US2510010A

US2510010A - High-frequency antenna system

Info

Publication number: US2510010A
Application number: US31302A
Authority: US
Inventors: John D Callaghan
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1948-06-05
Filing date: 1948-06-05
Publication date: 1950-05-30
Anticipated expiration: 1967-05-30
Also published as: FR993777A

Description

May 30, 1950 J. D. CALLAGHAN 2,510,010

HIGH-FREQUENCY ANTENNA SYSTEM Filed June 5, 1948 2 Sheets-Sheet l knpmox. 47 F2 [73 .b'MTFZ iF-nppxox /17 Fl 31 g n H M INVENTOR JOHN D CALLAGHAN AT oRNEY M y 19.50 J. D. CALLAGHAN 2,51%,010

HIGH-FREQUENCY ANTENNA SYSTEM Filed June 5, 1948 2 Sheei s-Sheet 2 lily-3 INVENTOR JOHN D. CALLAGHAN BY n:

ATTORNEY atented May 30, 1950 John D.- Callaghan,Merchantville; Na" assignar to Radio Corporation of America, a corporation of Delaware Applicant June 5, 1948, sesame. 31,3"02

This -inventlon-rel atesgenera-11y tdhigh hey-broad bandrec rig antenna systems; an anti-sunny to an a angement for simul tsfieousry feeding energy from a plurality of antennas resonant to difierent frequencies into t'hesanie transmission line} It is particularly an I ableto televisionreceiving systems;-

Giif the ebiect' oi'tl i-inv'entien-is to enable a plurality of receiving antennas of d-ifierent d-i-' her-learns which are adapted to receive waves of different frequencies-to feedthe same transmis sierrline (extending to a receiver) over dilrerent branch circuits in such manner that each branch and associatedantenna has negligible effect on theflow of high-frequency energy from the other branch toward the common transmission line,

Another object is to enabletwo high frequency directive receiving antennas of different d-i'i 'nen sions which are oriented indifier'ent directionsto be coupled into acommon transmission line in such'mann'er as topreventthe flow of energy of any one antenna circuit into theother antenna circuit; while preserving the directivity pattern 03: each: antenna and maintaining maximum efficiency in the collection of energy and the transmission thereofirom each antenna to the icomrnon transmission line.

1 To achieve the results of the invention, use is- :made of a circuit arrangement which enables the zurirestricted flow of energy from each branch circuit and itsassociated receiving antennaatew'ard the common transmission line extending to the receiver; while making each branch appear :at-thejunction to the common transmission line was a circuit of extremely high impedance to the :flow of energy from the other branch circuit. A section of line of predetermined length is placed across the antenna of larger dimension at a particu'lar location in order to provide a short circuit for any signals of a frequency adapted to be collected on the shorter antenna; The arrangement is such that at a particular frequency relationship" of twoto-one any tendency toward second harmonic operation of the larger antenna is suppressed, thus preventing interference from energy collected by the larger'antenna at its secand harmonic mode of operation with-the direc' tivitypattern of the smaller antenna.

A more detailed description of the invention follows in conjunction with a drawing wherein;

Fig. 1 illustrates diagrammatically an antenna system in accordance with the invention in which two receiving antennas of different dimensions reada common transmission line over individual branch circuits;

; tion Fl;

stated above,- that a signal of frequency F2 is Fig; 3 illustrates a perspective new of a are ferredform of mechanical construction orth'e antenna arrangement or th inventien; and shows suitablesupporting arms and mountings for the to Fig. 1'-

nio re' detain there is r cuits TI and T2 to a: common trans liners, in t extending: td a receiver as a television receiver; Antenna Al has a lar er dimension thari AZ and isada ted to re= serve signals er rrequeney Fl which is'lower' than: the frequency ofthe signals F2 adapted to be received on antler-inane; By way of example" only, let it be assumed that antenna A2 is tuned to a frequency which is twice the frequency of the signals adapted to be received on antenna Al.- Beth antennas A1 and A2 are shown to be of the folded dipole type although if desired, either or both of these antennas may beof the single dipole type red at the center. The length of antenna A2; from one end to the other is made to be approx-1 niately a one half wavelength at it frequency of operation F2. The length of antenna Al from one end to the other isma-deto be approximately a one-thalf Wavelength at its frequency of opera- It will be noted; from what has been higher than a signal of frequency FL It should be noted that there is-providedl acrossantenn'a AI at the junction point of this antenna with the branch line TI, a section of line Th4 which is open a'tits end removed from the antenn'a. Line section T4 has a length of onequarter of a wavelength at the higher frequency F2. Branch line Tl has a length which is three= quarters of a wavelength atthe higher frequency made to the electrical lengths of these line sections and antennas rather than to the actual physical lengths.

