Title of Invention

"A LOW LOSS BAND PASS FILTER WITH THE CASING"

Abstract

This invention relates to a window-cut band pass filter with window-cut resonators. Particularly this invention relates to a window-cut band pass filter with window-cut resonators coupled with inductive strips in bilateral finline for low loss performance at millimeter wave frequency range, and the casing thereof and products thereof. The window-cut band pass filter has a cascade of said half wave resonators, being window-cut resonators coupled with inductive strips in finline or bilateral fine line configuration for higher frequency range particular for millimeter wave frequency range. The casing comprises of two said blocks.

Full Text

TITLE: A Window-cut Band Pass Filter and the Casing thereof. FIELD OF THE INVENTION: The present invention relates to a window-cut band pass filter with window-cut resonators,,, particularly to a window-cut band pass filter with window-cut resonators coupled with inductive strips, more particularly to a window-cut band pass filter in bilateral finline with window-cut resonators coupled with inductive strips, even more particularly to a window-cut band pass filter in bilateral finline with window-cut resonators coupled with inductive strips for higher frequency range, still more particularly to a window-cut band pass filter in bilateral finline with window-cut resonators coupled with inductive strips for millimeter wave frequency range and the casing and products thereof. PRIOR ART: Band pass filters with low pass-band loss and high stop-band attenuation are extensively used in communication and radar systems, particularly in diplexers and triplexers. The most popularly used band pass filters of prior art are generally comprising of inductive strips and half-wave resonators. These band pass filters known in the prior art comprise of alternatively arranged inductive strips and half-wave resonators. Such known band pass filters are of two classes, when considered for low loss performance at higher frequency range, particularly millimeter wave frequency range. class-A of such known band pass filters of prior art are of pure metal insert configuration and class-B of such known band pass filters of prior art are of large gap bilateral finline configuration. The class-A band pass filters, that is, pure metal insert waveguide filters known in the prior art offer the advantages of low loss performance similar to that of conventional waveguide filters. The class-A band pass filters, however, have a major drawback. The dimensional tolerance of these filters is as stringent as in an air filled waveguide filter. The class-B band pass filters, that is, band pass filters in large gap bilateral finline configuration, which are particularly with the said gap equal to the waveguide height have the advantage of alleviating the drawback of class-A band pass filters. However, the class-B band pass filters overcome the problem of class-A band pass filter only to some extent by concentrating most of the energy within the dielectric substrate. Another drawback of class-B band pass filters known in the prior art, is the loss caused due to the dielectric substrate. The low loss band pass filters are the essential requirement for application in millimeter wave frequency range of communication and radar systems. Therefore, the class 'B' band pass filters known in the prior art, as stated above need improved low loss characteristic for application in the millimeter wave frequency range of communication and radar systems and hence, are not suitable as such for the application in the millimeter wave frequency range of communication and radar systems. Therefore, it is clear from the foregoing description that, the class-A and class-B band pass filters, known in the prior art, for low loss performance at higher frequency range, particularly millimeter wave frequency range need further improvement, due to the main drawbacks, as stated here in above. OBJECTS OF THE INVENTION : An object of the present invention is to propose a band pass filter along with its casing for low loss performance at higher frequency range, particularly at millimeter wave frequency range, more particularly at the lower range of the millimeter wave frequency range having minimum possible insertion loss in the device . Another object of the present invention is to propose a window-cut band pass filter and its casing for higher frequency range, particularly millimeter wave frequency range, more particularly at the lower range of the millimeter wave frequency range having minimum loss due to the dielectric substrate. Still another object of the inventions to propose a window-cut band pass filter having window-cut resonators coupled with inductive strips and constructed in bilateral finline configuration particularly for use at higher frequency range, more particularly for use at millimeter wave frequency range and