US2234333A - Demountable antenna - Google Patents

Description

March 11, 1941 G. H. BROWN ETAL DEMOUNTABLE ANTENNA Filed Feb. 25, 1959 Enventors o w n,

George HBP Jess E stein 53 Robert ewis Gttouug Patented Mar. 11, 1941 UNITED STATES PATENT OFFICE DEMOUNTABLE ANTENNA Application February 23, 1939, Serial No. 257,988

7 Claims.

This invention relates to demountable antennas and more especially to a short wave, nondirective, demountable antenna in which the input impedance matches a conventional transmission line.

Numerous difiiculties are encountered in designing short wave antennas. It is'fundamental that optimum eificiency is secured only when the antenna impedance matches the transmission line.

10 Many operators and engineers are unable to make an impedance match. A second requirement is that the antenna be mounted rigidly and as high as possible. A high antenna usually requires a transmission line for coupling to the transmitter. It is not uncommon to find that the antenna currents introduce electromotive forces in the transmission line. These forces have a deleterious effect on the radiated field. A third requirement is that the insulation withstand the applied potentials as well as the efiects of weather. It is often difficult to obtain proper mechanical strength with the desired insulation.

Therefore, among the objects of this invention are to provide a mechanically simple, inexpensive rugged antenna. Another object is to provide an antenna which may be attached to a standard transmission line without adjustments in the field. An additional object is to provide an antenna which is grounded for lightning. A further object is to provide an antenna which will not establish currents in the transmission line connected thereto. A still further object is to provide means for preventing antenna currents from inducing electromotive forces in its transmission line and providing means for utilizing said prevention means as another antenna system.

The invention will be described by referring to the accompanying drawing in which Figure l is an elevational view, partly in section, of one embodiment of the invention; Figure 2 is a plan view; and Figure 3 is a schematic dia gram of the dual antenna arrangement of the invention.

Referring to Fig. 1, a quarter wave concentric line section 1 is secured on any suitable supporting member 3 such as a grounded metallic pipe, wooden mast or the like, by means of brack ets 5. The quarter Wave line includes an outer conductor 1 and an inner conductor 9. The inner conductor 9 is connected to the outer conductor by a base plate H which preferably includes drain holes lit. The inner conductor is spaced from the outer conductor by insulators 55 I 5, IT. A quarter wave antenna i9 is conductively fastened to the inner conductor by a fitting 2| which is preferably made so that the antenna may be detached for shipment.

A transformer 23, which is a second quarter wave concentric line, is attached to the first mentioned quarter wave line. The transformer includes an outer conductor and an inner conductor 21. The inner conductor 21 is spaced from the outer conductor 25 by insulators 29. A conductive connection 3| is made between the upper terminals of the inner conductors 9, 21. The lower portion of the transformer 23 includes a fitting 33 which is arranged so that a conventional transmission line 35 may be connected to the inner 21 and outer 25 conductors of the quarter wave transmission line 23 as shown by the broken line portion of the figure.

Referring to Fig. 2, it may be seen that a conductive member 31 is secured to the outer conductor of the first quarter wave line near its top. The member 31 includes four uniformly spaced fittings 39. The fittings 39 are adapted to receive quarter wave rods 4|. While the primary purpose of the rods is to shield completely the antenna rod [9 from the associated quarter wave lines I, 23 and the transmission line 35, the rods may be used as the elements of a turnstile antenna. Other sets of rods may be suitably spaced from the upper set to obtain the full efliciency of the turnstile antenna described in U. S. Patent 2,086,976 which issued on July 13, 1937, to G. H. Brown and is assigned to the same assignee as the instant application.

It should be understood that if the shielding rods 4| are used as the elements of turnstile antenna, they must be of suitable length and spacing for the operating frequency. The length of the shielding rods should preferably be between /6 and of the wave length applied to the vertical rod antenna I9. The transmission line connections to the turnstile elements are fully described in the above mentioned patent.

The operation is as follows: The currents applied to the transmission line 35 are applied to the transformer 23. The function of the transformer is to match the impedance of a conventional 70 ohm concentric line to the antenna which has an impedance of 21.5 ohms. The currents from the transformer are applied near the base of the vertical antenna It]. The base is insulated by the quarter wave line I, which is grounded or short circuited II at its base. The quarter wave section, therefore, offers high impedance at the end adjacent the antenna. Briefly, the quarter wave section I is the base insulator for the antenna. The four quarter wave rods 4| have proven sufficient shielding to prevent currents in the vertical antenna from inducing electromotive forces in the transmission 5 lines I, 23, 35.

