Low loss quasitransversal microwave filters with specified amplitude and phase characteristics

A microwave filter synthesis procedure for almost arbitrary phase and amplitude responses is described. Although based on a passive transversal filter implementation, it contains an efficient numerical algorithm to allow for losses in the delay line and multiple reflections between taps; this permits large amounts of energy to be drawn from the delay line so that the filter can have reasonably low loss. The performance of chirp filters and a phase shifter implemented in copper stripline and microstrip are presented as a demonstration. A fractional bandwidth of 150% has been achieved for the chirp; this is about double that produced by previous design methods. It is intended that eventual implementations will include superconducting linear phase filters, chirp devices and amplitude or phase equalisers.