Balanced-to-Single-Ended Filtering 180° Hybrids With Arbitrary Power-Division Ratio

Abstract

In this article, a balanced-to-single-ended (BTSE) 180 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> hybrid with arbitrary power-division ratio and bandpass filtering response is presented based on the 2-D square patch resonators. With resorting to the TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{01}$</tex-math> </inline-formula> and TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{10}$</tex-math> </inline-formula> orthogonal degenerate modes in a square patch cavity, the desired in-phase and out-of-phase characteristics between output ports can be simultaneously accomplished. The electric field distributions on the patch under operation of TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{01}$</tex-math> </inline-formula> and TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{10}$</tex-math> </inline-formula> modes are inspected to guide the design process. Theoretical analysis results demonstrate that the proposed hybrid flexibly allows for effective control of arbitrary power-division ratio by arranging two output ports at proper positions. Meanwhile, the filtering response can be realized using two stacked patch resonators with proper coupling strengths according to the filter specification. Moreover, the isolation performances between balanced input ports and single-ended output ports are evaluated for all the power-division ratios. For validation, two 2nd-order filtering BTSE hybrids with different power ratios of 1:1 and 10:1 are designed. Measured results of both two fabricated circuits exhibit good performances in terms of filtering response, power splitting distribution, common-mode suppression, in-phase and antiphase difference, as well as isolation and port matching.