An Extended $4 \times 4$ Butler Matrix With Enhanced Beam Controllability and Widened Spatial Coverage

A new beam-switching array system, capable of providing four sets of switchable beams, is proposed and demonstrated. The core building block for fulfilling the design is the phase reconfigurable synthesized transmission line (PRSTL), whose electrical length is switched between two states as a 1-bit phase shifter. By cascading the PRSTLs to the outputs of a standard Butler matrix, the progressive phase shifts between adjacent antenna elements can be controlled in a variety of fashions. The new design aims to provide a low-complexity solution to expand the beam controllability as well as spatial coverage of a conventional beam-switching system. As a demonstration, an extended 4 × 4 Butler matrix, with 16 switchable beams, is realized using microstrip technology. The average transmission loss of the feed network is acceptable as 1.7 dB. In the measurement, the linear array shows an equivalent half-power beamwidth of 118°, covered by 13 beams, with the peak gain varying from 7 to 10 dBi. The gain ripple within the equivalent beamwidth is less than 0.9 dB. The output 1-dB compression point (P
_{1 dB}
) is measured as 29.5 dBm, and the dc power consumption is very low (microwatts) in all switching states.