GB2337860A

GB2337860A - Frequency selective surface filter for an antenna

Info

Publication number: GB2337860A
Application number: GB9913784A
Authority: GB
Inventors: John J Macek; Mark E Bever; Te-Kao Wu
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1997-04-29
Filing date: 1998-04-27
Publication date: 1999-12-01
Anticipated expiration: 2018-04-27
Also published as: GB9913784D0; GB2337860B

Abstract

A frequency selective surface filter (50) particularly useful in connection with a transmit antenna (10) for passing and rejecting signals in multiple frequency bands. The frequency selective surface filter (50) contains two dielectrically separated conductive layers including a first conductive layer (52) having an array of double-slots made up of an inner slot (64) and an outer slot (66). The double-layer configuration further includes a second conductive layer (60) made up of an array of single conductive loops (62).

Description

2337860 FREQUENCY S.2 ECOT WE SURFACE FILIMER FOR AN AN -iENNA EACKGROUND

OF 7HE MBM0N

1 Technical Field:

This invention relates generally to a frequency selective and, more particulady, to a frequency selective surface filter for passing and rejecting signals in multiple selected frequency bands and for use in correcl,-icn with an antenna.

2. Discussion:

Frequency selective surfaces have been used in connection witth wireless transmission systerns such as antenna systerns to reject the transmission of sicnals in a selected frequency band, while allowing signals in a selected frequency band to pass thrcuch the frequency selective surface.

Accordingly, the frequency selective surface can advantageously be used to filter cut sianals at a cerLain frequency. Frequency selective surfaces are especially useful for satellite antenna systems where multiple signals at ditferent frequencies may be present and only selected frequency signals are to be transmitted to or from a given antenna system device.

Known frequency se!ec,#live surfaces have generally consit-sted of an array of conductive e!e.ments fabricated on a dielectric medium. The dielec",,ric medium is generally transparent to signal radiation, while the conductive elernents are to seC-C",I!VC-:y allcW si"cnals c-,' certain frequericks c pass ch, and rei-4 c.cra.c at Cher Typically, C-e ccrdLc;., a,--= ccr,-&7icLre,-. aS Iccps, LSLa,.lv Wnlicured as Iccr.s cr c.rctjlar Icci:s. C----!-,era!ly the dir-,,er-,sicris cf 'Ulle ccrdLc..:,jia e!c-m, entS the and re7=-c4..,icr, band cf the frecLe.?-,c, sL,r,-ac-=. The use c.F,ar-i array cf c::rve.,i'LiCnal SirCle CCndUCIE'Ve ICCCS Cf identiCal size and sellace will prcvide a sincle narrow band cf However, the SIncle loop cent7icLra'Licr, crily -c'lcrial rejecition in a rathe- r.a,--,zw Z_ iiac:L,ency reic-c,.ticn tarid.

More recently, a dcuble-t'cc.p frequency se!ect,,ive surface has been use,d in c--nr-ieclkjon with a dlual re-.7jec'cr antenna. One e.-am, ple of such a dcLt17=-- lecc frecuericy se!ec4.ive sz-lr-.ac-z is described in U.S. Patent No. 5, 373,302, e?-,11i "DoL,ble-Lcco Frequency Selective Surfaces For Multi Frequency Divislcn Multiplexing in a Dual Refflector Anterina,', issued to WU cr, Dec=r,-, be:" 1-3-, The aforementioned issued U.S. patent is incorporated herein by re-;'=- rerc-z. 71-1e doLble-Icco frequency se!ecb'ive surface configuration provides an array cf 'ENO difierent size conductive [coo elernents on a sub-re-.lector which reflect Sic-rials at two difierent frequency bands back into a main reflector. While dual frequency J.

reflection bands are obtainable, each cú the re'ReCtion bands eA C-cJv&Y re,:riec' ts sianals over a nar-icw rance of frequencies.

