Four-port triple notched wide-band MIMO antenna and verification by theory of characteristics mode for multiple applications

Abstract

This paper presents a compact four-port multiple-input-multiple-output (MIMO) antenna featuring a triple notched-band characteristic for wideband, multiple applications. The single-element antenna is systematically developed and analyzed using the Theory of Characteristic Modes (TCM), where eight modes are investigated to understand the fundamental resonances and to engineer three distinct notched bands centered at 4.12 GHz, 5.58 GHz, and 7.88 GHz for mitigating interference from C-band, WLAN, and X-band (Downlink/Uplink) systems. The final single element has a compact footprint of 26 × 18 × 1.6 mm 3 on an FR4 substrate, achieved through a six-step evolution process involving strategic slotting on the patch, feed, and ground plane. It operates across an ultra-wide bandwidth of 3.23–15.66 GHz. The single element is then extended to a 4 × 4 MIMO configuration with an overall size of 56 × 56 mm 2 . A novel interconnected ground structure is employed to enhance port isolation, resulting in a measured transmission coefficient (S-parameters between ports) of less than − 12 dB across the entire operating band from 3.01 to 16.0 GHz. The MIMO antenna demonstrates excellent diversity performance, with an Envelope Correlation Coefficient (ECC) below 0.01, Diversity Gain (DG) exceeding 9.997 dB, and Channel Capacity Loss (CCL) under 0.02 b/s/Hz. Furthermore, a Specific Absorption Rate (SAR) analysis at 3.5 GHz, 9.0 GHz, and 14.0 GHz yields values of 1.11 W/kg, 1.35 W/kg, and 1.44 W/kg (for 500 mW input power), all well below the FCC safety limit of 1.6 W/kg, confirming its suitability for wearable communication systems in UWB, X-band, and Ku-band applications. A comparison with state-of-the-art designs confirms the proposed antenna’s superior performance in terms of bandwidth, compactness, and interference mitigation.