Multiport characteristics of a wide-band cavity backed annular patch antenna for multipolarization operations

This paper focuses on the multiport characterization of antennas. In particular, special attention is given to the cavity backed annular patch antenna (CABAPA) for multipolarization operations. We will show that the reflection coefficient is not the best representative parameter to determine the frequency response of the multiport antenna and its radiation performance. Therefore, we seek a new generalized parameter that conveys the frequency response of multiport antennas. The total active reflection coefficient (TARC) is introduced as the square root of the sum of all incident powers at the ports minus radiated power, divided by the sum of all incident powers at the ports. The TARC is a function of frequency and is a real number between zero and one. With this definition we can characterize the multiport antenna´s frequency bandwidth and radiation performance. A method for calculating the TARC is detailed for different port excitations directly from the scattering matrix of the antenna and independent of the feeding network. First, the CABAPA is analyzed by the method of moments. Next, the corresponding scattering matrix is employed to calculate the TARC for different polarizations. The calculated results, when compared to the measured results, show good agreement. The measured -10 dB TARC bandwidth of the CABAPA is 30% compared with 68% as measured using only the s₁₁.