On the Design Consideration for Prototyping of Flexible Phase-difference Butler Matrix

A design of an easily implemented flexible phase difference (F-PD) Butler matrix is discussed. To address the difficulty of circuit realization, a suitable dielectric material is carefully selected considering the operating frequency and requirements of microstrip line dimensions, hence a 0.406 mm thick RT/Duroid RO4003C dielectric substrate is chosen. To verify the design, a 2.4 GHz circuit prototype is realized for the measurement. Several key performances of Butler matrices, including transmission coefficients, reflection coefficients, and progressive phase differences are characterized experimentally. Measurement results demonstrate that when the input port of P1 is excited, the reflection coefficients are less than −10 dB within a 200 MHz (8.33%) bandwidth. Along the same bandwidth, the transmission coefficients are more than −9 dB and the progressive phase differences of −30° with small phase imbalances of ±12° are achieved.