US 3721990 A
A low cost, physically small, all channel television antenna system is provided for reception in high signal strength areas. The antenna is characterized by a loop having a pair of separated gaps, one of which is a feed gap and the other an impedance termination gap for operating as a directional reception antenna at the low and high VHF television frequency bands. Inboard the loop is placed a television band UHF dipole antenna. The input terminals of the dipole antenna and the feed terminal of the loop antenna are each coupled to a combiner with a single output from the combiner.
Description (OCR text may contain errors)
United States Patent 91 Gibson et al.
[ 1March 20, 1973  PHYSICALLY SMALL COMBINED LOOP AND DIPOLE ALL CHANNEL TELEVISION ANTENNA SYSTEM  Assignee: RCA Corporation, New York, N.Y.
 Filed: Dec. 27, 1971  Appl. No.: 212,431
[5 6] References Cited UNITED STATES PATENTS 2,657,312 10/1953 Saranga ..343/726 7|\T p73 28 5 COMBINER 7/1970 Shelton et a1 ..343/727 3,611,389 10/1971 Coors 3,623,110 11/1971 Doi et al ..343/726 Primary ExaminerEli Lieberman AttorneyEdward J. Norton et al.
[5 7 ABSTRACT A low cost, physically small, all channel television antenna system is provided for reception in high signal strength areas. The antenna is characterized by a loop having a pair of separated gaps, one of which is a feed gap and the other an impedance termination gap for operating as a directional reception antenna at the low and high VHF television frequency bands. Inboard the loop is placed a television band UHF dipole antenna. The input terminals of the dipole antenna and the feed terminal of the loop antenna are each coupled to a combiner with a single output from the combiner.
12 Claims, 5 Drawing Figures PATENTEUmzoma 34.721 0 SHEET l-UF 2 N PB 33 65 COMBINER p 1m 43 NW l9 17RELIATIVE FIELD STRENGTHS PATENTEUIiRZOIBH 3,721,990
SHEET 2 [1F 2 lie. 4
LOW PASS FILTER n J m m 5 w n u u n n n u G. m n %R G. 25255 3% WEEK E l I F U F half inch wide. The metal strips 47A and 47B are colinear and are coplanar to the dipole antenna 30. For the above example, there is a 2% inch spacing between the near ends of strips 47A and 478. The director 47 is for the above example 2% inches forward of feed terminal 35, 36 of dipole antenna 30. The director element 49 is made up of colinear metal strips 49A and 49B which are coplanar to and forward of director 47 and dipole 30. The metal strips 49A and 498 for the above example are each one-half inch wide, 6 inches long and are spaced 2% inches forward of director 47. The metal strips 49A and 49B are for the above example spaced one-half inch apart at their near ends. Director 51 is similarly constructed in the above example of a pair of inch wide metal strips 51A and 51B. The metal strips 51A and 51B are colinear to each other and are coplanar to and forward of directors 49, 47 and dipole 30. The metal strips 51A and 51B are in the above example each 6 inches long, 2% inches forward of director 49 and are spaced one-half inch apart. By the use of directors 47, 49 and 51 the UHF antenna system 34 made up of the directors 47, 49 and 51, the dipole antenna 30 and the reflector 47 becomes more directional with more antenna gain than that of a single bow tie antenna for signal coming from the direction of the feed terminals and 17.
Additional improvement in the directivity of the UHF antenna system is provided by the L-shaped slots 53, 55 in band 11 and the L-shaped slots 57 and 59 in band 13. FIG. 3 illustrates a typical UHF frequency band antenna pattern taken in the horizontal plane for a UHF/VHF antenna system as described above without the slots. This pattern was measured at 600 MHz. FIG. 4 illustrates a typical pattern for the antenna system with the slots at the same UHF frequency band or channel as in FIG. 3. This pattern is again measured at 600 MHz. Notice the reduction of the strong side lobes at 90 from the main lobe.
The slots 53 and 55 intersect opposite edges 61 and 63 of band 11 about 6 inches from terminal 17. 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 53 and 55 are one-fourth inch wide. Similarly slots 57 and 59 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 )2 inches. The slots 57 and 59 are one-fourth 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 h inch gap between terminals 15 and 17, the overall length is over l2 inches or at least a half wavelength at a frequency within the UHF television frequency band.
Referring to FIG. 5, the combiner may be simply a high pass and low pass filter combiner. In the combiner between the television output lead terminals 71 and 73 and the UHF dipole antenna 30 lead terminals 41 and 43 there is a high pass filter to present a high reactance to VHF signals and pass UHF frequency signals. In the combiner 20, a low pass filter is designed to present a high reactance of UHF frequency signals and pass signals in the low and high VHF television frequency bands.
