CA2186948C - A folded single mode dielectric resonator filter with couplings between adjacent resonators and cross diagonal couplings between non-sequential contiguous resonators - Google Patents

Abstract

The invention relates to a single mode multi-cavity microwave filter that includes a housing formed with a plurality of walls which define at least two rows of side-by-side dielectric loaded cavities, wherein sequential cavities are coupled to one another via slots or probes in the walls therebetween and at least one pair of non-sequential adjacent cavities are coupled via a slot or probe. The coupling via the slots is defined mathematically as positive coupling. The probe is selectively configurable to provide positive or negative coupling relative to the sign of the slot coupling. Further, at least one nonadjacent, non-sequential pair of cavities is coupled via a second probe that may be configured to provide either positive or negative coupling relative to the sign of the slot coupling. The filter housing supports a plurality of adjustable fins which extend into the slots, one fin to each slot, to selectively adjust the size of the slot.

Description

2~g~
DIELECTRIC RESONATOR FILTER

Techn~ l Fi~
The present invention relates to "~ /c fiiters and, more particu-larly, to a single mode multi-cavity dielectric resonator ",i~,,u.~_~c filter for use primarily in electronic communications, such as in a communications satellite.
Bac~grr)llnd Art Multi-cavity ",i.i,-.~ ./c filters are used in communication satellites, particularly those that are launched into geosynchronous orbit for communi-cations with ground stations. A plurality of filters are used in a typical satellite, each filter able to separate and isolate a specific signal or frequency bandwidth from all of the signals and frequencies lldllalll~ d to the satellite.After sepd,d~iul-, each signal is amplified to aI,~I,y~l,en the signal, whereaf-ter, the amplified signals are LldllsllliIL~:d bacl~ to ground stations. A single satellite may be equipped with twenty to sixty such filters, dep~lnli"y on its mission.
A group of n~ c filters d~ ,lulJed during and since World War 11 are referred to as waveguide or cavity filters. These filters are hollow structures and are sized to resonate at specific frequency bd,l ~ lls in response to ",iw-. ~.~c signals communicatecl to the filter structures. A
cavity resonates using a specific ele~A,u",dy"~; resonant mode. Various modes have been defined over the years by the l.E.E.E. The resonant mode dominant in a filter is dependent upon the geometry of the filter structure. Filters which resonate using one mode only are referred to as single mode filters. In recent years, dielectric l~:ao~ldl.lla have been introduced into cavity resonator structures, in part to improve output response and reduce the size of the cavity. Cavities with dielectric WO 9~/27317 PCT/CA9'i/00177--- ~.
~solldlul~ are often referred to in the art as "loaded cavities .
Multiple cavity filters have also been developed in recent years. One such filter is described in U.S. Patent No. 5,220,300 to Snyder wherein a series of linearly arranged cavities are each loaded with a dielectric resonator. The wall formed between each pair of adjacent cavities is provided with a sized iris (or opening). Each iris provides a means for coupling magnetic energy between adjacent l~s.oldlul~. Further, a tuning screw partially extends into each iris for tuning the iris coupling.
Unfortunately, the linearly arranged filter design may not provide the desired bandpass output necessary for some satellite communication , ,~
There have also been numerous attempts at building dual mode filters, where either a cavity structure or a loaded cavity structure is designed to resonate using two modes or "dual modes". One such filter is disclosed in U.S. Patent No. 3,697,898 to Blachier et al. The '898 patent discloses a multi-cavity filter c~,ll,uli~i, 19 an elongated cylinder. Planar walls formed within the cylinder define a plurality of cylindrical cavities. Each cavity is coupled to adjacent cavities via a ~r~ 'Iy sized iris formed in the wall v a~n. The '898 filter design, has several .I,~ a~;k~.
For instance, in a communications satellite, a typical desired output from a ,~ c filter includes a high degree of linearity for the amplitude of the passband frequency range (the desired output) and linearity for the group delay response, in order to minimize distortion in the signal passing through the filter, while Illdilll.~;.lilly high rejection slopes flanking the filter passband. Dual mode filters typically require external egll~ tinn to achieve the desired p~lrUlllldll~.e. Extemal eql~ finn llec~ the use of ferrite coupling circulators, thus incurring the mass and volume penalty ~cco~i~tPd with such devices.
~ual mode filters typically require one coupling screw 35 for each resonator to properly couple the two modes and two tuning screws cavity, one tuning screw to tune each resonant mode. A fair amount of time is required for proper tuning of each pair of adjacent sequential filters in order . _ _ _ _ _ _ _ _ _ _ _ . . . . .

