Compact filtering balun with ultra‐wide stopband based on π‐type capacitive networks

Abstract

In this letter, a new compact filtering balun with an ultra-wide stopband is proposed on the ceramic substrate. Four coupled line units are utilized to design the distributed balun with a second-order filtering response. Then, three-/twoport inductively loaded π-type capacitive networks without high-order harmonics are equivalent to distributed three-/two-port distributed coupled line units; therefore, the proposed compact lumped filtering balun based on these π-type capacitive networks inherently have ultra-wide stopband characteristics. To verify the design concept, a prototype with 15-dB bandwidth across 0.85-1 GHz is designed at 0.95 GHz, and its amplitude and phase imbalances are 0.4 dB and E4.5°, respectively. The upper stopband attenuation higher than 20 dB of the balun is extended to 12.9 f 0 , where f 0 is the center frequency, and its size is only 0.0025λ g 2 , where λ g is the guide wavelength.

Compact filtering magic‐T using a hybrid microstrip‐cavity structure

“…1,2 It is the integration of in-phase and out-of-phase power dividers (PDs)/combiners, which provides inphase and out-of-phase power splits and port isolations. Recently, codesign components [3][4][5][6][7][8] have been extensively reported for miniaturization and low loss. Filtering magic-T 9-12 except for the above power splitter function, also integrates the filtering response.…”