A Low-Profile Microstrip Patch Antenna With Enhanced Bandwidth and Pattern Diversity Using Even- and Odd-Order Modes

A low-profile microstrip patch antenna with pattern diversity is proposed. In our design, even- and odd-order modes are employed to enhance the impedance bandwidth for the conical and broadside radiation beams, respectively. Initially, an array of concentric shorting pins is introduced to reallocate the resonant frequencies of TM01, TM11, and TM02 modes closely to each other. Then, a longitudinal slot and a novel metallic disk are utilized to reduce the frequency of its TM12 mode, while their influences on the antenna gain are extensively studied. Moreover, two original shorting pins are modified to further push up the resonant frequency of TM01 mode. Furthermore, in-phase and out-of-phase signals provided by the feeding scheme are introduced to excite even- and odd-order modes, respectively, thus guaranteeing the high isolation and realized gain. Finally, a prototype is fabricated and measured to verify the simulated results. Good agreements between the measured and simulated results are observed, indicating good performances with a wide overlapped impedance bandwidth of around 9% ranging from 2.38 to 2.60 GHz and a high gain of around 6.5 dBi for the conical beam and 8.8 dBi for the broadside beam. Most importantly, these attractive performances are obtained with a low profile of only 0.033 lambda(0) (lambda(0) is the wavelength at 2.49 GHz).