US2837742A - Television antennas - Google Patents

Description

June 3, 1958 v R. s. WEISS 2,837,742

TELEVISION ANTENNAS Filed Oct. 15, 1956 INVENTOR Ro ert S. Weiss BYzygmn. (x- M ATTORNEYS TELEVISEON ANTENNAS Robert S. Weiss, South Euclid, Ohio, assignor to Finney Manufacturing Company,-Bedford, Dhio, a corporation of Ohio Application October 15, 1956, Serial No. 615,809

16. Claims. (Cl. 343-749) This invention-relates to radio frequency antennas and particularly to antennas for television reception,

One of the principal problems facing the television antenna industry has been to provide an antenna having highgain with a reasonably uniform impedance over the entire low and high band frequency ranges established for commercial television broadcasting. In my U. S. Patent No. 2,726,390, granted December 6, 1955, I disclosed and claimed howa conventional driven dipole, of either the straight or folded dipole type, having a length selected for operation in a low frequency range, such as the low band of commercial television frequencies (54 to 88 me), maybe modified by a closely spaced parasitic element to greatly improve its operation over the high band television frequencies (174 to 216 me). The effect on the high band operation is to give the array closely similar gain, directivity, and impedance characteristics over that band to those which are characteristic of a three-element collinear array dimensioned for the same frequency range, without materially altering the charac teristics of the dipole in the low band range for which it is dimensioned. In the case of a half-wave dipole for low band, for example, the parasitic element was a nondriven dipole substantially /3 the resonant length of the driven dipole, and was centrally aligned in spaced parallel relationship therewith. By adjusting the spacing of the driven and non-driven dipoles within the range of about 1% and 7% of a half-wave to which the driven dipole is resonant (i. e., 1% to 7% of the resonant length of the half-wave driven dipole), the non-driven dipole had little effect on the characteristics of the driven dipole in the low band. However, in the high band, the resulting array could be given an impedance of substantially the desired 300 ohms, a directivity pattern having narrow forward and rearward lobes with virtually no side lobes, and substantially the same gain as a three-element collinear array dimensioned for the same frequency range.

Such an array as thatjust described has its sharpest directivity pattern and maximum forward gain at high band and low band frequencies which are substantially in the ratio of 3:1, e. g., high and low band frequencies of 195 me. and 65 me. respectively. Though having good broad band characteristics over a substantial range in both bands, the pattern and gain in each band naturally deteriorates appreciably in both bands at frequencies substantially above and below the two optimum frequencies. Thus, the low band frequency for which the driven dipole is cut determines the proper length of the non-driven dipole and the optimum frequency of operation in the high band,'i. e., substantially three times the optimum low band frequency. While the three-to-one ratio of the optimum high and low band frequencies can be varied somewhat by departing from the ideal three-to-one ratio of the half-wave resonant lengths of the driven (low band) and non-driven (high band) dipoles, or by changing theirspacing and/ or other physical dimensions, this involves departing from the ideal or theoretical design atent relationships of the array with a corresponding sacrifice in overall performance.

The present invention is an improvement over the invention of myprior patent, the principal object being to provide an array of the kind just described .in which the ratio of the optimum high and low band frequencies may be other than three-toone, without the sacrifice in overall performance that heretofore resulted. Other objects of the invention are to do this in a simple and inexpensive manner suitable for commercial mass production of television antennas in the present highly competitive market.

The invention is characterized by interposing a plurality of condensers symmetrically in the driven dipole, with which a closely spaced non-driven dipole is associated as described above. The condensers are selected or tuned to have a particular capacitive reactance at the desired, low, half wave resonant frequency of the driven element containingthem. By reason of the inherent frequency sensitivity of a condenser, its capacitive reactance atthe much higher high band frequencies is necessarily relatively small.

The effect of interposing a capacitive reactancevin a driven element of a given-physical length is to reduce its effective electrical length, the amount of such reduction being proportional to the interposed capacitive reactance and to-the current therein. According to the theory of operation disclosed in'my above mentioned patent, the instantaneous current in the driven dipole-at its halfwave resonant frequency is zero at its extremeends and maximurnat its center. At a high band frequency at which the resonant length of the driven-dipole is 3 halfwaves, however, there arethree half-wave current loops providing two additional Zero current pointslocated opposite the extremities of the non-driven dipole. Therefore, when the condensers are positioned at or'near these last mentioned points, their capacitive reactance and hence their effect on the electrical length of the driven dipole on'high band is very small and generally negligible. At low band frequencies, on the other hand, the inherent capacitive reactance of the condensers is much greater because the frequency is lower, and the-instantaneous current'is higher when they are so positioned. Thus, they have a pronounced effect in shortening theelectrical length of the driven dipole at low band frequencies but little effect at high band frequencies.