In rricre recent tirries, it has becor-ne desirable to prcvide sicnal fliterinc for anterina cceral.fc.rs. The r-tuitibe-=m phased Errav antenna haS bc-=.rl -I- deveicced es--ec.a,'lv far use on a satellite system whicl- can be ccera- ic- at 4.1 Vaf"icuE- cceratinc FCr exam.p.le, in a systern, a ar,4L,-=r-.ra r-may be operable to transimitt st.c-rals at the MCand suc,!.& as -40.2 to 21.2 GH'2, whHe a re:---=.ve antenna rnay be ccerail.;ie ILC r=-,-.=7ve s.icna!s at frezuencies in the Q-band such as 41 GHz. Further, c, CSSI.ink ccr-,.r,iL,r,ica'Lion among satellites r,-,ay cceraLz- at fr-=cLeic.,es in the V-hand such as 62.6 GHZ Ore problern ti-ia'L rnay arise with the transmit antenna is that, the antenna's trans.mit c,.rcLItry generally ernplcys power amplifiers which exhibift non linear characteristics, These pcwer anipliflers as we!l as at.?-,er mcri linear circuitry which are czrrirncnly provided in active antennas may prcduc-= high frequency seccnd and third harm, onics. The high frecuency sec,-;nd and 'Ullird.

harnicnics, cenerated by the transi-nit antenna can interfere with- the and c,rossl,ink channels, unless adequate st:crial flitering is prcvided. Such a flitering de,jic-z for sca---:=-;,crne satteflite systems and the like- is generally required '10 be srnall and as lichtweicht as possible.

It is therecre desirable to provide for a frequency surFace that provides both signal passing in a specifited frequency band and s:cral rejection in rnultiple frequency rejection bands. It is also desirable to prcvid---for such a frequency se!ec"..ive surfac-e that re-alizes wide bandwidth tieZLlc-ICY re,c-c,icn. It is further desirable to prcvide fcr a frequency selective surtace- for use with an active antenna. It is particularly desirable to provide such a f- ieauc-.ncY & A e a rr f S se,ecive surfac-fliter 111cr filterrc cut unwanted slanals, caused by th pli ier' high frequency harmonics, especially with a transmit antenna. Yet, it is further desirable to provide a frequency selective surface with multiple frequency rejection bands in a compact, low cost and lightweight package suitable for use on a spaceborne or ground antenna system.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a frequency selective surface filter is provided for passing and rejecting multiple frequency bands.

The frequency selective surface filter comprises a dielectric medium that is substantially transparent to electromagnetic signal transmission and having a top surface and a bottom surface; a plurality of double-loop slots disposed in a first conductor material on one of said top and bottom surfaces of said dielectric medium, each of said double-loop slots an inner slot encircled by an outer slot for providing a first frequency pass-band and a second frequency pass-band while rejecting signals in a first frequency rejection band; and an array of conductive loop elements disposed on the other of said top and bottom surfaces of the dielectric layer, for providing a second frequency band.

includina The frequency selective surface is compact and lightweight and is particularly useful in connection with a transmit antenna such as a multibeam phased array transmit antenna. According to one application, the frequency selective surface filter is disposed in communication with the multibeam phased array transmit antenna to allow for the transmission of signals within a first designated frequency band. The frequency selective surface filter filters out signals within the rejection bands, especially those signals having frequencies associated with second and third harmonics caused by non-linear elements in the transmit antenna.

BRIEF DESCRIPTION OF THE DRAWINGS other objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description and upon reference to the drawings in which:

