US2582634A

US2582634A - Television antenna assembly

Info

Publication number: US2582634A
Application number: US136548A
Authority: US
Inventors: Jr John Paul Jones
Original assignee: Philco Ford Corp
Current assignee: Space Systems Loral LLC
Priority date: 1950-01-03
Filing date: 1950-01-03
Publication date: 1952-01-15
Anticipated expiration: 1969-01-15

Description

Jan. 15, 1952 Filed Jan. 5, 1950 J. P. JONES, JR 2,582,634

TELEVISION ANTENNA ASSEMBLY 2 Sl-lEETS-Sl-IEET l I 1 l a l 1 I 2 J 4 .4 6 7 8 7 l0 l2 /3 IN V ENT 0R.

BY Qua/ M? Jan. 15, 1952 J JONES, JR 2,582,634

TELEVISION ANTENNA ASSEMBLY Filed Jan. 5, 1950 2 SHEETS-SHEET 2 INVENITOR.

JOH/V FAUL uo/vif &//7

wowml iw Patented Jan. 15, 1 952 can, mommies; in, Pottstowm Pa :assignor to tPhilco Gorporation, Philadelphia, Pal,--a corpo-- :ratl'ontohlennsylvania Application January 3, 1950,.seris1 No. 136,"548" The invention herein deserlbed and' claimed: relates to an improved antenna assemblyfor television receivers.

Present television receivers" are required to receive signals in two I non-contiguous 'higlr 'frequency bands one of which (the lowenb'a nd i extends from 54" -tO' 88 megacyclesand includes channels Nos. 2 through 6- andthe other of which (the upper band)- extends from 174 to" 216 megacycles and includes channels' Nos-"l' through-I3.

In some areas a single'dipole'may be satisfactory for the reception of s'ignals-i-nbdth bands, but in many areas "bWO' separate dipoles" are advantageously "employed, 'one' for the low-band and the-other for the high-band channels;

' The present invention relates-- particularly to an antenna assembly comprising a high-band dipole, a low-band dipole, astub interconnecting the high-band and low-ban'd dipoles, and a single or common twin-lead transmission" line connecting both dipoles to the televisionreceiver.

I have found that the overall efiectivenessof the above antenna assembly may be increased very' substantially by connecting a small-pinechanically rigid, loop inductor across the terminals of the high-band dipole. when this is done, the effectiveness of' theass'embly compares very favorably with that or an antenna assembly comprising a plurality offoldedudipolescach -of which is cut to the individual requirement of a particular channel and 'each' of which is connected to the television receiver' by a separate twin-lead transmission line. "Such-"an arrangement is, of course, too complex to be commercially practical, but it provides an "excellent reference for purposes of comparison since a folded dipole of such lengthas to benaturally resonant to the frequency oftheindividual channel would provide very satisfactory reception on that channel, assuming a 300-ohm itwin-lead transmission line-tube employed, as is ordinarily the case. V

The theory underlying th improvementwhich the addition, of the small loop z inductorreflects is .not simple, and is-complicatedzby the;fact that 'we are dealing with a. relatively widerrange of frequencies (54 'to. 216 megacycles) The-length of the stub which intercomiectsrthez high-band and low-band dipoles isyconventionally ;made

about one-half wavelength at .thelcenter' frequency of the high band. done in order that the low-band dipole may beeennected-to the transmission line at or near a voltagenode with respect to :thehigh-band frequencies.- :Unior- -tunate1y,. astub equalto one' halr-iwavelengmiat 'thecenterfrequency-of the 'h-igh bandcloselyapproaches one-quarter wavelengtl r at i "the low-- band frequencies, particularly at the frequencies near the upper edge of thelo'w bandfi-tleas-t some of the low-band channelswilli therefor'e', see a low-impedance one-quarter wavelength open line when lookin at the highmand dipole from thetermina'ls of the low-band sip-01a Ithas been found, experimentally, that the low band channel which 'is attenuated-the mostisatli-att channel whose one=quarter wavelength equals the length of thestub plusthe length of-one'arm'of the high-band dipole. The addition-of the" small loop inductor across the terminals of the'high- 'band dip'ole', as "proposed 'bythe presentinvention, effectively changesthe impedance-seen by the low-band channels from a low-impedance one-quarterwa'velengtlr open li 'ne to arhigh-"impedanc'e one-quarter Wavelength shorted 'lin'e, thus improving very substantially the low baml channels. To avoid attenuating the highsband channels, the loop inductor is made Iargeenough to present a reasonably hignimpedance' (about '250' ohms) to the high-band freque'ncies as seen "from thelterminals o'f the'loop. Thus, the highband channels are not adversely afiectedlb the addition. of the loop inductor. 7

It is a primary obj ect of the present invention to provide -fora television receiverirequired to receive signals in two non-continuous high-frequency I bands, an antenna assembly-of relatively simple construction capable nevertheless of .op-

eratingas- -efectively as the more complexassembly :of a plurality of vindividual dipoles :each

naturally resonant .to' on'eaoiV.the:.channels in- "valved.

transmission" line connecting both dipoles to television receiver.

These and other objects, advantages and teatures of the present-invention 'will'be best'under- 'stood from aconsideration of the following ,de-

tailed description and accompanying drawing wherein: 1

Figure shows the loop inductor of the present invention incorporated into an antenna assembly comprising a plain high-band dipole-and a plain low-band dipole mounted on a common mast, one

above the" other; V

"Figure 2 *SHOWS"th loll mdufiflfof the present invention incorporated into an antenna assembly 4 ing one-quarter wavelength at one of the mid low-band frequencies.

