US2158875A - Antenna system - Google Patents

Description

- Room 7 May 16, 1939. M, LEEDS 2,158,875

ANTENNA SYSTEM Filed May 28, 1937 TUNING EQUIPMENT TRANSMIT TER Inventor I Laurance M. Le ds, 9 His Attorney.

Patented May T6, 193 9 UNITED STATES Search Room PATENT OFFICE ANTENNA SYSTEM Lauranee M. Leeds, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application May as, 1937, Serial No. 145,251

11 Claims.

My invention relates to antenna systems and more particularly to such systems adapted for transmission and reception of radiant energy of different frequencies.

In police radio applications it frequently happens that oscillations of a medium high frequency are employed for transmission of signals from a central station house to police motor vehicles though the protected municipality and ultra high frequencies are employed for transmission from the vehicles to the central station house. Of course, antennae must be provided at the central station house for radiation of these medium high frequency and for reception of the ultra high'frequencies. My invention has for one of its objects to reduce the cost of these antennae. A further object of my invention is to reduce the cost of such antennae without in anywise reducing the efficiency of the antennae. V

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single flgure represents an embodiment of my invention.

Referring to the drawing I have shown therein an antenna tower I. This tower may be one adapted for radiation of medium high frequencies such as frequencies within the range of from 1500 to 2500 kilocycles, this tower being connected to the signal transmitter 2 through tuning equipment 3 and a concentric transmission line 4 and, of course, being insulated from ground by means of insulators 5. This tower may be 100 to 200 feet in height, or even higher, dependent upon the frequency employed, and commonly it is of structural steel construction-and comparatively expensive. At 6 I have shown a receiver which may be located in proximity to the transmitter employed with the transmitter tower and which may operate at ultra high frequencies, that is, frequencies in the range of from 30 to 42 megacycles, for example. The antenna employed in connection with such a receiver is commonly fifteen to thirty or more feet in length and, particularly in municipal areas, it is desirable that it be elevated to a considerable extent above the ground. In accordance with my invention the receiving antenna is mounted on top of the radiating tower I, this receiving antenna being indicated at 1. This antenna is connected to the receiver 6 through a concentric transmission line 8 which extends down the tower and to the receiver.

The antenna may be of any well-lmown construction but I prefer to employ one comprising a vertical conductor, which, in accordance with my invention, is conductively connected to the tower and extends above the tower whereby it operates as a section of the vertical tower radiator, thus increasing the length of the tower as a radiator of the transmitted oscillations. This vertical conductor may have a length equal to /4 of a wavelength of the waves to be received, the lower quarter of a wavelength operating together with the arm 9, which projects from the base of conductor 1 and extends upward parallel with conductor 1 by a quarter of a wave length, as a quarter wavelength transmission line section, or impedance network, matching the impedance of the transmission line with that of the upper half wavelength of the conductor 1. That is, the outer conductor of the transmission line is connected at the midpoint of the base of the arm 9 whereas the inner conductor of the transmission line is preferably connected to the conductor 9 and at such a point that the transmission line is terminated in an impedance equal to its own surge impedance. In this way the transmission line is terminated in its surge impedance and the dissymetry produced by reason of the fact that the conductor 1 is longer than conductor 9 is balanced by the connection of the inner conductor to the shorter arm.

This connection of the receiving antenna to the transmission line is described and claimed in my copending application, Serial No. 57,343, filed January 3, 1936, Patent No. 2,124,424, dated July 19, 1938, entitled Antenna system, and which is assigned to the same assignee as my present application.

Of course the receiving antenna and transmission line 8 extending down the tower are at the same potentials at which the tower operates. It is necessary to prevent these potentials from affecting the receiver and at the same time to prevent any material short-circuiting of the tower to ground. This is effected by forming the transmission line into a coil ill at the base of the tower as shown and grounding the shield at the end of the coil adjacent the receiver, the input terminals of the receiver being connected between ground and the inner conductor. This coil together with the capacitance of the insulators plus any additional capacity in shunt with the coil which may be provided, such as the capacitance which I have indicated at i I, may be adjusted to form an antiresonant circuit at the frequency of waves radiated by the tower I.