4~ -3- ~ :
to get the desired frequency bandwidth output.
In a communications satellite, a plurality of filters are employed. Each filter must be built and tuned to provide a specific frequency bandwidth output. Mass production of such filters is desirable, but difficult to achieve.
For instance, multi-cavity filters which empioy iris coupling, typically requireeach iris to be custom sized to ensure ~,u,ua~dliun of the desired mode and/or frequency bandwidth output, thus cu",, ' " ,9 the manufacturing process.
A nldlll~llldLi1al analysis of a l,,i-,,u. ~/c filter typically yields a series of IlldLllt:llldLiudl equations which are l~,u,~se"Ld~i~/e of the idealized configuration of the filter. For instance, the couplings between sequential adjacent cavities and the It:~U~dlUI~ therein, are assigned a sign, positive or negative, for IlldLll~llld~iual and Ll,eo,~ical purposes. Knowing the relative sign of each coupling in a filter is important in terms of predicting the outputof the filter, such as the frequency bal)d~ l" the insertion loss, etc.
For most practical ~ s it is desirable to attenuate as strongly as possible unwanted signals which may exist very close to the edges of the usable bandwidth output of each filter. In an attempt to provide better attenuation, cross-coupled filters have been attempted in the past. In such attempts, non-adjacent and non-sequential cavities within a filter structure have been coupled.
One form of a cross-coupled dielectric resonator filter is described in an article entitled "G~ ldli~d Dielectric Resonator Filters" by A. E. Atia and R. R. Bonetti, Comsat Technical Review Vol. Il, No. 2, 1981, pp 321-343. The article describes a folded filter formed with a plurality of cavities therein. The folded structure includes two rows of cavities, the first row having cavities 1 through n, and the second row having cavities n+l through 2n. The folded structure is such that cavity 1 is adjacent to cavity 2n, cavity 2 is adjacent to cavity 2n-1 .... and cavity n is adjacent to cavity n+l. The bottoms of adjacent cavities are covered witll stripiines, each stripline common to at least two ~avities. A stripline is typically an elûngated flat strip WO 95~27317 PC'r/C~95/00177--~I 86 -4- ' ~
of, for instance, a conductive metal. In some ,, ' hS, a s*ipiine~ is formed directly on a substrate in a manner similar to the manufacture of a circuit board or the like. In the Atia et al. p~ , a dielectric resonator is disposed in each cavity, and is isolated from the stripline by a dielectric support. In these filters, coupling is obtained between the ,~ol1dLu,a by means of the stripline whose ends are positioned under the l~, Id~UI::7. The sign (positive or negative, in a IllCI;h~llldli~,dl sense) of each coupling is ""i"ed by the length of the stripline such that each multiple of a quarter wavelength changes the sign of coupling. For instance, if a quarter wavelength stripline r~,ul~sell~ a positive coupling, then half a wavelength stripline ~,u~selll~ a negative coupling and a three-quarter wavelength stripline ,~p,~ser,~ a positive coupling.
The pll' ' ~ entitled "General Prototype Network-Synthesis Methods For ~ ~. ve Filters" by R.J. Cameron, published in the ESA
Journal 1982, Volume 6, pages 193-206, discloses a variation of the stripline coupling disclosed by Atia and Bonetti. The filter disclosed in the Cameron article has a folded structure similar to the structure disclosed in the Atia and Bonetti article. However, in Cameron, there are two rows of cy"i,l~lic~lly shaped, resonator loaded cavities offset from one another such that each cavity is adjacent to as many as two non-sequential cavities. For instance, cavity 1 is adjacent to cavities 7 and 8, cavity 2 is adjacent to cavities 6 and7 and so on. Each cavity in the filter is coupled to adjacent sequential cavities by a stripline. Each cavity is further coupled to as many as two adjacent, nonsequential cavities via further striplines. For instance, cavities 1 and 8 are coupled via a stripline in contact with the resonator in each cavity. Cavities 1 and 7 are coupled via another stripline in contact with the resonator in each cavity. Cavities 2 and 7 are coupled via a stripline in contact with the resonator in each cavity. Cavities 2 and 6 are coupled via a stripline in contact with the resonator in each cavity, and so on. The coupling between non-sequential cavities is referred to as diagonal cross-coupling. The sign of the coupling (in a ~lldtll~llldLiual sense) is, as above, . , ,,, .. ,,, ., .,, ,, .. . .. ,,,, . , .,,,, , ,,,, .. ,,,, ... ,, ,, . ,,, ., .,,,, ., _ _ _ _ _ _ _ WO 95~27317 PCT/CA95/00177 2?86g~8 -5 - .
d~l~""i"ed by the length of the stripline and further may be changed by twisting a portion of a flat stripline 180 degrees thus forming a partial loop in the stripline. Since striplines are usually formed on a substrate twisting of the stripline is not practical in manufacturing methods since the substrate would l1ece~d, ily have to be partially removed from the stripline in order to twist it.
Another example of cross coupling is disclosed in U.S. Patent No.
2 749 523 which discloses a non-dielectric resonator filter in which negative coupling is provided between at least two It:SOlla~UI~. At least three jllYt~rOSed cavities are coupled in series via irises. The inlet and outlet irises of each cavity are located either on two opposite walls or else on two pe, u~"~ .ular walls with the cavities being cu~ e~l~d sequentially in series.
A cable or waveguide having a probe at eacll end provides coupling between non-sequential cavities in the series of cavities.
Dicrl~cll~e of Inven~
The invention relates to a single mode "~ /c filter having a unitary multi-cavity housing formed with a plurality of walls defining a plurality of cavities that are sequentially oriented in first and second side-by-side rows each row having a plurality of cavities. A cyli"~ r shaped dielectric resonator is supported within each of the cav~ties. The wall between each of any two adjacent sequential cavities is provided with a slot or probe to couple ele~ llu"layllt:lic energy between adjacent sequential ,~or, r~. An input device is disposed adjacent to and co""e. l~d to a first cavity in the first row, and an output device is disposed acljacent to and cùlllle~:~d to a cavity in the second row.
A slot or probe coupling is positioned in the wall between at least two non-sequential adjacent cavities one cavity in the first row and the other cavity in the second row thus cross coupling said two non-sequential cavities the probe having opposite ends eacll of which extend in a direction generally parallel or pe".,~l ,.li.ular to or which conform to the curvature of WO9S/27317 ~ PCT/CA9S/00177--21869,~8 -6- ' the c~ dl iu~'ly shaped It~ OIlc~tVl:i.
In one ~IllI.odilll~lll of the present invention, the probe ends are symmetrical about the wall between the adjacent cavities. Further, the coupling accor"~ ed by the slots fommed in the walls is defined Illd~llellldLic"l!y as positive, and the coupling a~ u"l~ ,lled by the symmetrical probe ends of the probe is defined mathematically as negative.
In another ~IIlbo~ of the present invention, the probe ends are asymmetrical about the wall between the adjacent cavities. Further, in this e"luo~i",t:llt, the slot couplings are defined IlldLllellld~iu.~l!y as positive and the coupling by the asymmetrical probe ends of the probe is defined IlId~ lIIdliC~.!y as positive.
In yet another ~I,,L,o~i,,,~,ll, the filter may include four contiguous cavities wherein a probe having opposite probe ends is disposed in the walls defining the four contiguous cavities much that the probe ends extend into two non-sequential, non adjacent cavities of the four contiguous cavities to couple radiant energy ~ L~h~ ~.
The invention further relates to a single mode dielectric resonator filter capable of selectively providing arbitrary amplitude and group delay response via a culllL,il~d~ioll of main line couplings between sequential ~0 adjacent l~ull ' .~, cross coupling between non-sequential adjacent , and cross diagonal couplings between non-sequential contiguous l~sol~dlul~. The cross diagonal coupling may be utilized to pre-distort the filter to co""~ ' for the distortion caused by the dispersion ~.lldld~,Lt:ri~ .s of dielectric loaded cavities.
Brief Description sf Drawin~; s Some advantages of the disclosed invention will become apparent from a reading of the following description when read in conjunction with the a~,co,l,,ud,,ying drawings in which:
Fig. 1 is a perspective view of the exterior of a filter housing and ,,, , .,, ,. .,: .: . . .

