Extension of Butler Matrix Number of Beams Based on Reconfigurable Couplers

• Published in: IEEE transactions on antennas and propagation Vol. 67; no. 6; pp. 3789 - 3796
• Main Authors: Ding, Kejia, Kishk, Ahmed A.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antenna array feeds; Bandwidth; Beamforming; Butler matrices; Complexity theory; Couplers; Crossovers; directional couplers; multibeam antennas; Parameters; Phase shifters; reconfigurable antennas; Reconfiguration; Switches
• ISSN: 0018-926X; 1558-2221
• DOI: 10.1109/TAP.2019.2902668

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 <inline-formula> <tex-math notation="LaTeX">2^{N} \times 2^{N} </tex-math></inline-formula> BM can be increased to <inline-formula> <tex-math notation="LaTeX">3\cdot 2^{N} </tex-math></inline-formula> 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 <inline-formula> <tex-math notation="LaTeX">4\, \times \, 4 </tex-math></inline-formula> BM for 2.4 GHz applications is fabricated and tested. Over a 30% relative bandwidth is achieved with phase errors less than ±12°, amplitude unbalances lower than ±1.7 dB, isolations better than −15.5 dB, and a return loss better than 11.5 dB.