Comparative D/Q and Characteristic Mode Analysis (CMA) of Rectangular and Circular Microstrip Patch Antennas for Bandwidth Optimization

The concept of antenna performance characterization has recently been fundamentally augmented to include its near and far field behavior in terms of its impedance (or the quality factor, Q) and directivity (D) parameters, respectively, obtained through full-wave (MoM) solutions. Separately, the antenna performance is also quantified through characteristic mode analysis (CMA) by computing the modal significance from the MoM solution. These two generally different approaches, have been applied here to probe-fed rectangular and circular microstrip patch antennas for a comparative assessment of their respective 2: 1 VSWR bandwidth enhancement characteristics. This assessment is carried out by following an earlier approach of coaxial feed location optimization, and it is shown here numer-ically and experimentally to yield a 2:1 VSWR bandwidth of 33% for rectangular microstrip patches designed on $\epsilon_{r}=6$ substrate (TMM-6). Following a similar approach, the preliminary results here show that the circular patch produces far less bandwidth than a rectangular patch subject to the same design optimization method. The results have a significant impact in practical design of electrically small patch antennas with restricted SWaP (Size, Weight and Power) criteria.