By Way of example, for an antenna operating at approximately 41.5 megacycles, the first quarter wave section has an outer conductor of 1" inside diameter and a length of 71%5. The inner conductor has an outside diameter of and a length of 71 A. The antenna is 71% long. The second quarter Wave section has an outer conductor of inside diameter and a length of 71%;". The inner conductor has an outside diameter of and a length of 71%;". The transformer 23 or second quarter Wave section is designed to match the antenna to a 70 ohm transmission line. Since the outer conductors of all of the concentric transmission lines are at the same potential, the outer conductors may be conductively connected together and to ground.

Thus, the invention has been described as a simple, rigid, ultra high frequency antenna Which may be connected to any conventional '70 ohm transmission line. No field adjustments are required to match the antenna and line. The antenna support may be insulated or conductive. The shielding elements of the vertical antenna may be used as the elements of a turnstile antenna. The base of the vertical antenna is insulated by a quarter wave line. The vertical antenna rod and the shielding rods may be demounted for shipment. The transformer section, as well as the antenna system, may be designed for different operating frequencies and for lines of different impedance.

We claim as our invention:

1. An antenna device including, in combina- 40 tion, a quarter wave concentric line comprising inner and outer conductors, said inner and outer conductors being connected together at one end, an antenna conductor, means connecting the other end of said inner conductor to said antenna conductor, a second quarter wave concentric line comprising inner and outer conductors, one terminal of the inner conductor of said second line being connected to said antenna conductor at its base, the other terminal of the inner conductor and the outer conductor of said second line being arranged for connection to a transmission line, and means for grounding said outer conductors.

2. An antenna device including, in combination, a quarter wave concentric line comprising inner and outer conductors, said inner and outer conductors being connected together at one end,

an antenna conductor, means connecting the f other end of said inner conductor to said antenna conductor, a second quarter wave concentric line comprising inner and outer conductors, one terminal of the inner conductor of said second line being connected to said antenna conductor at its base, the other terminal of the inner conductor and the outer conductor of said second line being arranged for connection to a transmission line, means for grounding said outer conductors, and means for shielding said antenna from said first and second mentioned quarter wave lines.

3. An antenna device including, in combination, a quarter wave concentric line comprising inner and outer conductors, said inner and outer conductors being connected together at one end, an antenna conductor, means connecting the other end of said inner conductor to said antenna conductor, a second quarter wave concentric line comprising inner and outer conductors, one terminal of the inner conductor of said second line being connected to said antenna conductor at its base, the other terminal of the inner conductor and the outer conductor of said second line being arranged for connection to a transmission line, means for grounding said outer conductors, and four quarter wave conductors located near the base of said antenna for shielding said quarter wave lines from said antenna.

4. A demountable antenna structure including, in combination, a quarter wave antenna conductor, a first quarter wave concentric line, means connecting one terminal of the inner conductor of said line to said quarter wave antenna conductor, means connecting the other terminal of said inner conductor to the outer conductor, a second quarter wave transmission line, means connecting one terminal of the inner conductor of said second line to a point near the junction of said quarter wave antenna conductor and first named inner conductor, means connecting the outer conductors of said lines, and means for connecting a transmission line to the remaining terminal of the inner conductor of said second line and to the outer conductor of said second line.

5. In an antenna structure of the character of claim 4 means effectively shielding said first and second named transmission lines from said antenna. Y

6. A demountable antenna structure including, in combination, a quarter wave antenna conductor, a first quarter wave concentric line, means connecting one terminal of the inner conductor of said line to said quarter wave antenna conductor, means connecting the other terminal of said inner conductor to the outer conductor, a second quarter wave transmission line, means connecting one terminal of the inner conductor of said second line to a point near the junction of said quarter wave antenna conductor and first named inner conductor, means connecting the outer conductors of said lines, means for connecting a transmission line to the remaining terminal of the inner conductor of said second line and to the outer conductor of said second line, means effectively shielding said first and second named transmission lines from said antenna, and means for utilizing said shielding means as the elements of a turnstile antenna for establishing a rotating field having a Wave length of other than four times said quarter Wave antenna conductor length. I

7. A demountable antenna structure including a quarter wave antenna conductor, a quarter wave line for insulating the base of said antenna conductor, a second quarter Wave line for coupling said antenna to a transmission line, a plurality of conductors located near the base of said antenna for shielding it from said quarter wave lines, and means for utilizing said shielding means as the elements of a turnstile antenna for establishing a rotating field having a wave length of other than four times said quarter wave antenna conductor length.

GEORGE H. BROWN. JESS EPSTEIN. ROBERT F, LEWIS.

Images