the present invention provides a structure for smaller base station filters . specific embodiments and various features and aspects of the invention are described below . fig1 a is a partially broken - away perspective view of a filter 10 having a rectangular - shaped metal case 12 , according to an embodiment of the present invention . fig1 b shows a perspective view of the interior of the filter of 10 fig1 a , providing two cavities ( i . e ., 14 a , 14 b ) separated by a wall 15 , wherein each cavity houses a transverse magnetic ( tm ) dual mode resonator . a first tm dual mode resonator 16 is formed by resonator members 16 a , 16 b crossing each other at a mid - point to form a “ cross ” or “ x ” in cavity 14 a . a second tm dual mode resonator 18 is formed by resonator members 19 a , 19 b crossing each other at a mid - point to form as a “ cross ” or “ x ” in cavity 14 b . the filter case 12 further houses input pins ( i . e ., 18 a , 18 b ) coupled to coaxial connectors ( i . e ., 20 a , 20 b ). in this structure , there is coupling between the input pin 18 a and the resonators 16 a , 16 b . similarly , there is coupling between the input pin 18 b and the resonators 19 a , 19 b . the resonators comprise low loss dielectric material such as e . g . ceramics . other materials can also be used . the example filter 10 operates in the frequency range 1920 - 1980 mhz with four resonators ( two cavities ). further , table 1 below provides additional specifics : in table 1 , f represents frequency , and k 12 , k 23 represent resonance modes coupling coefficients for different frequencies . in addition , the coupling qe from input pin to a resonator mode is about 23 at f = 84 . 4 mhz . in this example , the filter structure has a height and width of about 26 mm , represented by simulated performance data discussed further below . smaller dimensions may also be provided , for example the size 22 mm may be preferred . all tuning is preferably from the same direction . fig1 c shows details of input pin 18 a spacing relative to a tm dual mode resonator formed by resonators 16 a , 16 b in the cavity 14 a of the filter 10 of fig1 b . in this example , the input pin 18 a is a 5 mm input metal pin , and coupling to the input pin 18 a depends on the gap distance between the ceramic resonators 16 a , 16 b and the input pin 18 a , as shown by example in table 2 below . one approach is to use a screw or a step in the corner . however , this embodiment uses a step 26 to preset the coupling and a screw 28 for fine - tuning . fig2 shows a perspective view of interior of cavity 20 in another filter including a tm dual mode resonator formed by resonators 22 and 24 , wherein the resonator 22 has offset arms 22 a and 22 b , according to an embodiment of the present invention . the arms 22 a and 22 b are offset to contribute to the coupling between the two resonators by rotating the field to less orthogonality . in that case there is less metal in the cavity , which means better q - value . this embodiment uses a step 26 to preset the coupling and a screw 28 for fine - tuning . fig3 a shows a side view of the interior of a cavity 31 in another filter 30 including a tm dual mode resonator formed by resonators 32 a , 32 b wherein the resonators 32 a , 32 b are tilted with respect to one another to form an “ x ”, according to an embodiment of the present invention . the input pin 34 is also shown in fig3 a . with tilted resonators ( arms ) there is harder coupling between the pin 34 and resonator modes . as described further below , the coupling depends on the tilt angle between the two resonators 32 a , 32 b . a square step in the lower corner is no longer needed . fig3 b is a graph showing an example frequency response of the filter of fig3 a . fig4 a shows a side view of the interior of a cavity 41 in another filter 40 including a tm dual mode resonator formed by resonators 42 a , 42 b wherein the resonators 42 a , 42 b form a “ cross ” or “ x ” that is tilted up in the cavity 41 , according to another embodiment of the present invention . the input pin 44 is also shown in fig4 a . fig4 b is a graph showing an example frequency response of the filter of fig4 a . referring back to fig4 a , the entire tm dual mode resonator “ cross ” or “ x ” is turned ( tilted ) slightly , so that the input can couple to the second mode as well . this additional coupling creates a zero in transmission on the higher side of the spectrum , wherein as schematically shown by example in fig6 : coupling k 02 → transmission zero at high side harder coupling → zero at lower frequency fig9 is a diagram shown an example coupling transmission zero for a filter including tm dual mode resonators , according to an embodiment of the present invention , wherein : fig5 a shows a side view of the interior of a cavity 51 in another filter 50 including a tm dual mode resonator formed by resonators 52 a , 52 b wherein the resonators 52 a , 52 b form a “ cross ” or “ x ” that is tilted down in the cavity 51 , according to an embodiment of the present invention . the input pin 54 is also shown in fig5 a . the entire tm dual mode resonator cross ( or x ) is turned ( tilted ) slightly , so that the input can couple to the second mode as well . as in fig4 a , the tilted cross ( or x ) results in a better attenuation on the higher side of the spectrum . fig5 b is a graph showing