Design of a Broadband Circularly Polarized Antenna by Using Axial Ratio Contour

A novel method of using axial ratio (AR) contour to design a broadband circularly polarized (CP) antenna is presented in this letter. By resolving a radiated CP wave into two orthogonal far-field components, the resulted AR will be determined by the radiated power and phase differences between the two orthogonal components. Therefore, a series of AR contours can be obtained for different AR values of the radiated wave. In the AR contour, details of phase-advance, phase-lag, power-advance, and power-lag can be simultaneously observed along with the resulted AR. Based on these analyses, the AR contour is first utilized to directly design a broadband CP antenna instead of using the traditional AR versus frequency curve to achieve optimal AR bandwidth. Compared to the traditional AR curve, the method of using AR contour to design CP antenna is more effective and informative. The designed broadband CP antenna was also fabricated and measured for the final performance verification.