Low-profile triple-band microstrip antenna via sharing a single multi-mode patch resonator

A low-profile microstrip patch antenna (MPA) operating in triple WLAN bands (2.4 /5.2 /5.8 GHz) with stable broadside radiation is proposed by employing TM10, TM12, and TM30 modes. Firstly, the TM12 mode of the MPA could be excited at around 5.8 GHz by properly selecting its dimensions. Meanwhile, a linear slot is etched out at the center of the radiating patch to transform the radiated fields of TM12 and TM30 modes into the broadside radiation with low sidelobe level. Secondly, the shorting pins are symmetrically loaded underneath the patch, aiming to improve the input impedance matching of TM10 mode and push up its resonant frequency to around 2.4 GHz. Thirdly, a pair of parallel slots is near the radiating edges of the patch radiator, thus extending the surface current distribution of TM30 mode and reallocating its resonant frequency to around 5.2 GHz. In final, the prototype antenna is fabricated and measured to validate its working principle. The results illustrate that this low-profile MPA makes these three radiative modes resonate at around 2.44, 5.22, and 5.82 GHz, respectively. Most importantly, a stable normal radiation pattern with low cross-polarisation and sidelobe levels is maintained for the proposed antenna as well.