Dual-band Butler matrix for WLAN systems

This paper shows the design of a dual-band Butler matrix aimed to cover the bands corresponding to the standards IEEE802.11a/b, with particular interest in WLAN systems, at the 2.4 GHz and 5 GHz bands. Measurements of the individual dual-band components which compose the Butler matrix are presented. Those components are: quadrature hybrid and 0 dB coupler. The phase shifter design is also described. A final design of the Butler matrix is proposed and measured. Over the proposed frequency range, the Butler matrix exhibits phase errors and couplings of within 13.5° and - 6.7 ± 0.8 dB, respectively. A performance prediction of the Butler matrix connected to an array of isotropic and perfectly matched antennas separated half-wavelength in air is also briefly commented.