Broadband Circularly Polarized Spiral Antenna Array Using Sequentially Rotated Technique

A circularly polarized (CP) spiral antenna array for wideband application is presented, which employs a simple single-arm spiral antenna (SASA), as the radiating element. By introducing a small round disc backed near the antenna center and loading a termination resistor, the SASA achieves a wide impedance bandwidth without a balun circuit and a good axial ratio (AR) performance, respectively. A total of four array elements are used in the 2 x 2 configuration to obtain a higher gain. Particularly, a method of sequentially rotating the elements is used to improve the axial ratio. The array performs an impedance bandwidth for VSWR <= 1.5 of 40% ranging from 1.25 to 1.88 GHz, an excellent AR of better than 0.74 dB, and a gain variation from 11.34 to 14.56 dB within the operating band. Measured and simulated results presented for the array confirm its wide impedance, axial ratio, and gain bandwidths. Acceptable agreement between the simulation and measured results validates the proposed design.