Abstract: A microwave filter for filtering a microwave signal is disclosed. The microwave filter has at least one band edge at a band edge transition frequency. The filter comprises an input port and an output port. The filter also comprises a plurality of single resonators connected in parallel between the input and output ports. The filter further comprises a frequency independent electrical coupling between the input and output ports connected in parallel with the resonators. A subset of the resonators has Q values each of which are at least a factor of three higher than the Qs of each of the remaining resonators.

Abstract: A band combining filter for filtering a microwave signal having at least one band edge at a band edge transition frequency. The filter comprises a plurality of filter sections. Each filter section comprising 3dB hybrid couplers having input ports and output ports and resonators connected between the input ports and the output ports of the couplers. The filter sections are connected in cascade such that the outputs of one filter section are connected to the inputs of the next filter section in the cascade. A subset of the filter sections are high Q filter sections with the Q values of the resonators of those filter sections having values each of which are at least a factor of three higher than the Q values of the resonators of the remaining filter sections.

Abstract: A tuneable bandpass filter includes a plurality of coupled resonators. A common structure of the filter includes at least one common coupling or one common resonator. An upper loop includes first and second end resonators coupled together by a signal path and further includes at least one further signal path extending between end resonators. The further signal path includes at least one further resonator with the end resonators being coupled to the common structure. A lower loop includes first and second end resonators coupled together by a signal path and further includes at least one further signal path extending between end resonators. The further signal path includes at least one further resonator with the end resonators being coupled to the common structure.

Abstract: A band combining filter for passing signals in a communications band includes a plurality of cascaded directional filters. Each directional filter has at least two inputs and at least two outputs. The nth directional filter is arranged such that output signals O1 and O2 from the first and second outputs are related to input signals I1, I2 to the first and second inputs by the relation ( O 1 O 2 ) = ( R n ? ? 1 T n ? ? 2 T n ? ? 1 R n ? ? 2 ) ? ( I 1 I 2 ) with R and T being reflection and transmission functions respectively. The directional filters are connected in a cascade with the first and second inputs of the nth directional filter being connected to the first and second outputs of the (n?1)th directional filter respectively in the cascade.

Abstract: A tuneable bandpass filter comprising a plurality of coupled resonators, the filter comprising a common structure comprising at least one common coupling or one common resonator; an upper loop comprising first and second end resonators coupled together by a signal path, the loop further comprising at least one further signal path extending between end resonators, the further signal path comprising at least one further resonator, the end resonators being coupled to the common structure; a lower loop comprising first and second end resonators coupled together by a signal path, the loop further comprising at least one further signal path extending between end resonators, the further signal path comprising at least one further resonator, the end resonators being coupled to the common structure; the resonators being coupled together such that the bandpass filter can be divided into a low pass sub filter and a high pass sub filter, one of the sub filters being arranged to receive the output of the other.

Abstract: A band combining filter comprising a plurality of cascaded directional filters, each directional filter having at least two inputs and at least two outputs, the nth directional filter being arranged such that the output signals O1 and O2 from the first and second outputs are related to the input signals I1, I2 to the first and second inputs by the relation ( O 1 O 2 ) = ( R n ? ? 1 T n ? ? 2 T n ? ? 1 R n ? ? 2 ) ? ( I 1 I 2 ) with R and T being reflection and transmission functions respectively, characterised in that the directional filters are connected in a cascade with the first and second inputs of the nth directional filter being connected to the first and second outputs of the (n-1)th directional filter respectively in the cascade.