Uniplanar Compact 180° Hybrid Coupler With Fast and Accurate Wide Power-Division Ratio Switching Ranges and Enhanced Bandwidth

Abstract

In this article, a uniplanar compact 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 coupler with fast and accurate wide power division ratio (PDR) switching ranges and enhanced bandwidth is proposed. The structure consists of two novel 90 <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> couplers, one wideband 90 <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> phase shifter (PS), and two tunable p-i-n diode-based PSs. The key uniqueness is that a symmetrical compact wideband 90 <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> coupler is presented as the core component. By using two three-folded-coupled lines and one unequal-width three-coupled line section, the proposed compact wideband 90 <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> coupler can be fabricated without patterned ground plane or any lumped element. Compared with conventional two-section branch-line couplers, this new coupler not only effectively reduces the circuit size by 57.76% but also improves the bandwidth from 37% to 48.45%. Then, compared with the varactor-based couplers, by adding p-i-n diodes at the end of the quarter-wavelength lines, the proposed 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> tunable coupler finally features fast and accurate wide PDR switching ranges and wide bandwidth. Good performances in return loss, isolation, insertion loss, phase differences, and amplitude imbalances can be achieved for all states. For verification, a 90 <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> coupler and a tunable 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> coupler are designed, simulated, and measured. The measured results match well with the simulated results, validating the proposed design theory.