CA2130750A1 - Dual band signal receiver - Google Patents

Abstract

A dual band signal receiver (10) is provided with relatively coaxial antenna assemblies (12, 11) electromagnetically coupled to respective upper and lower band rectangular waveguides and ports through suitable polarization switching assemblies. The upper band rotatable antenna assembly (12) consists of a dipole feed (14) having driven dipole element (16), parasitic dipole elements (17), and a corner reflector element (70) electromagnetically coupled to the upper band rectangular waveguide by a suitable transmission line extending substantially along the longitudinal axis or centerline of the lower band cylindrical waveguide.

Description

W093/~7466 ~ 3 ~ PCT~US93/01622 , . ~
' DUA~ BAND 8IG~L R~CEIVER

This is a continuation of co-pending U.S. application Serial : Number 07/840,334 filed February 24, l992.
FI~D OF T~ INVENTION
~: :The present inv~ntion relates to prime focus antenna feeds : for receiving microwave signals transmitted from a satellite in geosynchronou6 orbit about the earth, and in particular to prime focus polarization switches~having one antenna responsive to a first frequency range and another antenna responsive to a second frequency ~range 90 ~as~ to; permit simultaneous reception of satellite~microwave signals~within each of the first and second ~ ;`frequency ranges. The~invention has particular use in connection "'~ with~:satellite~ ~broadca~st~"receive only" (TVRO) television systems~
: : : : BAC~GRQ~ND OF ~H~ INVENTION
Satellite~broadcast;:~;"receive only~' television signals are very:~weak~and:require~:thé use~of a large antanna with a large collecting~area,:in,;~order to receive~a useful signal. It is common for~the'larg,e~collecting area to constitute a paraboloidal re M e*tor :dish~ The:;signal collected and reflected by the paraboloidal`~dish~;'is~focused:by~the refIector surface to a point in~'f~ront~o:f' the:~dish. ~The~distanoe~ of~:the focal point ~of any pa~ticular dish from the dish is dependent upon the curvatur~ of the~: reflecting ~surfa~e:~ of ~the dish, which is usually paraboloidal.
:The~sign~l reflected from the dish is normally detected by a: device~referred to~as:~a~prime focus ~eed antenna. As will be understood by those skilled in the relevant art, the prime foGus ~: ~

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ovarall p~r~ormance ach~eved. While tl e overa~l ft~nct~on o~
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waveguld~ or th~y may b~ eoncentr~c~lly plac~d ~round tho Out~ia~
o~ t~ aperture. Th~ natu~, nu~ar and ~l~ae~eI3t or! su~h oxru~at~ons ~pend llpOJl: th~ paxt~cu~ar r~rQ~Dent~ of~ the :
y~ in whi-::h th~ wavQ~uid~ i~ to 1D~ u5~d. Untll f~rly D SHEET

W~3/17466 ~ 1 3 ~ 7 ~ o PCT/US93/~1622 recently, TVR0 satellite signals have been transmitted principally in the opexat?ng frequency ~and of from 3.7 to 402 ~H~, an operating band referred to by persons in the field as the C-band. C-band waveguide antennas are positioned at the focal point of a suitable parab~loidal reflector dish and such antennas have had to demonstrate superior performance characteristics for reception of TVR0 signals at C-band. This has been due, for the most part, to the relatively low power at which C-band signals are transmitte~ from the orbiting satellites used to transmit such television information. The most commonly used scalar rings for c-band TVR0 communications are those shown in U.SO Patent Des. 272,9lO to Taggart et al., owned by the assignee of the pes~nt invention.
In~he past few years, some TVR0 satellit~ channels have, fo~ many reasons, also been transmitted at frequencies within the ::range of from 10.95 to 12.75 GHz, a frequency band referred to by ~persons in the: field as the Ku-band. Thu~, some satellite television stations are transmitted in the C-band range, while othe~æ~ are transmitted~ in ths Ku-band freguency range.
ccordingly,~ it had~become desirable prior to 1986 for TVR0 earth stations~to~ have system~components capable of receiving and processing both C-band and Xu-band signals simultaneously without the components used to receive at one frequency intexfering with :: :
~: the efficiency of the signal reception at the other frequency.
Prior type~ of dual frequency feed assembly used heretofore have consisted of C-band and Ku-band waveguides arranged together in a~common feed assembly so that at least one of the waveguides is offset from the boresite of the parabolic reflector. Such W093/17466 ~ 3 ~ 7 5 u PCT/US93/01622 - !, devices adequately received C-band and Ku-band signa~
~imultaneously but were relatively expensive and occasionally yielded inconsistent r~ception guality due to offset phase centers of the C-band and Ku-band waveguide apertures.
Accordingly, it has been understood in the TVR0 art since at least about 1986 (and in related commercial art long before that~ that substantially co~mon phase centers for dual frequency feed assemblies may be achieved by the use. of concentric waveguides, the smaller highe~ frequency waveguide being ~ocated coaxially with respect to the larger lower frequency waveguide.
There has developed beretofore a proliferation of TVR0 and other microwave waveguide junctions consisting of coaxial waveguides for simultaneous reception:of multiple frequency ranges.
For example, U.S. ;patent 3,864,687 to Walters et al~
describes a ooaxial horn antenna provided with three cylindrical waveguide~ 12, 14 and 16 which are progressively sized to provide an~ inner radiating~ aperture 18, a concentric intermediate aperture~20 and a~concentric outer aperture 22 at the fro~t end of~the assembly. The~beamwidths of the frequencies propagated within~ these waveguide~s;are controlled by stepping the forward ends~of:the~horns, with the inner horn projecting furthest. The phase centers of ~the concentric waveguides are purportedly substantially constant over:the band of coverage.
U.S. patent 3,665~,481~to Low et al. discloses a multi-frequency feed assembly ~or use with a singl~ dish reflector.
The feed assembly consists of a plurality of coaxial waveguide pipes including a circular inner pipe 16 for receiving the highest frequency signal, an intermediate pipe 18 and an outer : , ~ : 4 W093/17466 ~ PCT/US93/01622 .. .
~lpe 20 for receiving the lowest frequency. The space between the intermediate pipe 18 and the outermost pipe 20 de~ines a coaxial tracking waveguide 21 containing inwardly projecting probes. Illumination of the dish reflector is effected efficiently by the use of an outer flared horn section 12 for the tracking waveguide and an outer flared horn section 44 for the inner highest frequency waveguide 16. In this arrangement, the innermost and highest frequency waveguide 16 is spaced from all the;~walls of the surrounding lower frequency waveguide region 21.
U.S. patent 31086,203 to Hutchison ~iscloses a waveguide structùre for multiple frequencies having an outer circular waveguide 10, a ~cylindrical core 16 and an inner circular wa~veguide 22. ~ The ~cylindrical core and ~he outer circular waveguide ;define a~coaxial region 18 therebetween. Lower frequency~signals;are~coupled into the coaxial region 18 and are de~ected therein~by~probes extending radially into the coaxial space~ The~coaxial region propagates the coaxial TEll mode. The inner~waveguide 22 propagates signals of a different frequency without~interfering~with~signals in the coaxial region 18. A
probe~30~couples signals from the inner waveguide to a receiver U.S.~patents 4,~819,~005 and 4,821,046 to Wilkes show similar dual~frequency microwave~feed assemblies for use with a parabolic ; reflector. Both patants show coaxial circular waveguides where the higher freque~ncy;~waveguide is disposed in and concentric with the surrounding lower ~band waveguide. The diameters of the waveguides are adjusted so that the innermost waveguide does not degrade~the performance of the lower frequency surrounding ~: :

v~ V ~^ V G C
~ ~ 3~) 7 S O IPEA~ 21 ~EC 199~
;;!waveguide. The preferred frequencies are the C and Ku frequene-,~
bands for satellîte communications.
U.S- Patent 3,508,277 to Ware et al. discloses the use of two cylindrical waveguides mounted coaxially with respect to each other. Flared horns are provided at the ends of the waveguides for feeding multiple signals to a common load such as a parabolic reflector dish. The patent discloses an inner circular waveguide or transmission of~the signals in the upper frequency band and an outer circular waveguide for transmision of the signals in the l:ower frequency band.~:~Ware at al. deliver the higher frequency signal directly: out~ the~ back wall of the surrounding lower frequency waveguide.~
U.S.~patent 3,325,817~ to Ajioka e~ al. appears to show a dual ~frequency~:~feed~ assembly :in which a ~igher frequency pyra~idal~horn lO;~is~mo~nted coaxially within a surrounding lower frequency~pyramidal:~horn 12.~ The higher frequency horn 10 is centered along the longitudinal axis 14 of the lower frequency horn~12.~ The signal:;may:~be transmitted from (or received by~ the higher~frequency horn~lO~which~ spaced from the sidewaIls o~
thé:~ surround~ng~ lower ;~frequency waveguide and extends longitud:inally through~the~lower~frequency waveguide to d~liver the~higher frequency~signal:th-rough th~ rear wall 24 o~ the lower frequèncy: waveguide~ The~ presence ~of:~th~ higher frequency waveguide~ wit~in~the~ lower~ frequen Q ~waveguide along the :longitudinal axi~ Or ~ the latter so a~ to space the former from the~sidewalls of the~latter~provides an uninterrupted signal path f:or: the: lower frequency signal, which is detected by a pair of lower frequency pro~es 2~6 and 28 located near the rear wall of , :

