Threedimensional effects for radio frequency antenna modeling
Abstract
Electromagnetic field calculations for radio frequency (RF) antennas in two dimensions (2D) neglect finite antenna length effects as well as the feeders leading to the main current strap. Comparisons with experiments indicate that these 2D calculations can overestimate the loading of the antenna and fail to give the correct reactive behavior. To study the validity of the 2D approximation, the Multiple Antenna Implementation System (MAntIS) has been used to perform 3D modeling of the power spectrum, plasma loading, and inductance for a relevant loop antenna design. Effects on antenna performance caused by feeders to the main current strap, conducting sidewalls, and finite phase velocity are considered. The plasma impedance matrix for the loading calculation is generated by use of the ORION1D code. The 3D model is benchmarked with the 2D model in the 2D limit. For finitelength antennas, inductance calculations are found to be in much more reasonable agreement with experiments for 3D modeling than for the 2D estimates. The modeling shows that the feeders affect the launched power spectrum in an indirect way by forcing the driven RF current to return in the antenna sidewalls rather than in the plasma as in the 2D model. Thus, the feeders have much more influence than the plasma on the currents that return in the sidewall. It has also been found that poloidal dependencies in the plasma impedance matrix can reduce the loading from that predicted in the 2D model. For some plasma parameters, the combined 3D effects can lead to a reduction in the predicted loading by as much as a factor of 2 from that given by the 2D model.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 September 1993
 Bibcode:
 1993STIN...9430105C
 Keywords:

 Antenna Design;
 Antenna Radiation Patterns;
 Cyclotron Resonance;
 Electromagnetic Fields;
 Loop Antennas;
 Plasma Currents;
 Plasma Heating;
 Radio Antennas;
 Radio Frequencies;
 Three Dimensional Models;
 Electrical Impedance;
 Estimates;
 Inductance;
 Maxwell Equation;
 Phase Velocity;
 Two Dimensional Models;
 Communications and Radar