Ultra-compact dual mode dual band filter based on separate electric and magnetic coupling paths

Abstract

A pair of dual mode independent controllable resonators used to realize dual band pass filter with good frequency selectivity and isolation is presented. The resonators are directly connected to input/output and are coupled through electric and magnetic coupling in two different paths. Magnetic coupling between the resonators is achieved using a common grounded via-hole between the two set of quarter-wavelength resonators. Electric coupling is achieved through open edge coupling of the resonators. Two independent resonators with Separate Electric and Magnetic Coupling (SEMC) paths produce an independently controllable dual band filter response and also additional transmission zeros (TZs) at the edges of the pass bands. The TZs are introduced to improve the selectivity of the filter. Filter exhibits desired pass band response at the Universal Mobile Telecommunications System (UMTS) band (1.95-2.2 GHz) and Worldwide Interoperability for Microwave Access (WiMAX) band (3.4-3.6 GHz). Proposed compact filter is implemented on RT/Duroid 5880 (er = 2.2) substrate with thickness of 0.785 mm and surface area of 15 × 12 sq. mm.