Figure 1 is a partial cut-out view of a multibeam phased array page 6 follows transmit antenna having a frequency selective surface filter disposed on the top surface thereof; Figure 2 is a cross-sectional view of a single-screen frequency selective surface filte Fiaure 3 is r; a top view of a portion of the single-screen frequency selective surface filter of Figure 2; Figure 4 illustrates one example of the signal transmission response that may be realized for thesingle-screen frequency selective surface filter; Figure 5 is a cross-sectional view of a double-screen frequency selective surface filter having two conductive layers according to the present invention; Figure 6 is a bottom view of a portion of the bottom layer of the double- screen frequency selective surface filter of Figure 5; Figure 7 is a top view of a portion of the top layer of the double-screen frequency selective surface filter of Figure 5; and Figure 8 illustrates one example of the signal transmission response that may be realized for the double-screen frequency selective surface filter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to Figure 1, a multibeam phased array transmit antenna -6 45 provided with a frequency se!ec4,ive fiter 20 or 0-0 in acc-k;rdar-,c- := with thle present inventlion. The phased array antenna 110 is suited for use in c--rjr.ec4.,;cr. with ca- sa4,e;1i4Le ccr,.1r-,, LrnicaLicn syste.m w,ic.h m, ay iric.,'ude bclh and. r=-c-=;ve antennas for cor,-,r-..urIca-lLirc with ground based cGr-,,r-,iunica"L,,cr, systerris. As cne exam, ple, the trans,-,.it antenna may be ccera,-,le for trar-,srnit4,irc; sicnals havina frequencies of apprcx,r,-ia'Le!y 20. 2 to 21.2 GHz within the K-band, while Cie, rec&Ve antenna may be operable to rec-=;ve signals having frequencies c-1 approx,,mately 40.4 to 45.5 GHz within the Q-tand. In addition, a sallellite system rnay inc!ude antennas for and receivine cross link communication s'lanals annong various a& L frequencies of acprcxi 60.6 to 63.6 GH.z within the V-band. The phased array antenna 10 as si-lown and explained in connection with the present is a trans,-iiit antanna. -,cwc-ver, it should be appreciated that the frecuency se!ec..Ave sur'fac-e fliter c-7-,::lcyed in connection with the antenna 10 rnay be applicable for use in c,--r.rc-c4kicn with various commiercial and mnilitary antenina and radorne systenns fcr bCh receive and transmit antennas, and the frequency bands of operation may be sealed to other frequency bands, without departing frcm the principles of the present invention.

The rrullihe-mn, phased array antenna 10 as shewn includes an array of metalized plastic feed horns 12 conflicured side-by-side in a planar or arrancement. However, antenna 10 may inc,,ude a single radiating elernem multiple radiating e!em, ents cnficured in varicus other configurations ircL:.dinc a --r -i- curved configuration. The antenna 10 described herein is a transmit antenna for transmitting transmit signals at frequencies of 20.2 to 21.2 GHz within the K-band. The antenna 10 includes a circularto- rectangular transition element 14 and a beam forming network with amplifiers 16. In addition, the multibeam phased array antenna 12 has a linear-to-circular polarizer 18 disposed at the output of the feed horns 12. The frequency selective surface filter 20 or 50 as explained herein rejects signals which may be produced as high frequency second and third harmonics due to the non-linear characteristics of the amplifiers 16. The frequency selective surface filter 50 of the present invention rejects signals with certain frequencies so it will not interfere with other antenna operations.

Referring to Figure 2, the frequency selective surface filter 20 is shown in a cross-sectional view containing a single conductive screen. The single conductive screen is hereafter referred to as the single-screen frequency selective surface filter 20. The single-screen frequency selective surface filter 20 contains a single conductive circuit layer 24 made up of a conductor printed or otherwise fabricated on top of a thin planar dielectric layer 22. The conductive pattern provided on the single conductive circuit layer 24 may be printed or etched on the dielectric layer 22 in accordance with well known printed circuit manufacturing techniques. The thin dielectric layer 22 may include a dielectric substrate such as a known thin space qualified material such as polyamide or other suitable material. one known dielectric is identified as Kapton which is manufactured by E.I. duPont page 9 follows O de NerncurS and Ccr.-.ra.-,v, Inc.

1 - al =?.

The s'lr.cle conductive sween 24 is up. c^ a C-^r-,dLClkive r.,-, jal such aS c::ccer or c-ki.ter silitable and is as s,'tcwn in Ficure 3.

