Broadband Beam-Forming Circuit Using Microstrip Multilayer Couplers

Multipath antenna arrays require broadband small-sized beam-forming circuits for its implementation. For Butler matrix circuits implemented on the basis of directional couplers, the embodiments are developed of broadband power tap devices using coupled lines. However, as a rule, the current topologies feature relatively large amplitude unbalance within the working frequency band. In order to reduce the flatness of both the working attenuation and the transient attenuation, a microstrip topology is developed of the multilayer directional coupler using coupled lines. Distinctive feature of this topology is the uncommon configuration of the coupling aperture. The coupling aperture shape is optimized within the 4-8 GHz frequency band according to the criterion of the minimum deviation of the amplitude-frequency characteristics from the idealized values. Within the octave band the developed coupler features the flatness of the working attenuation and the transient attenuation of 0.6 dB as well as the phase unbalance equal to 1.2°. The maximum overall size of the coupler topology does not exceed a quarter of the wavelength. Based on the coupler the four-beam beam-forming Butler circuit is developed. The results of both electrodynamic simulation of the circuit and the experimental studies of the made model are presented. It is determined that they are in good agreement with each other. The experimental values of the transient droop and the operating attenuation of the matrix circuit deviate from the level of 6 dB by no more than 2.5 dB. The maximum phase imbalance does not exceed 8° from the nominal value.