Design of Low-Power Pass Filter for Energy Selective Antenna Back-End Protection

In this study, spoof surface plasmon polariton (SSPP)–based low-power pass filter is designed to provide dual protection to a receiver operating at the back end of an energy-selective antenna (ESA). The proposed filter operates without any external DC power supply or bias circuit and uses a PIN diode (SMP1345-079LF) whose on/off state is determined by the incident signal power level. Under low-power conditions, the filter exhibits a passband characteristic with an insertion loss of approximately 2 dB over the 2.0～2.6 GHz frequency range, whereas under high-power conditions, a strong blocking performance with S21=−57.6 dB at 2.3 GHz and a −10 dB bandwidth of 300 MHz is achieved. The filter is implemented by arranging a total of ten SSPP unit cells and realized on an FR4 substrate with a thickness of 1.0 mm for ease of fabrication. To verify the designed performance, the proposed filter is fabricated using an LPKF, and the measurement results confirm that the desired low-power transmission and high-power blocking characteristics are effectively achieved in the target frequency band.