The frequency se!ec'l.'ive surface.20 irc,;Ld.z--c a cridded Scuare ariay r-,ia,-;e up C, a 111rz4 plurality of paralle! ccr-,dLc4,ive lines 25 perpen icul rly second plurality of parallel conductive lines 28. The cridded square a.- ay therefore provides for a plurality c-t- square regicr-is separated by the perpendicularly parallel ccrdL.,cNive lines 21.- and 28. The width of ttle c-ndLc4,ive lines 26 and 28 is rep rese by W, The distance between adiacent paralle! conductive lines 26 and also berweeri adjacent parallel coriductive lines 28 is represente.d. by P. The distance P represents the periodic interval of the sc:Lare regicris provided by conductive lines 2S and 28. In the crididied 5Guare anay rnade urD of conductive lines 26 and 28 provides a low frequency ralecticr, band which advantagecusly FiIters cut lcw frer-quency sicnals.

The rnLI'L'ibe-=rn, phased array antenna 10 further inc!Lides an a-,pv c. I:

double-Icep ccriductive eler-rents Prcvid.ed in the square recions. E-ach ci: the double-lccp conductive e!eriierits is rnade Lip cf an inner-c3nductive Icep 32 czr,ficured within an cuter conductive loop ^0. The inner conductive square loop 12 has a widlh idei'ifie.' as M, while the outer conductive s,,-,uare lccrD 50 has E width identified as M. The frequency rejection bandwidth may be re-clized as a function of the widths W2 and Wz. Ac--zrdinc-iy, widths W.7 and W, are re!a.'Le,-.J with a Lwidened 5.ze to provide widened band of re;--4,ic.n. The inner and cuj,;r 1 J-4.

tip c-..;nduct'ive square Iccps 120 and 122 are separated by a rcnc3rdLcllivc- isclation loop SA which has a w!d4LI"i identified as G27. Ac--cr--inciv, tihe cuter c--rdLC.:vc 5,uare loop SO is separated, from the inner ccndLc'tive sc:Lai-e loop -2 by a dlistance c2. In addition, cuter ccnductive squaire]cop SO is separated f-orn the ccriductive crid lines 2-16 and 28 via a non-conductive recicn by dist in.c 1 a The array cf dcutie-lcop conductive e!er.-ients rnade Lip of cc.ndLc. ivcleaps 30 and 32 provides for a first frequency rejection band and a seci-rjd frequency re,,e--',lcn band. The inner ccnductive scuare Icco 2. 2 is configure'd wit.h an cuter conductive c.,rcur,-ifere.nce cf a distance equal to or clcs-= to the wave!er,c,Lh of sicnals to be reiected by inner conductive square lcoo 32. Sirnilairly, the outer conductive scuare loop 30 has an cuter conductive con-Ficured of a distance approxirnately equal to or close to the wave! en c th c-l' :z,cnals thal. are to be re'-ted with the cuter cznduclive loop 30. The distance cf the of e-=ch of the conductive Iccps 20 and 32 is ec:Lal to the wave!encth c-l' a frecue:-ic,.i substantially centered in first and second re;ec:kion 1 bands. Depending on the widths W2 and W2 of the conductive loops SO and 1212-, respectively and the aL"LerLvat.icn ac.ceptance, the first and second re;ec',ICn b.=nds extend over a rance of frequencies in a rejecticn bandwidth.

Accordinc to one example, the sA.'nele-sc,,ee.n frezuency sur.-ac-= flite. 20 may inc!Llde the following gearnetric pattern dir-,nerisicns:

1k P = 0.1378]riches (3.5Omm W, = 0.0043 Inches(O.11m) W3 0.0 04-5 [nches(o.limm) 92 0.0043 Inches (0.11m) W2 0.0172 lnCheS(O.44mm) 0.0172 Inches (0.44m) As evidenced by the above example, the s,nale-screen freque.ncy selective sur'tace filter 20 can be conficured with small dimens'lons and r-iiay consume a sm. all volume. The above example provides _generic cecme+jic dimensions suitable for achieviria a slanal transmission response 40 such as that. provided in Figure 4 which shows signal transmission in decibels (dE) versus frequency achievable with the s,ngle-scree.n frequency selective surface filter 20.

The sincle-screen frequency selective surFace filter 20 essentially provides three re,ie,--tion bands 44, 46 and 48, while allowing slanal transmission in a desired frequency band as evidenced by the passband 42.

