US2594055A - Antenna coupling system - Google Patents

Description

April 22, 1952 C. J. MILLER ANTENNA COUPLING SYSTEM Filed June 29, 1949 TRANSMITTER TRANSMITTER WITNESSES:

INVENTOR Coleman J. Miller.

ATTORNEY Patented Apr. 22, 1952 ANTENNA COUPLING SYSTEM Coleman J. Miller, Catonsville, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 29, 1949, Serial No. 101,942

This invention relates to antenna systems, and it has as an object the provision of an antenna system which can be used efficiently at two different frequencies.

Ordinarily where two carrier waves having different frequencies are transmitted from one location, it is customary, for efficient operation, to use a separate antenna system for each frequency. While so-called band antenna systems have been designed for use with different frequencies, in such systems the impedances of the antennas have been matched by circuits connected in shunt to the antennas, for matching the impedances of their associated transmission lines at the different frequencies for preventing reflection losses and the formation of standing waves on the lines. For many duties such a broad-band system is not as suitable for the efficient transmission of two frequencies as separate antenna systems matched to the two frequencies. It has also been proposed to use a single antenna for the transmission of several frequencies, and to manually adjust the physical length of the antenna so as to match the different frequencies. While such antennas are more efficient than those used in broad-band antenna systems, their complications and their inability to handle efficiently, the simultaneous transmission of two frequencies, prevents their use for many duties.

This invention provides for the efiicient use of a single antenna with two different frequencies. The antenna is a dipole, the length of which is such that it is resonant at a frequency midway between the two frequencies with which 5 Claims. (Cl. 250-33159) an antenna which can be efficiently used simulwave sections of transmission lines as coaxial init is to be used. A parallel tuned circuit which also i resonant at the frequency to which the dipole is resonant, is placed in series with each of the two transmission lines connected to the dipole. At the higher of the two frequencies, the reactance of the dipole will be inductive, and the reactance of the tuned circuits will be capacitive, the total reactance being zero. At the lower of the two frequencies, the reactance of the dipole will be capacitive, and the reactance of the tuned circuits will be inductive, the total reactance being zero. Thus the antenna is matched to each of the two frequencies.

A feature of the invention is that it provides an antenna which can be efficiently used simultaneuously with two different frequencies.

Another object of the invention is to provide an antenna for use with two frequencies and having zero reactance at each frequency.

Another object of the invention is to provide nor conductors, and which form parallel tuned circuits in series with the antenna and the transmission lines.

Referring now to Fig. l, the lower frequency transmitter I!) which operates at, for example, a carrier frequencyof me. is connected through the filter H to the transmission lines l2. The transmission lines are connected through the parallel-tuned circuits l3 consisting of the inductors l4 shunted by the capacitors 15, to the quarter-wave arms 16 of the half-wave, dipole antenna l1.

The higher frequency transmitter I8 which operates at, for example, a carrier frequency of 150 me, is connected through the filter l9 to the transmission lines l2.

The filters II and I9 are band pass filters which pass only the frequencies of the carriers and their sidebands, of the transmitters Ill and I8 respectively.

The dipole antenna H is cut to resonate at a frequency of me. which is approximately midway between the carrier frequencies of the two transmitters. The parallel tuned circuits I3 are also tuned to resonate at the mid-frequency of 125 mc., and for accomplishing this, the inductors [4 may each have an inductance of .02 microhenry, and the capacitors l5 each may have a capacity of 80 micromicrofarads.

In operation, at the higher carrier frequency of the transmitter [8, the reactance of the dipole antenna will be inductive, and the reactance of the parallel-tuned circuits l3 will be correspondingly capacitive whereby the total reactance is zero. At the lower carrier frequency of the transmitter I ii, the reactance of the dipole antenna will be capacitive, and the reactance of the parallel-tuned circuits 13 will be correspondingly inductive whereby the total reactance will be zero. Thus the single antenna offers zero reactance at the carrier frequency of both transmitters, and is equally effective at both frequencies.

The two transmitters can be operated simultaneously without interaction or, of course, can be operated alternately.

There is no broad-band effect except that inherent in the physical size of the dipole. A dipole having a large cross-sectional diameter will be broader banded than one having a smaller diameter.

Fig. 2 of the drawing illustrates a conventional dipole construction which may be used in the practice of this invention, the dipole including the parallel-tuned circuits 13 illustrated by Fig. 1. The quarter-wave, dipole arms 15 are tubular, and are closed at their outer ends 20 and are open at their inner ends 2|. The coaxial inner conductors 22 are shorted at their outer ends to the outer ends 20 of the .dipole, and are connected at their inner ends to the transmission lines 12. The radiating surface of the antenna is the outer surface of the dipole, and the parallel resonant circuits corresponding to the circuits 13 of Fig. 1, are formed by the proper sizing and spacing of the opposing outer surfaces of the inner conductors 22 and the inner surfaces of the dipole arms, l6.

While the invention has been described in connection. with radio transmitters, it. can also be used with. radio receivers.

I claim as my invention:

1. An antenna system for use with two radio frequency sources. having different frequencies, comprising a dipole antenna. resonant. at a frequency midway between said frequencies, a pair of transmission lines for connecting said. frequency sources to said: antenna, and means forming parallel-tuned .circuits in series with said transmission lines and said antenna, said circuits being resonant at said midway frequency.

2'. An antenna system as claimed in claim 1 in which the dipole arms are coaxial conductors shorted at their outer ends. and are-connected to the transmission lines by inner conductors, and in which the parallel-tuned circuits are-formed by the opposedouter surfaces of the inner conductors and the inner surfaces of the dipole arms.

3. An antenna system as claimed in claim 1 in which the parallel-tuned circuits areshunt connected inductors andcapacitors connected in tenna resonant at a frequency midway between.

said frequencies, a pair of transmission lines connected to said transmitters, and means providing parallel-tuned circuits resonant at said midway frequency connected in series with said lines and the arms of said antenna.

COLEMAN J. MILLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,545,041 Doring July 7, 1925 1,610,073 Alexanderson Dec. 7, 1926 1,730,903 Schmidt et al Oct. 3, 1929 1,969,328 Roosenstein Aug. 7, 1.934 2,019,341 Dome Oct. 29, 1935 2,128,400 Carter Aug. 30-, 1938 2,284,434 Lindenblad May 26, 1942 2,311,364 Buschbeck et a1. Feb. 16, 1943 2,480,172 Willoughby Aug. 30, 1949 2,490,957 Gluyas, J-r Dec. 13, 1949 2,493,514 Wehner Jan. 3, 1950 FOREIGN PATENTS Number Country Date 157,060 Great Britain Dec. 18, 1920 534,894 France Apr. 4, 1922 OTHER REFERENCES Two Transmitters on One Aerial, by Morton and Whitehead; Electronic Engineering, May 1948, pages 157 to 159.

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