Wideband Radiation Reconfigurable Microstrip Patch Antenna Loaded With Two Inverted U-Slots

Abstract

A wideband rectangular microstrip patch antenna with reconfigurable radiation patterns is proposed in this paper, which contains two symmetrically inverted U-slots, and incorporates two coaxial probes along the resonant length of the patch. By controlling the phase shift of applied currents through these probes, the antenna can be set to excite either the SUM or the Difference mode, in accord with the TM₀₁ and TM₀₂ modes, respectively. Unlike previous endeavors on U-slot microstrip antennas, a wide impedance bandwidth of 68% is realized, along with stable polarization and symmetrical radiation patterns. It is worth mentioning that the thickness of the substrate is very small, which is in the order of <inline-formula> <tex-math notation= LaTeX >$0.02 \\lambda _{d}$ </tex-math></inline-formula>, where <inline-formula> <tex-math notation= LaTeX >$\\lambda _{d}$ </tex-math></inline-formula> is the wavelength in the dielectric medium at the center frequency of 3 GHz. The slot and patch parameters are numerically analyzed to achieve wide bandwidth along with symmetric radiation patterns. The realized null depth in the Difference mode is well below −30 dB, which makes the proposed antenna well suited for monopulse radar applications. The antenna covers a frequency range of 1.98–4 GHz. A prototype is fabricated and tested. Good agreement between the measured and simulated results is observed.