I have found that the addition of the loop inductor I1 to the antenna assembly shown in Figure 2 effects a very-material improvement in the operating efficiency of the antenna assembly, particularly at the low-band frequencies.

In'Figure' 4, the loop inductorl! is shown em- 'ployed in an antenna assembly in which high- Referring now to Figure 1,--the antenna 'as-' sembly there shown includesa high-band dipole l mounted at or near the top of mast I l, a lowband dipole 12 mounted on mas-t ll below the.

high-band dipole 10, a stud H interconnecting the terminals of the high-band and low-band dipoles, and a transmission line extending from the terminalsof the low-band dipole [2 to the television receiver (not shown).

-with respect to the high-hand frequencies.

Transmission line l5, which extends from the terminals of low-band dipole l2 to the television receiver (not shown), is conventionally a length of parallel-wire or twin-lead having a characteristic impedance of 300 ohms.

In accordance with'my invention, a small inductor 11 of predetermined configuration anddimensions is connected across the terminals of high-band dipole I0 in the manner shown in Figure 1; ,In the preferred embodiment, inductor ll comprises a C-shaped length of conductive material terminating at theends in lugs l8, l9, as clearly shown inrFigure 6. While the inductor, may be formed of any material having good conductive' properties, it is preferably formed of aluminum wire having a diameter of the order of one-eighth inch. The diameter of the C-shaped loop is-about three and one-quarter inches, which is equivalent to about one-eighteenth wavelength at the center-frequency of the high band, and the total length of the'inductor, from lug center to lug center is'about nine and one-half inches, which is equivalent to about one-sixth wavelength-at the center-frequency of the high band.

The inductor is very readily installed, as by means of a couple 0fb0lts and nuts, and is sufiiciently. rigid towithstand bending by the Wind.

In Figure 2, the high-band dipole l0 and lowband dipole H! are secured to a spacer bar. and

disposed in a common horizontal plane. The two dipoles are separated in ,space byone-quarter wavelength at the center-frequency of the high band in order that'low-band dipole 12 may function as. a reflector for high-band dipole. l0. Stub 14, however, has the same length as it has in Figure 1, namely, one-half wavelength at the centerfrequency of the high band. Thus, low-band dipole l2 is connected at a'voltage node with respect to high-band frequencies. The (ii-shaped loop inductor l 'I' is connected across the terminal -of high band dipolelfl, in the same manner as in Figure 1. A reflector bar 21-is provided for i l wr a d p e lLthesnac e th wee v low-band channels.

'band dipole l0 and low-band dipole l2 are each provided with a reflector, identified by

numerals

40 and 42 respectively. Stub M has a length equivalent to one-half wavelength at the centerfrequency of the high band, as in Figures 1 and 2.

In Figure 5, afolded dipole 50 is substituted for the plain high-band dipole l0 shown in Figure 4.

In Figure 3 I have plotted a graph to show the relative effectiveness of my improved antenna assembly. In Figure 3, one hundred per cent efliciency corresponds to the results obtained from a folded dipole cut to proper length for the particular channel. The curves A correspond to the results obtained'from an antenna assembly similar to that shown in Figure 1 comprising a plain high-band dipole, a loop inductor connected across the terminals of the high-band dipole, a plain low-band dipole, a stub (having a length equivalent to one-half wavelength at the mid high-band frequency) interconnecting the highband and low-band-dipoles, and a single twinlead transmission line. The curves B correspond to the results obtained from an antenna assembly similar to that shown in Figure-4, i. e. having a high-band reflector and a low band reflector (in addition to components similar to those just described in connection with Figure 1).

It will beobserved from the curves shown in Figure 3 that the operating efficiencies of my improved antenna assemblies compare very favorably with, those of an assembly wherein an individual folded dipole isprovided for each channel. If, however, the O-shaped loop inductor is removed, the efficiencyof the two-band dipole antenna assembly drops very materially at the It will also be observed from curves A and B of Figure ;3 that the response of my improved antenna assembly (both with and without reflectors) is ,fairly flat over the entire range of lowband; and high-band frequencies. The flatness of the responseover the low band was obtained by cutting the low-band dipole to channel No.3 after determin g that stub l4 and loop inductor I! were together. equivalent to a one-quarter wavelength closed line at channel No. 5. By so doing, the flatnessof the response over the, lowband frequencies was improved over that which would have been obtained had the low-band dipole been cut to the same frequency with respect to which stub l4v andinductor l1 represented a one-quarter wavelength closed line.

Having described-my invention, I claim:

A two-barid'high-frequency antenna assembly comprising: a first dipole naturally resonant-at a frequency substantially midway between the end frequencies of the high band; a second dipole naturally resonant at a. frequency about midway between'the low-band center-frequency and the lower .endefrequency of the low band; a stub inond dipoles, said stub having a selected'length equal to one-halfwavelength at the center-frequency of the high; band, which is also about one- '75' quarterwavelengthnat a. frequency near'the up- 5 per end of the low band; a common transmission line connecting both said dipoles to signal utilization means, said transmission line being connected to the terminals of said second dipole di rectly and to the terminals of said first dipole by way of said stub; and an inductor connected across the terminals of said first dipole, said inductor comprising a C-shaped loop of mechanically rigid conductive material having a loop diameter of approximately one-eighteenth wavelength at the center-frequency of the high band and a conductor length of approximately onesixth wavelength at the center-frequency of the high band, said C-shaped loop inductor and said stub together being equivalent to a one-quarter 6 wavelength shorted line at a low-band frequency about midway between the low-band center frequency and the upper end-frequency of the low band.

JOHN PAUL JONES. JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,474,480 Kearse June 28, 1949 2,510,010 Callaghan May 30, 1950 15 2,511,574 Finneburgh June 11, 1950