It is generally desirable thatthe condensers be'located substantially opposite the extremities of the non-driven dipole so as to minimize their effect at high band frequencies. However, it should be apparent from the foregoing that this is riot essential, since the effect of the condensers is more pronounced at low frequencies than at high frequencies, other factors being equal. For example, if thecondensers are moved closer to the center of the driven'dipole-where the instantaneous current is a maximum,-their-efiect at low band frequencies increases at the same time thattheir effect at high band frequencies increases. Thus, the electrical length of the driven dipole will beireduced more at low band frequencies than at high-bandtfrequencies, and the overall effect of agreater electrical length of this element on low hand than on high band is still achieved. 'Appropriate adjustment of the lengthof the non-driven dipole in such a case retains essentially the same overall'mode of operation, though other:effects, such as impedance changea'may limit the extent to which such departures from the generally preferred arrangement can be effectively used.

The character of the invention and its various advantages and objectives will more fully appear from the following description of illustrative embodiments of the invention.

As is true of the invention of. my U. S. Patent 2,726,390, the present invention is applicable both to simple, straight dipoles and to folded dipoles and the like. Because the folded dipole form of the invention has well known advantages for television reception, it is the preferred type for use in accordance with the invention, though the in vention is not limited to use of a driven dipole of this particular type.

Referring to the accompanying drawing- Figure 1 is a diagrammatic perspective view of a straight driven dipole and a non-driven dipole forming an antenna array in accordance with the invention;

Fig. 2 is a similar diagrammatic perspective view of a driven folded dipole and a non-driven dipole forming an antenna array in accordance with the invention;

Fig. 3 is a front elevation of a preferred folded dipole construction for use in the array diagrammatically shown in Fig. 2; and,

Fig. 4 is a fragmentary elevation of a portion of the folded dipole construction shown in Fig. 3.

In Fig. 1 there is shown a straight driven dipole, generally designated 10, having an overall length L. The dipole has a feed gap at its center, and transmission line, leads 11 are connected to the dipole 10 at opposite sides of the gap for feeding, or being fed by, a radio frequency transmitter or receiver. A pair of condensers 12 are symmetrically interposed in the dipole 10 so as to divide it into three parts connected in series through the condensers. As shown, these three parts have the same overall length L/ 3.

A non-driven dipole 13 is disposed adjacent the driven dipole 10 in closely spaced parallel relationship there with. Depending upon various dimensional factors, the distance of the non-driven dipole from the driven dipole may range from about 1% to about 7% of a half-wave for which the driven dipole 10 is a half-wave element (i. e., 1% to 7% of the half-wave resonant length of the driven dipole 10). The non-driven dipole is preferably disposed in the same horizontal plane as the driven dipole so that itmay lie directly between the driven dipole and the source of a signal to be received, or a point to which a signal is to be transmitted. The center of the nondn'ven dipole is in transverse alignment with the center of the driven dipole, as indicated by the horizontal line H-H, passing through the center of the two dipoles, and the vertical line VV, passing through the center of the feed gap of the driven dipole. As indicated by the dimension lines in Fig. 1, the extremities of the non-driven dipole are opposite (i. e., transversely aligned with) the condensers 12.

In designing the antenna of Fig. 1, the overall length of the driven dipole 10 is selected to have a resonant length of three half-waves at the higher of the two frequencies for which the antenna is intended to provide optimum performance. The non-driven dipole 13 is designed to have a resonant length of one half-wave at the same frequency. This frequency may, for example, be about 195 me. Without the interposed condensers 12, therefore, the driven dipole 10 would have a half-wave resonant frequency of about 65 mc., whereas it may be desired to have the optimum low frequency response occur as high, for example, as 88 me. at the extreme upper end of the low television frequency band. To accomplish this, condensers 12 are interposed in the driven dipole 10 as shown, and their capacity is adjusted until the right value is obtained to give the driven dipole 10 an effective resonant length to operate as a half-wave dipole at 88 me. As explained above, the capacitive reactance of the condensers at 195 me. will be practically negligible and will have no appreciable effect upon the operation of the array at the latter frequency.

