US 2419577 A
Description (OCR text may contain errors)
April 29, 1947.
L. L. LIBBY ANTENNA SYSTEM Filed March 12, 1945 INVENTOR. LESTER L. 1/55) BY Aft/7 ATTORNEY Patented Apr. 29, 1947 UNITED; STATES; PATEN T OFFICE? ANTENNA SYSTEM.
Lester L.'. Libby, East range,N.J., assignor to- Federal Telephone and Radio: Corporation, New York, N. Y., a corporation of. Delaware Application March 12, 1945, Serial No. 582,206
The present invention-relates to antenna systems particularly ofa the shielded loop type designed to be used over a broad band of the higher frequencies.
In the copending application of E. Daubaras 1, for Loop antenna systems, Serial No. 478,079, filed March 5, 1943, assigned to Federal Telephone and Radio Corporation, the assignee of the present application, a shielded loop antenna system is described in which each of a pair of resistors is connected in series between one end of the loop and a balanced dual transmission line.
These resistors serve to attenuate the effects of undesirable resonances appearing in the system. In order to maintain the electrical balance or symmetry of the system and have proper operation, it is essential that these two resistors be exactly alike. not only in their resistive values but also in any inherent capacitances and inductances therein. Such matching is difficult to obtain, and diflicult to maintain due to temperature variations and variations caused by aging.
An object of the present invention is the provision of an improved antenna system, particularly of the loop type.
Another object of the present invention is the provision of a loop antenna system in which the resistive means for attenuating the effects of resonances in the system are mounted in the loop.
Another object of the present invention is the provision of a loop antenna system utilizing resistive means for attenuating the offensive resonances therein which dispenses with the necessity of matching resistors.
Other and further objects of the present invention will become apparent and the foregoing will be best understood from the following description of an embodiment thereof, reference being had to the drawing, in which:
Fig. 1 is a diagrammatic view of an antenna system embodying my invention; and
Fig. 2 is a set of curves used in describing my invention.
In the embodiment of my present invention illustrated in Fig. 1, the numeral I generally designates a shielded loop antenna having an inner'conductor or antenna loop 2 and a shield 3 having a gap 4 at the top thereof and being coupled at the lower end thereof to a balanced dual transmission line 5 which is terminated by a terminating resistance 6 which may be located within the chassis of a utilization device 1. The terminated end of this balanced dual transmis- 2. sionline may alsobe connected-to the primary 8 are transformer9-havingits secondary In connected inany suitable manner in thetranslating;
Since the system so far described is in effect a resonant circuit, it will, as is to be expected, have a resonance peak in its response curve. Moreover, since the resonant circuit is of the transmission line type, it will have more than one of said resonance peaks over a broad band. This is illustrated in Fig. 2 in which relative response is plotted linearly along the Y axis and frequency is plotted logarithmically along the X axis. Curve ll represents the response curve and indicates the type of peaks that might be obtained in one such system without the use of my invention.
In accordance with my invention, I provide 'a simple means for attenuating these peaks. I ace complish this by providing a resistor l2 positioned at the gap and in series with the conductive loop 2. It is preferred that said resistor I2 have a value of the order of one-half to two times the surge impedance of the line formed by the inner conductor or antenna loop 2 and the shield 3. Of course it is to be understood that this value may be varied, the choice of the value of this resistor being made in accordance with a preference between amplitude of response versus fiatness of response.
Since resistance I2 is arranged at the gap, it is symmetrically disposed in relation to the entire antenna system. Therefore according to my present invention matching of resistances which serve to attenuate the peaks of curve I I no longer is necessary.
Curve l3 represents the improvement over curve II that might be obtained with one value of resistance l2. For greater values of resistor than that producing curve l3, the response curve will be flatter, but the amplitude of response over the entire range will be less.
While I have described the details of one embodiment of my invention, it will be apparent that my invention may be used in other embodiments varying from that described. For example, while I have described a shielded loop antenna employing my invention, it will be obvious that it also has application to antennas that are not shielded. Furthermore it will be apparent that the termination of the dual transmission line may be other than that hereindescribed.
Accordingly, while I have described above the principles of my 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 on the scope of my invention as set forth in the objects of my invention and the accompanying claims.
1. In an antenna system including a shielded loop antenna said shield having a gap therein, a transmission line coupled at one end to said loop antenna and terminating means coupled to the other end of said transmission line; means for attenuating the effects of resonances in said system comprising resistive means mounted within said loop antenna in series therewith and having a value in the order of one-half to two times the surge impedance of the line formed by the loop and its shield.
2. The antenna system according to claim 1 wherein said resistive means is symmetrically positioned within said loop antenna.
3. In an antenna system including a shielded loop antenna comprising a conductive loop and a shield surrounding said loop and having a gap therein, a transmission line coupled at one end to said shielded loop antenna, and terminating means coupled to the other end of said transmission line; means for attenuating the effects of resonances in said system comprising a resistor arranged in series with said loop and positioned at said gap.
4. The antenna system according to claim 3 wherein said resistor has a value of the order of one-half to two times the surge impedance of the line formed by the loop and its shield.
LESTER L. LIBBY.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS