Two-Tone Suppressed Third-Order Intermodulation Transponder Based on Transmission-Line-Based Fourth-Order Filter Combined Matching Network

This paper presents a 3^{rd} -order intermodulation transponder designed to achieve high suppression of fundamental two-tone signals simultaneously. In previous papers, a nonlinear response system combining matching and suppression has never been considered. The core innovation lies in the proposed output matching network, which effectively shifts the output impedance of the diode to the load impedance at the target intermodulation frequency of 2.3 GHz and to short at the fundamental frequencies of 2.4 and 2.5 GHz. It achieves a high conversion gain and provides a substantial isolation between a two-tone fundamental input port and an intermodulation output port through a sharp band-pass filtering characteristic. For validation, we fabricate and measure the proposed intermodulation transponder with dimensions of 72.5\times53 mm2. The measurement results demonstrate a peak conversion gain of −26 dB at an input power of 8 dBm and an intermodulation frequency of 2.3 GHz. Furthermore, the proposed transponder exhibits suppression characteristics of at least −7 and −23 dBc for the two-tone signals at 2.4 and 2.5 GHz, respectively. A conversion gain of over −30 dB is maintained across an input power range of 3-19 dBm at 2.3 GHz.