an example frequency response of the filter of fig5 a . fig7 a shows a side view of the interior of a cavity 71 in another filter 70 including a tm dual mode resonator formed by resonators 72 a , 72 b which form a “ cross ” or “ x ” that is tilted down in the cavity 71 , according to an embodiment of the present invention . the input pin 74 is also shown in fig7 a . the entire tm dual mode resonator cross ( or x ) is turned ( tilted ) slightly , and the input pin 74 is tilted relative to the resonators 72 a , 72 b . with a tilted input pin 74 , the coupling to mode 2 can be harder . in this way the transmission zero can be placed in the filter skirt very close to the passband . fig7 b is a graph showing an example frequency response of the filter of fig7 a . in fig7 b , the notch placed on the high side is very wide , and deep , with − 60 db as close as 2100 mhz . fig8 shows a perspective view of a filter 80 including a case 82 that forms two cavities 84 a , 84 b , which is a dual cavity implementation the example in fig7 a , according to an embodiment of the present invention . in fig8 , the cavity 84 a houses the tilted input pin 88 a and a first tm dual mode resonator 85 formed by resonators 85 a , 85 b as a “ cross ” or “ x ”. the cavity 84 b houses the tilted input pin 88 b and a second tm dual mode resonator 87 formed by resonators 87 a , 87 b as a “ cross ” or “ x ”. fig1 a is a perspective view of a filter 100 having a case 102 that provides two cavities 104 a and 104 b , according to an embodiment of the present invention . the cavity 104 a houses input pin 108 a and a tm dual mode resonator formed by resonators 106 a , 106 b as a “ cross ” or “ x ”. the cavity 104 b houses input pin 108 b and a tm dual mode resonator formed by resonators 109 a , 109 b as a “ cross ” or “ x ”. further , there is a loop 110 passing through an opening 17 in wall 15 between the two cavities 104 a and 104 b , providing coupling between resonator modes 1 and 4 . coupling is accomplished with a closed loop coupling 110 , which need not be connected to the cavity walls . the loop 110 is twisted in the form of a laying figure “ 8 ” for proper phase of the coupling . the loop 110 can for example be printed on a double - sided substrate card ( e . g ., teflon substrate ). loops with different widths provide different position of the transmission zeroes . fig1 b is a graph showing an example frequency response of the filter of fig1 a . coupling with a quadruple can make double transmission zeroes very close to the passband . fig1 a is a detail perspective view of the cross - coupling 110 in the filter of fig1 a . fig1 b is a detail side view of the cross - coupling 110 in the filter of fig1 a . fine tuning can be performed with a screw 126 that blocks the loop 110 . fig1 a shows a top view of an example magnetic field 121 for tuning frequency , influenced by a metal 120 along the side of a filter cavity 122 which houses a tm dual mode resonator 124 , according to an embodiment of the present invention . fig1 b shows the magnetic field 121 , influenced by a metal 120 along a corner of the filter cavity 122 . the magnetic fields is influenced by a metal along the side , wherein the frequency is changed as a result . in the corner there is less influence i . e . less changes . a screw into the cavity will influence the field in the same way . deeper penetration influences more of the field . fig1 shows perspective view of a filter 130 with a casing 127 , implementing two a cavity ( 132 a , 132 b ) version of the examples in fig1 a and 12b . the cavity 132 a houses input pin 138 a and a tm dual mode resonator formed by resonators 136 a , 136 b as a “ cross ” or “ x ”. the cavity 132 b houses input pin 138 b and a tm dual mode resonator formed by resonators 139 a , 139 b as a “ cross ” or “ x ”. to tune electric fields there have to be holes in the ceramic resonators 136 , 139 in two orthogonal directions . this embodiment instead tunes the magnetic fields 121 ( fig1 a - b ) close to the cavity walls 127 . in each cavity , resonance modes 1 and 4 are easily tuned with a screw ( e . g ., 137 a or 137 b ; 135 a or 135 b ) from the top . modes 2 and 3 are tuned with a metal bar 120 that is moved from the bottom and up . the bar can be moved with a screw from the top , placed in the corner . to prevent the moving bars from generating pim the moving parts can be covered with a thin dielectric film . fig1 shows perspective view of a filter 140 with a case 142 providing two cavities 144 a and 144 b , according to an embodiment of the present invention . the cavity 144 a houses input pin 148 a and a tm dual mode resonator formed by resonators 146 a , 146 b as a “ cross ” or “ x ”. the cavity 144 b houses input pin 148 b and a tm dual mode resonator formed by resonators 149 a , 149 b as a “ cross ” or “ x ”. metals in the cavities 144 a and 144 b are for tuning couplings . coupling between modes 1 - 2 and 3 - 4 can be done with screws 147 a from the top . coupling of the modes 3 - 4 is done in the aperture opening 143 in the separating wall . even this coupling can be done with a screw 147 b from the top , placed in the opening 143 . in the tilt up case ( fig4 a ) there may be a 4 mm long screw 43 with diameter of 6 mm , or a 10 mm long screw with 5 mm diameter , to get a shift of 10 mhz in k 23 . fig1 a shows example diagram of frequency tuning