US3761933A

US3761933A - Loop antenna with distributed impedance near the terminating gap

Info

Publication number: US3761933A
Application number: US00290801A
Authority: US
Inventors: P Smalser
Original assignee: RCA Corp
Current assignee: RCA Licensing Corp
Priority date: 1972-09-21
Filing date: 1972-09-21
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25
Also published as: JPS4971851A; CA988204A; DE2347718A1; JPS5335426B2; GB1442138A

Abstract

A low cost, physically small loop antenna is provided. The loop antenna is characterized by a metal band arranged in a loop having a pair of separated gaps, one of which is a feed gap and the other an impedance terminating gap. A resistance is coupled across the impedance termination gap. The metal bands have slots therein near the terminating gap to provide a distributed reactance near the terminated gap.

Description

mite States Patent 1 Smalser LOOP ANTENNA WITH DISTRIBUTED IMPEDANCE NEAR THE TERMINATING GAP Inventor: Paul Joseph Smalser, Deptford NJ.

Assignee: RCA Corporation, New York, NY.

Filed: Sept. 21, 1972 Appl. No.: 290,801

US. Cl. 343/740, 343/744 1:11.01. H0lq 11/12 Field of Search 343/739, 740, 741,

References Cited UNITED STATES PATENTS ll/l97l Dol et al 343/744 1451 Sept. 25, 1973 Primary ExaminerEli Lieberman A!t0rneyEdward J. Norton et a].

[57] ABSTRACT A low cost, physically small loop antenna is provided. The loop antenna is characterized by a metal band arranged in a loop having a pair of separated gaps, one of which is a feed gap and the other an impedance terminating gap. A resistance is coupled across the impedance termination gap. The metal bands have slots therein near the terminating gap to provide a distributed reactance near the terminated gap.

5 Claims, 4 Drawing Figures Patented Sept. 25, 1973 2 Sheets-Sheet 1.

TUNER Win Patented Sept. 25, 1 973 2 Sheets-Sheet mi MSEE l I l I I I 1-- WITHOUT SLOTS WITH sLors wnnour SLOTS ram: 35 :55

LOOP ANTENNA WITH DISTRIBUTED IMPEDANCE NEAR THE TERMINATING GAP BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a low cost, physically small loop antenna and more particularly to an improved very high frequency antenna designed for operating over the entire range of the VHF television channels. 2. Description of Prior Art A real and substantial need has existed for a truly low cost structurally very small antenna for efficient reception over the entire very high frequency (VHF) television frequency bands of 54 to 88 MHz and 174 to 216 MHz. Further, there is a need in order to discriminate against multipath signals for the antenna to have a minimum level back lobe and to have a means in which obstructions that cause ghosts in the television picture be nullified.

The loop antenna is described by Harold H. Beverage in U.S. Pat. No. 2,247,743. While this antenna structure provides a cardioid shape in the plane of the loop for some of the VHF television frequencies when properly designed using a single resistor, this cardioid shapes varies greatly over the entire VHF television frequency bands. At some desired VHF television fre quencies the back lobe becomes significantly large and permits ghosting. It is also desirable in order to minimize the above described ghosts that the antenna pattern have deep nulls in the radiation pattern in the rear of the antenna so that an obstruction located in the rear of the antenna be located when the antenna is properly oriented at one of these nulls to nullify the effect of the obstruction and eliminate ghosts in the television picture. It is therefore desirable that these nulls be both significant in the rear and that they be substantially at the same azimuth angle regardless of the operating frequency of the antenna.

SUMMARY OF THE INVENTION A loop antenna for operation over the entire very high frequency television frequency bands is provided by a pair of metal bands arranged in a loop. The loop has a pair of gaps with the first gap forming a pair of feed terminals and the second gap being directly opposite the first gap and having thereacross a resistance. The metal bands have slots near the termination gap to provide a distributed reactance termination in series with the resistance. The dimension of the loop between the points on the loop midway between the pair of gaps is less than a half length of an operating very high frequency wave. The value of the resistance and distributed reactance being selected so that the loop has a maximum response to signals in the very high frequency band in the direction of the first feed terminal Description of the Drawings A more detailed description follows in conjunction with the following drawing in which:

FIG. 1 is a perspective view of the all channel antenna system according to the present invention.

