Physically small combined loop and dipole all channel television antenna system

[57] 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.

Claims, 5 Drawing Figures

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PATENTEDMAR20i973

3,721,990

SHEET 1 OF 2

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PATENTEDHAB20I373

3.721,990

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3,721,990 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 2½ inch spacing between the near ends of strips 47 A and 47B. 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 49B for the above example are each one-half inch wide, 6 inches long and are spaced 2½ 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 ½ 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, 2½ 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 15 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 2¾ 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 % 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 ½ inch gap between terminals 15 and 17, the overall length is over 12 inches or at least a half ⁵⁵wavelength at a frequency within the UHF television frequency band.

Referring to FIG. 5, the combiner 20 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 ₆₅high 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 ⁵ 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 VHF/, high VHF band ¹⁰ 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 ₁₅ 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 20 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 25 (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 ³⁰ 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 ³⁵ 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 spac₄θ ing 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 45 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. 50 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.