US2210491A - High frequency antenna - Google Patents

Description

Aug. 6,- 1940. I R. F. LEWIS HIGH FREQUENCY ANTENNA rmksm/rrze agp/i Filed Oct. 51, 1938 mam/r752 Snventgr Milt Islam Womm Patented Aug. 6,' 1940 anali PATENT oF cE HIGH FREQUENCY ANTENNA Robert F. Lewis, Runnemede, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 31, 1938, Serial No. 238,036 Claims. (01. 2 50 3s) I I My invention relates to ultra high frequency antennas, and more particularly to a unitary metallic antenna structure which produces a vertically polarized wave having either a substantially 5 uniform rotating field, or a directional pattern, as

desired.

The practice today is to employ a single vertical nection with police car communication systems.

Dipole antennas and the so-called turnstile antenna, which is a highly eflicient antenna that has been developed for certain types of ultra high frequency work, are not adaptable to police work, forthe reason that they radiate horizontally polarized waves. To properly receivesuch waves,

the receiving antenna must be of a type'which is responsive to horizontally polarized waves.

Nearly all antennas which are small enough for use on a car and which are responsive to horizontall polarized waves are also highly directive, and consequently are not suited for such use for the reason that automobile antennas must be equally effective in all directions. It is, therefore, a further object of my invention to provide an antenna which isnon-directive and which radiates or receives vertically polarized waves.

It is known that there are areas or dead spots in which reception is'very poor. One method of avoiding dead spots is to transmit a signal simultaneously from more than one point, thus providing more than one path for the radiated wave between the transmitter and receiver. A plurality of antennas at different horizontally spaced points can be energized in a manner that will produce a field which is substantially uniform in all directions, but this condition is only fulfilled when the radiation from all antennas is simultaneously received. It is evident, therefore, that such a 45 system will not prevent fading. It is, therefore,

a further object of my invention to reduce dead spots by utilizing a plurality of antenna sections vertically positioned one above the other.

Another disadvantage of the antenna arrays of the prior art, which I propose to overcome in the present invention, is the. requirement for insulation between different members of the-radiating system. If an antenna tower contains insulated sections, the structure is weakened and its cost 1 is increased... The antenna, according to my this invention; and

present invention, is made as a unitary metallic structure which does not require any insulating membe'rsx- It is, therefore, a further object of my invention to provide a unitary antenna structure which isstructurally rigid and economical.

The question of feeding antenna arrays must also be considered. .In antennas of theprior art which use a plurality of, antenna sections having different phase relations, each section must be separately fed, separately tuned, and adjusted for the proper impedance match to the feed lines and for the proper phase. This requires the use of stand-off insulators to carry the feed lines, and increases the complexity of the device. It is a further object of my invention, therefore, to provide an ultra high frequency antenna which requires a'minimumnumber of feed lines.

My invention will be better understood'from the following description when considered in connection with the accompanying drawing. Its scope is indicated by the appended claims. Similar reference numerals refer to similar parts throughout the several drawings. j

Referring to the drawing, I

Figure 1 is a schematic diagram to aidin the explanation of this'invention'; v

Figure 2 is a schematic diagramfurther illustrating the principle of operation of this invention; 1

Figure 3 illustrates a preferred embodiment of Figure 4 illustrates one method of" feeding the antenna shown in Figure 3.

Fig. lfis a sketch to illustrate the principle of operation of this invention. Three folded over half-wave sections l5, and I9 are connected to gether at their open ends by two straight half wave conductors H and I3. Each leg of the folded over section is approximately a quarter wave long, and it 'thus constitutes a resonant phase inverter. At ultra high frequencies, this type of inverter is practical because its overall length is not great. A transmission line 23 is connected to the lower quarter wave inverter l9. The an-. tenna is energized by a transmitter!!! to which the transmission line is connected. Standing waves are set up throughout the entire system by the connection to one inverter. Thus, it is not necessary to run a separate transmission line up to the upperv antenna conductor H.

It is well known that the voltage, or currents, on the opposite legs of a folded half-wave resonant line, at any instant, are of opposite phase. Consequently, there issubstantiallyno radiation from the phase inverting sections l5, Hand [9. The

currents at any instant are indicated by the arrows and are seen to be in phase in the vertical antenna sections II and I3 which connect the folded sections.

Referring now to Fig. 2, two sections like that of Fig. l have been placed back to back with the closedends of the quarter wave sections adjoining. The two sectionsare fed so that the currents in the radiating sections are out of phase. This is accomplished by transposing the connections from the. transmission line to one of the sections. The conductor whichis connected to the lower arm of the quarter wave section i9 is connected to the upper arm of the quarter wave section 25. Consequently, instantaneous currents in the vertical radiators H and I3 are out .of phase with the currents in the vertical radiators l2 and [4. As before, radiation from all the horizontal conductors is cancelled out.

