Stability Analysis and Design of a Negative Resistance Amplifier in Microwave and Radar Communication Systems

This paper presents a Negative Resistance Reflection Amplifier (NRRA) design for loss compensation in Negative Group Delay (NGD) networks. The NRRA uses microwave transistors in negative resistance mode, outperforming conventional amplifiers with higher gain in controlled bandwidth and better noise performance. The study presents a comprehensive design methodology combining full-wave simulations and experimental validation. Simulation results demonstrate exceptional performance, with the reflection amplifier achieving a peak reflection gain of 25.84 dB at 1.29 GHz and maintaining negative resistance characteristics across a 0.5-2GHz frequency range. The reactive impedance component was successfully minimized to near-zero levels between 1.2-2 GHz through strategic implementation of gate-tuning capacitors. Experimental validation confirmed stable operation with 15dB gain after implementing critical stability enhancements, including optimized low-pass filters (1nF feed-through capacitors) and a redesigned biasing network (1kΩ gate resistor, 10Ω drain resistor). Nyquist stability analysis (STABN_GP2 in Microwave Office) confirmed robustness, with no encirclement of the -1 point. Initial 30 MHz oscillations (500 MHz-3 GHz) were eliminated through component optimization. While the prototype demonstrates excellent gain performance, the study identifies a fundamental trade-off between gain and bandwidth, with the current design limited to narrowband applications. These results represent important progress in active microwave circuits, particularly for applications requiring precise loss compensation in NGD networks and antenna matching applications where both transmit and receive capabilities are required. Finally, the paper concludes with specific recommendations for future bandwidth enhancement through alternative transistor configurations and advanced biasing techniques.