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.Comment: 8 pages, 8 figure

Modal analysis of radiation and energy storage mechanisms on conducting scatterers

The manifestation of radiation and stored energy by electric currents on conducting bodies is studied via modal expansions. The novel modal expansions are based on the quadratic operators which map a current distribution to each quantity. Adaptations of the continuous forms of these operators into the Method of Moments is reviewed. The discrete modal expansions are studied on several example objects, leading to conclusions regarding the sparsity of the radiation mode spectrum. Analytic forms for the sparse radiation modes on electrically small objects are derived. Negative energy current distributions are studied using the energy storage modal expansions. The role of ground plane radiation on the determination of an embedded antenna's Q factor is studied using radiation modes, giving a new perspective on the convergence behavior of this parameter with respect to ground plane size. Leveraging the invariance of radiation modes on small objects, an example procedure for the design of an embedded antenna array using radiation modes is presented

Optimal Planar Electric Dipole Antenna

Considerable time is often spent optimizing antennas to meet specific design metrics. Rarely, however, are the resulting antenna designs compared to rigorous physical bounds on those metrics. Here we study the performance of optimized planar meander line antennas with respect to such bounds. Results show that these simple structures meet the lower bound on radiation Q-factor (maximizing single resonance fractional bandwidth), but are far from reaching the associated physical bounds on efficiency. The relative performance of other canonical antenna designs is compared in similar ways, and the quantitative results are connected to intuitions from small antenna design, physical bounds, and matching network design.Comment: 10 pages, 15 figures, 2 tables, 4 boxe

Iterative Calculation of Characteristic Modes Using Arbitrary Full-wave Solvers

An iterative algorithm is adopted to construct approximate representations of matrices describing the scattering properties of arbitrary objects. The method is based on the implicit evaluation of scattering responses from iteratively generated excitations. The method does not require explicit knowledge of any system matrices (e.g., stiffness or impedance matrices) and is well-suited for use with matrix-free and iterative full-wave solvers, such as FDTD, FEM, and MLFMA. The proposed method allows for significant speed-up compared to the direct construction of a full transition matrix or scattering dyadic. The method is applied to the characteristic mode decomposition of arbitrarily shaped obstacles of arbitrary material distribution. Examples demonstrating the speed-up and complexity of the algorithm are studied with several commercial software packages.Comment: 5 pages, 2 figures, 2 algorithm