As thus constructed it will be seen that my arrangement obviates the necessity for additional means to support the receiving antenna. At the same time, by mounting the receiving antenna on top of the radiating tower, it operates as a part of the tower with respect to the radiation of energy, thereby reducing the cost of the radiating tower. In other words, in accordance with my invention a section of the radiating tower is, in fact, employed as the receiving antenna.

While I have shown a particular embodiment of my invention it will of course be understood that difierent arrangements of the transmitting and receiving antennae may be employed, and that I contemplate by the appended claims to cover any such arrangements as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a radiating antenna tower, a receiving antenna mounted on top of said tower and electrically connected thereto to assist radiation of energy thereby, and a receiver connected to said receiving antenna to receive energy intercepted thereby.

2. In combination, a radiating antenna tower and a receiving antenna mounted on top of said tower, said receiving antenna being conductively connected to said tower and acting as a radiating element thereof.

3. In combination, a vertical radiating conductor, a receiver, means to radiate oscillations from the entire vertical conductor, a connection from a point elevated on said vertical radiating conductor to said receiver, and means including said connection and a portion of said vertical radiating conductor above said connection to impress on said receiver received oscillations of frequency different from the frequency of oscillations radiated by said entire vertical conductor.

4. In combination, a radiating tower, a short wave antenna, said short wave antenna being mounted on top of said tower and electrically connected thereto to act as a part of said radiating tower with respect to oscillations of the frequency radiated by said tower, a receiver connected to said short wave antenna, and means to prevent oscillations of the frequency radiated by the tower from being impressed on said receiver.

5. In combination, a continuous vertical conductor adapted for operation at a certain wavelength, a source of oscillations of said wavelength connected between ground and one end of said tower, a receiver adapted for operation at a shorter wavelength, an arm projecting from said conductor having a portion substantially parallel with said conductor, said portion being shorter than the portion of said conductor above the point of attachment of said arm by such an amount that the difierence is the length of receiving antenna for said receiver, a transmission line extending from said arm to said receiver, and means utilizing said arm to match the impedance of said line with that of the portion of the vertical conductor above the upper end of said arm.

6. In combination, a long single conductor, means to radiate high frequency energy from said conductor, and means utilizing only a small portion of said single conductor for reception of high frequency energy.

7. In combination, a vertical conductor,

conductor being a single continuous conducting element having only distributed impedance, means to utilize the whole conductor as an antenna operating at a certain wave length, and means to utilize only the upper portion of said vertical conductor as an antenna operating at a different wave length.

8. In combination, a single continuous antenna conductor having only distributed constants, a plurality of high frequency equipments, one of said equipments being connected between one end of said conductor and ground, and the other of said equipments being connected to an intermediate point on said conductor, the connections to said one equipment including means to transmit energy with respect to which the entire conductor operates as an antenna, and the connection to the other equipment including means to transmit energy with respect to which only a portion beyond said intermediate point from said one end operates as an antenna.

9. In combination, a vertical continuous conductor uninterrupted by concentrated impedance, high frequency equipment connected between the bottom of said conductor and ground, and operating at a frequency at which the entire conductor operates as an antenna, a second high frequencyequipment, a transmission line extending from said second high frequency equipment to a point elevated on said conductor, said transmission line being connected and arranged to transmit between said second equipment and conductor energy with respect to which only a portion of said conductor above said point operates as an antenna.

10. In combination, a structural steel tower, a conductor projecting from the top of said tower and conductively connected directly thereto, means to energize said tower and conductor with currents to be radiated by said tower and conductor acting together as an antenna, high frequency equipment, a transmission line extending from said conductor down said tower to said high frequency equipment, and means to transmit energy with respect to which only said conductor operates as an antenna between said equipment and conductor over said transmission line.

11. In combination, a structural steel tower, two substantially parallel conductors extending from the top thereof and rigidly conductively connected thereto to act therewith as a single antenna for long waves, one of said conductors being shorter than the other, a concentric transmission line extending along said tower having an outer shield conductively connected to the tower and an inner conductor connected to a point on one of said parallel conductors, short wave radio equipment, and means to transmit energy through said transmission line between said equipment and parallel conductors, said parallel conductors being so proportioned that the longer conductor acts as an antenna for said short waves and the short conductor cooperates therewith to match the impedance of the transmission line to that of the longer conductor acting as an antenna, and means to prevent transmission of long waves from said

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