A Novel Calibration-Free Remote Antenna Impedance Measurement

Abstract

Connecting the antenna under test (AUT) to a network analyzer through a feeding cable is a typical method for determining the input impedance. However, the induced current on the feeding cable obstructs precise measurement in the case of electrically small antennas (ESAs). A remote impedance measurement technique is proposed to address the drawbacks of network analyzer-based measurements. First, the AUT is connected to three standard loads, a short, an open, and a matched load consecutively. Then an electrostatic discharge (ESD) is used as an impulsive source to excite the AUT. Concurrently, a probe connected to an oscilloscope captures the impulse responses. Finally, the input impedance of the AUT is determined by extracting complex natural resonances (CNRs) from three impulse responses. Four different antennas are designed and prototyped. Then, using a full-wave simulator, their input impedances are computed and compared to those estimated using the proposed technique. The input impedances obtained by the proposed technique are very consistent with those from full-wave simulations.