Bandwidth enhancement and size reduction of microstrip slot antennas

Reduced size microstrip monopole slot antennas with different slot shapes-straight, L and inverted T, and placed on a small ground plane, are investigated. The ground plane size is 50 mm×80 mm, which is about the size of a typical PC Wireless card. Detailed simulation and experimental investigations are conducted to understand their behavior and optimize for broadband operation. It is shown that, the variation in the slot shape, from straight to L and T shapes, helps in generating additional resonances, which when coupled to the original resonances of the slot, further increases impedance bandwidths. The bent shapes of the L and T slots reduce their height and provide more space on the ground plane for electronics. A mirror image dual L-slot antenna, placed at two adjacent corners of the ground plane, is also investigated and optimized for the polarization diversity. They provide an impedance bandwidth of 87%, with near orthogonal radiation characteristics. The measured impedance bandwidths (S₁₁=-10 dB) of up to 60%, 84%, and 80% are achieved for these straight, L and inverted T slots respectively, by suitably selecting their design parameters. The simulation results are in good agreement with the experimental data considering several practical issues.