~ WO 95127317 218 6 9 ~ 8 PCT/CA95100177 cover in acco,ddllce with the present invention wherein the housing is formed with six cavities obscured by the cover;
Fig. 2A is a top view of the filter housing depicted in Fig. 1 with the cover removed revealing the six cavities fonmed therein;
s Fig. 2B is a section of the filter housing taken along the line 2B-2B in Fig. 2A, looking in the direction of the arrows;
Fig. 2C is a plan view of the undersurFace of the cover of the filter depicted in Fig. 1 shown removed from the filter housing;
Fig. 2D is a section of the filter cover taken along the line 2D-2D in Fig. 2C, looking in the direction of the anrows;
Fig. 3 is a section of the filter taken along the line 33 in Fig. 1 looking in the diredion of the arrows, on an enlarged scale, showing two dielectric ,t:son ' .:, disposed within their respective cavities, and a probe coupling thetwo ,t:s~
Fig. 4A is a partial section of the filter depicted in Fig. 1 taken along the line 4A4A, looking in the direction of the arrows, depicting an adjusting screw used for adjusting the resonator coupling slots between adjacent, sequential cavities;
Fig 4B is a partial section similar to Fig. 4A, depicting an alternate method of tuning the coupling slots using an adjustable fin;
Figs. 4C, 4D and 4E are top r~dy",~ d~y views of the portion of the filter shown in Fig. 4B depicting positions of the ~ lct~hlP tuning fin shown in Fig. 4B;
Figs. 5A, 5B, 6A, 6B, 7A, 7B and 8 are partial top views of the filter housing depicted in Fig. 2A showing various probe configurations which provide coupling between two adjacent, seq~ential or non-sequential cavities;
Fig. 9 is a graph depicting the measured bandwidth output obtained from the filter shown in Fig. 1;
Figs. 10A, 10B and 10C are partial top views of the filter shown in Figs. 5-8 depicting a single optional diagonal cross coupling probe which couples non-adjacent, nonsequential l~sulldlul~ and cavities as well as a _, . , WO 95/27317 PCT/CA9~/00177--~8~ 4$
probe coupling two adjacent It:SOIldlUI~ and cavities;
Fig. 11 is a perspective view of the exterior of an alternate ~",LJo.li",er,l of the filter showing the filter housing and cover, wherein the housing is formed with 10 cavities obscured by the cover;
Fig. 12 is a top view of the filter housing depicted in Fig. 11 with the cover removed revealing ten cavities formed therein;
Fig. 13 is a view of the undersurface of the cover of the filter shown in Fig. 11 shown removed from the filter housing, depicting ten dielectric I t:lSUI~d~Ul ~
lo Fig. 14 is a section of the filter taken along the lines 14-14 in Fig. 11, looking in the direction of the arrows, on a slightly enlarged scale, showing the dielectric ,~soll~Lu,~ disposed within the cavities, the resonator supports and tuning screws;
Fig. 15 is a schematic of another ~",LJO~ jIII~IIl of the present invention with the cover removed wherein each of the ten cavities has a dielectric resonator disposed therein, each cavity is coupled to adjacent sequential cavities by a slot fommed in the common wall II,e,~:L,~h.. " at least two adjacent non- sequential ~son ' .~ and cavities are coupled by a probe, and at least two non-adjacent, non-sequential cavities are coupled by a probe;
Fig. 16 is a top view of another alternate ~lbo~ a~l of the present invention wherein each cavity has a dielectric resonator disposed therein, each resonator and C011t:5pUll~ill9 cavity is coupled to sequentially adjacent cavities by a slot or probe formed in common walls and coupled to non-sequential adjacent cavities by probes disposed in common walls;
Fig. 17 is a perspective diagram depicting a dielectric resonator and the eleul,u",dyll~Li-, field pattem of the TEo1l mode;
Figs. 18A, 18B and 18C are plots of simulations of the output of the filter shown in Figs. 11-14;
Figs. 19A and 19B are plots of the measured output of the filter shown in Figs. 11-14;

