the minimum reactance for the input impedance. The metallic strip 7 in addition to mechanically supporting the conductor surface functions as a transformer or impedance matching device. Due to the currents which are mutually coupled between the conductor surface and the metallic strip 7, it is assumed that metallic strip 7 radiates and increases the impedance of the antenna of this invention relative to the impedance of an ordinary dipole. An ordinary dipole which is fed from a coaxial transmission line induces return currents on the coaxial feed line. However, in the loop antenna of this invention equal currents are induced around the loop, thus preventing any unbalance. We have found that by employing the above construction and properly locating the coupling point of end 9 of metal strip 7 to area 6, it is possible for some ultra high frequency television channels to feed the antenna from a transmission line without requiring the use of additional conventional balancing transformers or separate impedance matching transformers to connect the antenna to the line. However, if such matching of the antenna to feed lines is required it is possible to match the antenna impedance to the input impedance through the use of movable metal clamps 18 which when properly adjusted provide a proper match at the center point 4 or an additional line matching impedance transformer may be coupled between branch 12 and point 4. With the antenna of this invention any value of real impedance between certain limits may be obtained by adjustment of the impedance matching devices and the physical dimensions of the radiating structure. The impedance matching devices provide compensation to take care of any variation which may occur in the manufacturing of the loop.

Obviously, snow or ice formation in the space between areas 5 and 6 will adversely affect the characteristics of this antenna and, therefore, if desired the entire antenna structure can be enclosed within a suitable plastic housing or bag. In any event it is preferable to cap the center point 4 with a plastic coating 19.

Referring to Fig. 3, an antenna array utilizing the loop antennas 21 of Fig. 1 is shown wherein in order to feed the several radiating members a transmission line 22 couples R7 energy to any known type distributor 20, such as a balun transformer. From the distributor transmission lines 1.2 of equal dielectric strength and length distribute the energy to the loop distribution points such as 4 in Fig. 1. By providing a stacked vertical alignment of radiating loop antennas, it is possible to provide a high concentration of energy in the vertical plane omnidirectionally in the horizontal plane. Thus, in order to feed the several loop antenna members 21, the center points are coupled to the distributor 20. The radiating members are excited in the appropriate phase so that at any given instance the current flow in the radiating members of each radiation loop is in the same circumferential direction.

It should be distinctly understood that this particular antenna structure shown herein is given by way of example; the feed system of the antenna may take many other forms without departing from the spirit of our invention and likewise mechanical details of the supporting structure may be varied within the limits of our invention as desired by those skilled in the art.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

1. An ultra high frequency antenna system comprising a plurality of individual radiating members forming a substantially omnidirectional antenna, each of said members including first and second conductors each shaped to provide a substantially rectangular planar radiating surface, said conductors being disposed in spaced edgewise relation, a radiating transformer section asymmetrically connected to said conductors to provide asymmetrical electrical coupling thereto, and means to connect a source of ultra high frequency energy between said transformer section and the radiating surfaces of said conductors, said radiating transformer section comprising a metal strip spaced from the radiating surfaces of said conductors and having one end angled and connected to the outer edge of the radiating surface of said first conductor and the other end of said strip angled and connected to said second conductor at a point closer to the inner edge of said second conductor and said energy connecting mean having one lead thereof connected to said transformer and the other lead thereof connected to the inner edge of said first conductor.

2. An antenna system according to claim 1 wherein the combined effective electrical length of the planar radiating surfaces of said conductors is equal substantially to one-half wavelength at the mean operating frequency of said source and the effective electrical width of each such surface is equal substantially to one-half wavelength at the lowest operating frequency of said source.

3. An ultra high frequency antenna system. adapted for coupling to a main transmission line of given impedance comprising a plurality of individual. radiating members spaced to form a substantially omnidirectional antenna, each of said radiating member having first and second conductors each shaped to provide a substantially rectangular planar radiating surface, said conductors being disposed in spaced edgewise relation, a radiating transformer section including a metal strip disposed in spaced relation to the radiating surface of said conductors and having one end angled and connected to the outer edge of. the radiating area of said first conductor; and the other end angled and connected to said second conductor at a point closer to the inner edge of said second conductor, an energy dividing coupler for coupling said members to a transmission line, said coupler having a plurality of branches one for each of said members, each of said branche having two leads, one lead being coupled to said transformer section and the other lead being connected to the inner edge of said first conductor.

4. An antenna system according to claim 3 where each of said branches further includes an impedance matching device to match the impedance of said radiating members to said transmission line impedance.

References Cited in the file of this patent UNITED STATES PATENTS 1,960,006 Hagen May' 22, 1934 2,131,108 Lindenblad Sept. 27, 1938 2,153,298 Cork Apr. 4, 1939 2,618,746 Pauch Nov. 18,1952 2,656,463 Woodward Oct. 20, 1953 FOREIGN PATENTS 883,351 France July 2, 1943

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