The branch line T2 has a length which iss'o chosen that in combination with the antenna A2, this combination appears as an open circuit across the common transmission-line T3 at the junction point at the frequency Fl. Stated otherwise; the combination of transmission line T2 with antenna A2 is equivalent to a quarter wavelength of line 55 with the far end (the end removed from the common line T3) short circuited at the frequency Fl. Thus, any energy collected by the antenna Al and flowing over branch line Tl toward the line T3 will be presented with a high impedance circuit by combination T2, A2 and will not flow into this circuit T2, A2. The combination of antenna. Al and transmission line sections Tl and T4 present a high impedance circuit at the junction with the common line T3 for energy at the frequency F2. Thus, any signal or" frequency F2 collected on antenna A2 cannot flow into transmission line TI and can only flow into the common line T3. The line section T4 which is electrically a quarter wavelength long at frequency F2 acts, in effect, as a short circuit for signals of frequency F2. The open end of line section T4 is, in effect, inverted and becomes a short circuit at the junction point with line Tl for this same frequency F2. For the lower frequency Fl, the line section T4 acts as a capacity across the antenna Al and its magnitude is sufficiently small in relation to the frequency Fl so as to be of negligible effect on signals of this frequency Fl.

The distance or physical spacing between the antennas Al and A2 is approximately .6 wavelength at frequency F2 for optimum results.

If the antennas Al and A2 are so dimensioned that they are adapted to receive frequencies Fl and F2 respectively, whose relationship is threeto-one, then branch line Tl which is three-quarters of a wavelength long at F2 also becomes a quarter of a wavelength long at Fl. In this condition, the combination A2, T2 can be adjusted to present a slightly capacitive reactance across the junction point with common line T3 so that its capacitive reactance will cancel out the previously mentioned capacitive reactance caused by action of transmission line T4. This will come about due to the inverting action of transmission line section Tl when it is a quarter wavelength long at frequency Fl.

The equivalent electrical circuit of Fig. 1 is illustrated in Fig. 2 wherein each of the antennas Al and A2 are represented by a series circuit of inductance L, capacitance C and resistance R. The source of incoming waves of frequency F2 is shown as a generator in series with antenna A2, while the source of incoming waves of frequency Fl is shown as a generator in series with the an-.

tenna Al. The line section '12 connecting the antenna A2 to the common transmission line T3 is represented by two inductance coils, one for each leg of the line T2. These legs of line T2 are shown in series with the antenna A2 and connected between antenna A2 and terminals T3 representing the common transmission line. The quarter wavelengthstub line section T4 is represented by a series circuit of an inductor and a capacitor in shunt across the antenna Al and source Fl. The line Tl which is three-quarters of a wavelength long at the higher frequency F2 is represented by two parallel tuned circuits, each parallel tuned circuit representing a leg of the line or branch Tl. It should be noted that the common line T3 adapted to be connected to the receiver is connected in common to both branches of the system.

Although the line sections Tl, T2, T3, T4 are indicated in Fig. 1 as being of the two-wire type, it should be understood that if desired, each of these line sections may be in the form of a coaxial line. Either air or some other suitable dielectric may be employed between the conductors of the line section.

A practical embodiment of the invention actually tried out in practice is shown in Fig. 3. The smaller dimensioned antenna A2 is shown in association with a reflector A2R positioned parallel to the antenna A2 and suitably spaced therefrom in the same horizontal plane in order to improve the directivity characteristic in a direction away from the reflector and toward the folded dipole. The reflector A2R and the antenna A2 are mounted on a wooden cross arm W which, in turn, is mounted on a vertical metallic mast M. In the embodiment actually tried out in practice, this mast M was an aluminum tube. Positioned below is the antenna Al shown as a single dipole. Insofar as the principles of the present invention are concerned, it is of no consequence whether the antennas are single dipoles or folded dipoles. The larger dimensioned antenna in Fig. 3 has been given a prime designation because it is shown as a single dipole but it has the same reference character except for the prime designation as the larger dimensioned antenna Al of Fig. 1. A reflector AlR is shown parallel to antenna A'l and in the same horizontal plane and suitably spaced therefrom. A wooden cross arm Wl is used to mount the antenna A'l and its associated reflector AIR on the metallic mast M. The common transmission line T3 extending to the receiver is shown as a double wire line which is connected to the antenna A2 by means of branch line T2 and connected to the antenna A'l by means of the branch line Tl. The quarter wavelength stub line section T5 is shown as a pair of wires connected across the terminals of the larger antenna A'l and tacked or suitably attached to the bottom of the wooden cross arm Wl. Suitable stand-oil insulators SI, S2 and S3 and S4 maintain the transmission line sections taut and in suitable position relative to the mast M. In practice, these stand-off insulators may each be in the form of a metallic clamp having a rubber grommet or ring through which the line sections pass. It is desirable from a standpoint of mechanical strength and appearance to mount the small higher frequency antenna A2 at the top of the mast and the larger small frequency antenna Al or A l lower down on the mast. However, if reflections or other conditions make it necessary to mount the small antenna below the large one, the system will work equally well. Where this antenna is to be used for television purposes for which it is primarily designed, the

connecting line sections, stubs, etc., should'be kept tight at all times to prevent their moving in the wind; otherwise, picture flutter may be observed on the screen of the cathode ray tube of the television set on windy days.