WO 9~/27317 PCTICA95/00177 ~;t~fi~48 -9-Figs. 20A and 20B are plots of simula~ed outputs of the filter shown in Fig. 15;
Figs. 21A and 21B are plots of measured outputs of the filter shown in Fig. 15.
Best Mode(s) fQr (~rrying Out the Inven~i~ r With reference to the drawings whereill like reference cl)dlcn,~
represent like uu~ ,ùl~r,ts throughout the va~ious views, and with particular reference to Fig. 1, there is depicted a filter 5 which may be used in, for instance""i.,. ~ c ll~llallliSSi~ S, and more particularly for satellite communication ,, ' " ).)~.
The filter 5 in Fig. 1 includes a unitary housing 10 that is preferably fommed from a single block of material, such as aluminum, machined to fomm the shape depicted. It should be a,U,ul~ ~' that other materials may be used, aluminum being one of many materials suitable. The filter also includes a cover 12. At either end of the housing 10 are mounting legs 15 (the second mounting leg is not visible in Fig. 1), each leg 15 having mounting holes 20 for securing the filter to the structure (not shown) within, for instance, a communications satellite.
Fig. 2A depicts the filter housing 10 with the cover removed exposing six cavities C1-C6. The housing 10 is fommed with slots SL1-SL5, where the slot SLI is formed in the wall 25 between sequential cavities Cl and C2; the slot SL2 is fommed in the wall 30 between the sequential cavities C2 and C3;
the slot SL3 is formed in the wall 35 between sequential cavities C3 and C4;
the slot SL4 is formed in the wall 40 between sequential cavities C4 and C5;
and the slot SL5 is formed in the wall 45 between cavities C5 and C6.
The wall 50, between non-sequential adjacent cavities C2 and C5 is provided with an aperture 55 into which is positioned a probe 60 surrounded by an insulating material 67 (Fig. 2B). The probes are preferably wires made of beryllium copper, however, several other ele~L,i.,~l!y conductive materials will suffice. The insulating material 67 may be made of any non-~t~ o- ~
conductive material, however, in the preferred embodiment, the insulating material used is Teflon, Rexolite or a ceramic material such as boron nitride.
The probe 60 (see Fig. 2B) couples the cavities C2 and C5 in a manner which will be explained in greater detail below.
Referring now to Figs. 2C and 2D, the cover 12 is depicted.
Attached to the underside 65 of the cover 12 are six dielectric ,~son~'u,b R1-R6, respectively, mounted on tubular dielectric supports S1-S6 (only supports S2 and S5 are visible in Fig. 2D). The supports S1-S6 and It:501 ' b R1-R6 are positioned on the cover 12 such that when the cover 12 is in place on the housing 10, the dielectric l~bUIldLUlb R1-R6 are located close to the center of the cavities C1-C6, respectively, as is more clearly shown in Fig. 3.
The resonator R2 is bonded by adhesive to the support S2, and the resonator R5 to the support S5. Each support is in turn bonded to the cover 1~ 12. The resonator supports, such as S2 and S5 are made of a dielectric material having a dielectric constant preferabiy less than 4, such as a ceramic material DS4, manufactured by Transkch, Adamstown, Maryland.
The dielectric constant of the dielectric l~sol, ' b, such as R2 and R5, is preferably higher than 20. The dielectric ,~so,,dlurb are fommed of the M-Series material, manufactured by Murata Co., Kyoto, Japan. However, it should be d,u~ uial~d that the dielectric constant of the supports and the It:SOlldLurb is a variable factor, and the prefenred constant will be d~Lt:""i"ed by, among other conai~e,dt;~ , the pe,ru""d"ce ullaldull:libLi~,s desired from the filter and the materials used.
2~ The supports S1-S6 are generally identical, therefore the 35 des~ ,Liun of supports S2 and S5 are applicable to the remaining supports.
Further, the It:sulldLulb R1-R6 are likewise generally identical and therefore the description of the l~aol)dLulb R2 and R5 are applicable to the remaining I t:5CIl IdLv, b.
The supports S1-S6 are cylindrical in shape, having a central bore. A
tuning screw E2 is threaded into an aperture in the cover 12, and extends .. _ . .. . . . . _ . : .. .. . . . . . _ _ _ _ _ . _ ..

