The paper studies the method of using a ground slot for bandwidth improvement of compact ultra-wide band (UWB) antennas with microstrip line feed. Slots of different shapes such as triangular, rectangular, partially circular and hexagonal, placed on the ground plane under the feed line of the radiator are studied for impedance matching. The effects of the slots on the performances of the antennas, in terms of impedance bandwidth, radiation pattern, gain, and efficiency, are studied. Results of simulation tests show that a ground slot with proper dimensions placed under the feed line can improve the impedance matching and hence increase the bandwidth without affecting much the performance of the antenna. Results of studies also show that, by using a hexagonal slot on the ground plane under the feed line, a patch antenna with a compact size of 35mm × 23mm can achieve a bandwidth of 3.1-16.3 GHz for S -10 dB. Moreover, it has a stable omnidirectional radiation pattern across the whole bandwidth and achieves an average gain of 2.8 dBi and an average efficiency of about 88% across the UWB.
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