The line sections Tl, T2, T3 and T4 of Fig. 3:

were common 300 ohm impedance transmission lines made up of parallel copper wires molded in and spaced apart by a suitable dielectric such as The two cross arms poly-ethylene insulation. W and Wl were separated vertically in the embodiment successively tried out in practice by tion on television channels whose signals extend".

over a frequency range of fifty-four to eightyeight megacycles, while the antenna'AZ was de- 5. signedfor the reception channels: having frequencies in; the ran e: of: 174. to:2@li61megacycles. Although theiantennas shown in Figs. 1 and3 ,areindicated as beinggor-ientedzin the same direction, it should beunderstoodzthat,

in. practicethey. may. be; oriented: differently though remaining in parallel horizcntal planes; Withthe arrangement of'theinvention, one an-u tenna can be oriented differently from the other antenna with. a minimum of. interference from:

reflected energy picked up by the-other antenna.

Among the advantages of the present. inven--..

tion are:

1. Thenecessity of runningv separate transmisesion lines from each antenna to the receiverwisv eliminated.

2-. The necessity for having aswitch to; alternately-couple the antennas to the receiver when.

changing from one pair of frequencies tothe other is also eliminated.

3'. Maximumefficiency from each antenna. is.

achieved while enabling thedirectivityof the patterns of each antenna to bepreserved in different directions, and

4. The construction is simple, easy to build, and inexpensive to make.

What is claimed is:

1. A receiving antenna system comprising first and second dipole antennas of different dimensions spaced apart from each other in different substantially parallel planes, a common transmissionline extending to a receiver, branch lines coupling said antennasto a junction point onsaid common line, the smaller dimensioned dipole being, resonant to a frequency FE the larger dimensioned antenna being resonant to a lower. frequency. Fl, the branch line coupling said larger dimensioned antenna to saidcommon line having an electrical length equal to three-quarter wavelength at frequency F2, the combination of smaller dimensioned antenna and the branch line coupling the same to said common line having an equivalent electrical length which appears as a very high impedance to energy of frequency Fl at said junction point, and an open-ended line stub having an electrical length of onequarter wavelength at frequency F2 connected at one end to the terminals of the larger dimensioned antenna.

2. A receiving antenna comprising a folded dipole antenna and a larger dipole antenna spaced apart from each other in different substantially parallel planes, a parasitic reflector for each of said antennas, a common transmission line extending to a receiver, branch lines coupling said antennas to a junction point on said common line, the smaller dimensioned dipole being resonant to a frequency F2, the larger dimensioned antenna being resonant to a lower frequency Fl, the branch line coupling said larger dimensioned antenna to said common line having an electrical length equal to three-quarter wavelength at frequency F2, the combination of smaller dimensioned antenna and the branch line coupling the same to said common line having an equivalent electrical length which appears as a very high impedance to energy of frequency Fl at said junction point, and an open-ended line stub having an electrical length of one-quarter wavelength at frequency F2 connected at one end to the terminals of the larger dimensioned antenna.

3. A receiving antenna comprising a vertical mast, a folded dipole antenna supported from said mast in a horizontal plane, a larger dipole of; signals. on: television;

antenna. als -supported; from said; mast: and:

arranged in a; horizontal plane, spaced vertically from: said; folded; dipoleiantenna, a parasitic re fiector for'each antenna. supported parallel to? 5, and in the same-horizontal plane as its 3155,0011- ated. antenna, each antennaand associated-1 re;-- fiector being. positioned, on, opposite sides of; the. mast, a common transmission line extending-to; a receiver, branch lines coupling, said; antennas. to a junction point on said commonline, the: smaller dimensioned dipole being resonant to a; frequency E2, the, larger dimensioned antenna. being resonant to a lower frequency Fl, thebranch line coupling said larger dimensionedana tenna to said common line having anelectricalt length. equal to three-quarter wavelength at free quency E2); the combination of smaller dimen-.- sioned antenna and-the branch line'couplingithei: same. to. said common line having; an equivalent .electrical length which appears as a very high:-

impedance to-energy of frequency Fl at said junction point, andanopen-ended line stubi-having. an electrical length: of one-quarter wavelength: atifrequency F2 connected at one end to-the ter.=- minals;of;thelarger dimensioned antenna.