FIG. 2 is a side elevation of one of the metal bands in extended form.

FIG. 3 illustrates typical horizontal radiation patterns at an operating frequency of 185 MHz for the VHF loop element with and without the termination slots.

FIG. 4 illustrates typical horizontal radiation patterns at an operating frequency of 63.8 MHz for the VHF loop antenna element with and without the impedance termination slots.

DETAILED DESCRIPTION Referring to FIG. 1, there is illustrated a loop antenna element 10. The loop antenna element 10 includes a pair of semicircular metal bands 11 and 13. It is understood that the loop instead of being circular may be other contours such as square or rectangular. The loop antenna element 10 has an input feed gap across

terminals

15 and 17. The gap for the above example can be one-half inch. The

terminals

15 and 17 are coupled to a pair of conductors l9 and 21 which may be coupled to a television tuner. Remote from the input feed gap of the antenna element is a terminating gap between metal bands 11 and 13 having

terminals

23 and 25. Connected directly across the

gap terminals

23 and 25 is a resistor 27. The diameter of the loop antenna element 10 at points midway between the gaps is made less than half of the length of the operating wave )t/2). As an example, for operating over the VHF television frequency bands (54 MHz to 88 MHz and 174 MHz to 216 MHz) the diameter can be about 18 inches with the bands 11 and 13 each being about 27.5 inches long. The metal bands 11 and 13 in a preferred arrangement are 2 inches wide across width, w in FIG. 1 with a long taper near the feed

terminal terminating ends

15 and 17. This taper begins in the above example about 4 inches from each of the

ends

15 and 17. This tapering of the ends is to reduce the capacity near the feed terminals.

Referring to FIG. 2, the metal band 11 is shown in extended form. The end 17 is the feed terminal end and the end 25 is the terminating impedance end. The overall length for operating at the VHF television broadcast frequency (54-88 MHz and 174-216 MHz) is on the order of 27.5 inches long and the width as mentioned above is 2 inches with a taper at end 17 as described above and a sharper taper at end 25. The taper at end 25 begins about 1 inch from the end 25 and tapers from 2 inches to about one-half inch at the end 25. Near the end 25 is a pair of

slots

41 and 42 which extend from the edge 26 parallel to each other along a substantial portion (length l) of the length of the metal band 11. For the above example antenna these slots were made 9.5 inches long. The width of the

slots

41 and 42 are made 0.125 inch wide and at the center strip 49 between the slots is about one-half inch. The

slots

41 and 42 act to form distributed reactance sections each about 9.5 inches long in free space and each having a characteristic impedance in the order of ohms.

Referring to FIG. 1, a similar pair of

slots

45 and 47 extend from edge 24 of metal band 13. The band 13 is identical to band 11 with the

slots

45 and 47 being 9.5 inches long. The width of each of the

slots

45 and 47 is 0.125 inch wide and the center strip 51 between the

slots

45 and 47 is about one-half inch. The total impedance at the termination of the loop 10 appears as two distributed reactance sections in series with the resistor 27. The termination symmetry is provided by having the two distributed reactance sections on either end of the resistor 27.

Inboard the loop antenna 10 may be placed a UHF antenna system 30 as shown in phantom in FIG. 1. A more detailed description of this antenna is described in US. application Ser. No. 212,431 filed Dec. 27, 1971, by Donald W. Peterson and John James Gibson, now US. Pat. No. 3,721,990.

Additional improvement in the directivity for a UHF antenna system 30 when placed inside the loop antenna is provided by the L-shaped

slots

53, 55 in band 11 and the L-shaped slots 57, S9 in band 13. The

slots

53 and 55 intersect opposite edges 61 and 63 of band 11 about six inches from terminal 17. The

slots

53 and 55 extend toward each other for about a one-half inch and then they extend parallel each other for about 2 if; inches. The

slots

53 and 55 are it inch wide. Similarly

slots

57 and 59 in band 13 intersect

edges

65 and 67 of band 13 about 6 inches from terminal 15. The

slots

53 and 55 extend toward each other for about one-half inch and then they parallel each other for about 2 inches. The

slots

57 and 59 are A inch wide. Since the distance between the pair of

slots

53 and 55 and the pair of

slots

57 and 59 for the above described arrangement is 6 inches plus 6 inches, plus the one-half inch gap between

terminals

15 and 17, the overall length is over 12 inches or at least a half wave length at a frequency within the UHF television frequency band.

