Modeling and Control of Internal Oscillations in Energy-Synchronous Direct Antenna Modulation.

Internal oscillations in switched antenna transmitters cause undesirable fluctuations of the stored energy in the system, which is critical to the concept of energy-synchronous direct antenna modulation. A detailed circuit model for a direct antenna modulation system is proposed that includes the high frequency parasitics that lead to these oscillations. Analytical and numerical studies show that the proposed model accurately predicts the oscillations of the system and the resulting signal degradation. To mitigate the parasitic oscillations, a modified direct antenna modulation system with an auxiliary DC source is introduced to stabilize the stored voltage on the antenna. Measured phase shift keyed waveforms transmitted by the modified system show significant increases in signal fidelity, including a 10-20 dB decrease in error vector magnitude compared to an LTI system. Comparison to an equivalent, scalable time-invariant antenna suggests that the switched transmitter behaves as though it has 2-3 times lower Q factor bandwidth and 20% higher radiation efficiency.