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wo g3,l7466 ~ 1 3 0 7 ~ ~ PCT/US~3/01622 .requency waveguide 12. The phase centers of the higher and lower frequency feed horns are selected to be as nearly coincident as possible, given the tolerances of the particular reflector systems employed. ~Col. 3, lines 7-10).
U.S. patent 2,425,488 ("'488 patent") to Peterson et al.
also discloses the use of a pair of coaxial and concentric pyramidal waveguides for simultaneously receiving signals at different frequencies. The axes of both feed horns coincide.
A high frequency pyramidal horn is situated within the interior of a~surrounding low frequency pyramidal horn such that the high frequency~pyramidal~ horn~is separate or spaced from all of the walls of the low ~frequency pyramidal horn. The high frequency signal is coupled out~;laterally through the sidewall of the low frequency waveguidé thereby leaving an open waveguide space behind the high frequency waveguide in which a low frequency ;pick-up'~probe~24 is; located. In the embodiment shown there is ~:~d,' '~ added~structure in the~form of partitions 28 and 29 which provide un~iform~uninterrupted;~signal~paths~for the low frequency signal aroùnd~the~high frequency~waveguide. ~Col. 2, l'ines 44-46). The low ~frequency signal~;thereby passes around the high frequency feedhorn~to~the low~frequency pick-up probe 24, which is located just~in~front of the~;~rear~wall 25~of the low frequency waveguide.
The~partitions on~the upper and lower sides~of the high freguency waveguide are to provide for~a;smooth electrical path for the low reguency energy to, get to the back of the low frequency ; wave~u~ide for detection by the probe 24. Although the partitions Z8,~29 physically block part of the open space along the sides of the high frequency waveguide, it would be obvious to use WO93/17466 ~ 1 3 ~ 7 5 ~ PCT/US93/01~22 dielectric partitions to support the coaxial high frequ~n~
.. . .
waveguide in an application where the uninterrupted signal path for the lower frequency signal might preferably be annular or coaxial in cross section (i.e., to support a coaxial TEll mode3 such as when circular waveguides are used in place of the pyramidal horns, for certain applications mentioned hereinbelow.
By way of example, were the waveguides disclosed in Peterson et al. to be circular in cross section, the space within the low frequency waveguide behind the high frequency waveguide and ~ : :
between the rear wall 25 and the rear point of the higher ~ frequency waveguide would~constitute a circular waveguide section : and therefore support the dominant TEll circular waveguide mode ' ` .
common in TVR0 appIications.
U.S. patent 4,041,499 ("'499 patent") to Liu shows a dual fre~uency: feed similar to that of Ajioka et al. but which uses coaxial circular waveguides instead of pyramidal horns. Liu et al~ disclose a waveguide: antenna in which inner and outer waveguides are side-fed;by~fixed coaxial probes. The inner waveguide is fed with~a monopulse signal in the sum or in-phase ; mode~ and~: the outer~waveguide: is similarly sida-fed with a monopulse s:ignal: in: the:difference or out-of-phase mode. In fact,~;the~presence of~the circular higher frequency waveguide in Liu et al.:de*ines~an~ uninterrupted signal path for the lower fre~uency signals in~ the form of a coaxial transmission line cavi:ty within the surrounding lower frequency waveguide that extends to the rear wall of the lower band assembly. This means ~:~ that the dominant mod present in the lower band waveguide is the : ~ : :::
Ell coaxial waveguide mode.

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W093/17466 ~130 7 ~ ~ PCT/US93/01622 U.S. patent 4,785,306 ("'306 patent") to Adams shows a Ku band circular dielectric rod waveguide coaxially mounted in a lower frequency circular waveguide and spaced from all the wall~
of the surrounding lower frequency waveguide. In this patent, the signal on the coaxial dielectric rod is coupled into a cavity waveguide by bending the dielectric rod at approximately 45 degrees and letting it pass through the side wall of the urrounding lower frequency waveguide. The end of the rod is :
tapered to provide for efficient launching of the signal into the Ku-band cavity waveguide. The dielectric rod is bent at a 45 degree angle in order to minimize reflections of the C-band signals within the C-band circular waveguide, thus rendering the coaxial Ku-band feed~e~ssentially transparent to C-band signals.
This~patent teaches~ the use of a Ku-band waveguide coaxially mounted to be spaced from~all of the walls of a surrounding lower frequency circular C-band waveguide and the use of a signal transmission means~to ~couple the signal from the coaxially mounted~Xu-band waveguide~through the side wall of the C-band waveguide. ~In thi~s;~arrangement, the C-band signal is detected by~a probe situated at~the rear of~the C-band waveguide in the space~behind the~coaxial~Ku-band~waveguide. The C-~and signal has~an uninterrupted~signal~path around the Ku-band waveguide to the rotatable probe at the back of the C-band waveguide.
An important requirement in a dual frequency feed assembly for frequency re-use~ satellite systems, and in particular in ::
connection with TVRO~systems, is that the system be able to detect signals having different, usually orthogonal, ; polarizations. One~way to meet this objecti~e is to provide :::
g W093,'1~466 ~ PCT/~S93/01622 components able to switc~,:upon demand, from one polarization ~ 3 the incoming signal to the ~ther. For example, this requirement has given rise to the common use in TVR0 prime focus feeds of a small rotatable metal probe assembly located at the bottom or back of the waveguide and coupled electrically to the relevant tandard rectangular waveguide. Such a probe a-~sembly and feed horn for use at C-band is shown and descri~ed in U.S. Letters Patent 4,414,51~ to Taylor Howard, owned by the assign~e of the present application, although the probe assembly of the '516 Howard patent may be suitably scaled to work at any desirable frequency. The foregoing~'306 patent to Adams suggests the use : : : :
-~;- of rotatable probes for the purpose of polarization switching.
:
U.S.~Patent~ 4,740,795 ("'795 patent") to Seavey (of record in:applicant's parent application) discloses a dual frequency coaxial feed assembly~for receiving electromagnetic signals at wo different frequencies and conveying them to an external ~ignal utilization device. The feed assembly consists of a waveguide for C-band signals having a circular aperture at one , :
end and~being closed~at the other end. A rotatable dipolar probe :is ~mounted at the closed: end of the C-band waveguide for receiving~C-band signals~entering and propagating within the :wavegui~e from ~the~ aperture. The probe, which is within a circular C-band waveguide section, couples the C-band signal to a rectangular wavegu'ide section mounted on the exterior of the C-band waveguide housing.~ From the rectangular waveguide section, the C-band~ signal is appropriately amplified and processed. A Ku-band circular waveguide cavity and circular ~, :
aperture is coaxially and concentrically mounted within the ~ ~ 10 WO93/l7466 PCT/US93/01622 ,................................ W i ~3~D rl~
~urrounding C-band circular waveguide. This structure enables simultaneous reception of both the C-band and Ku-band frequency ranges~ The Ku-band waveguide is smaller in diameter than the : surrounding C-band waveguide and it is spaced from all of the working walls of the C-band waveguide. The Xu-band signal is coupled out of the Ku-band circular waveguide by a rotatable dipolar probe element which is supported by dielectric means within the cavity. 'rhe Ku signal is coupled through a suitable .
transmission means:to;a rectangular waveguide ~ection mounted on the exterior of the C-band waveguide casting. The rotatable dipolar~probes are;connected to rotate together on a common axis within their respective~waveguides. In this Seavey patent, the C-band cavity consists of~two portions: a coaxial annular portion surrounding the~ Ku-band :waveguide and a circular waveguide po~tion behind:the~ Ku-band~waveguide in which the rotatable C-band~ probe~is~ loGated.~ The two portions are electrically i~te~rc~nnected by~four coaxial lines so that C-~and signals in¢ident at the~C-band:~aperture have an uninterrupted signal path thr~ugh;;the coaxial;:C~band cavity around the Ku-band waveguide and~into the~circular~C-band cavity containing the C-band probe détector. :
U:.S~ patents~4,903~,037~ ("'037 patent") and 5,107,274 to Hitchell:et al.;(of record;~in applicant's~parent application) and International Application No. PCT/US90/04356 (W0 91/02~90) to Blachl~ey~(of record~in;applicant's patent application~ describe essentially the dual frequency feed assembly of Seavey in which a pair of circular waveguidës 14 and 16 are coaxially mounted such that the smaller higher frequency waveguide 16 is within the W093/17466 ~13 ~ 7 S O ; PCT/US93/01622 larger lower frequency waveguide 14. The waveguides are designè~
to operate simultaneously in the C and Ku-band frequency ranges.
The larger C-band waveguide 14 contains antenna probe 33 to detect the C-band signals and the smaller Ru-band waveguide 16 contains antenna probe 20 to detect the Xu-band signals. Each antenna probe 33 and 20 is coupled to a respective waveguide section 41 and 31 to couple the signals to an external amplifier.
In contrast to Seavey,~Mitchell et al. and Blachley mount their Ku-band waveguide by means including a coaxial line for coupling the Ku-band signal~ to the ;exterior of the C-band waveguide castin~. Mitchell et al. and Blachley also utili2e a cumbersome harp structure to rotate the entire Ku-band assembly, which includes the probe fixed therein, for polarization switching.
Mitchell et al. and Blachley describe their centra' purpose as~being to avoid degredation of the C-band signals by making the Ku-band cavity substan:tially 'itransparent" to C-band. This is seen~to be~accomplished in~two ways: (1) by adjusting the length oP the ;Ku-band~ waveguide assembly, and (2) by empirically establ~ishing~an optimum~axial pos~ition for the Ku-band assembly within;~and;~spaced rearwardly or inwardly from the C-band aperture ;plane. ~ With respect~to~the first technique, the '037 patent discloses~that~the~K:u~-band cylinder or assembly is approximately 1.6 inches~long.~ Col~ 4, l~ines 57-59). This length is approximately one-half wavelength of the propagating ~-band signal within the surrounding C-band waveguide With a length near 1.6 inches the~Ku assembly operates on the fundamental principal of a "halfwave plug" provided that it is positioned somewhat inwardly of the C-band aperture, as shown in Figs. 2 and ~ 12 ~, ~::: ~ :

pCllU~ q3 1 ~
hl~7 ~p , IP~ 21 DEC l993 5-7 of the '037 patent. Under these circumstances, it is well known in the relevant art that, as a halfwave plug, the Ku-band assembly is rendered essentially invisible, or re~lection free, by a familiar consequence of two equal, but oppositely phased, reflections~ One reflection arises within the C-band cavity at the input side of the assembly and the other substantially aqual and cancelling reflection arises at the output side, l.6 inches further down the C-band cavity. The two reflections essentially cancel each other thereby rendering the Xu-band assembly ~f l.6 inches in length essentially invi~ible to the C-band signals within the waveguide4 As~shown by Mitchell et al. in Figs. 8 and 9 of the '~037 patent, this placement of the Ku-band assembly inwardly of or "behind" (Col. 4, line 13) the C-band aperture opening;has produced an~enhancement of the C-band performance relative to such performance in the absence o~ the Ku assembly.
(Col.~4,~Iines 31-38). ~ ~
In *he structure~disclosed by Mitchell et al~, moreover, the signa-l~from the Ku-band circular waveguide is coupled to a coaxia1 transmission~;1ine~that~passes substantially radially or latera}ly outward~from the~Ku-band waveguide and through ~he side wali~of the~C-band~waveguide. In this respect, ~itchell et al.
and~Aaam~;~('3~06 patent)~disclos~ well known equivalent structures for~; tX-~purpose~of coupl~ing signa1s away from the Ru-band wavegu:ide. Mitchell~et al. use a radially extending coaxial line and Adams uses a nearly radially extending dielectric rod. As in the~ '306 patent~to Adams, the existenc~ within the Mitchell et ~al. C-band cavity of the laterally extending Ku-band txansmission line pre~ents one from drawing a line with a pencil ~, ~ 13 :: :

wo 93tl7466 h 13 0 7 ~ O PCT/US93/01622 . ., 0 ompletely around the outside of the higher frequency feed horn assembly without being interrupted by khe transmission line.
Accordingly, Mitchell et al., and Adams disclose coaxial feed assemblies in which the higher frequency feed i spaced from the walls of the surrounding lower frequency waveguide, excep~ for , the connecting link represented by the transmission line carrying the higher signal to the exterior of the feed assembly.
Seavey ('795) does not differ in substance from these structures. Seavey happens to use a waveguide cavity, as does ~Peterson et al. ('488~patent) to convey the detected Ku-band signal to the exterior~of the lower frequency waveguide. Seavey simply selected, as'~a matter of choice, a di~ferent partition arrangement for mounting~the Ku-band (higher frequency) wave'guide within and~ spaced from the working walls of the C-band (lower fr~quency)~waveguide. In all these structures the mounting means for~the,~Ku-band~waveguide is essentially invisible to the C-band signal.
For~waveguide assemblies of thè type disclosed by Mitchell e~al.~ Seavey ('~795)~Adams or Peterson et al., moreover, the ; doninant~C-band signal~mode is refl~ected from the rear wall of the~ band~ circular~ waveguide to produce a standing wave configuration'within~the waveguide. The pick-up probe within the waveguide is~ located~ at~ a standing wave maximum to provide ; e~ficient ~oupling ,or excitation of the mode with or by the probé.~ m is reflect~ion~`from the rear wall and the location of the probe within the C-band waveguide do not affect the radiation pattern esta~lished by the feed assembly.
Finally, Mitchell et al. mount the Ku-band signal launch box ~ ; 14 :~:: :: ~ : :

W093/17466 ~1 3 0 7 ~ ~ P~T/VS93~01622 ..... ~
"vl the scalar rings making the illumination characteristics of the feed unadjustable. Accordingly, the mechanism disclosed by Mitchell et al. la~ks a means for lowering the noise temperature of the device in response to varying installation parameters.
: Ideally, a feed assembly should have a radiation pattern :~ such that it radiates toward the paraboli~ reflector to illuminate the entire surface with little or no spillage, or loss : , of radiation around the sides of the reflector. As has been demonstrated by the art disclosed above, the most common choice :of a feed assembly for~a~parabolic reflector i5 the waveguide.
;,Antennas, L.V. Blake,~September 1991, Munro Publishing Company, pp. 264-265. :~ ~
The radiation pattern of the~waveguide is established by the physlcal si3e of the~aperture opening of the waveguide and the electric $.~,1d :established at:that opening. For example, in waveguides~of the~type utilized;by Mitchell et al., the beam of rad~iati~n~ used~ to~ illuminate~ the paraboIoidal reflector is dependent upon;the:èlectric field established in the aperture of the:~waveguide~by the~:TEll~mode that is incident on the waveguide aperture.;~Thus:the~surface~area defined by the aperture rim is in~fact~the~most~important~working wall o~ the waveguide. Energy f~the~appropriate~:fre~quency underqoes a transition upon being : incident:at that surface:~or wall of the waveguide~
; In such waveguide~feeds the TEll mode can be excited by a variety of different~:means such as by a probe of the type disclosed by Howàrd~;;or~by coupling signal energy into the -circular waveguide:by~means of another waveguide using slot coupling, as in Ware~et al., or other means. Such different .

WO93~17466 ~ 1 3 U 7 ~ ~ PCT/US93~0162z means for exciting the TEll mode ~an be located at any arbitra~
distance from the aperture and these means and whare they are locat~d have no e~fect on the radiation pattern produced by the circular waveguide aperture with an incident TEll mode. It is : only the physical size of circular aperture and the electric field established a* the aperture ~y the incident TEll mode that det~rmines the radiation pattern of a wavegui~e assembly.
;~Contrary to the functioning of waveguid~s, a dipole antenna ~ does not have a radiation pattern focused by a physical aperture :~ ; and is known to be ill-equipped to the task of illuminating a reflector dish with a focused radiation pattern, as is desirable ~ at the~TVRO frequencies of interest. Sometimes a double-dipole :~; endfire array may be used. Blake, supra. But these have been found~us~eful only at s~ignificantly lower frequencies than Ku-band and ~have:~ not been known to work in dual frequency feed asse ~ lies.~S. Silver,~Microwave Antenna TheoEy and Desiq_, Vol.
12:~of~MIT Radiation~Laboratory Series, McGraw-Hill, New York, 194:9.~:The dipole array of the pr~sent invention ~herefore cannot be~ said::to have been~known or suggested in the art known herétofore.~
Another of the important requirements in a feed assembly for ;a~dual~requency,~frequency re-use satellite system is that the feed:`~a~ssembly~have low~cross-polarization characteristics. This : is~ impor$ant becausé of the dual polarized nature of TVRO
satellite~ signals and the;relatively closely spaced broadcast satellites in orbit~around the earth. Cross-polarization is undesirabIe because of the possible existence of co-channel ~ cross-talk caused by~substantial interference between signals at :~ : 16 :; ~ :
:
:

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~1 307S0 ` ~8 21 DEC l993 ~
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the same fraquancy but having orthogonal polarization characteristics.
Whether an antenna assembly has suitable low cross polari.zation feed characteristics is a complicated ~unction of the particular antenna with which one is concerned. In general it is neces ary to :have substantially equal E and -H plane patterns~ i.e., rotational symmetry, in order to achieve low cross-polarization characteristics.
It is understood in the relevant art that the circular ~:~ waveguide, particularly with the proper mode and a corresponding aperture diameter, provides very good rotational symmetry in its : radiation pattern and resulting low cross-polarized feed characteristics. In circular waveguide feeds, the cross-polarization characteristics depend on the relative size of the circula~r aperture in terms of the relevant wavelength, and upon :~ the ~ixture of modes that one excite~ in the aperture of that cir~ular waveguide.~ Accordingly, it has becom~ recognized in the ;art that in circumstances where cross polarization cannot be :tole~ated, ~such as;~is generally the case in TVRO reception, cir~ular wav~Qguides~having an aperture dia~eter approximately equal :to one wavelength of ths frequenay of interest are esp~clally: usefull~:b~cause such circular waveguides have been hown ~o exhi~it rota~ionally symmetri~l radiation patterns and relatively low cross~polarization characteristics. Such circular waveguides have accordingly com~ into wide use in TVRO
applications.
In contrast, the dipole antenna i5 well understood to have a radiation patt~rn that is not rotationally symmetri~al and ~: 17 :: , .. ._~, ST T~E S~

therefore exhibits re}ativeQ~ ~ ~poor cross-polarization chara~teristics. As stated above, the dipole has been known heretofore to represent a relatively poor choice for use in a : TVRO feed assembly.
~: Where dipoles have been included heretofore in connection : with broadcast television reception from satellites they have ; mostly appeared as dipolar probes within waveguides, as in the ~: foregoing '795 patent to Seavey and (in some embodiments) U.S.
: ~ :
patent 4,504,836 ("'~36 p~tent") to Seavey. As a further example, U.S. p~tent 4,862,187 to Hom ~of record in applicant's : parent application) discloses the use of dipole elements in a feedhorn for a satellite dish. Hom discloses a feedhorn lo :~
having a metallic housing 12:which defines a throat 18 formed within a~meta~llic cup~;20. Dipole antenna elements 38,40 are situated:~within the cup 20 which constitutes a waveguide. Thus, the radiation pattern:and cross polarization characteristics of the~assembly of Hom~are~determined by~the waveguide aperture.
..Wherè dipole antennas: have been used heretofore as feeds without~a~waveguide they ;have~ not been seen in dual frequency ass ~ lies nor~to~function~suitably~for TVRV. The '836 patent to~S~eavey~discloses~ th~e~use of a particular dipole antenna for C-bànd~ope~ration~in-~a~single frequency ~eed. In one embodiment, the~ dipole~ 15 ~is within~ and near the rear wall of a circular ::
waveguide 12. In such an embodiment, the radiation pattern and cross-polarization~characteristics of the feed would be determined essentially by the nature and function of the waveguide. In another embodiment, as shown in Figs. 7 and 9, the depth:of the circular waveguide cavity is reduced (Col. 4, lines W~93/17466 PCT/~Sg3/01622 ~ :~ 3 ~ 7 ~
8-l9) and the dipole with its elements drooped is placed outside the face of a corrugated ring structure. ~ Without substantial inf luence of a waveguide r the corrugated ring structure is required to shape the ra~iation pattern of the feed. However, good cross polarization results from this embodiment are unlikely in light of Fig. 8 whiCh shows cross polarization in the H plane of this embodiment at about -20dB when it should theoretically be zero. Even in the 45 degree plane, where the ~ross polarîzation lobes:are usually a maximum, the desired value for ,: ~
frequency re-use systems should be below 30dB in order to avoid TV pidture interference. Seavey fails to provide cross polarization levels in~the 45 degree plane and the levels he does provide do not appear suitable. Thus the Seavey '836 patent does not; disclose or suggest the~use of the dipole array of the present invention, and~especially does not suggest the use of a dipole~array in ~a dual frequency feed.

8U~MAQY~OF_T~ INV~NTIO~
In contrast;~to~the foregoing, the present invention providës~q~dua~l~ frequency~prime focus feed assembly, preferably for ~TVRO ;~reception,~ which comprises a Ku-band antenna feed con ~ ing of~an array of~interactive~elements in~luding a driven dipole~t~qether~with~specific parasitic elements. Significantly, the~Ru-ba~nd~dipole;feed~of the present~invention does not use a waveguide. The K~-band;dipole feed and surrounding C-band wa~eguide are substant~ially coaxial and have commonly driven rotatable assemblies;~which ~couple the signals to respective launch boxes mounted substantially adjacent the bottom or rear wall~of~the C-band waveguide. The Xu-band dipole feed eliminates .;
~ I9 :

WO93/17466 ' ' PCT/US93/01622 U ~ 5 ~
the high-band waveguide and probe assembly within the ~urroundii~
low-band waveguide, as has been known in the art heretofore.
Means are pr~vided for conducting the Ku-band signal to its respective lau~ch box along substantially the centxal axis of the C-band waveguide and to the back wall thereof so as to minimize ; any disturbance of~the~C-band electrlc field and any substantial contribution to the noise~temperature of the device. In fact the presence of the dipole~array and its signal conductor extending substantially concentrica~l1y through the C-band waveguide creates or~deines a coaxia~ waveguide for the lower frequency C-band signal~in~which the coaxial,~;not c~ircular, TEll waveguide mode is~dominant throughout~the~C-band waveguide. The absence of a ,circular ~C-band cavity~and~ circular~ TEll mode in the C-band càvity~mean's, in~efect,;~;that~the 'dipole feed assembly of the pres ~ ~in~ention~;~ls~not;~spaced from all the walls of the C-band wavegu~de~
The dlpole~feèd of~the~p~resent~invention preferably consists rray~ ing~a~driven d~ipol~e, a~parasitic dipole and a ¢ ~ er~reflector.~ The~;desired radiation pattern of the dipole a,rray~if~the~pre ~ invéntion~is~estab1ished as a result of the ~ ~ of and,spacing~betwéen~the driven~dipole elements and 'f`.~ t ~,~,paras,itic~ref~le,ctor~;elements of the array. In contrast to wavegu'id~è assemblies,~the ~dipole feed~ of the present invention "~i[~ doès~not hàve~a~physical circular aperture with an electric field e~stabli~shed~by~an'~i~ncident TEll~mode and does not have a circular Ku-band~ waveguide.~ The~TEll mode cannot~ exist in free space where~the~Ku-signal is~detected by the dipole and does not exist along~the transmission path ~from~ the dipole to the launch box.

~, , , ~

WO93/17466 ~ 7 5 ~ PCT/US93/01622 ~. . .
'~rhe TEll mode exi~ts only within a waveguide and in accordance with this invention, no circular waveguide is used for detection of the Ku-band signa~. The Ku-band dipole feed of ~he present invention does not contain a probe and does not work in the same way as the probe used heretofore with waveguides to excite or couple to the TEll mode in the uaveguide. Moreovar, providing a launch box for the Ku-band signal at the rear of the device contributes to asse~bly efficiency and permits ull illumination adjustment of suitable corrugations of scaler rings which may be mounted around the periphery of the radiating apertures.
In one embodiment, the Ku-band signal is extracted from the Ku-band dipole antenna through a coaxial transmission line which extends substantially parallel~to and adjacent the longitudinal axis of the C-bsnd~waveguide, thereby creating a coaxial line ;cavity within the C-band~waveguide for propagation of the C-band signal. ~'In this respect, the~cavity for the C-band signal in a ;feed having the present invention is not properly considered to ~ constitute a circular~waveguide,cavity.
,R ~ The,transmission~line exits through the rear wall of the C-band~;coaxial~ waveguide and couples to the Ku~band launch box prefëràbly mounted~in~the~;webbing between the C-band waveguide and~ ;its~associated~waveguide launch box. The ,preferred arrangement provides;for~low production cost, a minimum number of;component parts~and, due to its light weight and standard siz~e,~-facilitates ~in-the-field replacement of standard C-band feeds.
8RIEF DE~CRIPTION OF T~ DR~WING~
Fig. l is a perspective view of a dual band signal ,~, ::::
:

W~93t17~6~ PCT/USg3/01622 . ~ .
~30750 ` ``-receiver of the present invention showing a two element yagi ty~' dipole antenna array with parasitic dipole elements and corner : reflector;

Fig. 2 is a side elevation sectional view of the ~mbodiment of the i m ention depicted in Fig. l;
., .
Fig. 3 is a side elevation sectional view similar to Fig. 2;
Fig. 4 is a side~elevation sectional view of another embodiment of the~present inventlon;
Fig. 5 is a side elevation sectional view of yet another embodiment :of the present invention;
Fig. 6A is an~exploded view of a portion of the dipole antenna~arrangement show1ng a rotary ioin~, rotary drive elements and:~coaxial:cable; :~
F}g. 6B~is a~side elevation sectional view comprising the~ remainder of the~exploded view of Fig. 6A and showing the low-band~waveguide~in~which~ the dipole is to be~mounted;
::Fig. 7A is~a~:detail section of a portion of the dipole array~o~ the present~:invention in~ exploded format;
Fig.~7B~ is~;a~detail section ~f:the Ku-band coaxial cabl:e~and~coupling~elements~forming the remainder of the exploded vie:w of~Fig~. 7A~
Fig.:8A is an~:exploded view of the support section for the~dipole array of the:present invention; and :Fig.~ 8B~is~ a s~ide elevation partially in section of drive elements and transmission line elements for coupling to the àntenna~ elements of Fig.~:~A.

PC~i 9 5 1 U 1 ~
~13~75~ i~Ug 21DEC 1993 ~r'`'~ .
.: 8~I~F D~8CRI~IO~ oF THE P~@~R~BD ENBODIM~T8 Ref~rring now to the drawings, and in particular to Fig. 1, there is shown a dual frequency signal receiver 10 which consist~
of a flrst signal receiving assembly 11 and a second signal receiving assembly 12 mounted coaxially therewith. In the preferred embodiment, the first signal receiver assembly 11 consists of a standard cylindrical waveguide portion 13 of cir¢ular cross-section sufficient to permit prspagation ther~in o~ a selected mode for microwave signals i~ th~ relatively low-band r~quency ~ange of ~rom 3.7 to 4.2 GHz, known as the C-band for TVRO transmi~sions.
The second signal receiver assembly, or ~eed, 12 is not a waveguide and consists of an array 14 of electrically interactive : conductive elements which are sized and spaced so as to cooperate to receive microwave signals within the relati~ely high-band frequency rang~ of from 11.7 to 12.2 GHz, known as the Ku-band for T~RO transmissions. The array 14 conæists in part o~ a fir~t .
pair 16 of oppositely ;ext@nding antenna arms which compriæe a ;two~element Yagi-~ype:dipole antenna. The arms 16 are in~line oppositely extending acti~e or driven el~ments 16 in the ~o~m of small rods having a length scaled to the Ku frequency band of int~estO A second:~pair 17 of oppositely extending antenna arms is spaced from and positioned directly behind and parallel to the , : driven ~rms 16. The ~rms comprising the second pair of antenna , ~ :
arms are parasitic élements preferably having substantially the ; same SiZQ and shaps as the driven element~ 16. In some circumstances, however, it may be preferable for each of the ~: parasitic arms 17 to be slightly longer than and to protrude `- 23 ~ S~

W093/17466 ~1 3 ~ 7 5 ~ PCT/US93/01622 `Deyond the outer end of ~he corresponding one of the driven pair of dipole arms 16. The relative lengths of the driven and parasitic arms of the dipole feed may be determined to meet desired performance criteria.
With reference to Fig. 2, and as shown in more detail in the : exploded view of Fig. 7A and the assembled view forming part of ~: :
Fig. 8A, the driven arms 16 and the parasitic arms 17 may be for~ed as part of a conductive, hollow and substantially tubular metal casting 60. The~ casting 60 is grooved at its outer end :
along its longitudinal axis on diametrically opposite sides, as shown by reference numeral ~61 (Fig. 7A), to define a known type of balun feed for the driven:dipole arms 16. A conductive feed wire 62 extends~longitudinally through the center of the casting 60,~parallel to the groo~es 61, and i5 conductively connected at onè~end~, for example ~by soldering ~as a~ 62a), to one of the drivén~dipole elements~l6, as shown in the assembled view of Fig.
8A. - With ~espect~to~Figs.~7A;and 8A, a plastic insulator 6~
having a ~ central bore: ~63a through which the feed wire 62 is `positio~ed~may be used~to~support the feed wire 62 within and to insulate~it from the;:;cast~ing 60 itself. A plastic ~leeve 64 fits ver~thé~free end or~pin;~68 of the feed wire 62 to insulate the pin;~rom~and;to secure ie~by~friction to an interior portion of a larger~diameter metal~sleeve 66.~:The slaeve ~6 is secured over and surrounds the pin 68 of the wire 62 but is positioned so that a portion of the sleeve~extends concentrically away from the pin leaving a space 67~:within the sleeve between the pin 68 and the distal end 69 of the sleeve. As will be readily understood by ~ ~ :
those skilled in the art~, the sleeve 66 is one-half wavelength :: ~

WO93/17466 ~3U 7 ~ ~. . PCT/US93/01622 ;ong (at Ku-band) and its purpose and that o~ the space 67 there~n is to define a half-wave rotary joint, as will be explained in further detail below.
Referring to Figs. 1, 7~ and 8A, the dipole array 14 also consists of a flat reflector plate 70 which is fixedly attached to, or may be formed as part of the casting 60 and has a planar sur~ace 71 adjacent and paralle~l:to each of the parasitic dipole :arms 17. A second planar;surface 72 ~Fig. l) is part of a second :
flat reflector pIate:and it too is adjacent and substantially para~lel to the parasitic: dipole arms 17. In the preferred embodiment,: the two planar surfaces 71 and 72 meet at a corner 73 and together define ~what is understood in the art to constitute a corner~reflector. In the present arrangement, the corner 73 lies parallel~:to and directly behind the parasitic rèfleator;~arms~l7.
The~ distances~ between the driven dipole arms 16, the parasitic~dipole~arms~l7,~the surfaces ~1 and 72 and the corner 7~3~`~are~selected:to~faciliate~:the~ establishment of a desirable radiation~;pattern~for~the~Ku:-band array, which doe~ not have the :advanta~e:of ~a circular:waveguide for such a purpose. The paraæitio;and~driven~elements of the dipol:e array function in a known manner through radiation interference to enhance radiation in:~:the~ forward~:direction~and, in effect, to cancel it in the rearward direction, This reflection action through wave int;erference is crucial~to the production of a suitable radiation beam~ or pattern effic:iently to illuminate the paraboloidal reflector. ~ :~

~ . , With reference to Fig. 1 and in accordance with standard : 25 : :

~ ~ 3 ~ 7 5 ~ 3, . ~ ~ ~ PCT~US93fO162~

practice, the low-band receiver 11 is a pipe or waveguide hav~
a physical opening or aperture defined by the rim 15 of waveguide 13. The waveguide 13 may also be provided wi~h an annular metal choke plate 18 at or near the periphery of its aperture. A
plurality of forwardly projecting concentric corrugations or metal rings l9, referred to as scalar rings, may be pl'aced in spaced apart positions on the ~orward facing surface of the choke pIate 18. The rings 19 dePine a plurality of co~centric grooves 21,~the number,~ width~and depth of which may vary, as desired.
n most instances, the choke plate 18 is slidably arranged on the periphery or outer circumference of the low-band waveguide 13 and releasably held~in~the~desired~location ~y suitable set screws (not shown). Adjustment of the position of the choke plate and rings~rel,ative to~thè~;radiating aperture of the waveguide has been:~found, useful ~in :~ shaping the radiation of illumination pattern~o`f~the ~signal~receiver~. However, the choke plate and nnular rings~have~-~sometimes been formed of a single casting ;t~gether with the:~cylindrical waveguide 13 and therefore may not be~:ad}ùstable relative~to~the waveguide~13 and its aperture 15.
Th,e~dipole;array~ 14~is preferably mounted at the aperture l5~of~the~C-band~signal:~receiver ~ll substantially coaxially therewith~:along its~centerline. In ord~r that the phase center for~the~C-band wave~gu;ide~13 and the phase center for the Ku-band dipo,le~array ~14::are;~substantially the same, the array 14 is mounted so that the~driven dipole arms 16 are substantially at the plane containing~the rim 15 defining the aperture to the C-band:waveguide, as:~shown in Fig. 2. In this way, the operation of the Ku-band dipole~ feed is not in any way affected by the ; 26 ' ~

WO93/17466 X1~V 7 S ~ PCT/US93/0162~

;
presence of the larger C-band waveguide feed.
Means such as a plastic centering or throat support 22 are provided for positioning and securing the dipole array 14 in place. The throat support 22 may take any desired configuration including a butterfly or spider arrangement having a plurality of spaced apart legs, as desired. The configuration of and the plastic material of the throat support 22 are selected so as to minimize any disturbance of the microwave electric field conducted through the:radiating aperture of C-band waveguide 13 and yet to enable low cost and reliable reproduction. The plastic material for the throat support 22, f~r example, is preferably a castable form of plastic having low loss electrical characteristics, such as plastic manufactured by General Electric Cor~. and sold in connection with the trademark (LEXAN).
:With reference to~Fig. 1, the C-band assembly 11 generally ~ ~ , consists of the cylindrical waveguide portion 13 and a rectangular waveguide~sub-assembly, generally indicated by referen~e numeral 23. ~It:has been known heretofore to cast the waveguide 13 and the~ sub-assembly 23 either separately for s~sequent~interconnection or~together in a single casting, as desired.~ The sub-assemb~y 23: comprises a C-band rectangular launch~box:24 preferably~situated just behind the botto~ or rear wall of the:cylindrical~waveguide }3. The launch box 24 is typically a standard~rectangular WR22g waveguide having a port ;and flange 26 adapted~for~standard interconnection with an elbow transition 27 to a suitable LNA. The WR22s waveguide may be cast together with the cylindrical waveguide 13 in a single casting, ::or separately cast ~and suitably joined to the cylindrical ~ 7 : : ~ :