In e-Rect, the intersecting parallel conductive lines 26 and 28 Provide a iew-l,reque.ncy refecticn band 44 which fliters out low frequency signals, including low frequency noise induc-ed signals. Far an attenuation drop of fifteen dec.bels 11L (15 dB), the low-frequericy rejection bandwidth extends from frequencies of about zero to three GHz. The outer conductive square loop 30 provides frequency rejection band 46 to reject those signals of approximately 40.4 to 45.5 GHIz. The inner conductive square loop 32 provides frequency rejection band 48 to reject signals having frequencies of approximately 60.6 to 63.6 GHz. Thebandwidth of each of rejection bands 44, 46 and 48 may vary depending on the preferred attenuation. Accordingly, rejection bands 44, 46 and 48 effectively filter out noise induced signals as well as high frequency second and third harmonics which may be present due to the non-linear effects, especially those associated with the amplifier circuitry. Accordingly, the muitibeam phased array transmit antenna 10 may operate ef.fectively within the designated pass band 42, while reducing or eliminating problems associated with unwanted high frequency harmonics.

According to the present invention, the frequency selective surface fliter 50 includes two conductive screen layers for providing wide band frequency fliterina. The double conductive screen is here-=fter referred to as the double-screen frequency selective surface filter. Referring to Figure 5, the double screen frequency selective surface filter 50, shown in a cross-sectional view, includes a dielectric medium 58 with a first conductive screen 60 printed or otherwise fabricated on the top surface of a thin dielectric medium 58. Similarly, frequency selective surflac-e filter 50 includes a second thin dielectric medium 54 with a second conductive screen 52 printed or otherwise fabricated an the bottom surface of the second thin dielectric medium 54. In addition, frequency selective is flite:- SC, Se:aral:nC a!-,d sec::rd fa arld E-4, the and c--r.dLc,.t:lvc- scree-ns E0 and 52. TI-e 1L.t.lri Sa and E4 rnav ir.,c:ud-z a rnatenal w ficr 2/2, wh5e lave-r -Ee may irc;u,_.;=- cr ctl'ier s u it a C i e die!ec41,-:1c n-. edt i L, m, which, is sim, iiar'iy cansparerit. LC c cne 'Lhe dielectric and E4 may each include a thickness of 25= (one mil), w-hile -E.ie t-h. icker die- electric isolation layer- -';5 may include a thickness of 4.8m.m (189 mil).

tc Ficure 6, ',he bCCLcrri conductive screen 52!S SI-Cw,7 "c inc!L,de an astray cf doLble-s,-.,Lar-= s!cts each cf which inc;udes an inner rcr, c--r,dL,c',ive sIc.t 64 and ain cl..,ter slIct C-6 bc4Lli in ccr-,(tLC, jve screen layer 52. The inner and cuter sIcts 64 and EE are via a cr,r,duc.,ive recicr, 68. Further, 'le cuter scts 66 are sezarated fi-cr:- , cuter skts by c:3rdLc.,1ilve line-s- 69. Ccnductive lines EG have a width as c.. The c,-jrduc.;4...Ave re.=icn Ea separating slIcts 64 and E6 has a - scuare ccrl.1:icuraL.icr, withi a width identifted as c-. 7he cuter sIct 66 has a wid.th identified as W,, whiie the inner sAct, 64 has a width ideritified as W2. TIhe c,- jrdLc.';ive line=- 6G are separated by a distarice P which dieffines the pericdic interval d the dcuble-square s,'cts.

The bct&Lcrri c--rdu(7,ive screen 52 prcvides frst and sec-,rd fre;-ue:-, cy as a functicr, cf the cf the inner and cLter s,cts 64 and ee'.

