Distortion Analysis for the Assessment of LTI and Non-LTI Transmitters

Bounds on the frequency domain behavior of electrically small antennas are adapted to assess the time-domain distortion or fidelity achievable by simple linear time-invariant (LTI) systems. Rigorous expressions for a TM
₀₁
spherical shell are used as a direct analog to the well-known Chu limit on an antenna's bandwidth-efficiency product. These expressions are shown to agree with results obtained using narrowband single resonance approximations, allowing for the analysis of arbitrary small dipole-like structures through bounds on their single-frequency Q-factor and efficiency. The resulting expressions are used as a basis for assessing the performance gains of electrically small non-LTI (e.g., direct antenna modulation) transmitters for which Q-factor and impedance bandwidth are not defined but which can be analyzed directly in the time domain via distortion.