US2455888A - Antenna - Google Patents

Description

G. H. BROWN Dec. 7, 1948.

ANTENNAy Filed Aug. 12, 1944 I VEN TOR. ylrowm Innen-Wire transmission lines.

Patented Dec. 7, 1948 Grenrge lilrown, 'Princeton-N. J., assiale 'to .Radin4Corfporaticm,l of America., Aia corporation:

` of. Delaware Y y invention `relates rto 'radio yantennas and has iorz-its'principal object Athe provisionfomeans Iorepreuenting direct feed-tlnough of .radiofreen'sleiueyv energy from one antenna toanothernear- .byfantenna c certain typesof radio reliectionrobject ydetecting-systems, signals are radiated- .from 4one antenna ,and ylcrckecl .up by 'another antenna after 'neallection ,-by :an object. In ysuch systems it `is generally highly desirable to.rninirnize 'or pre'- Vent the transmissiomorenergy directlyiromrone oxiithecantennasz'to thefother without reflection from the i'obj'ect, :thesame time',` .the .antennas must. be plfaced' .relatively near -to reach. other. Groundedslrietds. interposed-'between the: time antennas have. been found to be.v Aineiective, par- 'ticularlyzatitthe higher frequencies, because four'- re'nts'induced .in the 'shields by ytime 2transmittin2,r antenna .cause 'they shields'to. reradiate; Thu-s the shield tend'sto function merely as: av coupling.. .1e-le'- ment...=between. the two antennas. 1n accordance with the present invention, the ttwo'ant'ennas; are isolated from each other byxshslel'ds 'consti-'noted toi form: zarplurality of shortcircuitedquarter-Wave As is `Well' lmnwfn toit-hose skilled in the art, .a short-circuited'trans.- missionV line presents substantially i'nni'te. :im-- pedance to the: flow of current at the frequencyzat which the line-is off-'one-quarter Wavelength. 'The instant invention utilizes. this phenomenon lby placing '1a .plurality oi' such linesqiny ,pcsitinnsgsucli as to prevent the-.flaw of currents which` tend to cause Mie-transfer of energy from one. antenna to tire-ether. v v

1 The invention will' be described Withreference scribedlfabove. Each of the'antennasisfd'irective, f

and :c'omprisesa .di-pole, l locatedzat. thefocus of a;..eylindrical1 parabolicf reflector 3..' Each ,of the neectors :3 .is provided with side walls; 5 fand." 1;. Inrthe-absence'of :any further shielding meansyb'ertween the dipoles I, energizationso. the antenna.

A Wi1lind1-1ce-currents ,in its side Walls- Tliese vcurrents lWil-ll in-y turn. induce currents in the side walls', 5- ofthce antenna B, causing radiation theretreintathe-dipoley I of the -antennailv .-fllo pneitentthe. above-descrlbed couplingfacf nciaims. (c1. 25o-esi tion from taking; place, .a plurality :ci .nat plates 9 of conductive material are placed between the antennas .A .and ;-B with each. :connected y :at l,one of its edges to a conductive sheet tt yextending irom V`tlfie-giilallfil; ofthe antenna A, parallel tothe line between the antennas, to theA wall. 5 oi the famiennaflB-v.4 Thepplat-es1f9f-ate gparalle-lto the Walls 5 and 1 and are spaced at intervals-of approximately one-tenth Wavelength at the frequency at which the `system is .to operate. 'Each ci" vthe plates .9' extend's forwardly one-quarter wavelength'from its ,point oi" connection to 'the sheets Il... The wall .Toi the antenna A, together with the nearestof lthe plates 9', .acts asia quarter Wavelength. open- Wire line, short-circuited' at its rearward end by the `sheet ll., thus .presentinga substaritiallyiilnnte .impedance between the'ior'- wand' edges of the Wall. "l and the first plate 9; Silnilarly,.eaeli pair of. adjacent `.plates '5 .presents aihigninipedance to the flow o'f current iro'mone plate `vto the other. As aresult of. this action, cnrrent...is. eiectiyely prevented from lowilngl Yin thev wall '.1 of theant'ennaA or any of thepl'ates 3. Thereforasubstantially zero coupling .appears between the antennasiA and'. B. l .It is found in practice that the. intermediat plates 9 between. the -rst and l'ast plate.I may be omitted, leaving. only the irst plate 95 adjacent the Wall `I ofthe antenna A and the last plate: `9 adjacent. .the Wall .5. of the. antenna. Withoutv serinuslyaffecting the deg-ree of isolation provided. Althougnthe inventionlias beendescribed ywith reference to a specic type of'antenna system, it ,to be. understood that its. usev is not limited, 'to antennas of the. type shown,l nor tofantennasf-employing, parabolic .reflectorsv It will be clear to those,.skilled1inl the. .art W-itlioul'.I further discuslof all' of the conductors connected together. to

cause operation as short-circuited quarter wave lines.vr

1 A.Ref'erring, to:Figure 3,.. an-v effect simi-lar izo-that provided by the plates 9 of Figure 1 may be secured bymeans of a plurality of quarter-Wave rods `I3 connected atpoint's 'I5 alongfa conductor l1 l'The points |15 are. spaced at. intervals. substantially less. .than .one-.quarter Wave1ength,and

cooperate in pairs as short-circuited open-'wire quarter wavey lines.