IL i he Inner skt 64 has a c,.rcur-,,-'-rat IC. IC= of a distance equal to one walieler-,c-llll-i of the de-:-trirc the fir-C passband. The outer sIct EC- sir-,,llarilv has a rICS of a d151anC= e,ual to cne wavelength of the frequency d=-::1rirc 'Ul-le second passband. 7he fir%-zlk and second pas-ssbands extend ever a- band cf,' frequencies. Ac=rdingly, signals within the firs, and second passbands are able to resonate throuch 'the bo"Lcr-,i conductive screen 52, while other frequency signals, are The top condluctive screen 60 is ccn.-iaLred with an array of s. Arclesquare conductive leaps 62 printed er othe.,-vvise fabricated on the tc.0 SLr,"ace of die!ectric rnediurn 58. Each cf the conductive square leops 62 has a circumference of a distance equal to one wavelength of the frequency that, deffines the rejection band. The rejection band provided by conductive loops 62 e.:Fj:c-c.&,ive!y extends ever a ranee of frequencies. Accordingly, the sincle-square Iccp configuration rejecIts slignals within the re,ection band as a function of '"he dimensions of the sincle-square loop. The rejection band provided by the top conductive sc,reen 60 rnay be se!ec4.ed equal to one of the first or second passbands provided by the bottom conductive screen 52 so as to achieve multiple rejection bands and allow transr.nissicn of sianals within one frequency passband. Ac-cording to one example, the bottom ccndLctve screen 152 rnay be c.-nficured with the follcwina d!melslcns:

i.

P = 0.1496 Inc.1.1es (3.8OMM) W., = 0.0091 InCl-eS (6. 24m) 0 91 = 0.00935 Inches (0.24m) W2 = 0.0C,9-4,5- fric;-1c-s.(0.24mm) c- = 0.02E05 Inches (0.7lmm) In c::)nnec.4icn with the abcvc--ide.nlified example, the tcc c::ridLc,. ive scie=-n 60 may be carificured with the f.cilcwinc dir-sie.,isicns:

P = O.OGGE Inches (2.53m) W= 0.00ES2 Inches (0.16m) c = 0.03735 Inches (o.gsmm) Acccrdina to the abave-1dentifled example of filter W10, the d. CLblescreen conficuraian cf the frequency se!ective surface filter 950 r-, iav provide operational characteristics as shAcwn by the transmission response 70 in the graph of Figure 8. The frequency selective surac:-: filter 5.0 provides a fi-e-i-lericY passband identified as 72 which defines the frequency rance over which signals are allowed to radlate thrcuch frequency seketive surface filter 50. The frequenwi se!e=ive surface filter 50 alsc e77jeeively provides wide frequency reecticn bands 11 j 1 1W 74 and 76. In effect, the outer slot 66 of bottom conductive screen 52 allows signals with frequencies of approximately 20.2 to 21.2 GHz to radiate through bottom conductive screen 52. Similarly, the conductive loops 62 of the top conductive screen 60 allow signals with frequencies of approximately 20.2 to 21.2 GHz to radiate through top conductive screen 60. The bottom conductive screen 52 effectively rejects signals with frequencies in the rejection band 74. The top conductive screen 60 effectively rejects signals having frequencies of 60.3 to 63.6 GHz.The bottom conductive screen 52 does provide some attenuation of the V-band frequencies and the top conductive screen 60 does provide some attenuation of the Q-band frequencies. Therefore, the combination of the top and bottom conductive screens 60 and 52 effectively rejects signals within the widened rejection band 74 and signals within the widened rejection band 76, while at the same time providing little or no attenuation of the frequencies in the passband 72.

The frequency selective surface filter 20 or 50 offers multiple frequency rejection bands in a thin, lightweight and low cost package. The single-screen frequency selective surface filter 20 provides good performance with low frequency filtering in a very thin package, while the double-screen frequency selective surface filter 50 is able to achieve widened frequency rejection to improve filtering at desired frequency bandwidths. In addition, the frequency selective surface filter 20 or 50 includes equal rectilinear (x and y) line dimensions suitable for use for both vertical and horizontal polarizations, and also suitable for circular polarization. Accordingly, the frequency selective surface filter 20 or 50 is small and lightweight and advantageously suitable for use in connection with a transmit antenna.

)l In view of the foregoing, it can be appreciated that the present invention enables the user to achieve a compact frequency selective surface filter suitable for use in connection with a tramsmit antenna. Thus while this invention has been disclosed herein in combination with a particular example thereof, no limitation is intended thereby except as defined in the.following claims.

