A Multifunctional Compact Pattern Reconfigurable Antenna with Four Radiation Patterns for Sub-GHz IoT Applications

A compact pattern reconfigurable antenna with four radiation patterns is proposed for sub-GHz IoT applications. The antenna has two functional modes; Mode I has three uncorrelated patterns, while Mode II has electric and magnetic omnidirectional patterns. The resonant frequency of the antenna is 868 MHz with measured overlapped-6 dB impedance-bandwidths of 22 MHz and 20 MHz for Mode I and Mode II, respectively. The antenna is integrated in an 80\times 55 mm2 terminal. The radiating elements consist of two meandered slots and one meandered monopole. Four pattern configurations are obtained with an average peak gain of 0 dBi, and an average radiation efficiency of 43.3%. Two of the patterns are with 5 dB directivity, and the other two are omnidirectional patterns. Pattern reconfigurability is achieved using four PIN diodes. The antenna is fabricated on a low-cost FR-4 substrate. By removing FR-4 material inside the slots, slots' radiation efficiencies were improved by 2.25 dB.