A Reconfigurable Antenna With Sum and Difference Patterns for WLAN Access Points

This letter presents a reconfigurable antenna with sum and difference patterns for the applications of wireless local area network (WLAN) access points. The proposed antenna consists of a 2 × 2 circularly polarized (CP) stacked-patch antenna array and a switchable monopulse comparator network. Utilizing this comparator network to excite the CP antenna array, sum, azimuth difference, elevation difference, and bidifference beams are produced and can be switched by controlling the dc voltages on the p-i-n diodes. Measurement reveals that the antenna's return loss is better than 10 dB in the frequency ranges of 2.26-2.58 GHz, 2.24-2.62 GHz, 2.25-2.61 GHz, and 2-3 GHz at the sum, azimuth difference, elevation difference, and bidifference modes, respectively. The measured axial ratios, gains, and radiation patterns also show that this antenna can be applied to enhance the communication-area coverage capability for WLAN access points.