casing for the same, even more particularly for use at the lower range of the millimeter wave frequency range having convenient size and capable of fabrication by industrial process on industrial sea Ie . Yet another object of this invention is to .propose a window-cut band pass filter and its casing which obviates the disadvantages of the class-A and class-B band pass filters known in the prior art as stated herein above. Further, in accordance with the present invention, the assembled device proposed during this invention comprises essentially of a window - cut band pass filter and a casing for the same, wherein the casing comprises of two blocks, namely an upper block and lower block. According to the presently disclosed invention, the window-cut band pass filter mainly comprises of window-cut resonators and inductive strips. According to the preferred embodiment of the present invention the resonators are half wave resonators and are arranged alternatively with inductive strips. According to the most preferred embodiment of this invention the metallised dielectric substrate is essentially cut to form window - cut half wave resonators which in turn are alternatively coupled with inductive strips. The metallised dielectric substrate/ as referred herein above/ particularly relates to the commercially available non-metallised dielectric substrate/which in-turn is first metallised to the desired thickness of the metallised coating or to the commercially available metallised dielectric substrate, and the finally metallised dielectric substrate is then essentially cut to form window-cut half wave resonators which in turn are alternatively coupled with inductive strips according to the most preferred embodiment of the presently disclosed invention. Still according to the most preferred embodiment of this invention, the dielectric substrate is metallised essentially on both sides of the substrate, and the said metallisation is essentially in similar pattern on both sides of the dielectric substrate. The most preferred embodiments, as stated here in above, definitly offers advantage of minimised loss due to dielectric substrate, very high Q-factor, more relaxed dimensional tolerance and flexibility for final trimming, According to one of the preferred embodiment of the present invention, the window-cut band pass filter is preferably made of a dielectric substrate, which in-tum has preferably dielectric constant of 2 to 3, more particularly of 2.22 and metallisation is done, according to the known methods of the prior art, essentially on both sides of the substrate with a conducting metal, such as copper. In accordance to the present invention, the casing of the present invention comprises of mainly two blocks, named an upper block and lower block. The window-cut band pass filter according to the present invention sits on the flat and angular groove provided for the same on the lower block. The upper block rests onto the lower block fitted with window-cut band pass filter and is tightened with the assembly screws through the partly non-threaded and partly threaded holes provided for the purpose in the upper and lower blocks, and the said holes of upper and lower blocks are in continuous alignment. The foregoing features and other features of the presently disclosed invention will be more apparent when read in conjunction with the following figures, as the present invention is explained with the help of these figures, which are not intended to limit the scope of the present invention. Any such modification by the persons having knowledge in this field of band pass filters or the allied devices may be covered within the scope of the present invention. DESCRIPTION OF THE ACCOMPANYING DRAWINGS : Figure-1 shows the top view of the window-cut band pass filter according to the one of the preferred embodiment of the present invention. The bottom view corresponds with the top view of the window-cut band pass filter. Figure-1 a shows the cross-sectional view of the window-cut band pass filter according to the one of the preferred embodiment of the present invention as shown in figure 1, through the line B'-B'. Figure-1b shows the cross-sectional view of the window-cut band pass filter according to the one of the preferred embodiment of the present invention as shown in figure 1, through the line A'-A'. Figure-2 shows the top, side-perspective view of the upper (outer) surface of the upper block of the casing according to one of the preferred embodiment of the present invention. The cross sectional view is also shown there-in. Figure-3 shows the top view (Figure-3a) and side view (Figure-3b) of the lower (inner) surface of the upper block of the casing shown in figure-2 Figure-4 shows the top, side-perspective view of the upper (inner) surface of the lower block of the casing according to one of the preferred embodiment of the present invention. The cross-sectional view is also shown