Since the gain of the above described antenna system and more particularly the loop antenna element 10 is poor, it is desirable that the signals be additionally amplified before coupling over leads 71 and 73 to the television set. In this case, the output from the UHF loop element 10 at terminals 19 and 21 may be applied to a balun to convert from a balanced transmission line to unbalanced or coaxial type. The output from this balun is passed through a low VHFI, high VHF band splitter or filter and the selected outputs are separately amplified and the recombined. The output from UHF antenna dipole 30 is coupled through a balun and then may be amplified and combined with the amplified VHF signals. A balun is usually required before amplification since the amplifiers are usually constructed to be coupled to an unbalanced line such as a coaxial line. Since the television set usually accepts only a balanced line (twin lead) the output of a single ended UHF/VHF combiner is coupled to a balun to convert to a balanced line before being applied to the television set.
Additional gain in the UHF television frequency band can be had without increasing the size of the loop 10 by making the flat metal sheets 31 and 33 longer (each about 1 inch longer for example) and by bending the sheets 31 and 33 at right angles as shown by dashed lines 75 and 76 in FIG. 1. This structure introduces some additional VHF capacity across the VHF loop. This capacity effect may be overcome by the high pass filter between the pair of terminals 41 and 43 and the pair of terminals 71 and 73.
In the above described arrangement the UHF dipole 30 and associated UHF antenna system is inside the plane of the loop element 10. Equally well, according to the teaching herein the dipole antenna 30 and associated antenna system can be placed inboard the loop with the antenna 30 and associated system either slightly above or below the plane of the loop. The spacing slightly above or below the plane of the loop would provide in accordance with the example herein, less than one half a UHF television frequency band wavelength spacing between the plane of the feed of the VHF loop element and the plane of the feed of the UHF dipole antenna.
In the construction of the antenna system described above, the spacing and support for the metal elements can be a substrate of low dielectric foam or low dielectric plastic, not shown, to which the elements are fixed. The spacing between strips 47A and 47B is made large to accommodate a mast (indicated by dashed line 81) between them. The substrate, not shown, is affixed to the mast 81.
What is claimed is:
1. An antenna system for operation in the very high frequency band and in the ultra high frequency band comprising:
PHYSICALLY SMALL COMBINED LOOP AND DIPOLE ALL CHANNEL TELEVISION ANTENNA SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a low cost combined UHF (ultra high frequency) and VHF (very high frequency) band antenna system and more particularly to an improved all channel television antenna system specifically designed for high signal strength areas and operating over the entire range of television channels from channels 2 to 83.
2. Description of Prior Art A real and substantial need has existed for a truly low cost, structurally very small and rigid antenna for efficient reception over the VHF television frequency band and the UHF television frequency band. Further there is a need for such an antenna to be sufficiently directive to discriminate against multipath signals in high signal strength areas.
Conventional indoor antennas are generally low cost but are not sufficiently directive to discriminate against alternate path signals commonly encountered and the result is often ghosts in the television picture. Conventional outdoor antennas are more directional than conventional indoor antennas but they are large, bulky and more costly.
SUMMARY OF THE INVENTION ,being directly opposite the first gap and having thereacross a resistance. The dimension of OF loop between points on the loop midway between the pair of DESCRIPTION of DRAWINGS A more detailed description follows in conjunction with the following drawings in which:
FIG. 1 is a perspective view of the all channel antenna system according tothe present invention.
FIG. 2 is a typical horizontal radiation pattern for the antenna loop element.
FIG. 3 is a typical horizontal radiation patten for the UHF antenna dipole with reflectors and directors inside VHF loop element without slots.
FIG. 4 is a typical horizontal radiation pattern for the UHF antenna dipole with reflectors and directors inside the loop element with slots.
FIG. 5 is a diagram of a UHF/VHF combiner.
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 1/2 inch. The terminals 15 and 17 are coupled to terminals 19 and 21 of a UHF/VHF combiner 20.
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 predominantly resistive impedance 27. The diameter of the loop antenna element 10 at points midway between the gaps is made less than half the length of the operating wave. As an example, for operating over the VHF television frequency bands the diameter can be 18 inches with the bands 11 and 13 each being 28 inches long. The metal bands 11 and 13 can be 2 inches wide across width, w in FIG. 1 with a taper near the terminating ends 15, 23, 17 and 25. This taper begins in the above example about 4 inches from each of the ends. This tapering of the ends is to reduce the capacity near the terminals. The positive resistance 27 can be 395 ohms.
