Dual-Mode Loop Antenna With Compact Feed for Polarization Diversity

Design, prototyping, and testing of a dual-polarization loop antenna is presented for possible use in wireless local area network (WLAN) applications. The antenna design consists of a rectangular loop, a coplanar waveguide (CPW), and a microstrip line. The loop antenna operates in two orthogonal one-wavelength modes, which are excited by one CPW feed structure. The overall dimension of the prototype is only 40 × 53 mm², including the feed structure. The measured -10-dB reflection coefficients bandwidth of the two modes are 770 MHz (32.1%) and 730 MHz (30.4%) at the operating frequency of 2.4 GHz. In the WLAN band, the ports isolation is better than -21.3 dB. Gains of the two modes are better than 2.9 and 4.1 dBi. Radiation patterns are measured and compared to simulation results. The proposed antenna has the advantages of compact dimension, wide bandwidth, good ports isolation, and low cross polarization.