A Low-Profile Wide-Bandwidth Planar Inverted-F Antenna Under Dual Resonances: Principle and Design Approach

A low-profile planar inverted-F antenna (PIFA) under the operation of TM_0,1/2 and TM_2,1/2 modes in a single patch resonator for bandwidth enhancement is proposed. Initially, our study demonstrates that all of the even-order modes can effectively be suppressed by employing a rectangular PIFA instead of the conventional microstrip patch antenna. Then, a pair of shorting pins is appropriately loaded underneath the side-shorted radiating patch to investigate the variation of their odd-mode resonant frequencies. The results indicate that the resonant frequency of TM_0,1/2 mode (<inline-formula> <tex-math notation="LaTeX">$f_{0,1/2}$ </tex-math></inline-formula>) is dramatically increased up while almost maintaining that of TM_2,1/2 mode (<inline-formula> <tex-math notation="LaTeX">$f_{2,1/2}$ </tex-math></inline-formula>). After that, the width of the radiating patch is progressively enlarged in order to move the <inline-formula> <tex-math notation="LaTeX">$f_{2,1/2}$ </tex-math></inline-formula> more closely to the <inline-formula> <tex-math notation="LaTeX">$f_{0,1/2}$ </tex-math></inline-formula>. By using this approach, the dual radiative resonant modes can be reallocated in proximity to each other. Additionally, a narrow slot is etched out on the radiating patch so as to counteract the equivalent inductance caused by the shorting pins and probe. As such, a wide-bandwidth with stable radiation pattern is achieved for the PIFA under the operation of these dual-resonant modes. After the extensive analysis is executed, the proposed antenna is fabricated and tested. Simulated and measured results are found in good agreement with each other, demonstrating that its impedance bandwidth is tremendously widened to about 15.3% with appearance of two in-band attenuation poles. In particular, a low-profile property with the height of 0.036 free-space wavelength is achieved.