Synthesis of a New Class of Extracted Pole Filters Without the Ideal Phase Shifters

Abstract

This article proposes a novel approach for extracted pole (EP) filter synthesis. The pole producing elements can be extracted without introducing phase shifters. It is made possible by extracting lowpass elements in the prototype without reducing the order of filter functions. Using the proposed elements as added redundancy, the nonideal effect in the physical model is absorbed by adjacent resonators. Those novel approaches break through the conventional framework in EP filter synthesis. The synthesized results do not introduce extra spikes caused by nonideal phase shifters in the conventional EP filters. The new theory enables the application of EP filters in broadband situations. This work also reveals the equivalence between the frequency-dependent couplings and the PPEs. The validity of the demonstrated method is illustrated via an 11-pole filter with two transmission zeros. The simulated and measured results have no extra spikes caused by the nonideal phase shifters, which verified the effectivity of the proposed theory.