4.. Areceiving antenna; system in accordance withclaim3,,characterizedin this, that awooden; cross. arm; supports each antenna and its asso ciated reflector from said mast, and" said lines; all have acharacteristic impedance. of;300ohms..

5. A receiving antennasystem comprisinggfirstz and: second dipole antennas of different dimensions spaced. apart from. each otherin different? substantially parallel planes, a. pair of terminals,. branch lines. coupling said antennas; to' saidterminals, the smaller dimensioned dipole being; resonantto a given frequency, the largeridimenssioned antenna being. resonant toa lower free quency, the branch line couplingsaid larger dimensioned antenna to said terminals having an electrical length equal to three-quarter Wavelength at said given frequency, the combination of smaller dimensioned antenna and the branch line coupling the same to said terminals having 1 an equivalent electrical length which appears as a very high impedance to energy at said lower frequency at said terminals, and an open-ended line stub having an electrical length of onequarter wavelength at said given frequency connected at one end to the terminals of the larger dimensioned antenna.

6. A receiving antenna system comprising a folded dipole antenna and a larger dipole antenna spaced apart from each other in different substantially parallel planes, a parasitic reflector for each of said antennas, a pair of terminals, branch lines coupling said antennas to said terminals, the folded dipole antenna being resonant to a given frequency, the larger dimensioned an- 30 tenna being resonant to a lower frequency, the

branch line coupling said larger dimensioned antenna to said terminals having an electrical length equal to three-quarter wavelength at said given frequency, the combination of folded dipole 65 antenna and the branch line coupling the same to said terminals having an equivalent electrical length which appears as a very high impedance to energy at said lower frequency at said terminals, and an open-ended line stub having an 79 electrical length of one-quarter wavelength at said given frequency connected at one end to the terminals of the larger dimensioned antenna.

7. An antenna system comprising first and second folded dipole antennas of different dimensions spaced apart from each other in different substantially parallel planes, a pair of terminals adapted to be connected to a common transmission line extending to a transducer, branch lines coupling said antennas to said terminals, the smaller dimensioned dipole being resonant to a given frequency, the larger dimensioned antenna being resonant to a lower frequency, the branch line coupling said larger dimensioned antenna to said terminals having an electrical length equal to three-quarter wavelength at said given frequency, the combination of smaller dimensioned antenna and the branch line coupling the same to said terminals having an equivalent electrical length which appears as a very high impedance to energy at said lower frequency at said terminals, and an open-ended line stub having an electrical length of one-quarter wavelength at said given frequency connected at one end to the terminals of the larger dimensioned antenna.

8. A receiving antenna system comprising first and second dipole antennas of difierent dimensions spaced apart from each other, said antennas being arranged to receive energy of predetermined polarization, a pair of terminals adapted to be connected to a common transmission line extending to a receiver, branch lines coupling said antennas to said pair of terminals, the smaller dimensioned dipole being resonant to a given frequency, the larger dimensioned antenna being resonant to a lower frequency, the branch line coupling said larger dimensioned antenna to said pair of terminals having an electrical length equal to three-quarter wavelength at said given frequency, the combination of smaller dimensioned antenna and the branch line coupling the same to said pair of terminals having an equivalent electrical length which appears as a very high impedance to energy at said lower frequency at said pair of terminals, and an open-ended line stub having an electrical length of one-quarter wavelength at said given frequency connected at one end to the terminals of the larger dimensioned antenna.

9. An antenna system including a pair of terminals, a length of transmission line coupled to said pair of terminals and having an electrical length substantially equal to one wavelength at a given frequency, a dipole antenna resonant to a frequency lower than said given frequency coupled to said length of transmission line at a point three-quarter wavelengths at said given frequency from said pair of terminals, a second dipole antenna resonant to said given frequency, a section of transmission line coupling said second dipole antenna to said. pair of terminals, said section of transmission line having an electrical length at which the combined impedance characteristic of said second antenna and said section of transmission line appears at said terminals as a very high impedance to energy at said lower frequency.

JOHN D. CALLAGHAN.

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

UNITED STATES PATENTS Number Name Date 2,297,329 Scheldorf Sept. 29, 1942 2,397,645 Brown Apr. 2, 1946 OTHER REFERENCES Publication: Amphenol Television Antenna," Mod-e1 1l4005, Manual File I1.7, 54-58 mo. and 174-216 1110., American Phenolic Corp Chicago 50, 111., March 1, 1948.