As explained in my U. S. Patent 2,726,390, it is not essential that the non-driven dipole be disposed between the driven dipole and the source of a signal to be received or a point to which a signal is to be transmitted. Also, as pointed out above, it is not essential that the condensers 12 be aligned with the extremities of the nondn'ven dipole, though they are preferably located at points of relatively low instantaneous current in the driven dipole when operating at the frequency at which its resonant length is three half-waves.

The overall effect of the condensers 12, in a typical case, is to raise the frequency of resonance of the driven dipole 10 as a half-wave dipole from about 65 me. to about 88 me, without materially changing its resonant frequency as a three half-wave dipole. Thus, while the electrical length of the driven dipole 10, without the condensers 12 being interposed therein, would be substantially three times the electrical length of the non-driven dipole 13, at all frequencies, the presence of the condensers 12 reduces the effective electrical length of the driven dipole 10 at 88 me. to substantially less than three times the electrical length of the non-driven dipole 13.

Referring next to Fig. 2, the antenna array illustrated therein is identical with that illustrated in Fig. 1, except that a folded dipole 20 is substituted for the straight dipole 10, and a pair of condensers 22 is interposed in each span of the folded dipole in transverse alignment with the extremities of the non-driven dipole 13. As indicated by the horizontal line H-H, passing centrally through the non-driven dipole 13 and through the driven dipole 20 between the two spans thereof, and by the vertical line VV, passing centrally through both spans of the driven dipole 20, the non-driven dipole is substantially centrally aligned in a horizontal plane with the driven dipole 20. As indicated by the dimensional lines, the condensers 22 are located so as to be transversely aligned with the extremities of the non-driven dipole 13 and so as to divide each span of the driven dipole 20 into three parts of substantially equal length L/3.

As in the case of Fig. 1, the effect of the condensers 22 at the half-wave resonant frequency of the non-driven dipole 13 is practically negligible. By properly adjusting the capacity of the condensers 22, however, the electrical length of the driven dipole 28 at its own half-wave resonant frequency may be reduced to substantially less than What its electrical length would be Without the presence of the condensers 22. This renders the driven dipole resonant as a half-wave element at a frequency in the low band that is substantially greater than one-third of the frequency at which the array as a whole is resonant in the high band.

Referring next to Figs. 3 and 4, the folded dipole of Fig. 2 may be mounted on any suitable electrically conductive bracket 25 supported by a horizontal cross arm 26 (shown in section). A pair of oppositely extending conductor tubes 27 may be rigidly mounted at their inner ends in the bracket 25 to form the center part of the upper span of the folded dipole. An insulator 28 may be mounted below and supported from the bracket 25 for carrying a similarly disposed pair of oppositely directed tubes 27 constituting the center part of the lower span of the folded dipole. Terminals 30 connected to the inner ends of the tubes 29 may provide connections for the leads 31 of a transmission line. The two outer parts of the upper and lower spans of the folded dipole may be formed of U-shaped rods 32 of relatively small diameter having their ends projecting telescopically into the outer extremities of the tubes 27 and 29 with a space between the exterior surface of the rod and the interior surface of the surrounding tube. The ends of each U-shaped rod may be embedded in a suitable rigid thermoplastic material, having dielectric properties, formed as a cylindrical plug 33 having a slightly enlarged outer end portion 34 forming a stop shoulder. The ends of the U-shaped rod 32 may be firmly anchored in the plug 33 by being flattened as shown at 35 and by molding the plug 33 around the ends of the rod. By simply forcing the plugs 33 into the outer ends of the tubes 27 and 29 until stopped by the portions 34, each U-shaped rod is firmly supported by the tubes 27 and 29. The spaces therebetween, in the areas of their overlap, are filled with the dielectric material of the plug 33 and provide the desired condensers, corresponding to the condensers 22 in Fig. 2. The dimensions of the parts described in connection with Figs. 3 and 4 may obviously be selected to provide a condenser capacity of any desired value.

The structure shown in Figs. 3 and 4 is simple and inexpensive to manufacture, and yet it is strong and rigid so as to be admirably suited for use in outdoor antennas of substantial physical size.

From the foregoing description of the present invention and illustrative embodiments thereof it will be appreciated that the various objects of the invention are accomplished with but slight physical modification of conventional antenna elements, and that the electrical characteristics sought are obtainable in a manner suitable for solving a wide variety of antenna problems and particu- -larly for causing the gain of a dipole antenna to peak at any'two low and high band broad-casting channels with optimum effectiveness. It will also be appreciated that the particular details of the illustrative embodiments of the invention described herein may be modified in various ways without departing from the principles of the invention disclosed herein. Accordingly the invention is not limited to such details, except as required by the terms of the appended claims.