\15 0

Claims

A frequency selective surface filter for providing multiple frequency rejection bands, said frequency selective surface filter comzr2jsina:

a dielectric medium that, is substantially transparent to electromagnetic signal transmission and havincr a top surface and a bottom surface a plurality of double-loop slots disposed in a first conductor material on one of said top and bottom surfaces of said dielectric medium, each of said double-loop slots including an inner slot encircled by an outer slot for providing a first frequency pass-band and a second frequency passband while rejecting signals in a first frequency rejection band; and an array of conductive loon elements disposed on the other of said top and bottom surfaces of the dielectric layer, for providing a second frequency band.
2. The frequency selective surface filter according to claim 1, wherein said frequency selective surface filter is disposed in communication with a multibeam phased array antenna.
3. The frequency selective surface filter according to claim 1 or claim 2, wherein said frequency selective surface filter is disposed in communication with a transmit antenna, said frequency selective surface filter filtering out higher frequency harmonics produced by non-linear characteristics of circuitry components in the transmit antenna.

[m
4. The frequency selective surface filter according to any preceding claim, wherein said dielectric medium has substantially planar top and bottom surfaces.
The frequency selective surface filter according to any preceding claim, wherein each of said conductive loop elements comp-,:ises a single conductive loop.
6. ' The frequency selective surface filter according to any preceding claim, wherein said conductive loop elements are configured as square loops.
7. The frequency selective surface filter according to any preceding claim, wherein said double-loop slots are each configured as square slots.
8. The frequency selective surface filter according to any preceding claim, wherein said dielectric medium comprises:

a first thin dielectric substrate providing the top surface; and a second thin dielectric substrate providing the bottom surface.
9. The frequency selective surface filter according to any preceding claim, wherein said dielectric medium further comprises a dielectric isolation layer disposed between the first and second thin dielectric substrates.

_3
10.

An antenna comprising: one or more radiating elements electromagnetic radiation; transmit circuitry for generating signals for transmission from said one or more radiating elements; and a frequency selective surface filter according to any preceding claim.

for radiating b

9. The frequency selective surface filter according to any preceding claim, wherein said dielectric medium further comprises a dielectric isolation layer disposed between the first and second thin dielectric substrates.

7P 10.

An antenna comprising: one or more radiating elements electromagnetic radiation transmit for radiating circuitry for generating signals for transmission from said one or more radiating elements; and a frequency selective surface filter according to any preceding claim.

21k Amendments to the claims have been filed as follows 1. A frequency selective surface filter for providing multiple frequency rejection bands, said frequency selective surface filter comprising:

a dielectric medium that is substantially transparent to electromagnetic signal transmission and having a top surface and a bottom surface a plurality of double-loop slots disposed in a first conductor material on one of said top and bottom surfaces of said dielectric medium, each of said double-loop slots including an inner slot encircled by an outer slot for providing a first frequency pass-band and a second frequency pass-band while rejecting signals in a first frequency rejection band; and an array of conductive loop elements disposed on the other of said top and bottom surfaces of the dielectric layer, for providing a second frequency rejection band.

2. The frequency selective surface filter according to claim 1, wherein said frequency selective surface filter is disposed in communication with a multibeam phased array antenna.

3. The frequency selective surface filter according to claim 1 or claim 2, wherein said frequency selective surface filter is disposed in communication with a transmit antenna, said frequency selective surface filter filtering out higher frequency harmonics produced by non-linear characteristics of circuitry components in the transmit antenna.

1 )A L 4. The frequency selective surface filter according to any preceding claim, wherein said dielectric medium has substantially planar top and bottom surfaces.

S. The frequency selective surface filter according to any preceding claim, wherein each of said conductive loop elements comprises a single conductive loop.

6. The frequency selective surface filter according to any preceding claim, wherein said conductive loop elements are configured as square loops.

7. The frequency selective surface filter according to any preceding claim, wherein said double-loop slots are each configured as square slots.

8. The frequency selective surface filter according to any preceding claim, wherein said dielectric medium comprises:

a first thin dielectric substrate providing the top surface; and a second thin dielectric substrate providing the bottom surface.