A Square-Loop Antenna With 4-Port Feeding Network Generating Semi-Doughnut Pattern for Vehicular and Wireless Applications

Recently, a printed square-loop antenna (SLA) over a hybrid high impedance surface (HHIS) was reported, which can steer its beam in four directions in space using an RF switch diverting the input power to one of the four input ports of the antenna. In this letter, for the first time it is shown that the same planar antenna can be used to generate a semi-doughnut radiation pattern if all its four ports are excited simultaneously with a signal of the same phase and amplitude. Importantly, the letter provides a complete antenna and feeding network integrated design and validates the simulated and experimental results. For the test frequency band of 4.4-5.4 GHz, the HHIS-based SLA exhibits a doughnut pattern of a maximum directivity of 4.4 dBi. For a 50-Ω input impedance, the antenna has an impedance bandwidth of minimum 500 MHz.