What is claimed is:

l. A radio frequency antenna comprising a driven dipole having a low half-wave resonant frequency and parasitic means associated therewith to improve its response at a subsantially higher frequency of resonance of said dipole, said dipole having a pair of condensers interposed therein in symmetrically spaced relationship on opposite sides of the center thereof, and said condensers being selected to have a capacitive reactance at said low frequency sufiicient to substantially reduce the resonant length of the driven dipole at that frequency and a relatively low capacitive reactance and, therefore, relatively little effect on the resonant length of said driven dipole at said higher frequency of resonance.

2. A radio frequency antenna comprising a driven dipole having a low half-wave resonant frequency in the range of 54 to 88 inc. and parasitic means associated with said dipole to improve its response at a substantially higher frequency in the range of 174 to 216 me, said dipole having a pair of condensers symmetrically interposed therein in spaced relationship so as to divide the dipole longitudinally into three parts of substantially equal resonant length, and-said condensers being selected to have a capacitive'reactance at said low resonant frequency sufficient to substantially reduce the resonant length of the driven dipole at that frequency, but having a relatively low capacitive reactance and relatively little effect on the resonant length of said driven dipole at said substantially higher frequency. I

3. A radio frequency antenna comprising a driven dipole having a low half-wave resonant frequency and parasitic means associated therewith to improve its response at a high frequency at which the resonant length of the driven dipole is substantially three half-waves, said dipole having a pair of condensers symmetrically interposed therein in spaced relationship so as to divide the dipole longitudinally into three parts connected in series through the condensers, said condensers being selected to have a capacitive reactance at said low resonant frequency sufiicient to substantially reduce the resonant length of the driven dipole at that frequency and being interposed in the driven dipole at points of relatively low instantaneous current at said high frequency so as to have relatively little effect on the resonant length of the driven dipole at said high frequency.

'4. A radio frequency antenna comprising a driven half-wave dipole for a low frequency and parasitic means associated therewith to alter the current therein and improve its response at a high frequency at which its resonant length is substantially three half-waves, said dipole having a pair of condensers interposed therein spaced relationship so as to divide the dipole longitudinally into three parts connected in series through the condensers, and said condensers being tuned to have a substantial capacitive reactance at the half-wave resonant frequency of the driven dipole and being located at points of relatively low instantaneous current at said high frequency, whereby the effective electrical length of the dipole as a whole at its half-wave resonant frequency is substantially less than its electrical length at said high frequency.

5. A radio frequency antenna comprising a long driven dipole having a low half-wave resonant frequency and a short non-driven dipole having a high half-wave resonant frequency, the resonant length of the driven dipole at said high frequency being substantially three times that of the non-driven dipole, the two dipoles being disposed in spaced parallel relationship with their centers in transverse alignment, the spacing of said dipoles being less than 7% of a half-wave at said low frequency so as to enhance the gain of the array at said high frequency without appreciably affecting its gain or impedance at said low frequency, and a pair of condensers symmetrically interposed in said driven dipole so as to divide it longitudinally into three parts, said condensers being selected to have a capacitive reactance at said low resonant frequency sufiicient to substantially reduce the resonant length of the driven dipole at that frequency, but having a relatively low capacitive reactance and relatively little effect on the electrical length of the driven dipole at said high frequency.

6. A radio frequency antenna comprising a long driven dipole having a low half-wave resonant frequency and a short non-driven dipole having a high half-wave resonant frequency, the resonant length of the driven dipole at said high frequency being substantially three times that of the non-driven dipole, the two dipoles being disposed in spaced parallel relationship with their centers in transverse alignment, the spacing of said dipoles being less than 7% of a half-wave at said low frequency so as to enhance the gain of the array at said high frequency without appreciably affecting its gain or impedance at said low frequency, and a pair of condensers symmetrically interposed in said driven dipole so as to divide it longitudinally into three parts connected in series through the condensers, said condensers being selected to have a capacitive reactance at said low resonant frequency sutficient to substantially reduce the effective electrical length of said driven dipole at said low frequency and being interposed in the driven dipole at points of relatively low instantaneous current at said high frequency so as to have relatively little effect on the electrical length of the. driven dipole at said high frequency, whereby the electrical length of the driven dipole at said low frequency is substantially less than its electrical length at said high frequency.

