Compact broadband Butler matrix in multilayer technology for integrated multibeam antennas

A compact broadband low-loss 4×4 Butler matrix is presented, for the first time in multilayer asymmetric technology. A coupled-line 3 dB compensated microstrip multilayer directional coupler is utilised as a basic element of the Butler matrix. Excellent performance is achieved over one-octave frequency band in terms of amplitude and phase responses. A tandem connection of two 3 dB directional couplers with reference lines is used as a crossover of transmission lines giving, additionally, the needed broadband 45° phase shift; moreover, no interlayer connections are necessary. The network can be easily applied in integrated planar and conformal multibeam antenna arrays as a surface mount element.