Referring to Figure 4, a further modification of the invention comprises a plurality of parallel conductive discs I9, connected at their centers to points 2l on the conductor I1. In order to provide high impedance resonance between the adjacent discs i9, the radii ofthe discs are not necessarily one-quarter Wavelength, because each pair of discs acts as a radial parallel conductor line, with tapered constants, that is the capacitance per unit length is largest at the outer end,- gradually decreasing as the inner end is approached. Denoting the radius of the conductor Il as a and the radius of each discs I9 as b, a and b must be so related that:

2 b 2 2 l 2 b- J1 i K e=^ eKe Where A is the wavelength, Jo() is the Bessel function of the first'klnd and and first order. l

I claim as my invention:

1. In a system including two antennas, ap-` paratus for preventing direct-path transmission between said two antennas including a plurality Vof screens of conductive material each having substantially parallel front andback edges, and

each substantially one-quarter wavelength wide from front to back, and means supporting said screens in spaced planes perpendicular to the line between said antennas, said supporting means comprising a conductor extending generally parallel to said line and connected to each of said screens at its back edge. 2. In a system including two antennas, apparatus for preventing'directfpath transmission between said two antennas including la plurality of discs of conductive material disposed in spaced planes perpendicular to the line between said antennas, and a conductor extending generally parallel to said line and connected to each of said discs. j y

3. In a system including two antennas, apparatus for preventing direct-path transmission rbetween said two antennas including a plurality of discs of conductive material disposed in spaced 'planes perpendicular to the line between said antennas, and a conductor extending generally parallel to said line and connected to each of said discs, the radius a of saidconductor being related to the radius b of each of said discs by the equation:

Jrerfocaarmffra y and 4. In a system including two antennas, apparatus for preventing direct-path transmission between said two antennas including a plurality of discs of conductive material disposed in spaced 4 planes perpendicular to the line between said antennas, and a conductor extending generally parallel to said line and connected to each of said discs, the diameters of said conductor and said discs being such that the radial distance from the edge of each disc to the point of connection of said disc to said conductor lies between one quarter 'wavelength and one eighth wavelength at the lowest frequency at which said antennas are series resonant.

5. In a system including two antennas, apparatus for .preventing direct-path transmission `between said two antennas, including a plurality of parallel-conductor transmission line sections,

means supporting said line sections between said antennas and perpendicular to the line between -said antennas, said supporting means shortcircuiting each of said line sections at least at one point thereon to provide high impedance paths between said antennas.

6. In a system including two antennas, apparatus for preventing direct-path transmission between said two antennas, including a plurality of plates of conductive material each having sub-l stantially parallel front and hack edges, and each substantially one-quarter wavelength wide from front to back, and means supporting said plates in spaced planes perpendicular to the line between said antennas, said supporting means comprising a sheet of conductive material secured to said back edges only of said plates.

' 7. In a system including two antennas,` apparatus for preventing direct-path transmission between said two antennas including a plurality of substantially flat bodies of conductive material each having a front edge and a back edge and each substantially one-quarter wavelength wide from front to back, and means supporting said bodies in spaced planes perpendicular to the line between said antennas, said supporting means comprising a conductor extending generally parallel to said line, connected to each of said bodies at its back edge.

.8. In a system including two antennas, apparatus for preventing direct-path transmission between said two antennas, including a plurality of bodies of conductive material each having substantially parallel front and back edges and each substantially one-quarter wavelength wide from front to back, and means supporting said bodies in spaced planes perpendicular to the linebetween said antennas, said supporting means comprising a conductor extending generally parallel to said line, connected to each of said bodies at a point one-quarter wavelength distant at its back edge only. i

9. In a system including two antennas, apparatus for preventing direct-path transmission between said two antennas, including a plurality of bodies of conductive material each having substantially parallel front and back edges and each substantially one-quarter wavelength wide from front to back, and means supporting said bodies in planes perpendicular to the line between said antennas, at intervals of approximately onetenth wavelength at the frequency at which the system is to operate, said supporting means comprising a conductor extending substantially parallel to said line, connected to each of said bodies at its back edge. 10. An antenna system( comprising two antennas spaced from each other, a sheet of conductive material disposed substantially in a plane parallel to the line between said antennas, and a plurality of plates of conductive material each 5 6 having substantially front and back edges and REFERENCES vCITED dlsposed m planes perpendlcular to Said Ime at The following references are of record in the intervals of substantially less than one-quarter ,Y wave-length at the lowest frequency at which said me of this patent' antennas are series resonant, each having its back 5 UNITED STATES PATENTS edges only connected to said sheet. Number 11. The invention as set forth in claim 1o, 2261 272 ,Newe Novntelgu wherein each of said plates is substantially one- 2275312 Tuniek "Feb '10 1942 quarter Wavelength long from front to back at 231:196 Lindenb: Apr: 28 i942 the lowest frequency at which said antennas are 10 series resonant.

GEORGE H.'BROWN.

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