2 ~ 8 6 ~ 4 8 ~ ;
from the cover into the bore of the support S2. A tuning screw E5 is likewise threaded into the cover 12 and extends into the bore of the support S5. The upper ends of each tuning screws E1-E6 are visible in Fig. 1. The tuning screws E1-E6 are generally identical and therefore the des..,i,uLiu,, of the tuning screws E2 and E5 are: ,~, ' ' ' to the remaining tuning screws.
The filter housing 10 and cover 12 are held together by a plurality of screws 70, however the cover 12 could also l~e welded, bonded, clipped or otherwise fastened to the housing 10 by any of a variety of means.
Referring to Figs. 1 and 2A, two accesses Al and A2 to the filter are provided by two generally U-shaped probes 75 and 80, which are disposed at respective ends of the filter. For instance, access Al can serve as an input junction to the filter 5 and the access A2 can serve as an output. In Fig. 2A, the probes 75 and 80 are shown as U-shaped wires. However, it should be u"de,~luod that other shapes could be used as will be ~lld~ luod 15 more clearly with regard to the des.. ,i,uliull of the coupling probes depicted in Figs. 5-8 below.
Fig. 4A depicts the slot SL4 formed in the wall 40. A tuning screw T4 rotatably threaded into the cover 12 is used to tune the coupling between the I~SU~ldlu,~ R4 and R5 (not shown in Fig. 4A). Tuning screws T1-T5 are provided in the slots SL1-SL5 respectively. Each tuning screw is generally the same and therefore the des.,,i,uliù,~ of one is applicable to all of the tuning screws T1-T5.
Fig. 4B depicts an alternate means for tuning slot couplings between r~son ' a and/or cavities in a manner believed to be new and unique. A fin 82 attached to the lower end of a screw 83 is used in place of each of the tuning screws T1-T5, one fin 82 5llhstitllt~od for each tuning screw. Each fin 82 acts in a manner analogous to an air duct baffle, in that the fin 82 blocks portions of the magnetic flux lines that couple two adjacent ,~o~ . The tuning fin 82 may be made of a number of materials such as aluminum or copper. Figs. 4C, 4D and 4E depict three positions of the many positions WO 95127317 ~ PCTICA95100177--2~86~48 -12-` ~:
possible for adjusting the fins 82. For instance; when the fin 82 is in the position depicted in Fig. 4C, the coupling between the l~:~ulldlUr~ R4 and R5 is at a maximum. In the position depicted in Fig. 4D, the fin 82 partially inhibits the coupling between the l~SOlld~ul:~. In the position depicted in Fig.4E, the fin 82 reduces the coupling bet~veen the It:SulldLUl~ R4 and R5 to a minimum. It should be u"de,~tuod that one fin 82 may be used in each of the slots SL1-SL5 and that each fin 82 is generally identical.
Therefore, the des~ i,.,tiu,~ above is applicable to each fin 82 when 5, Ihstitl ItPd for the tuning screws T1-T5. Further, there may be filter " ,~ ,s where several slots may be provided with a tuning screw and other slots are provided with tuning fins. Such ~IIlL,illdliull~ of tuning screws and tuning fins are within the c~ll'~.ll, ' ' ' scope of the present invention. It should be d,U,~ ' ' ' that tuning fins 82 may also be employed in waveguide cavities without the presence of a dielectric resonator.
With reference again to Fig. 2A, the oli~lltdliûl~ of the two rows of cavities, the first row being cavities C1-C3, and the second row being C4-C6, is referred to hereafter as a folded configuration. One of the purposes of folding the resonator cavities C1-C6 into two rows is to provide common walls between non-sequential cavities, into which cross couplings, which provide special features to the filter's bandwidth output ulldldult:li,Liu:,, may be inserted. The special features with respect to the output of the filter will be discussed further be below.
The probe 60 in Fig. 2A provides cross coupling within the filter 5 between non-sequential adjacent l~sù"diu,~ R2 and R5, Fig. 3. The coupling between cavities, in a Illeu,~Li~.dl or Illdlll~lllaliudl sense, is given a sign, either positive or negative. The sequential couplings provided between l~:,OI1dlUI:, via slots SL1-SL5 are chosen in a Illdlllellldliudl sense to be positive couplings. The sign of the probe coupling (positive or negative relative to the positive coupling of the slots SL1-SL5) can, according to the teachings of the present invention, be selectively dt~ ""illed. The probe 60 . _ . . ,, _ . . .. .. _ . . .. .. . . ... . . _ . . _ . . _ . . _ _ _ _ _ _ WO 95/~7317 ~18 fi 9 4 8 PCT/CA95/00177 is shown in greater detail in Fig. 5A, in a parLial view of the filter 5. The probe 60 as depicted in Fig. 5A, provides limited negative coupling between these two It:501 ' .a by means of the electric field lines, i.e. they convey a portion of the energy of resonator R2 in phase opposition to the vicinity of resonator R5. The negative coupling makes it possible to move the ~,d,)a",iaaion zero on either side of the amplitude-frequency response curve of the filter, as will be explained in greater detail below. However, the probe configuration depicted in Fig. 5A provides resonator coupling that is limited and therefore may not be advantageous in some filter designs. Further, the probe 60 does not provide a means for changing the sign (positive or negative) of the coupling.
Alternate e",L,odi,llel,ts of the probe 60 are described with reference to Figs. 5B, 6A, 6B, 7A, 7B and 8.
The probe 60' in Fig. 5B provides coupling between the two sequential ,t:sor,dLura R5 and R6. The probe 61 in Fig. 6A is S-shaped, having a body portion 56 with extending legs 85, the legs 85 being asymmetrical with respect to the wall 50. The probe 61 provides coupling of the resonant energy of the l~s~l~dlu~a R2 and R5, and the asy"""~Lli..dl extension of the legs 85 produces a positive coupling. An alternate embodiment of a probe 61' (Fig. 6B) includes a body portion 57 where the legs 85' have a curved contour COII~a,u~ll.lillg to the curvature of the It:So~ ula R2 and R5, which increases the efficiency of the coupling. The curved contour of the legs 85' conforms to an arc which may share a common center point with the dielectric ll:Sol~ldLura R2 and R5.
In the embodiment depicted in Fig. 7A, a probe 62 has U-shaped legs 90 which are symmetrical about the wall 50. The probe 62 provides coupling between It:sondLura R2 and R5 which is negative. In Fig. 7B, the probe legs 90 are fommed with a curved contour cor,t:a,uu"~i"a~ generally to the curvature of the II:aOll~ura R2 and R5.
In Fig. 8, a probe 63 includes two loops 91 and 92 made by means of a conductive wire which is folded in the vicinity of its ends so as to form WO 95/27317 ;, ~ PCT/CA95/00177--~ 86g~ ~8 ,4 ~, the two generally U-shaped loops, in a horizontal plane on opposite sides of the wall 50, so as to bring the opposite ends of the probe 63 into contact with the common wall 50 The probe 63 in Fig 8 provides negative coupling due to the opposite directions which the loops take on opposite sides of the common wall in cu~ i"d~i~n with being in contact with the wall 50 Magnetic flux lines from the resonator R2 pass through the portion of the coupling loop 91 adjacent the resonator R2, induce a current in the probe 63 which passes through the cavity wall 50 to the loop 92 in the resonator cavity C5 In resonator cavity C5 the direction of the current in the probe wire 92 tends to produce a magnetic flux the direction of which will be in opposition to the direction of the magnetic flux of the resonator R5 within that cavity C5, thereby producing a negative-value coupling As was discussed above, the two accesses Al and A2, Fig 2A, are provided with probes 75 and 80 The probes 75 and 80 may be replaced IS with other probe shaped like any of the probe legs 85, 85, 90 or 90, Figs 6A, 6B, 7A, and 7B respectively, as dictated by the desired output of the filter Fig 9 is a graph depicting the frequency bandwidth output of the filter shown in Figs 1 through 3 The ~iy"iriual ~ce of portions of the output curve will be discussed further below.
Fig 10A depicts a probe 95 which may optionally be employed in the filter 5 to diagonally couple ~t:sol~d~ur~ R2 and R6, or other contiguous, non-adjacent pairs of It7SUlld~UI::. (such as Rl and R5, R3 and R5 or R2 and R4) The filter housing 10 is provided with an opening 97 The opening 97 is 2~ fitted with an insulating material 98~ The insulating material 98 isolates the probe 95 from the housing 10. The probe 95 has legs 99 which are asymmetrical about the opening 97 In an alternate t:",~o~i",~"~ depicted in Fig 10B, the probe 95 has legs 99 which have a curved contour generally cu"~po"d;"g to the curvature of the ~s~n~ur~ R2 and R4 The curved contour of the legs 99 is such that the legs are each spaced at a uniform distance from the curved ... . . , _ .... _ . . . , _ _ . . , _ .. , _ . .. . . .. _ . . . _ .. . .. . . . . ..

