Signal Fidelity in Degenerate and Nondegenerate Mode Parametric Amplifier Receiving Antennas

TL;DR

This paper analyzes the fidelity of signals received by electrically small antennas loaded with time-varying parametric elements, comparing degenerate and non-degenerate mode designs under practical $16$QAM signals. It combines MoM-based impedance modeling with harmonic balance and transient simulations to show that degenerate mode introduces a phase-dependent idler-signal interference within the output band, degrading symbol fidelity despite apparent bandwidth gains. The results demonstrate that non-degenerate parametric reception yields better information throughput and more stable fidelity than degenerate designs, which can exhibit phase-dependent distortions and elevated EVM for QAM-based schemes. These findings challenge the sufficiency of conventional bandwidth and received power metrics for evaluating degenerate parametric receivers and point to mitigation strategies such as phase-incoherent designs or balanced architectures to preserve signal integrity in practical communications.

Abstract

The gain, received power bandwidth, transient characteristics, and signal fidelity of two time-varying electrically small antennas based on parametric amplifier design are studied using practical QAM signals. Results show that interference from the difference harmonic present in the response of degenerate-mode parametric amplification decreases its signal throughput relative to a reference linear time-invariant (LTI) receiver, despite its apparent increased received power bandwidth in the frequency domain. The analysis also demonstrates that a non-degenerate parametric receiver, lacking this detrimental effect, exhibits increased signal throughput over the reference LTI receiver.

Figures (6)

• Figure 1: Loop antenna and incident plane wave modeled as a two-port network $\mathbf{Z}_\mathrm{ant}$ and voltage sources $v_1$ and $v_2$ with L matching network. For the LTI design, $C(t)$ is static and $R_\mathrm{c}=0$.
• Figure 2: Received power as a function of frequency, computed using CMMoM, HB, and transient methods. Markers for CMMoM and HB simulations indicate power at 100 MHz for the DTV design with power from the idler harmonic included.
• Figure 3: Magnitudes of baseband step responses $y(t,\phi)$ from each design under varying input signal phases, relative to the pump signal. All incident phases lead to identical LTI and NDTV responses, while the DTV system has a phase-dependent characteristic, leading to multiple unique traces.
• Figure 4: Noise-free, unequalized constellations from each system using a 2048-symbol 16QAM PRBS at 0.5 Msym/s.
• Figure 5: Post-equalization EVM for each system at varying data rates in the presence of AWGN. A constant internal noise temperature was used across each data rate and system, with the LTI system showing SNR $\approx$ 30 dB at 0.25 Msym/s.