The resulting radiation low and high VHF television frequency patterns from the structure described above are cardioid in shape in the plane of the loop as shown in FIG. 2. As can be seen the antenna possesses good directive gain due to its pattern characteristics. For a more detailed description of the loop antenna see US. Pat. No. 2,247,743 of Harold H. Beverage.
Inboard the loop antenna 10 is a flat UHF fanlike or bow tie antenna dipole 30. The bow tie antenna dipole 30 includes a pair of triangle shaped flat metal sheets 31 and 33 having a feed gap across terminals 35 and 36. The flat metal sheets are each in the shape of an isosceles triangle with the sharpest angle of the triangle being between the equal sides. The portion of the sheet having the sharpest angle provides the feed terminals of the dipole 30. The length and the shape of the dipole is such as to provide a UHF dipole over the entire UHF television frequency band. For this purpose the dipole 30 can be 14% inches long from extreme end 37 to extreme end 39. The width of dipole halves 31 and 33 at extreme ends 37 and 39 can be 3% inches. The gap between terminals 35 and 36 can be three-eighths inch. The terminals 35 and 36 are coupled to terminals 41 and 43 of UHF/VHF combiner 20.
Rearward of the antenna dipole 30 with respect to the feed loop element 10 is a reflector 45 for dipole 30. The reflector 45 lies in the same plane as the metal dipole sheets 31 and 33, and is for the above example positioned about 2% inches rearward from the center feed at terminals 35 and 36, and for the above example is 14% inches long to act as a reflector for dipole antenna 30. The reflector 45 can be for the above example a flat metal strip one-half inch wide. By the use of reflector 45, the combined UHF antenna system 34, becomes more directional in that improved reception of signals coming from the direction of the feed terminals 15 and 17 is provided.
Between the dipole antenna 30 and the feed terminals I5 and 17, there is provided three director elements 47, 49 and 51. The director element 47 is made up of a pair of metal strips 47A and 473 each of which can be for the above example 6 inches long and oneing very high frequency wave such that said loop has a maximum response to said signals in the direction of said first gap and a lesser response in the opposite direction,
an ultra high frequency dipole element fixed substantially inboard said loop and having a total length to act as a half wavelength dipole element for a frequency within the ultra high frequency band, said dipole element having terminal means adapted to be coupled to a second transmission line.
2. The combination claimed in claim 1, wherein said dipole element is a bow tie antenna element adapted to provide reception over the entire television ultra high frequency band.
3. The combination claimed in claim 1, wherein the feed terminals of said loop are aligned with the feed terminals of said dipole element.
4. The combination claimed in claim 3, including a thin metal strip fixed rearward of said dipole relative to the terminals of the feed of said loop element.
5. The combination claimed in claim 4, including a pair of colinear thin'metal strips forward of said dipole element between the dipole element and said loop element feed.
6. The combination claimed in claim 3, including a combiner, said combiner having a pair of input terminals and an output terminal, said combiner including between a first of said pair of input terminals and said output terminal, a relatively low pass filter for providing low loss coupling of signals within the very high frequency band and for presenting a high reactance to signals within the ultra high frequency band, said combiner including between a second of said pair of input terminals and said output terminal a relatively high pass filter for providing low loss coupling of signals within the ultra high frequency band for presenting a high reflective reactance to signals within the very high frequency bands, said first transmission line being coupled between said first input terminal of said combiner and said feed terminals of said conductive loop elements, said second transmission line being coupled between said second input terminal and said feed terminals of said ultra high frequency dipole element.
7. The combination claimed in claim 1, wherein said loop has slots therein with at least one slot being a given distance from the first feed terminal of said loop and at least one other slot being said given distance from the second feed terminal of said loop.
8. The combination claimed in claim 7, wherein said given distance is at least a quarter wavelength at a frequency within said ultra high frequency band.
9. The combination claimed in claim 1, wherein said conductive loop is just slightly larger in diameter than the length of said dipole element.
10. The combination claimed in claim 1, wherein said very high frequency band includes said low and high very high frequency television frequency bands and the circumference of the loop is less than a half of an operating wave at the low very high frequency television band.
11. The combination claimed in claim 10, wherein said dipole element is fixed inboard the loop element with the plane of the dipole element spaced less than a half a television ultra high frequency band wavelength from the plane of'theloop. A
12. The combination claimed in claim l1, wherein