Compact Frequency-Reconfigurable MIMO Antenna for Microwave Sensing Applications in WLAN and WiMAX Frequency Bands

In this article, a compact frequency-reconfigurable multiple-input multiple-output (MIMO) slot antenna is presented for microwave sensing applications in the S- and C-bands. The antenna-based sensor that consists of four positive intrinsic negative (PIN) diodes is switchable electronically between wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) frequency bands, i.e., 2.4–2.48, 3.4–3.6, and 5.3–5.9 GHz, with a frequency ratio of 2.5:1. A novel C-shaped meander line resonator is incorporated to the antenna for obtaining high isolation between the antenna elements and low envelope correlation coefficient (ECC), which results in improved performance of the microwave sensor. The antenna has been fabricated with low-cost FR4 substrate using an MITS FP-21T precision machine and four PIN diodes. The measured isolation greater than 25 dB and the ECC less than 0.08 have been noticed over the three frequency bands. The peak realized gains of the antenna are 1.06, 1.02, and 2.46 dBi at 2.45, 3.5, and 5.7 GHz, respectively.