WO93/17466 PCT/US93/0162~
7 5 ~
waveguide, as desired.
With ref~rence to Figs. ~ and 6B, the polarizatio~ switch of the C-band r2ceiver for TVR~ reception is preferably a small rotatable metal probe assembly, generally indicated by reference numeral 28. The probe assembly 28 preferably consists of a pair of probes 29 and 31 interconnected by a transmission line section 32. The probe assembly set forth in U.S. Patent 4,414,516 to H.
Taylor Howard has~been found to be particularly desirable for TVRO reception because of its exceptionally low-loss :
characteristics. Other types of rotatable probes, whether monopole or dipole, may~,~however, be used for C-band reception within~the C-band waveguide 13 with adequate results.
In the preferred embodiment, the probe ass~mbly 28 is fixed into a cylindrical plastic drive shaft or holder 33 which extends through~ ~he cavity of the WR229 waveguide 24 in a direction sùbstantially perpend~iCulqr to the direction of propagation of energy~therein. The~probe~assembly 28 is held in the drive shaft holder 33 such that a portion 30 of the transmission line 32 of the~probe~asse ~ ly~extends~along~the rotational and longitudinal axis~;of thé~holder ~33,~as does~ the probe 31. The holder 33 extends through the side wall of the WR229 waveguide and through the~;bqck~or~ rear~wall~34 of the waveguide 13 to terminate just inside the latter.~Rotational movement is imparted to the holder 33~by a suitable servo motor 36 (Fig. 1) mounted on the outside o~ the WR229 wavegui~de~2;4. A suitable plastic material for the holder 33 is preferably that which is manufactured by Oak Materia~s Gxoup Inc. and;sold in connection with the trademark , (REXOLITE) because it is~an insulating material having a styrene W~93/t7466 ~1 3 ~ ~ 5 ~ P~T/US93~01622 ~ase known for it~ low-loss characteristics at the frequency ranges of interest. The rotational axes of the holder 33 and probe assembly 28 are substantially coincident with the centerline or longitudinal axis of the cylindrical waveguide 13.
The probe 31 launches the C-band signal in the WR229 waveguide in the same direction regardless of the polarization status of the æignal. The probe 29 moves back and forth within the C-band waveguide 13 in a plane perpendicular to the longitudinal axis ~ ;~of the waveguide. ::
:: : :
Because of the polarization characteristics of Ku-band broadcast signals reflected by the parabolic reflector dish, the driven dipole arms 16 of~ the dipole array 14 are preferably rota~table for~the purpose of polarization switching. In the present e~bodiment, the arms 16 are rotated by rotating the entire dipole array.~:~ The structure of the preferred embodiment ::for :~otating the dipole~array is depicted in various forms in igs~ 2~,~ 3, 6A,~;6B~ and~;8B. ~Referring to Fig. 2, the Ku-band dipole ~:array 14~ is; provided with a rotatable drive assembly indicated~ generally~by~reference:~numeral 41. As shown in more detail~in~Figs.~ 2,~ 3:~and 6B,~the drive assembly 41 Consists of a~;~first~:plastic ~extension element, or lower drive bar 44, eccentrically and fixedly~mounted at one end into the plastic rotatable:holder 33:f~or the C-band probe assembly 28. The lower ::drive bar 44 is mounted into the holder 33 from within the C-band waveguide and preferably ~extends~parallel to and as close as ; reasonably possible to:~the~:centerline or longitudinal axis of the waveguide 13. The plastic material of the l~wer drive bar 44 is a~gain selected to ensure~l~ow-loss electrical effi~iencies and low :::

~ 9 ~i / 0 1 6~ 22 $ ~ ~ 2 1 D E C 1993 cost manufacturing efficiencies. For this reason, a castable plastic ~nsulating material is pr~erred. One such suitable plastic ~aterial is manufactured by Hoechst C~lanese Corp. and ~old in conn~ction with the trademark (~UREL). In thi~
embodiment, it is desirable that the lower drive bar 44 not have a large cross sectlon and thus, to preserve suitable rigidity, it extends only part way into the waveguide 13 in the direction of and toward the Ku-band dipole array 14.
: A~ shown in Figs. 2, 3, 6A and 8B, the drive assembly 41 : also consists o~ a second plastic drive element, or upper driva bar, 43 which may be ~ormed as an integral extension of the Ku-~band dips:~le array 14. In the preferred embodiment, however, the upper drive bar 43 engages but is not integral with the dipol~3 assembly and~ extends within the C-band waveguide 13 in a : : ~
direction towards th~ free end o~ the lower drive bar 44. DUREL
brand plastic may also be used for the upper drive bar.
The upper driv~ bar may be collinea~ with the rotational axi~ o~ the dipole array and with the cent~rline of the C-band waveguide 13~, as shown schematically at 50 in the alternate e~ odiment o~ Fig, 4;. Alternatively, with re~renc~ to Fig. 6A, ;the~upper drive bar 43 may be provided w~th an offset bend by ~hich a por~ion 43a:is ¢oncentric with the centerline of the C-band waveguid~ 13 and anoth@r portion 43a extends parallel to and slightly below the centerline of the C-band waveguide. The o~se~ portions 43a and 4~3c are joined by a rigid interconne-cting link 43b. Such an arrangement is depicted in Fig~. 2, 3, 6A, and 8B.
Since the lower drive bar 44 i5 offset slightly relative to ~v~srnurE ~$~

, 1, r~3r~ J/ Ul~L~.
~13~75U ~ WS 21DEC l99~
... .
the longitudinal axis of the C-band waveguide, the drive bars 43 and 44 may be offset relative to each other~ Accordingly, a small interconnector member 46 may be employed rigidly to tie toget~er the ~uxtaposed ends of each of the drive bars 43 and 4~.
The interconnector 46 may be formed integrally wi~h the lower drive bar 44 to define a single shaft and adaptor, as shown in Fig. 6B. Accordin~ly, polarization switching of both the low-band and high-~and antenna assemblies may be accomplished by the same servo motor 36. The dæive bars 43 and 44, as well as the connector 46 are preferably made of the DUREL brand low-loss plastic, but oth~r materlals may be suitable according to the desires of those skilled in the relevant art.
Other techniques may be utilized by those ~killed in the relevant art for drivingly interconnecting the high and lsw-band antenna assemblie~ 60 tha th6y rotate together. For example, a~ single drive shaf~ may compri~e a continuous cylindr~cal protrusion (not shown)~extending toward a~d connected directly to the high~band dipole:feed substantially along the centerline ~, ..
of the waveguide 13. Other and various technique~ of obta~niny simultaneous rotation o~ the high and low band antenna assemblies , ~
may ~e us~d~without departing from the scope of th~ invention, ~- subj ~G~ only to pr~ctical cost restriction and to th~
requirement that 108s a~a noise temperatur~ of the resulting device be at an~absolute~minimum.
Referring now to Figs~ 2, 3, 6A, 7B and ~, the K~-band ~ ~ signal which i5 ex~racSed ~rom ~ree space by the dipole array 14 :~ is coupled out of the dipole feed by a fixed length o~ coaxial ~: transmission line 80. The transmission lin~ 80 extends , _ -W093/17466 PCT/US93/016~2 7 ~ ~ ~
~u~stantially coaxially and nearly concentrically relative to the longitudinal axis of the C-band waveguide 13 from the dipole feed to t~e rear wall 34 of the C-band waveguide. In the present embodiment, the transmis~ion line 80 is shaped somewhat like the upper drive bar 43. That is, it contains a portion ~Oa ~ubstantially parallel to the longitudinal axis of the C-band waveguide and a portion 80c (seen be~t in Figs. 7B and 8B) which lies s~bstantially along the longitudinal axis of waveguide 13, : and~may be parallel to offset portion 43c of the upper drive bar 43.: The port:ions 80a and 80c are interconnected ~y offset portion 80b.
: The portion 80a of the transmission line 80 is elongated and tra~erses the rear wall~:34 of the C-band waveguide. The center conductor 79 of the; coaxial line extends from one end of the :coaxial:line, as :shown in Figs. 2, 3, 6A, 7B and 8B, into a rectangular Ku-band: waveguide or launch box 90 mounted at the ear of the casting for the C-band wave~uide, as shown in Figs.

2~ 3 and 6B.: The Ku-band~signal is launched by the conductor 79 in~o~;~he rectangular waveguide 90. From the waveguide or launch box~ 90,~ the~ Ku-band ~signal~ is coupled to downline signal processing circuits~ which do not form part of the present inveneion.
With reference~to Figs. 7B, 8A and ~B, the other end 81 of the transmission line 80 contains the protruding center conductor or pin:75 which is:adapted to:be electrically interactive with the:~dipole feed pin 68 of the Ku-band conducting feed wire 62 which, as described above, is conductively connected, as at 62a, with one arm of the:driven dipole arms 16. As mentioned above, ~:: : 32 :

