Accounting for spurious couplings in quadruplet microstrip filters

A technique for overcoming the effects of spurious couplings in quadruplet filters is suggested. The method involves inverting the polarity of one of the stray couplings and adjusting the direct and self-couplings accordingly. Distortion of S-parameters and group delay usually associated with the presence of stray couplings is hence overcome. An application of the method using microstrip rectangular open loop resonators is presented.