A Low-Profile Differentially Fed Microstrip Patch Antenna With Broad Impedance Bandwidth Under Triple-Mode Resonance

A low-profile differentially fed microstrip patch antenna with broad impedance bandwidth is proposed by incorporating a resonant mode of the slot into TM₁₀ and TM₁₂ modes of the patch resonator. Initially, the shorting pins are symmetrically placed underneath the patch so as to push up the resonant frequency of TM₁₀ mode in proximity to that of TM₁₂ mode (<italic>f</italic>₁₂). After that, the central slot could be employed to excite an additional mode resonating closely to the <italic>f</italic>₁₂ by increasing the slot length. Additionally, a pair of small circular disks is introduced below the radiating patch for good impedance matching. Finally, the wideband antenna is fabricated and measured to validate the predicted performance. The results illustrate that the antenna has gained a broad impedance bandwidth of about 55% (1.62–2.85 GHz) with three in-band attenuation poles while maintaining the normal radiation pattern. In particular, a low-profile property with the height of about 0.06 free-space wavelength is achieved.