W~93/17466 Z13 U 7 5 ~ PCT/US93/01622 . .
in the preferred embodiment the electrical interconnection between the center conductor pin 75 and the feed pin 68 of conducting wire 62 constitutes a half-wave rotary joint. This is accompli~hed by placlng such pins in closely spaced-apart juxtaposed relationship within the confines of the surrounding half-wave metal sleeve 66, as shown in Figs. 7A and 8A. This arrangement defines a gap 82, seen best in Figs. 2 and 6A, between the juxtaposed pin 75 of the~coaxial center conductor and pin:68:of the Ku-band~feed wire. Accordingly, the feed wire 62 :
of~ the dipole array~may rotate with the array about its :longitudinal axis relative to the fixed pin 75 of the coaxial transmission line; 80.~ The microwave signal is nevertheless conducted ~between ~the~ pins without loss of efficiency in accordance with well~:understood microwave principles.
Various mechan~ical~ techniques may be utilized by those skilled~in~;the relevant:art for maintaining the gap 82 between the~:~coaxial:~line~pin~ 75~;and the feed pin 68. The technique e~ployed within~the~preferred~embodiment of the present invention is ~best understood~from~Figs. 7B and. 8B. As shown in these f~igure~s,~:~the~ end~81:~of~:the coaxial transmission line 80 may be providèd~with ~a ~plast~io~ sleeve 86 ~of just slightly larger diameter~ than ~the-~diameter of the coaxial line 80 and which rema~ins~in~place; as~;~resu~t~of an appropriate friction fit. A
smaller plastic sleeve 87 may be fit over the protruding pin 75.
Referring now ~to~Flg.: 8B, the offset por*ion 43c of the upper drive b~r 43~ may:~be~provided with an enlarged but hollow nub section 91 containing a central bore~92. The bore 92 i5 preferrably of stepped internal diameter, having a reduced ::~:::
~ 33 :: :
:: ~

~ l u G ~
13 0 7 5 ~ ~US 21 0 E C ~993 ~diameter portion 93 at the internal end juxtapo~ed to the end 81 of the transmis~ion line 80. The reduced diameter portion 93 corresponds to the diameter o~ the plastic sleeve 86. The ~oaxial line 80 and its sleeve 86 pass through the reduc2d diameter portion 93 and into the bore ~2. As shown in Fig. 2, the bor~ 92 also receives the distal end of the tubular &asting 60 f~r the dipole ~eed.
~ he assembl~d rotary joint i~ shown in Fig. 6A. The metal slee~e 66 is ~ituated between the insulator 63, associat~d with th~ tu~ular casting 60, and the plastic sleBve 86 associated with the end 81 of the coaxial line 80. The length o~ the me~al sleeve 66 i~ such that the gap 82 is maintained at all tim~
between the center conductor pin 75 and the feed pin 68. It will be understood by those skilled in the ar~ that those juxtaposed pin portions 75 and 68 define, in e~fect, guarter-wave stubs within the sleeve 66.
Referring now to Fig. 8A, the pla~tic throat support ~2 is : . : : :
~ pro~id~d with a central bore I01 into ~hich a plastic holder ~ , member 102 may be snap :fit. The holder member 102 contains a cen~ral bore 103, the:purpose of which is rotatably to receive the:tubu1ar casting~60 of the dipole ~eed when the device is ~ully~as3embled. Upon assembly, the tubular casting 60 and its d$pole ~aed is fre:e to rotate within and rel~tive to the snap ~i~
holder 102 and the throat support 220 The tubular casting 60 is pref2rrably s~bstantially collinear with the centerlin~ o the C-band waveguide 13 and~with the rotational axi~ of the C-band probe assembIy 28. Thus, as indicated above and seen from Fig.
2, the C-band probe assembly 28 and the Ku-band dipol~ ~eed may , .

p 1~ r If~(~US 9 3 / O 1 ~
) 75 ~ I~W5 210E~ 1993 be rotated together for polarization switching upon rotation of the probe holder 33 ~y the servo motor 36. A stainless steel compression spring 105 (Figs. 2,3) may be utilized within the plastic housing defined by.the snap-in portion 103 (Fig~ 8A) and the plastic support ~2 in order to retain the dipole feed in its proper axial position. It will be understood by those skilled in this art, that the position of the dipole ~eed relati~e to the f ixed plastic ~upport 22 could be established by many othar techniques such as a dielectric`washer or dielectric sleeYe between the front face of the mounting spider and the rear surface of the corner reflector.
~:~ With reference to Fi~. 4, there is shown an alternate embodiment of the dual band receiver of the present invention.
In~this embodiment, a dlpole feed 100, represent~d schematically, may~be~mountod over a~flat~metal back plan~ llQ which is part of a waveguide coupler lll mounted in coaxial position at the aperture of the C~band waveguide 13 within a plastic support 112.
, The~waveguide coupler lll contains a small enclosed rectangular waveguide cavity 52. The feed line 113 from. the dipole feed u~ ~: extends into the cavity S2 as does the center conductor of the ~ Ru-b~nd coaxial signal conductor line 54. The protru~ion o~ the :~ :: cen er:conductor of.the:coaxial line 54 into th~ interior of the caYity 52 fo ~ s a coupling probe 56 which extends substantially ~; parallel to~ and is:spaced from the fe~d wire 113. Ku-band waveguide signals are thereby coupled out of the high-band dipole feed and are transformed to coaxial mode for extraction along the :: :
coaxial tran~mission line 54. The Ku signal is coupled from the : ~ feed line 113 to the coaxial line 54 within the cavity 52 by : 35 ~: :
~8a~ r~

P(~TIIJS 93 /01~ 2 , ~ 1 3 U 7 ~ PEAIIJS 2 1 D E C 1993 means which wi}l be understood by those skilled in the relevant ark.
As shown schematically, the dipole feed 100 ~s mounted by a suitable upper drive bar 50 which itself tra~srses the back wall 53 of the waveguid~ coupler 111. The upper drive bar 50 extends concentrically within the C-band cavity and is c~nnected to a lower drive bar 51 extending ~rom a rotatable probe holder 49. The drive bars 50 and Sl may be interconneated by connecting element 55.
The coaxial cable 54 is ~ixedly mounted to and also ~xtends through the wall 53 of the wa~eguide coupler 111. The line 54 extends from the; back ~wall of the coupler 111 through the ~::
~ in~erior of the C-band waveguide 13. It is preferably positioned :: .
substantially parallel: to and adjacent the longitudinal axis or :centerline of the C-band:waveguide 13 to minimize disturhan~e of the:low-band electric field. In the preferred ~bodiment, the :line~54 is at least semi-rigid to minimize any tendency to vibrate or the like~ when: the signal receiver is subject to :environmental~stresses. ~
The;coaxial lin~;~54~:passes through the rear wall 34 of the C-band~wav~guide ~ubstantially adjac~nt the point of entry of the probé~sse ~ ly 28 and~términates in a launeh probe 57 (Fig. 4) wi~thin a rectan ~ lar~;~h~gh-band launch box 58. In the present e~bodiment~ the Ku-band launch 58 constitut~s a standard rectangular waveguide~of the~type known as WR75. This waveguide terminates in a port ~flange S9 adapted for connection to a suitable elbow transition (not shown) to an LNA. The WR75 waveguide is preferably:mounted b~hind the rear wall of the C-&U.J~5~

WO93/17466 `~~ 5 U PCT/US93/01622 . . .
band wav~guide 13 but in front of the C-band WR229 waveguide 24, essentially in the webbing of the low-band feed horn between the cylindrical waveguide 13 and the wg229 launch box 24.
In all embodiments of the presant invention, the WR229 and WR75 waveguides are situated so as to launch or propagate signals ,.
in substantially opposite directions, although the direction of .
launch is subject to modification without departing from the s¢ope of the invention. The WR75 waveguide may be formed as pa~t :
oP the same casting~as the C-band feed horn, or may be separately cast~ and mounted on the feed horn, as desired. Alternatively, ;the~WR229 and WR75 waveguides may be formed as a single unit casting and mounted on;the-C-band feed horn, or the entire dual frequency receiver may be a single casting. These alternatives may~be~ adopted by ~persons~skilled in the art without departing from~the ~scope of the~invention. The presence of the WR75 waveguide at thé~ba~k of the~C-band~waveguide adjacent the WR229 waveguide~has been~found particularly advantageous. It permits e~Ku-band~ coaxial~transmission line to be oriented in a direction substantially~perpendicular to the electric field in the~C-band~feed horn thereby minimizing loss or noise which might otherwise~re ult from~disturbance of the field. It a~so provides cost~ reduotion~alternatives~ and does not interfere with the de irable adjustabil:ity of:the:choke plate 18 and rings 19 (Fig.
l) relatlve to the~radiating aperture 15 of the C-band waveguide to optimize the illumination pattern of the device to suit the , ~ , :
particular size and~ conf~iguration of the reflactor dish with which it is used.
In some circumstances, it is desirable to receive or ~ ~:
~ 37 : ~ :
:
: ~
:: ~ :: : :

