Non-Foster Matched Antennas for High-Power Applications

A non-Foster matching network has been designed for a small cylindrical slot antenna, and its broadband matching capability has been examined at varying signal power levels. It has been observed that the non-Foster circuit (NFC) impedance changes considerably as the signal power increases, thus reducing its matching capability as well as introducing stability problems. To analyze its true advantage in transmit applications, the third-order intermodulation output intercept point (OIP3) and the gain-bandwidth product of the non-Foster matched antenna have been compared with the unmatched antenna, when both are attached to the same power amplifier. Simulations show that the unmatched antenna has a higher OIP3 and gain-bandwidth product, despite being more poorly matched. Although the OIP3 can be slightly improved by increasing the bias current of the NFC, improved linearization techniques should be studied to offset distortion effects in NFCs.