Bandwidth Enhancement of Microstrip Antennas using Crossing Avoidance of Characteristic Modes

In this paper, a method of designing antennas by avoiding crossing between the modes is presented. This is aimed at enhancing antenna bandwidth using ground fragmentation techniques based on the characteristic modes analysis (CMA) approach. A compact and flexible Saxophone antenna and a conventional rectangular microstrip antenna both dimensioned at 30 x 30 mm(2) (0.66 lambda(g) x 0.66 lambda(g)) are designed to operate at 5.8 GHz to validate the proposed method. The proposed saxophone structure with a full ground enhances the bandwidth up to 170 MHz (2.97%) relative to the conventional antenna. This is then improved up to 890 MHz (14.67%) and 794 MHz (13.58%) when integrated with a fragmented and a partial ground plane, respectively. In comparison, the conventional antenna exhibited a bandwidth of 360 MHz (6.38%) and 410 MHz (7.25%) for these cases. Modeling is performed using FEKO software based on two approaches: the method of moments (MoM) and CMA. Results show a satisfactory agreement of the predicted resonant frequencies from simulations and measurements.