Abstract: A linear actuator includes a drive arm and an extension arm each extending along a common drive axis. One of the arms has a plurality of resiliently deformable fingers extending beyond the end of the arm towards the other arm. At least one of the fingers has a thread on its inner face while the other arm has a threaded portion. At least part of the threaded portion is received between the fingers. The fingers are adapted to urge the threads of the two arms into interengagement such that rotation of the drive arm about the drive axis displaces the extension arm along the drive axis. The two threads are arranged such that when the ridge of one thread is received in the groove of the other thread the two sides of the ridge abut the two edges of the mouth of the groove.

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 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. At least one of the reflection functions Rn overlaps with the corresponding reflection function Rn?1 within the communication band but is different thereto.