In a folded over half-wave line, the mid-point is a maximum current-minimum voltage point,

and therefore all" such points on the resonant lines i5, l1, l9, 2!, 23 and 25 may be grounded. This is also shown in Fig. 2.

Having pointed out the general theory of m invention, a preferred embodiment will now be described.- Referring to Fig. 3 a grounded unitary metallic mast antenna 4! is shown which operates in accordance with the principles outlined above.

The structure comprises a plurality of sections similar to the one shown and described in Fig. 2. The sections are mounted on the metallic mast 4i and lie in vertical planes which are-at right angles. In the preferred embodimentof my invention, there is a total of sixteen vertical halfwave radiating conductors arranged in four groups, each group having four conductors connected in series by the folded over sections. Thus,

sections- 99 and 25 are in one plane, while the additional sections I90. and 25a are in a plane at right angles'thereto. A transmitter 20 is coupled .to atransmission line 21. An adjusting stub section 29 is connected across the line. At a convenient point, the line divides into a pair of lines 3! and 33. One of these lines may be of any convenient length, but the other, 33, for example, is made a quarter wave-length longer, as indicated by the loop marked 90 phase shifter. The lines 3|, 33 again divide and terminate respectively at the lower folded half-wave sections I9, 25, l9a, and 25a. The lines 3! and 33 are each utilized to energize diagonally positioned pairs of antennas in phase opposition, as shown in Fig. 4.

In addition, the currents in adjacent antennas are in quadrature phase relation due to the action of the 90 phase shifter 35. While other connections are possible, by which various directional patterns are obtained, they neednot be dis cussed here, as they are well known to the art.

Each of the folded half-wave sections has a high radio frequency current at the short circuited end. This current may flow throughthe mast, but it is desirable to connect low resistance con- 'is also to be noted that the mast 4| problems.

ducting elements between the parallel conductors. If the actual length of the horizontal conductors is made somewhat in excess of an exact quarter wave length, some degree of adjustment can be obtained by moving the shorting elements to tune each circuit to resonance.

It was seen in Fig. 2 that the short circuited ends of the quarter wave sections are at the same relative potential v end and thus can be connected together and grounded. The mast 4|, therefore, need not be insulated from ground. It passes through an equipotential region with respect to the four antenna elements. As a result any current of a given phase which is induced in the mast,

The eih ciency of this'antenna is indicated by I the fact that it is possible to obtain a gain several times that of a half-wave dipole antenna.

I have thus described an antenna which has high efficiency, radiates a uniform vertically polarized wave, and is free from complex feeding While it has been specifically described as a transmitting antenna, it is evident that it may be used for receiving. Also, more than four vertical sections may be used to increase the gain further. In such a case, the transmission line would not be connected to the lower end of the antenna but, preferably, would be connected in the center of the system.

I claim as my invention:

1. In an antenna of the character described, two pairsof radiating antenna elements disposed in vertical planes intersecting at right angles, each of said elements comprising a plurality of vertical coaxial half-wave conductors, and a plurality of folded half-wave conductors connecting adjacent ends of said radiating elements, said folded half-wave conductors also'servingto support said radiating elements.

2. In an antenna of the character described,

. two pairs of concentric vertical radiating antenna elements disposed in vertical planes intersect tenna elements concentrically disposed about said mast in vertical planes intersecting at right angles at said mast, each of said radiating elements comprising a plurality of half-wave conductors, a plurality of folded half-wave conductors horizontally extending from said mast and connected to and supporting said radiating elements.

5. In an antenna of the character described, a

vertical conductive mast for supporting said antenna, two pairs of vertical radiating antenna elements concentrically disposed about said mast and parallel'thereto and lying in vertical planes which intersect at right angles at said mast, each of said radiating elements comprising a plurality of coaxial half-wave conductors, a plurality of folded half-wave conductors horizontally extending from said mast and connected to andsupporting said radiating elements, and means for causing in-phase currents to flow in each conductor of said radiating elements. i

6. In an antenna of the character described, a vertical conductive mast for supporting said antemia, two pairs of vertical radiating antenna elements concentrically disposed about said mast and parallel thereto and laying in vertical planes which intersect at right angles at said mast, each of said radiating elements comprising a plurality of coaxial half-Wave conductors, a plurality of folded half-wave conductors horizontally extending from said mast and connected to and supporting said radiating elements, means for causing in-phase currents to flow in each conductor of each of said radiating elements, means for causing out of phase currents to 110W in oppositely positioned radiating elements of each of said pairs, and means for maintaining a quadrature phase relation between currents in one pair with respect to currents in the other pair.

ROBERT F. LEWIS.

Images