WO 95127317 218 6 9 ~ 8 PCTICA95100177 surfaces of the ,~sond~u,~ R2 and R4, respectively, or put another way, the radius of curvature of the legs 99 shares a common center point CP with that of the adjacent resonator. The probe configurations depicted in Figs.
10A and 10B provide positive coupling between It::,on ' ~.
The sign of the cross diagonal coupling described with respect to the probes depicted in Figs. 10A and 10B can be selectively d~L~ d. For instance, a probe 100 depicted in Fig. 10C provides negative coupling between the It~aOIldLu,~ R2 and R6, as will be explained further below. The probe 100 is provided with legs 101 which have a curved contour generally spaced to be at a uniform distance from the surface of the adjacent cyl;"d~ic~'!y shaped resonator.
The present invention is not limited to a six cavity and six resonator configuration. The number of cavities and It:Sul~dLul~ in a microwave filter is a function of the desired output requirements of the filter. For instance, an eight cavity/l~:sol, ' filter and a ten cavity/~t:,,o~ " and larger numbers of cavity/lt:sol-dLur filters are cu,ll~,,,, ' ' ' using the coupling means described above. A six cavit~ s~l ' - filter is referred lle~i"drL~ as a sixth degree hlter, an eight cavity/l~:,olldLol filter as an eighth degree filter, and so on.Fig. 11 depicts a tenth degree filter 102 having ten cavities. The filter 102 has a housing 105 and a cover 110. The housing 105 is depicted in Fig.
12 with the cover 110 removed, exposing the cavities C1-C10 and showing ten dielectric l~solldLu~ R1-R10 in phantom. The cavities C1-C10 are coupled to sequential adjacent cavities via a slot, such as the slots SL1-SL9, in a manner similar to the coupling described with respect to the ~ LJodi~ depicted in Figs. 1-3. Additional slots SL10 and SLII are provided for positive cross coupling of non-sequential, adjacent cavities Cl and C10, and cavities C4 and C7, respectively.
Fig. 13 shows the underside of the cover 110 with the ,~5011 ' ~ R1-RlO attached thereto via dielectric supports (not visible in Fig. 13).
Fig. 14 depicts, in a sectional view, the ass~:",L,led filter 102 with the resonators disposed within the cavities C1-C10 respectively, 2~86~g ~, The filter depicted in Figs. 11-14 is a tenth degree filter cu~ g two folded rows of five dielectric loaded resonator cavities. The filter 102 further includes two accesses Al and A2 at the ends of the filter housing 105 with each access constituted by a c;o~ e-.~iull which is Lel ~ dled in the firstand last cavities of the series of cavities. Each of the accesses Al and A2 is provided with a probe 107. Each probe 107 has a curved contour that is generally uniformly spaced from the curved surface of the adjacent resonator, such that the resonator and the probe share a common center point CP. With reference to Figs. 13 and 14, it should be dpplecidLed that the resonator tuning screws E1-EIO, the supports S1-S10, and the slot tuning screws T1-T9 are generally of the same construction as the resonator tuning screws, slot tuning screws and supports described with respect to the filter 5 in Figs. 1-3 above. Further, the slot tuning screws T1-T9 in the filter 102 could be replaced by the tuning fins 82 described with respect to Figs. 4B4E.
The filter 102 is further provided with cross coupling probes 62 which couple cavities C3 and C8, and cavities C2 and C9, respectively. However, it should be d~JIJle~id~d that the filter 102 could be proYided with any of the probes depicted in Figs. 5-8 and 10A and 10B. The types of probes used would be deLe""i"ed by the desired output of the filter.
For example, an altemate ~IIIbOdi,llell~ of the tenth degree filter of the present invention is depicted s~ e"~dli~ l') in Fig. 15 wherein ten cavities C1-C10 have ,eson tc ~ R1-R10 disposed therein. The housing 125 is fomned with slots SL1 through SL9, one slot in the wall fommed between each adjacent sequential cavities. Each slot is provided with a slot coupling adjusting fin 82. The slots provide coupling between each pair of adjacent, sequential ~esolld~ul~. For instance, the slot SLI couples ,esu,,dlula Rl and R2, slot SL2 couples ,es~",dLu,~ R2 and R3, and so on. Resolld~u,:, R2 and R9 are cross coupled by the probe 62 having legs 90 . Resonators R3 and R8 are also cross coupled by a probe 62 having legs 90'.
Non-adjacent, non-sequential leSOIl ' :~ R2 and R8 are cross _ . _ _ _ _ _ _ _ . . _ _ _ _ _ _ _ _ _ _ _ _ _ _ . .

' 17 diagonally coupled by the probe 100. Non-adjacent, non-sequential It:bUlldlUI:~ R3 and R7 are cross diagonally coupled by the probe 100. Both of these couplings are negative, relative to the positive slot coupling.
Non-adjacent, non-sequential I~Sol~dLu,~ R4 and R6 are cross diagonally coupled by the probe 95, providing a positive coupling. Further, cavities C1 and C10 are coupled by a slot SL10.
It should be d,U,UlL ' ' ' that variations of the couplings provided in the filter depicted in Fig. 15 are cor~ ' For instance, in some fflter : . r' ' 15~ only one cross diagonal coupling may be required, preferably between l~o~ R4 and R6. In other,, ' ' ~s, two cross diagonal couplings may be desirable. In this case, cross diagonal couplings between l~SulldLul~ R2 and R8, and R4 and R6 may be preferable.
Fig. 16 depicts yet another ~IllLJOuilllell~ of the present invention, wherein a housing 150 is provided with an input Al having a probe 155 and an output A2 having a probe 160. Ten cavities Cl through C10 are folded in pairs of cavities, such that there are five rows of cavities, Cl and C2 being the first row, C3 and C4 being the second row, and so on. In the LJOdilllèllL depicted in Fig. 16, slots SLI through SL9 are formed in the housing 150 walls, such that slot SL1 couples cavities Cl and C2, slot SL2 couples cavities C2 and C3 and so on. One resonator is disposed in each cavity, I~:SolldLu,~ R1-R10 disposed in cavities C1-C10, respectively. Each slot SLI through SL9 is provided with a slot adjusting fin 82. Further, several non-sequential adjacent cavity I~SUIld~ul:~ are coupled by probes 62, such 2~i as l~::SUlld~UI::. Rl and R4, R3 and R6, R5 and R8, and R7 and R10. There are also several cross-diagonal couplings included in the filter housing 150.
For instance, the first probe 95 couples cavities Cl and C3, a second probe 95' couples cavities C3 and C5, a first probe 100 couples cavities C6 and C8, and a second probe 100 couples cavities C7 and C9. It should be u,,de,aLuod that various cullluilldliol~s of cross couplings and cross diagonal couplings are possible in the filter 150. Not all of the couplings depicted in WO 95/27317 2~ 4 8 PCTICA95/00177--.
Fig. 16 are necessary in each filter ~j ' n. For instance one a~
may require only one cross diagonal coupling in order to provide the desired filter output and in another r;l ' ~ two or more may be required to provide the necessary output. In other e~ o~i",e~ts some of the cross couplings provided by the probes 62 may be sl~hstitll ' with additional slots or other probe configurations and probe shapes as discussed above with respect to Figs. 5A-8.
The design process for ~iu~u~ /c filters such as the various e",l-odi",t~ of filters described herein typically involves the l~u~se~ -of the filter using polynomial equations in order to predict the output of the filter. Some of the ~l~dldul~ iu~ of the filter may be predicted such as the filter's transfer 11ldld~ s (group delay Gq~ ln or lldll~lllis~ioll zeros or a Colllbilld~iull of both) are built into the poly,)Ol1lidla which under analysis yield an idealized prediction of the pe,ru""d"ce that the realized filter will hopefully yield. Such Illdlllt:llld~iual modeling of filters in general is well known. An example of such II,eù,~Liual Illdlll~ dti. dl modeling using polynomials may be found in for instance the p~ entitled "General Prototype Network-Synthesis Methods For 1~ IC Filters by R. J. Cameron published in the ESA Journal 1982 Volume 6 pages 193-206 which is i".. o,uu, ' herein by reference.
During the development of the el"bo~i"n:"ts of the filter of the present invention the ~I,eol~ dl ",dll,el"dLiual analysis indicated that predicted output of the several ~",~o.li",~"ts of filter were desirable if cross couplings(couplings between non-sequential II:DOI1d~UI~) were available. The probes 6û-62 provide the cross-coupling between adjacent l~:~UIId~UI~
The ,~ ~on~.~u,/cavity couplings provided by the slots are magnetic field-to-magnetic field couplings and are col,~i~e,~d to be positive in a lI ,eol t li..al I l Id~ l l Idliual sense. Typically if one coupling is electric where all the others are magnetic then the electric field coupling will be negative (in a ",dll,er"d~iual sense) with respect to the positive magnetic coupling.
Real-axis zeros were found to be desirable in the analysis of the filter to ~ = = .... _ _ _ _ _ _ _ _ . ... _ _ _ _ _ _ . .. _ .. _ _ WO 95~27317 ~ 1~ 8 6 ~ q 8 PCT/C~95100177 ' , .

