Compact UWB MIMO Antenna With Filter-Assisted Bandwidth Reconfiguration for WBAN-Enabled Medical IoT Applications

Abstract

A four-element bandwidth-reconfigurable multiple-input multiple-output (MIMO) antenna is presented in this paper for Wireless Body Area Network (WBAN) and medical IoT (M-IoT) applications. The antenna element in the MIMO scheme utilizes an ultra-wideband (UWB) monopole, which is bandwidth reconfigured to work in wideband and narrowband modes. Bandwidth reconfiguration is achieved through feedline selection, where a low-pass filter (LPF) is integrated to the primary transmission line to control the excitation of the monopole antenna. The proposed antenna operates in two distinct modes, viz. direct mode for WBAN and filter mode for M-IoT. In the direct mode, the proposed antenna offers UWB operation from 3.1 to 11.8 GHz, corresponding to a fractional bandwidth (FBW) of 115%. In the filter mode, the monopole is excited through the LPF, which restricts the bandwidth to 3.1–5.4 GHz resulting in an FBW of 56%. The LPF is a defected microstrip structure with split square resonator that offers a cutoff frequency around 6 GHz. Each filter-integrated antenna element occupies a compact area of 0.17 λ₀ × 0.25 λ₀ (16 × 24 mm²), while the complete four-element MIMO configuration measures 0.47 λ₀ × 0.47 λ₀ (45 × 45 mm²). The proposed antenna achieves a peak gain above 4 dBi with efficiency close to 80%. The performance of the antenna in the presence of three-layer human body model is evaluated to validate the suitability for WBAN and M-IoT environments. The MIMO metrics are evaluated and the results show a low envelope correlation coefficient (<0.1), high diversity gain (>8 dB), and channel capacity loss below 0.35 bps/Hz, confirming reliable operation of the proposed antenna in on-body conditions.