there-in. Figure-5 shows the top view (Figure-5a) and side view (Figure-5b) of the upper (inner) surface of the lower block of the casing shown in figure 4. Figure-6a shows the top, side-perspective view of the assembled device. The cross-sectional view is also shown there-in. Figure-6b shows the one end view of the assembled device, shown in figure 6a. DESCRIPTION OF THE INVENTION : In accordance with the present invention the window-cut band pass filter (1) [Figure -1] has two parallel sides 2 and 3 extending in longitudinal direction and another two parallel sides 4 and 5 extending perpendicular to sides 2 and 3. The window-cut band pass filter thus formed has two surfaces upper surface (6) and lower surface (7), which are essentially identical in all respects. The filter according to the present invention is made from a dielectric substrate (8a), which has certain thickness (8) and width (9) and length (10). The metallisation of the dielectric substrate (8a), used to manufacture the window-cut band pass filter of the present invention is done with a conducting metal, such as, copper metal, upto certain thickness (11) resulting in total thickness, referred as 11a of the filter on the outer ends (figure-1a), which is equal to the thickness of the dielectric substrate (8) plus twice the thickness of the metallisation (11). The window-cut band pass filter mainly comprises of inductive strips (12,13,14,15,16,17) and window-cut half wave resonators (18,19,20,21,22). The opposite ends of the filter are provided with cuts 23 and 24 referred as input/output sections. The inductive strips (12,13,14,15,16 and 17) have certain length (25) and width (26), similarly window-cut half wave resonators have certain length (27) and width (28). The thickness of all the window-cut resonators and the inductive strips of the proposed window-cut band pass filter is essentially equal to the thickness (11 a) of the window-cut band pass filter. The width (28) of all the window-cut half wave resonators (18,19,20,21,22) are essentially equal. The inductive strips 12 and 17, 13 and 16, 14 and 15 are essentially equal in dimensions and shape to each other. The window-cut half wave resonators 18 and 22, towards the opposite ends (9 and 10) of the band pass filter, are equal to each other, and window-cut half wave resonators 19 and 21, towards the centre, referred as line A'-A' in figure 1, are equal to each other in dimensions and shapes. The window-cut half wave resonator 20, at the centre, referred as line A'-A1 in figure 1, is slightly bigger only in fourth decimal, but more preferably equal in dimensions (length) and shapes to the adjacent window-cut half wave resonators, that is 19 and 21 window-cut half wave' resonators of the enclosed figure 1. The inductive strips, towards the opposite ends (9 and 10) of the window-cut band pass filter, that is 12 and 17 as referred in the figure 1, are smaller in length (25) and the inductive strips 13 and 16, towards the centre, referred as line A'-A' in figure 1, are larger in length (25) than that of the inductive strips (12 and 16) towards the opposite ends (9 and 10) and are in turn smaller to inductive strips 14 and 15, towards the centre, referred as line A'-A1 in figure 1. The window-cut resonators, 18 and 22, towards the opposite ends (9 and 10) are equal as stated above and have smaller length (27) than the window-cut half-wave resonators, 19, 20 and 21. The inductive strips are in continuous contact essentially through two parallel and opposite sides 29 and 30 of certain but equal breadth 31. The width (28) is same through all the window-cut resonators (18, 19, 20, 21 and 22) and the input/output sections (23 and 24). The window-cut resonators (18, 19, 20, 21 and 22) and input/output sections (23 and 24) are air filled and named as air regions. The width of the air-filled input/output sections (23 and 24) and also those of the window-cut resonators are the same, as stated here in above, and are equal to the narrow dimension (height) of the metal waveguide enclosure. The filter pattern is symmetrical about the central window-cut half wave resonator (20). Figure - 2 shows the top-side perspective view of the upper (outer) surface of the upper block (32) of the casing for window-cut band pass filter (1) proposed according to the most preferred embodiment of the this invention. Figure 2 also shows cross-sectional view of the upper block (32) merely for understanding. The upper block according to the most preferred embodiment of this invention comprises of two opposite and parallel longitudinal sides (33 and 34), two opposite and parallel vertical sides (35 and 36), and two opposite and parallel horizontal faces (37 and 38). The two opposite and parallel horizontal faces (37 and 38) are referred as upper (outer) surface (37) and lower (inner) surface (38) here in after. The upper (outer) surface (37) is provided with means (39) to accommodate the