A BIDIRECTIONAL CIRCULARLY POLARIZED ARRAY OF THE SAME SENSE BASED ON CRLH TRANSMISSION LINE

A bidirectional circularly polarized array of the same sense is proposed. The implementation is a combination of end-fire array, crossed dipoles, and composite right/left-handed transmission line (CRLH-TL). The proposed array consists of four dipoles spaced at a distance equal to lambda(0)/4 (lambda(0) is the wavelength in free space at the center frequency). For the bidirectional circular polarization of the same sense, the four dipoles are fed in-phase in a series-fed structure. A feed line that exhibits 0 degrees phase shift every lambda(0)/4 is needed. To satisfy the demand for the space distance and phase distribution in a series-fed array, the CRLH unit cell composed of lumped capacitors and inductors is employed and inserted in the feed line. Theoretical analysis is performed based on the balanced parallel stripline and design equations are presented for the determination of the lumped element parameters. The design method can be used in the design of the arrays with more elements. From the experimental results, the array offers a 4.2 dBic bidirectional circular polarization gain. The bandwidth between which the impedance matching is better than -10 dB and the axial-ratio is better than 3 dB is 300 MHz from 2.39 to 2.69 GHz.