NOVEL PHASE-SHIFTING CHARACTERISTIC OF CRLH TL AND ITS APPLICATION IN THE DESIGN OF DUAL-BAND DUAL-MODE DUAL-POLARIZATION ANTENNA

The phase-shifting characteristic of a novel composite right/left handed transmission line (CRLH TL) for two frequency points is analyzed in this paper. Samples of (90 degrees, 0 degrees) and (180 degrees, 0 degrees) phase-shifting TLs for two frequency points (f(1), f(2)) are deigned and the total length of the CRLH TLs has decreased by more than 77% compared to the conventional microstrip lines. Then a four way power divider made by three Wilkinson power dividers and interconnected with the (90 degrees, 0 degrees) and (180 degrees, 0 degrees) phase-shifting TLs is designed to feed an antenna with two different operating modes at two different frequency bands. Four radiating patches arranging symmetrically in a loop are printed in an upper substrate and connected with the four outputs of the feed network by four copper pins. When the four rectangular patches are excited by four sources with equal amplitude and phase at f(1), metamaterial antenna with conical beam and linear polarization (LP) is achieved; while four sources with equal amplitude but 90 degrees phase difference for each adjacent output at f(2) leads to wideband antenna with broadside beam and circular polarization (CP). One antenna prototype with dual-band dual-mode dual-polarization property is fabricated and good agreements between simulation and measurement results are obtained. This single-feed patch antenna is valuable in wireless communications for its radiation pattern selectivity and polarization diversity.