assembly screws. Such means (39) have countersink (40) to hold the screw's head and a non-threaded hole (41) to accommodate the threaded part of the assembly screw. According to the preferred embodiment the hole (41) can also be threaded. The upper (outer) surface (37) is provided with at least two or more sets of two such means (39). Both the opposite and parallel vertical faces (35 and 36) are provided with a set of two threaded holes (42) towards upper (outer) surface (37) to accommodate the waveguide flanges, and set of two semicircular grooves (43) towards lower (inner) surface (38) to accommodate alignment pins, when assembled. The lower (inner) surface (38) of the upper block (32) is provided with longitudinal channel (44), having two opposite and paralleled vertical faces (45 and 46) measuring to the depth of the channel (44) and one face (47) horizontal, and parallel to the upper (outer) surface (37) and the lower (inner) surface (38), measuring to the width of the channel (44). Figure-3 shows the top view (figure - 3a) and side view (figure - 3b) of the lower (inner) surface (38) of the upper block (32) of tne casing shown in figure - 2 and as explained herein above. The lower block (48), shown in figure - 4 comprises of similar structure as that of upper block (32), as described herein above, except for having two identical, and longitudinal, flat and angular grooves (62 and 63), provided on open edges of the channel (58). The lower block (48) according to the most preferred embodiment of this invention comprises of two opposite and parallel longitudinal sides (49 and 50), two opposite and parallel horizontal faces (51 and 52), and two opposite and parallel vertical sides (53 and 54). The two opposite and parallel horizontal faces (51 and 52) are referred as upper (inner) surface (51) and lower (outer) surface (52) here-in after. All the six faces and sides (49,50,51,52,53 and 54) of the lower block (48) are preferably of same dimensions as those (33,34,37,38,35 and 36, respectively) of the upper block (32) [figure-2]. The upper (inner) surface (51) is provided with, preferably all through holes (55) to accommodate the assembly screws. Such holes (55) are in same number as in upper block (32) and in alignment with the holes (41) of the upper block (32). Both the opposite and parallel vertical faces (53 and 54) are provided with a set of two threaded holes (56) towards the lower (outer) surface (52) to accommodate the waveguide flange, and with a set of two semicircular grooves (57) towards the upper (inner) surface (51) to hold the alignment pins, when assembled. The upper (inner) surface (51) of the lower block (48) is provided with longitudinal channel (58), having two opposite and parallel vertical faces (59 and 60) measuring to the depth of the channel (58) and one horizontal face (61), which in-tum is parallel to upper (inner) surface (51) and lower (outer) surface (52), and this face 61 measures to the width of the channel (58). The outer ends, towards the upper (inner) surface (51) of the channel (58) are provided with identical, and longitudinal, flat and angular, at 90° angle, grooves (62 and 63) parallel to each other and extending towards vertical sides (49 and 50). The grooves (62 and 63) have two faces 64 and 65, which are at right angles to each other as stated above. The horizontal face (64) of the grooves (62 and 63) measures the width of the grooves (62 and 63) and vertical face (65) of the grooves (62 and 63) measures the depth of the grooves (62 and 63) [Figure-5b]. Figure-6a shows the top, side-perspective view of the assembled window-cut band pass filter (1) in the upper block (32) and the lower block (48) of the casing. To assemble the window-cut band pass filter device, in accordance to the presently disclosed invention, the window-cut band pass filter (1) comprising of the substrate (8a) and metallised part (11b) on its both of the opposite surfaces 6 and 7 as described herein above, is first mounted on to the lower block (48) in the grooves (62 and 63) provided for the same (1) on its upper (inner) surface (51). According to the most preferred embodiment of the present invention the metallisation (11 b) of the substrate (8a) is essentially only on the surfaces 6 and 7, and essentially not on the longitudinal sides 2 and 3, and horizontal (or say vertical) sides 4 and 5, and also essentially not on the inner faces of the window-cut resonators (18,19,20,21 and 22) and of the input/output sections (23 and 24), referred as 4a in the figure-1. The surface 7 of the filter (1) sits firmly in the grooves 62 and 63 provided on the outer ends of the channel 58 of the lower block 48. The sides 2 and 3 having width 11a aligns and matches accurately with vertical face 65 of the grooves 62 and 63, and the identical and longitudinal sides 29 and 30 having width 31 matches and aligns with horizontal face 64 of the grooves 62 and 63. The surface 6 of filter (1) aligns and matches accurately with upper (inner) surface 51 of the lower block 48. Accordingly the grooves 62 and 63 serve to support the filter part 1 of the present invention, which fits firmly into these grooves (62 & 63), as indicated by matched surface 7 of part 29 of filter part 1 and face 64 of groove 62 of part 48, and side 2 of filter part 1 and face 65 of groove 62 of part 48 in figure 6b. Similarly by matched surface 7 of part 30 of filter 1 and face 64 of groove 63 of part 48, and side 3 of filter part 1 and face 65 of groove 63 of part 48, as shown in figure 6b. After mounting the window-cut band pass filter (1) onto the lower block (48) as described here in above, the upper block (32) having the longitudinal channel (44) comprising of two vertical faces 45 and 46, and one horizontal face 47 is then placed on the upper (inner) surface (51) of the lower block (48) so that its lower (inner) surface (38) matches and aligns with the face (51) of part 48. The parts 41 of the holes 39 of the upper block (32) aligns with the holes 55 of the lower block (48), and side 33 with side 49, side 34 with side 50, side 35 with side 53 and side 36 with side 54. The semicircular grooves 43 of part 32 aligns and matches with semicircular grooves 57 of part 48 and form circular holes 66 to hold the alignment pins for aligning the channels 44 and 58 in the two blocks 32 and 48 respectively. According to the preferred embodiment of this invention the holes 42 of part 32 and 56 of part 48 are of same dimensions and may also be rectangular in shape. These holes, 42 and 56, merely serve to connect the standard, rectangular waveguide flanges to the input and output ports. The channels 44 and 58 referred as waveguide channel, after assembling the parts 1, 32 and 48, towards the ends 35 and 53, and 36 and 54 may serve as input and output ports. If the ends 35 matched with 53 serves as input port then the end 36 matched with 54 serves as output port and vice versa. In accordance with the present invention, the dimensions of parts 61, 28 and 47 are equal to each other, and of part 59 are equal to 60, of part 64 are equal to 29, of part 65 are equal to sum of part 8 and twice the part 11 that is equal to part 11 a. Further, in accordance to this invention the width (64) and the depth (65) dimensions of the grooves 62 and 63 are essentially equal, and the sums of the dimensions of the parts 65 and 60 are equal to the sums of the dimensions of the parts 65 and 59. According to the further embodiments of the present invention the window-cut resonators (18,19,20,21 and 22) are square in shape, that is length (27) is equal to width (28), or rectangular in shape, that is part 27 is smaller than part 28 or vice versa. The inductive strips (12,13,14,15,16 and 17) are preferably rectangular in shape, that is part 25 is smaller than the part 26 or vice versa. The ends cuts 23 and 24 are of same dimensions and preferably rectangular in shape. According to the preferred embodiments of the presently disclosed invention the window-cut band pass filter (1) as described here in above is fabricated first by choosing a dielectric substrate (8a) fully metallised on both the surfaces (6 and 7). The substrate (8a) used according to the preferred embodiment of this invention is of thickness (8) equal to 0.1 to 0.5 mm, more preferably 0.127 mm and having dielectric constant of 2 to 3, more preferably of to 2.22. The pattern as shown in figure - 1. is etched on both the metallised surfaces (6 and 7) by known method of photolithography. When the pattern is formed symmetrically on both the surfaces (6 and 7) of the substrate (8a), the metallisation gets etched out essentially only in the regions of the resonators (18, 19, 20, 21 and 22) and at the input output sections (23 and 24). The substrate material is milled out from these resonator regions (18, 19, 20, 21 and 22) and from the regions 23 and 24 forming the input/output sections. The resonators formed according to the description given above are essentially window-cut half wave resonators (18, 19, 20, 21 and 22) and definitely offer the advantages as stated herein above and overcomes the drawbacks of the prior art as stated herein above. ADVANTAGES OF THE INVENTION : In accordance to this invention, the window-cut band pass filter and the casing for the same as proposed during the present disclosure, offers the additional advantages of the very high Q-factor and more relaxed dimensional tolerance, in-addition to the advantages of having minimum possible loss and being capable of production on industrial scale at economical price. The Q-factor, referred herein above or below, is equal to f0 / ∆f, where in f0 is the centre frequency and Af is the 3dB band width (the difference in the two frequencies on either side of f0 at which the loss is 3dB below that at f). It is further an advantage of the window-cut band pass filter as stated here in above, disclosed during the present invention, which can have flexibility for the final trimming on need basis. In accordance to the present invention, the presently disclosed window-cut band pass filter and its casing which may also be referred as Ka-band filter, made with at least five window-cut resonators offers 1.28 dB (decibel) insertion loss over a bandwidth of 500 MHz (mega hertz) and stop band rejection of 60dB at 750 MHz away from the centre frequency (f0 as referred above in Q-factor). WE CLAIM: 1. A low loss band pass filter and its casing/essentially window-cut band pass filter comprising essentially of cascade of half - wave resonators , said resonators being window-cut resonators coupled with inductive strips in finline or bilateral finline configuration for higher frequency range/ particularly for millimeter wave frequency range. 2. A low loss band pass filter as claimed in claim I/ wherein / said window - cut resonators and the said inductive strips are arranged alternatively. 3. A low loss band pass filter as claimed in claims 1 and 2 wherein said dielectric substrate is metallised on both sides of said substrate/ the metallisation being in similar pattern on both sides of said dielectric substrate. 4. A low loss band pass filter as claimed in claim 1 wherein said casing comprises of two said blocks. 5. A low loss band pass filter as claimed in claim 4/ wherein said two blocks of the said casing are upper and lower blocks. 6. A low loss band pass filter as claimed in preceeding claims/ comprising of two parallel and oppsite sides extending in longitudinal direction and another two parallel and opposite sides extending perpendicular to said longitudinal sides/ and has an upper surface and lower surface/ and said set of two parallel and opposite surfaces are essentially identical in all respects. 7. A low band pass filter as claimed in preceding claims, wherein said opposite ends of said filter are provided with said cuts/ which in-turn function as input/output sections. 8. A low band pass filter as claimed in preceeding claims/ wherein the thickness of all of said window-cut resonators and inductive strips is essentially equal to the thickness of the said window - cut band pass filter. 9. A low band pass filter as claimed in preceeding claims/ wherein the width of said window-cut half wave resonators is essentially equal. 10. A low band pass filter as claimed in preceeding claims/ wherein said window-cut half wave resonators/ '~l towards the said opposite ends of the said band pass filter/ are equal to each other/ and said window-cut half wave resonators/ towards the centre of the said filter are equal to each other in dimensions and shapes. 11. A low band pass filter, and the casing and products thereof as claimed in preceding claims, wherein said window-cut half wave resonator at the said centre of the said filter is bigger but more preferably equal in dimensions (length) and shapes to the said adjacent window-cut half wave resonators. 12. A low band pass filter, and the casing and products there of- as claimed in preceding claims, wherein said inductive strips, towards the said opposite ends of said band pass filter are smaller in said length and the said inductive strips towards the said centre are larger in said length than that of the said inductive strips towards the said opposite ends and are in turn smaller to the said inductive strips towards the said centre. 13. A low band pass filter, as claimed in preceding claims, wherein said inductive strips are in continuous contact through said two parallel and opposite sides of said equal breadth. 14. A low band pass filter, and the casing and products thereof as claimed in preceding claims, wherein the width of said air-filled input/output sections and of the said window-cut resonators is essentially the same. 15. A low band pass filter, and the casing and products thereof as claimed in preceding claims, wherein said upper block of said casing comprises of said two opposite and parallel longitudinal sides, said two opposite and parallel vertical sides, and said two opposite and parallel horizontal faces, wherein the said two opposite and parallel horizontal faces are said upper (outer) surface and said lower (inner) surface. 16. A- low band pass filter,. as claimed in preceding claims, wherein said upper (outer) surface is provided with said means to accommodate the said assembly screws and said such means have said countersink to hold , said screw's head and a said non-threaded or said threaded hole to accommodate the said threaded part of the said assembly screw and the said upper block is provided with at least two or more sets of two said means. 17. A low band pass filter, as claimed in preceding claims, wherein said both opposite and parallel vertical faces of the said upper block are provided with a said set of two threaded holes towards said upper (outer) surface to accommodate the waveguide flanges, and also the said set of two semicircular grooves towards said lower (inner) surface to accommodate alignment pins. 18. A low band pass filter, as claimed in preceding claims, wherein said lower (inner) surface of the said upper block is provided with said longitudinal channel, having said two opposite and paralleled vertical faces measuring to the depth of the said channel and said one horizontal face parallel to the said upper (outer) surface and said lower (inner) surface, measuring to the width of the said channel. 19. A low band pass filter, as claimed in preceding claims, wherein said lower block comprises of said similar structure as that of said upper block, and in addition of having said two identical, and longitudinal, flat and angular grooves, provided on said open edges of the said channel. 20. A low . band pass filter, as claimed in preceding claims, wherein the said all the six faces and sides of the said lower block of the said casing for the said filter are essentially of same dimensions as those of the said upper block. 21. A low band pass filter, as claimed in preceding claims, wherein the said lower block is provided with, preferably, said all through threaded holes to accommodate the said assembly screws. 22. A low band pass filter, as claimed in preceding claims, wherein the said lower block is provided with said- longitudinal channel, having said two opposite and parallel vertical faces measuring to the depth of the said channel and one said horizontal face, which in is parallel to the said upper (inner) surface and said lower (outer) surface of the said lower*block, measuring to the width of the said channel. 23. A low band pass filter, as claimed in preceding claims, wherein the said outer ends, towards the said upper (inner) surface of the said channel are provided with the said identical, and-longitudinal, flat and angular, at 90°angle, grooves, which in-turn are essentially parallel to each other and extend towards the said vertical sides of the said lower block and said grooves have said two faces, which are at right angles to each other. 24. A low band pass filter, as claimed in preceding claims, wherein the said filter and the said casing are assembled by first mounting the said window-cut band pass filter comprising of the said substrate and the said metallised part on its said both of the opposite surfaces onto the said lower block in the said grooves on its said upper (inner) surface and the upper surface of the said filter sits firmly in the said longitudinal grooves provided on the said outer ends of the said channel of the said lower block, and the said sides having said width aligns and matches accurately with the said vertical face of the said grooves, and the said identical and longitudinal sides having said width matches and aligns with the said horizontal face of the said grooves and the said upper surface of the said filter aligns and matches accurately with said upper (inner) surface of the said lower block and there after the said upper block having the said longitudinal channel and comprising of said two vertical faces, and one horizontal face is placed onto said upper (inner) surface of the said lower block and said all the six faces of the said upper block and the said lower block aligns with each other. 25. A low band pass filter, as claimed in preceding claims, wherein the said metallisation of the said substrate is essentially only on the said parallel and opposite surfaces and essentially not on the said longitudinal sides, and said vertical sides, and also essentially not on the said inner faces of the said window-cut resonators and of the said input/output sections of the said filter. 26. A low band pass filter, as claimed in preceding claims, wherein the said width of the said channels of the said lower and said upper blocks, and said width of the said window-cut resonators and said inductive strips are essentially equal to each other. 27. A low band pass filter, as claimed in preceding claims, wherein the said width and the said depth of the said both the grooves of the said lower block are essentially equal. 28. A Iow band pass filter, as claimed in preceding claims, wherein the said window-cut resonators are square or rectangular in shape, preferably rectangular in shape. 29. A low band pass filter, as claimed in preceding claims, wherein the said input / output sections provided at the said opposite ends of the said filter are of same dimensions and preferably rectangular in shape. 30 A low band pass filter, substantially as herein described and illustrated.

Documents:

2064-del-1996-abstract.pdf

2064-del-1996-claims.pdf

2064-del-1996-correspondence-others.pdf

2064-del-1996-correspondence-po.pdf

2064-del-1996-description (complete).pdf

2064-del-1996-drawings.pdf

2064-del-1996-form-1.pdf

2064-del-1996-form-2.pdf

2064-del-1996-form-3.pdf

2064-del-1996-form-4.pdf

2064-del-1996-gpa.pdf