5. Evaluation of the Transient Performance of Super-Wideband Printed-Circuit Antennas Using Time-Domain Electromagnetics

A time-domain electromagnetics code is used to evaluate the transient and radiation performances of three printed-circuit antennas for super-wideband (SWB) monitoring applications. For two antennas, one in microstrip and one in coplanar technologies, operating between 3 and 30 GHz with a return loss of 10 dB, it is demonstrated that the vertically polarized omnidirectional radiation characteristics in the lower frequency band change to a more directional pattern at higher frequencies and that the cross-polar field component increases with frequency and gives rise to possible dual-polarized applications for the microstrip antenna. In comparison, the coplanar antenna shows slightly better performance, especially with respect to its transient response. Its group-delay variation is only 180 ps compared to 250 ps of the microstrip antenna, and its amplitude response provides better polarization purity. The evaluation of the coplanar concept is extended to cover a bandwidth between 3 and 60 GHz. The time-domain evaluation, as validated by a frequency-domain technique, demonstrates that bandwidths in extent of decade bandwidths are possible with simple printed-circuit antennas. Characteristics and performances are presented for possible applications in future SWB monitoring systems, radar technology, through-wall imaging systems, and other future wireless services. Antenna dimensions are provided for future comparisons with improved and/or multi-level electromagnetics codes.