7. A radio frequency antenna comprising a long driven dipole having'a low half-Wave resontant frequency and a short non-driven dipole having a high half-wave resonant frequency, the two dipoles being disposed in spaced parallel relationship with their centers in transverse alignment, the spacing of said dipoles being less than 7% of a halfwave at said low frequency so as to enhance the gain of the array at said high frequency without appreciably affecting its gain or impedance at said low frequency, and a pair of condensers symmetrically interposed in said resonant frequency being substantially one-third that of the driven dipole at that frequency.

8. An antenna according to claim 7 in which said condensers are substantially aligned transversely with the ends of the non-driven dipole.

9. An antenna according to claim 7 in which the two outer parts of the driven dipole are telescopically connected to the center part thereof in overlapping relationship, and a dielectric material is disposed between the overlapping portions thereof to form said condensers.

10. An antenna according to claim 7 in which the center part of the driven dipole'is tubular, and the outer parts have end portions of small diameter extending telescopically into the center part in spaced overlapping relationship, and a rigid dielectric material fills the space between the overlapping portions to form said condensers and support said outer parts from the ends of said inner parts.

11. A radio frequency antenna comprising a driven folded dipole having a low half-Wave resonant frequency and parasitic means associated therewith to provide a gain peak at a substantially higher frequency of resonance of said folded dipole, said folded dipole having a pair of condensers symmetrically interposed in each span thereof in spaced relationship so as to divide each span longitudinally into three parts of substantially equal resonant length, said condensers being tuned to have a capacitive reactance at said low resonant frequency sufiicient to substantially reduce the resonant length of said folded dipole at that frequency, but having a relatively low capacitive reactance and relatively little effect on the electrical length of said driven element at said higherfrequency of resonance.

12. A radio frequency antenna comprising a driven folded dipole having a low half-wave resonant frequency and parasitic means associated therewith to improve its response at a high resonant frequency at which the dipole is three half-waves long, said folded dipole having a pair of condensers interposed in each span thereof in spaced relationship so as to divide each span longitudinally into three parts connected in series by said condensers, said condensers being selected to have a capacitive reactance at said low resonant frequency suflicient to substantially reduce the electrical length of the driven dipole at that frequency and being interposed in the driven dipole at points of relatively low instantaneous current at said high frequency so as to have relatively little eifect on the electrical length of the driven dipole at said high frequency.

13. A radio frequency antenna comprising a long driven folded dipole having a low half-wave resonant frequency, a short non-driven dipole disposed in spaced parallel relationship with the folded dipole with the centers of the two dipoles in transverse alignment, the spacing of said dipoles being less than 7% of a half-wave at said low frequency so as to enhance the gain of the array at a high resonant frequency at which the electrical length of the folded dipole is substantially three half-waves Without appreciably affecting the gain or impedance of the array at said low frequency, and a pair of condensers symmetrically interposed in each span of said folded dipole to divide it longitudinally into three parts connected in series through said condensers, saidcondensers being selected to have a substantial capacitive reactance at said low frequency and being located at points of relatively low instantaneous current at said high frequency, whereby the effective electrical length of said folded dipole at said low resonant frequency is substantially less than its electrical length at said high resonant frequency, the electrical length of the non-driven dipole at said high resonant frequency being substantially one-third that of the folded dipole at that frequency.

14. An antenna according to claim 13 in which said condensers divide each span of the folded dipole into parts of substantially equal resonant length and are substantially aligned transversely with the ends of the non-driven dipole.

15. An antenna according to claim 13 in which the two outer partsof each span of the folded dipole are telescopically connected to the center part thereof in overlapping relationship, and a dielectric material is disposed between the overlapping portions thereof to form said condensers.

1.6. An antenna according to claim 13 in which the center part of each span of the folded dipole is tubular, and the outer parts of each span have end portions of small diameter extending telescopically into the center part in spaced overlapping relationship, and a rigid dielectric material fills the space between the overlapping portions to form said condensers and support said outer parts from the ends of said inner parts.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,837,742 June 3,, 1958 Robert Sc Weiss It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 2, after "therein" and before "spaced" insert in a,

Signed and sealed this 9th day of September 1958.,

(SEAL) Attest:

KARL Ho AXLINE ROBERT C. WATSON Attesting Oflicer Commissioner of Patents

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