WO93~17466 PCTtUS93/01622 transmit circular polarization. For this purpose a dielectrfc insert may be diametrically and fixedly mounted within the circular waveguide 13 intermediate the probe asse~bly 28 and the C-band aperture 15. Such a dielectric and its orientation relative to the C-band cavity is disclosed in U.S. Patent 4,544,900, the description as to which is incorporated herein by referenae. A suitable~dielectric insert is slab-like or planar ha~ing a thickness~less~than its width. Where desirable, such a dielectric can be sub8tantially U-shaped with the open end of thé~l'U~" facing the~probe~assembly 28. The legs of the U may be shaped~, as having a diminishing diameter in step-wise fashion, if desired. The dipole feed assembly may be mounted within the slab,~thus~eliminating~the~need for the plastic spider 22. The dielèctric~slab can~be mounted at any appropriate angle with respèct~to;the~Yertical,~in Fig. l for example. The orientation Qf~the~slab at 45 to the electric field is well understood in art~ The~purpose~of~such~a~dielectri~ block is to produce e~-necessary~field~ conversion~to enable use of the dual re ~ ency~ receiver~ with~ circularly polarized mode of signal rànsmi~ssion~. The~use`~of such slabs or blocks does not affect thé scope~of the preseDt~invention.
Re~erring~to~Fig.;~5, there; i8 shown yet another embodiment ;of~the~pre:sent invention.~; In this mbodiment, the dipole feed, shown schemati¢ally by~reference numeral 120, is rotatably held by~a~suitable~plastic~support 121 at the~aperture of the C-band waveguide 13.~ The transmission line 122 for the Ku-band signal extends rigidly along the centerline of tha C-band waveguide to a~ waveguide coupler -123 near the rear wall 34 of the C-band WO93/17466 Z 1~ 7 ~ ~ PCT/US93/01622 '~aveguide. The coupler 123 contains a rotary joint of a type well understood by those skilled in the relevant art. The Ku signal is coupled out of the C-band waveguide to a rectangular launch box 124 from where it is extracted for further processing.
The C-band probe assembly 28 is fitted with a plastic arm 126 which may be substantially L-shaped and which is 'fixedly connected both to the probe assembly 28 at one end and to the , rigid transmission Iine of the dipoIe feed at its other end. In tbis ~way, rotational movement of the probe asse~bly 28 is ;transmitted directly~to the transmission line 122 and hence to the~dipole~feed l2b for;~purposes of polarization switching. In other respects~ this~embodiment is not substantially different from the other embodiments~of the present invention.
With~reference~to~Figs.~1 and 7A, it will be understood that the~ planar~surfaaes;~71~and 7~ of the metal corner reflector comprising~part ~of the dipole feed are obli~uely arranged relative to each other,~preferably~at an angle of substantially 120~dégrees~. The~d~irection of,the angle relative to the dipole nnà àrms, moreover~ is such that the lateral edge boundaries of~,~thé~ planar surface~s~ 71; and 72 define a plane which substantially cont~ains~ the~driven dipole arms l6, as shown in Figs'.~ 2~ and 3.~ It ~has~been ~o~nd that this particuIar angle between the~plates~'~of~the;corner refIector serves to shape the radIation pattern in; the E and H planes for the dipole feed so that~it is;substant~ial1y rotationally symmetrical and ~o minimize the~return loss effect~on the C-band signal within the circular waveguide 13. The~ unusual 120 degree angle for the corner refle~tor provides a beneficially narrow Ku-band pattern with ::
, ~C~IUS 93/01~^22 213 ~ 7 5 ti ~ 21 D E C 1993 less ef~ect on the C-band return loss than would be otherwise exp~cted. In essence, it has been found that such an arrang~ment provides better and more efficient illumination of thQ parabolic reflector dish.
It is important to note that the dipole fe~d of the pre~ent invention is not situated within a waveguide and does no~ require the presence of a waveguide in order to produce a suitably sy~metrical and narrow radiation pattern. The present dipole feed does not have a physical aperture with an ~lectric ~ield established therein by an incident TEll mod~, as i~ true with wav~guid~ antennas. ~he dipole feed functions e~sentially in free space, without:substantial influence from the nearby C-band wa~eguide. A TEll mode, in contrast, cannot exi~t in free space.
It can only exist within the wav~guide. Whil~ a simple dipole ca~ be used to excite and couple to a TE11 mode i~ it i~ within a wa~e ~ ide, s~ disclosed by Seavey, a probe o the type di~closed by H~ward or Mitchell et al, could not b~ substituted for the driven dipole arms in the Xu-band dipole feed o~ the present in~ention and~achieve the de ired results without furth~r exp~rimentation and~adju tment or addition of other components or~eatures.
It is apparent that those skilled in th~ art may make modi~icatlon ts the speeific embodiments de~crib~d herein without departing from the ~cope of the i~vention. Accordingly, the invention is not to;be limited exce~t by th~ spirit and scope of the following claims.

~V~UrE ~ME~

Claims

WHAT IS CLAIMED IS:
1. A dual frequency feed assembly comprising:
a lower frequency waveguide cavity and probe assembly therein, said probe assembly being mounted so as to rotate about the longitudinal axis of said waveguide cavity, said waveguide cavity having a rim defining an aperture in which lower frequency microwave signals are incident;
a higher frequency antenna assembly of interactive elements mounted coaxially with the lower frequency waveguide and with at least one active element of said interactive elements being substantially within the plane of the aperture of said lower frequency waveguide cavity, said interactive elements comprising first and second pairs of oppositely extending antenna arms, each arm of said second pair of antenna arms being spaced from and parallel to one arm of said first pair of antenna arms, and a reflector element having a reflective surface area adjacent and substantially parallel to each arm of said second pair of antenna arms, said second pair of oppositely extending antenna arms being closer to said reflective surface area than said first pair of antenna arms; and means for rotating said higher frequency antenna assembly about said longitudinal axis of said lower frequency waveguide cavity.
2. The dual frequency feed assembly of claim 1, in which the arms of said first pair of antenna arms are substantially collinear.
3. The dual frequency feed assembly of claim 1, in which the arms of said second pair of antenna arms are substantially collinear.
4. The dual frequency feed assembly of claim 1, in which said first and second pairs of antenna arms are substantially coextensive.
5. The dual frequency feed assembly of claim 1 in which said reflective surface area extends substantially parallel to each arm of said first pair of antenna arms.
6. The dual frequency feed assembly of claim 27 in which said reflector element comprises a pair of plates, and said reflective area constitute a substantially planar section of each of said plates, said planar sections intersecting at a corner, each of said planar sections being substantially parallel to each arm of said second pair of antenna arms.
7. The dual frequency feed assembly of claim 6, in which each of said planar sections is substantially parallel to each arm of said first pair of antenna arms.
8. The dual frequency feed assembly of claim 7, in which said second pair of antenna arms is substantially parallel to the line of intersection between said planar sections.
9. The dual frequency feed assembly of claim 8, in which said planar sections subtend an oblique angle relative to said first and second pairs of antenna arms.
10. The dual frequency feed assembly of claim 9, in which said planar sections subtend an angle of approximately 120 degrees relative to said first and second pairs of antenna arms.
11. The dual frequency feed assembly of claim 1, in which said first pair of antenna arms comprise a driven dipole antenna.
12. The dual frequency feed assembly of claim 1, in which each arm of said second pair of antenna arms comprises a parasitic dipole element.
13. The dual frequency feed assembly of claim 1, in which said interactive elements are fixedly mounted adjacent one end of a common tubular member.
14. The dual frequency feed assembly of claim 13, in which a feed wire is electrically coupled to one arm of said first pair of antenna arms and extends longitudinally within said tubular member from said one end thereof, said feed wire terminating in a feed pin within said tubular member.
15. The dual frequency feed assembly of claim 14, comprising a coaxial line for transmission of said higher frequency signal, said coaxial line extending longitudinally within said tubular member from the other end of said tubular member toward said feed pin, said tubular member being rotatable relative to said coaxial line.
16. The dual frequency feed assembly of claim 15, comprising means for rotating said tubular member relative to both said coaxial line and said lower frequency probe assembly.
17. The dual frequency feed assembly of claim 16, in which said rotating means comprises a dielectric drive shaft fixedly engaging each of said tubular member and said lower frequency probe assembly, whereby said tubular member and said probe assembly rotate together.
18. The dual frequency feed assembly of claim 17, in which said dielectric drive shaft comprises a lower drive bar and an upper drive bar, said lower drive bar mounted with said lower frequency probe assembly and said upper drive bar engaging said tubular member.
19. The dual frequency feed assembly of claim 18, in which said upper drive bar comprises a laterally projecting portion having a bore extending therethrough in the direction of the longitudinal axis of said upper drive bar.
20. The dual frequency feed assembly of claim 19, in which said coaxial line for transmission of said higher frequency signal traverses said laterally projecting portion of said upper drive bar through said bore, said upper drive bar being rotatable relative to said coaxial line.
21. The dual frequency feed assembly of claim 15, in which the center conductor of said coaxial line defines a conductive pin extending toward but spaced from said feed pin.
22. The dual frequency feed assembly of claim 21, in which both of said conductive pin and said feed pin are surrounded by a single metallic sleeve within said tubular member.
24. The dual frequency feed assembly of claim 22, comprising means for mounting said higher frequency antenna assembly against axial movement in the direction of said probe assembly, one end of said metallic sleeve abutting a portion of said tubular member, the other end thereof abutting said mounting means.
25. The dual frequency feed assembly of claim 7, in which a plane containing the distal ends of said intersecting planar sections substantially contains each of the arms of said first pair of antenna arms.
26. The dual frequency feed assembly of claim 1 comprising means for rotating said higher frequency antenna assembly relative to said lower frequency waveguide.
27. The dual frequency feed assembly of claim 1 in which said reflector element comprises a plate and said reflected surface area has a substantially planar section.
28. The dual frequency feed assembly of claim 25, in which each of said planar sections comprises a planar conductive surface.