produce what is known in the art as group delay eq~ tinn. Tldlla~ aiu zeros appear in the filter clldldul~riaLic or output of the filter as a result of combining positive and negative couplings in a single filter. The presence of l,d"a",i~aiv" zeros assists in providing a more desirable filter output.
In some filter ~ ,s Uulllbilldliulls of negative and positive couplings are desirable, and in other ,, ' ' la, all positive or all negative couplings may be desirable.
Fig. 17 is a diagram showing the distribution of the eleulL:u,,,du,,t~
field around a resonator R for a TEo11 type l~aolldl~ mode. The magnetic field lines H are shown as fine dashed lines alld the electric field lines E areshown as fine continuous lines. The geometrJ of the E-field and H-field are important to ~"de,aldll~;"g the various methods of providing cross-coupling, as will be further described below. The TEo1"~sond"ce mode for the I~SOll..~ula iS advantageous when ~r-~( ' ~' with the rectangular housing construction and makes it possible to obtain a filter having a Q-factor which is high, greater than 10,000.
Given the distribution of the magnetic field lines as shown in Fig. 17, it should be observed that in theory the probe ellds 85 and 90 of Figs. 6B
and 7B, respectively, can provide coupling more effficiently if the probes are disposed in a horizontal plane pe:l,u~diu~lar to the magnetic flux lines H.
The coupling probes described with respect to Figs. 5-8 are 'symmetric' couplings; that is, the effect of their presence is to introduce symmetric special features to the filtering ullaldu~L~ria~iua, eg. a pair of lldllblllisaiull zeros s~,:lll:lt:llicsll~/ disposed about the center frequency of the filter's usable bandwidth, or group delay flattening over a centrally pusiliu~ed portion of the filter's passband. Such symmetric features are achieved by coupling between two ,~sondLula which are separated by an even number of ,~su:,dlu,a in the sequence of I~SOlldlulS which form the main signal path. For example, the symmetric coupling probe 60 in Fig. 5A
provides a cross coupling between l~aOlldlula R2 ,~s~l,d~u,a having two other ~sondLu,a (R3 and R4) between them in the sequential main signal WO 95127317 I ~ , PCT/C~9S/00177--path. Therefore this cross coupling will produce a symmetric feature to the filter's transfer ul,a,duL~ s in this case a pair of L~ iull zeros s~""",t:L,ic~l'y disposed on the lower and upper side of the filter's passband as seen in the measured u lldld-l~lialics of Fig. 9. Fig. 9 shows the two I,cu,~,,,;, ,;v" zeros s~"""c,l,ic~"; disposed about the passband which are produced by the negative cross coupling probe 60 and the e~ a~c~",e"l in near-to-band selectivity that results. The lldll~ iUII zeros are the points where the plot dips down to points near the horizontal axis (near the -20.000 and 30.000 MHz marks).
When there are an odd number of l~olldlu,~ in the main signal path separdlil,g the two It:SOIldlUI~ coupled by any of the cross couplings the probes in Figures 5A-8 asymmetric features are introduced in the filter's rejection or group delay .I)alduk:liali.is. The asymmetric features may take the form of one or more l,d"~",i~aiu" zeros located on one side of the filter's passband only or as~"""~l,iu~ disposed on either side of the filter's passband. Wlth this asymmetric di~,u~sitiùn of lldl~ sioll zeros the slopes of the filter's rejection ullaldu1~libti~s will be different on the lower and upper sides of the filter's passband. Such asymmetric features are useful for satisfying desired ~ e~ for rejection which are different on the lower and upper sides of the filters center frequency or for correcting asymmetry in the group delay ~;lldldule~ of the filter. For example it may be desirable to have a slope in the group delay across a portion of the passband of the filter adjusted to counteract an opposite-going slope that is caused by dispersion Cllald.l~liali._~ of the dielectric resonator. The ~5 u all~lldlioll of the dispersive group delay slope with the slope caused by the asymmetrical cross coupling results in the desired flat group delay over the central portion of the filter's passband. If the dispersive group delay slope was not co",uensdL~d for distortion to the signal passing through the filter would occur.
In the present invention a convenient way to illlul~ lll the asymmetric cross couplings is diagonally through the comers of the cavities WO 95127317 PCT/CA9~i/00177 ~8~g -21- ~ ~
to be cross coupled, hence the alternative name diagonal cross coupling for the asymmetric coupling. Figs. 10A, 10B and 10C show cross coupling probes which couples I~S~ld~Ula R2 and R4, thereby producing asymmetric features to the filter's ulldld~,Le:riali~,s.
A series of simulated pe~ru""d"ce plots based upon a analysis of the 1Oth degree filter (depicted in Figs. 11-14) is shown in Figures 18A, 18B and 18C. The square lines on the plots indicate the upper or lower bounds of a typical desired output, and the curves indicate the simulated outputs. Figs. 19A and 19B are plots of measured l~ c,,,s~s to the filter depicted in Figs. 11-14. In some ~ " la, the output may be ~ccel,l ,-1 .1~
However, the addition of cross-diagonal couplings, such as those described with respect to the filter depicted in Fig. 15 provides an improved response over the plots in Figs. 19A and 19B. For instance, the Figs. 20A
and 20B are simulations of outputs from the filter depicted in Fig. 15, based upon a Ll,eor~Li,,al analysis of the filter configuration. Measured outputs yielded the plots shown in Figs. 21A and 21B, c~llfi,l"i,lg that the filter in Fig. 15 provides improved response with cross-diagonal coupling. The filter's special features (enhanced selectivity, flattened group delay) are caused by the combined action of the cross-coupling between adjacent non-sequential filter r~aond~ul~, and coupling between non-sequential, non-adjacent It:SUI,dLu,a.
As is ~e",ol,alldL~d by the measured output of the filter depicted in Figs. 11-14, the plot in Fig. 19A does provide the desired isolation (the desired isolation is depicted in dashed lines, the measured output is solid).
However, the group delay output shown in the plot in Fig. 19B has a slope that is partially below the desired output (the desired output is in dashed lines, the measured is solid). The slope at the top of the plot in Fig. 19B is generally attributable to the dispersion ullald~l~lialiu of the dielectric ,~sol1.. ~,:,. However, the ulldld~,L~:liali~ia of the filter can be pre-distorted by the addition of cross diagonal coupling of at least one pair of non-sequential, . . .

