Design of a four pole quasi-elliptic microstrip filter using the reflected group delay method

The reflected group delay method of designing filters is demonstrated for the first time on a four pole quasi-elliptic filter requiring cross coupling. A design procedure is proposed that involves creating optimization curves from a lumped element filter and involves using these curves to design a microstrip filter. To validate the proposed design procedure, a microstrip filter with a center frequency of 1 GHz and 5% bandwidth is designed, fabricated and tested. The limits of the proposed design method are investigated by determining the maximum absolute bandwidth this filter can have using this method.