A Miniaturized Broadband 1 × 4 Filtering Butler Matrix With 360° Continuous Progressive Phase Shift and Simplified Control

This article presents a novel, miniaturized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 \times 4$ </tex-math></inline-formula> filtering Butler matrix (BM) that provides 360° continuous progressive phase shift with a simplified control mechanism for broadband applications. The proposed filtering BM, which comprises a power-division module, a fixed-phase shift module, and a continuous-phase shift module, is based on a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 \times 4$ </tex-math></inline-formula> BM topology with two integrated single-pole-double-throw (SPDT) switches in place of a single-pole-four-throw (SP4T) switch in conventional design for miniaturization. The use of conductor-backed coplanar waveguide (CB-CPW)-based crossovers in the fixed-phase shift module enables a reduction in size, an enhancement in isolation, and an improvement in the balance of the output amplitude. To realize a 360° continuous progressive phase shift and a filtering frequency response, two phase shifters (PSs) with a continuous phase shift of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$135^{\circ } ~\pm ~8^{\circ } $ </tex-math></inline-formula> are used in the power-division module and four filtering phase shifters (FPSs) with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$90^{\circ } ~\pm ~5^{\circ } $ </tex-math></inline-formula> continuous phase shift are used in the continuous-phase shift module. The FPSs which are based on a composite right/left-handed transmission line (CRLH-TL) and coupled resonators demonstrate good out-of-band suppression performance when phase shifting. The combination of the three modules results in the formation of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 \times 4$ </tex-math></inline-formula> BM operating at 2.1–2.7 GHz, which offers a 360° continuous phase shift and a filtering frequency response. The simulated and measured results demonstrate the validity of this design method for continuous tunable <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$360^{\circ } ~1 \times 4$ </tex-math></inline-formula> filtering BM.