based on dimensions of a ceramic filter including a tm dual mode resonator 150 formed by resonators 150 a , 150 b as a “ cross ” or “ x ” having tilted arms , according to an embodiment of the present invention . fig1 b shows example diagram of frequency tuning based on dimensions of a ceramic filter having a tm dual mode resonator 152 formed by resonators 152 a , 152 b with tilted “ cross ” or “ x ”, according to an embodiment of the present invention . referring to the example in table 3 below , the frequencies and the coupling between the modes are dependent on the dimensions of the ceramic resonators ( 150 a , 150 b in fig1 a , and 152 a , 152 b in fig1 b ). as is known by those skilled in the art , in table 3 the terms f 1 , f 2 , etc ., represent resonance frequencies of first , second , etc ., resonance modes , and the terms k 0 , k 1 , k 12 , k 23 , etc ., represent resonance modes coupling coefficients . in table 3 “ gap ” is the distance between the ceramic resonators and the metal pins of the input , and “ wall ” is the width of the separating wall 15 between the cavities . the dimensions m 1 a , m 1 b , m 2 a , m 2 b , are shown in fig1 a - b . the frequencies have the strongest dependence , wherein a change of 0 . 1 mm in dimensions can result in 10 mhz offset . the filter may be first tuned with these dimensions to obtain a design centering . then , when the filter is produced simpler tuning with the tuning screws can be performed . the finished filter has only one small secondary effect in the tuning screws . tuning of f 1 will make a shift in k 12 a few mhz . table 4 below shows the difference in mhz when the screw for f 1 changes 12 mm , and the bar for f 2 changed 8 mm . k 12 is changed with a 3 mm screw on the right and on the left side of the resonators . fig1 a is an example diagram showing effect of tilt angle γ between resonators 160 a , 160 b forming a tm dual mode resonator 160 as a “ cross ” or “ x ”, in a filter cavity , according to an embodiment of the present invention . as shown by example in table 5 below , the angle γ between the two resonators 160 a , 160 b sets the coupling factor ( coefficient ) k 12 between the two modes . with orthogonal fields ( γ = 90 °) there will be no coupling . with angle γ & lt ; 90 ° there will be a certain coupling . the more the two resonators 160 a , 160 b are aligned , the higher the coupling . fig1 b is an example diagram showing effect of angles between resonators 162 a , 162 b forming a tm dual mode resonator 162 as a “ cross ” or “ x ”, and orientation of input coupling pin 164 , in a filter cavity , according to an embodiment of the present invention . when the arms , or the whole “ cross ” or “ x ” are tilted by an orientation angle φ , the resonators 162 a , 162 b are rotated around a centred point in the cavity . in this way the resonators 162 a , 162 b are kept as far away as possible from the walls of the cavity , and the q - value will be high . tables 6 - 7 below show effect of angle θ , and the orientation angle φ of the coupling pin 164 relative to the resonators 162 a , 162 b . angle θ affects the coupling since it , together with angle φ , sets the total angle γ between resonators 162 a and 162 b . qe 1 is the coupling from input pin 164 to resonator mode 1 , and qe 2 is the coupling between input pin 164 and resonator mode 2 . the qe 2 coupling depends on the angle θ . a smaller angle θ results in harder coupling from the input to mode 2 , which results in a transmission zero at the higher side of the spectrum . the total angle γ = θ + φ is chosen for the proper k 12 , and the tilt angle φ of the “ cross ” or “ x ” is chosen to obtain the proper qe 2 . even qe 1 is affected by the angle φ . however , this small change in qe 1 can be corrected with the distance between input pin and the resonator cross ( or x ). the value of qe 1 at φ = θ is a result of the metal screws in the cavity . fig1 is an example diagram showing effect of angles between resonators 170 a , 170 b forming a tm dual mode resonator 170 as a “ cross ” or “ x ”, and tilt of input coupling pin 172 , in a filter cavity , according to an embodiment of the present invention . compared to fig1 b , by further tilting the input pin 172 , the angle θ is decreased and the angle φ is increased . angle φ at 26 . 7 degrees results in smaller coupling to mode 1 ( higher qe 1 ). this was compensated , by moving the input pin closer to the “ cross ” or “ x ” formed by the resonators 170 a , 170 b . for angle θ = 51 . 7 results in a coupling to mode 2 ( qe 2 = 177 ) so high that the transmission zero is very close to the filters pass band . fig1 is a graph showing an example frequency response of the filter of fig1 . simulations were performed in hfss . in one simulation , the filter structure included tuning screws and a coupling screw of 4 mm diameter with the length of 1 mm . the coupling screw is placed in the upper left corner of the cavity . all mechanical parts in the cavity will influence the fields and have to be included when performing design centring . the coupling can be set over a range wide enough to be used for base station filters . the present invention has been described in considerable detail with reference to certain preferred versions thereof ; however , other versions are possible . therefore , the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein .