Interdigital filters with capacitively loaded resonators

Claim 1

A STRIP-LINE MICROWAVE FILTER ADAPTED TO PASS A PRESCRIBED BAND OF FREQUENCIES COMPRISING A PAIR OF SPACED PARALLEL GROUND PLANES, SPACED PARALLEL METALLIC BLOCKS INTERMEDIATE SAID GROUND PLANES AND IN ELECTRICAL CONTACT THEREWITH, AN INTERDIGITAL LINE COMPRISING TWO INTERLEAVING SETS OF PARALLEL ARRANGED METALLIC BARS, ONE SET OF SAID BARS AT ONE END BEING AFFIXED TO ONE OF SAID METALLIC BLOCKS AND EXTENDING TOWARD THE OTHER SAID METALLIC BLOCK AND INTO RECESSES FORMED THEREIN, THE OTHER SET OF SAID BARS AT ONE END BEING AFFIXED TO SAID OTHER METALLIC BLOCK AND EXTENDING TOWARDS SAID ONE METALLIC BLOCK AND EXTENDING INTO RECESSES FORMED THEREIN, THE WALLS OF SAID RECESSES BEING SEPARATED FROM SAID OTHER END OF SAID BARS A SLIGHT DISTANCE TO FORM A NARROW GAP WHEREBY SAID GAP DEFINES A CAPACITIVE COUPLING, EACH OF SAID METALLIC BARS BEING LESS THAN ONE-QUARTER WAVELENGTH OF THE MID-BAND FREQUENCY OF SAID BAND-PASS, AND MICROWAVE ENERGY COUPLING MEANS AT RESPECTIVE ENDS OF SAID INTERDIGITAL LINE.