Hybrid antenna efficiency measurements in fixed-geometry wheeler caps by wideband Q-factor estimation

An end-to-end methodology for wideband efficiency measurements in fixed-geometry Wheeler caps is described. The post-processing of measured data is based on a modified Q-factor method, which exploits inherently wideband Q-calculation formulas that are based on frequency derivatives of antenna input impedance and on the concept of matched VSWR bandwidth. The wideband WCap/Q-factor method is useful both for narrowband and wideband antennas, regardless of whether the latter exhibit closely or widely spaced multiple (anti)resonances. Experimental verification of the method includes the characterization of a small antenna in a 40%-wide, cavity-resonance-free band, as well as the measurement of a multi-band antenna in an 8:1 band (156%). Despite the bandwidth, the requirements for the hybrid WCap/Q-factor method are a properly designed cavity and two full-band input impedance measurements on a vector network analyzer.