WO 95127317 ~ ~ PCT/C~9S/00177 Lg -22-non-adjacent (or contiguous) cavities, as is depicted in the filter shown in Fig. 15. Indeed, the output measured from the filter depicted in Fig 15, as plotted in Figs. 21A and 21 B shows that the measured output of the filter is well within the desired output requirements. The cross diagonal coupling distorts the filter depicted in Fig. 15 to counteract the dispersion ul,a,dul~ iu of the dielectric I~SOIldlulb and yieid an output curve that is above the desired output (dashed lines in Fig. 21B).
The invention is not limited to the embodiments described herein, thus, for example, the number of r~sol1d~U~ may be different from 6 or 10 I0 and may be equal to an odd number. e.g. 5, 7, 9, . . . etc.
While the invention has been described in conjunction with various preferred e",bodilllerlt~ thereof, it will be ~ Idt:la~uOd that it is capable offurther Illù.li~,dLiol-s. The claims are intended to cover any variation, use orddd,uldliol1s of the invention which are generally consistent with the principles of the invention, and including such departures from the invention as come within known and customary practice within the art to which the invention pertains.
In~lllctri~l A~lrlirz~hilib!
For most industrial ~ of l"iu~....~/c filters, it is desirable to attenuate as strongly as possible unwanted signals which may exist very close to the edges of the usable bandwidth output of each filter. The sharper the attenuation. the better the pelru""al,c~. Cross-coupled filters have been attempted for this purpose, wherein non-adjacent and non-sequential cavities within a filter structure are coupled, i.e., "diagonal cross-coupling". Diagonal cross coupling improves the pe,rul",al,ct: of the filter. Itis herein disclosed how an even better response can be obtained by combining couplings between adjacent It:SOlldLul~ and cross diagonal couplings between non-sequential contiguous l~Sù~

Claims (13)

1. Claims A single mode microwave filter comprising:
   a unitary multi-cavity housing formed with a plurality of walls defining a plurality of cavities, that are sequentially oriented in first and second side-by-side rows, each row having a plurality of cavities;
   a plurality of cylindrically shaped dielectric resonators, one dielectric resonator disposed in each of said cavities, the walls between adjacent sequential cavities being provided with coupling means for coupling adjacent sequential resonators;
   an input device disposed adjacent to and connected to a first cavity in said first row;
   an output device disposed adjacent to and connected to a cavity in said second row;
   a probe disposed in the wall between at least two adjacent cavities, one cavity being in said first row and the other cavity being in said second row thus cross coupling said two cavities.
2. 2. A filter as set forth in claim 1 wherein said probe ends are symmetrical about said wall between said adjacent cavities.
3. 3. A filter as set forth in claim 2 wherein the slots formed in said walls couple resonant energy between said adjacent resonators, said slot coupling defined mathematically as positive, and said symmetrical probe ends of said probe couple energy between said resonators in said adjacent cavities, said probe coupling being defined mathematically as negative.
4. 4. A filter as set forth in claim 2 wherein the slots formed in said walls couple resonant energy between said adjacent resonators, said slot coupling defined mathematically as positive and said asymmetrical probe ends of said probe couple energy between said adjacent cavities, said probe coupling being defined mathematically as positive.
5. 5. A filter as set forth in claim 1 wherein said walls define at least four contiguous cavities, the filter further comprising a probe having opposite probe ends, said probe disposed in said walls such that said probe ends extend into two non adjacent cavities of said four contiguous cavities to couple radiant energy therebetween.
6. 6. A probe for use in a microwave filter, the filter being formed with at least one wall defining at least two cavities, each cavity being loaded with a cylindrically shaped dielectric resonator therein, said probe comprising:
   an elongated body portion mountable in said wall.
   first and second probe ends attached to said body portion, said probe being positionable within said wall with said first probe.
7. 7. A probe as set forth in claim 6 wherein said first and second probe ends are symmetrical about said body portion.
8. 8. A probe as set forth in claim 7 wherein said first and second probe ends are asymmetrical about said body portion.
9. 9. A probe according to claim 7, wherein said probe has an 'S' shape.
10. 10. A probe according to claim 7, wherein said probe has an 'U' shape.
11. 11. A filter as get forth in claim 1 wherein at least one of said walls is provided with a slot which provides communication between at least two cavities.
12. 12. A filter as set forth in claim 11 further comprising:
    a plurality of cylindrically shaped dielectric resonators, one dielectric resonator disposed in each of said cavities.
13. 13. A filter as set forth in claim 11 further comprising:
    a probe disposed in the wall between at least two non-sequential adjacent cavities, one cavity in said first row and the other cavity in said second row thus cross coupling said cavities.