Extension of Butler Matrix Number of Beams Based on Reconfigurable Couplers

A scheme to extend the beam number of Butler matrices (BMs) by utilizing reconfigurable couplers is presented and illustrated with experimental verification. The beam number of a traditional 2(N) x 2(N) BM can be increased to 3 . 2(N) by substituting reconfigurable couplers for all hybrids while maintaining the structure and other components as the original. Moreover, only N sets of different parameters are required for these couplers. The principle, properties, and the generalized expressions for the N sets of parameters are discussed and exhibited. The properties of the extended beams are illustrated in terms of beam directions and crossover levels. As an example, a switchable 12-beam forming network extended from a 4 x 4 BM for 2.4 GHz applications is fabricated and tested. Over a 30% relative bandwidth is achieved with phase errors less than +/- 12 degrees, amplitude unbalances lower than +/- 1.7 dB, isolations better than -15.5 dB, and a return loss better than 11.5 dB.