Referring to FIG. 3, there is shown a horizontal radiation pattern for the above described antenna with and without the terminating slots at a frequency of 185 MHz. Note the sizable back lobe associated with the antenna operating at this frequency without the terminating slots. Also note the lack ofa deep null in the rear portion of the antenna pattern without the terminating slots. Note in FIG. 3 the low level back lobe and the deep nulls in the rear radiation pattern with the terminating slots. if an obstruction such as a building that causes ghosts in the television picture is located in the rear portion of the antenna, the antenna can be oriented slightly so that one of the null areas is located toward the building and since the radiation pattern in the forward direction is relatively broad the input signal -will remain fairly strong and yet the ghosts caused by the building can be eliminated in the null. Similar patterns are associated with the above described antenna with the terminating slots at the other television high VHF band frequencies.

FIG. 4 illustrates a horizontal radiation pattern for the above described antenna with and without the terminating slots at a frequency of 63.8 MHz. Note again the reduction of the back lobe with the terminating slots and the deeper nulls in the rear pattern. Similar patterns are associated with above antenna with the terminating slots at the other television low VHF band frequencies. A comparison of FIGS. 3 and 4 reveals the similar pattern characteristics when operating with the same antenna with slots at frequencies within the high VHF frequency band or the low VHF frequency band. Since both the back lobe is reduced and the deep nulls are located at about the same azimuth angle regardless of the television VHF operating frequency with the above antenna with the terminating slots, the above antenna with the slots when properly oriented so as to nullify any particular obstructions in the rear should operate satisfactorily over the entire television VHF range of frequencies.

What is claimed is:

l. A loop antenna for operation over the entire very high frequency television frequency bands comprising:

a pair of metal bands arranged in a loop having a pair of gaps between said metal bands,

a first of said gaps forming a pair of feed terminals and a second of said gaps being directly opposite the first gap,

said loop being dimensioned to provide a linear distance less then a half wavelength at the highest frequency within said bands between points on said loop situated midway between the pair of gaps,

a resistance coupled across said second gap,

said resistance having a predetermined value providing a substantially maximum response to signals in the direction of said first gap in said bands, and

said metal bands having slots near the second gap which are dimensioned to provide a pair of distributed reactances of given values in series with said resistance,

said given values of said reactances and said predetermined value resistance cooperating to achieve low back lobes and said substantially deep and uniform nulls in the direction of the second gap over the entire very high frequency television frequency bands with respect to that obtainable without said slots.

2. The combination as claimed in claim 1 wherein said slots extend along said metal bands from the second gap toward the feed terminal gap.

3. The combination as claimed in claim 1 wherein each of said metal bands has identical slots symmetrically disposed relative to each other on each side of the second gap.

4. The combination as claimed in claim 1 wherein each of said bands has a pair of slots extending from said second gap along said metal band toward the feed terminal gap.

5. The combination as claimed in claim 4 wherein the length of said slots is about 9.5 inches and the width of said slots is about 0.125 inch.

Claims

1. A loop antenna for operation over the entire very high frequency television frequency bands comprising: a pair of metal bands arranged in a loop having a pair of gaps between said metal bands, a first of said gaps forming a pair of feed terminals and a second of said gaps being directly opposite the first gap, said loop being dimensioned to provide a linear distance less then a half wavelength at the highest frequency within said bands between points on said loop situated midway between the pair of gaps, a resistance coupled across said second gap, said resistance having a predetermined value providing a substantially maximum response to signals in the direction of said first gap in said bands, and said metal bands having slots near the second gap which are dimensioned to provide a pair of distributed reactances of given values in series with said resistance, said given values of said reactances and said predetermined value resistanCe cooperating to achieve low back lobes and said substantially deep and uniform nulls in the direction of the second gap over the entire very high frequency television frequency bands with respect to that obtainable without said slots.