A Compact Defected Ground Structure-Based High Isolated Monopole MIMO Antenna for USB Band Mobile Satellite Services

This article proposes to design an efficient multi-input multi-output (MIMO) system with decent isolating properties for the specific unified S-band (USB) mobile satellite service (MSS). The USB band (2 to 2.2 GHz) comprises a part of S-band (2 to 4 GHz) and is used for space research and satellite communication. The proposed MIMO is aimed to resonate at 2.2 GHz with coverage over the USB band. For this purpose, a meander line (ML) patch antenna with a partial ground monopole configuration is first proposed and optimized to enhance its radiation characteristics. Then, a mirror image of the ML monopole (MLM) is recreated to form a two-element MIMO (MLM-MIMO). An adequately designed MIMO antenna is highly beneficial for enhancing the reliabilities, channel capacities, and frequency reuse in newer-generation communication systems. But simultaneously, it also increases the mutually coupled effect among the adjacently placed electromagnetic (EM) radiators and deteriorates the compactness of the overall design. To overcome this challenge, a compact defected ground structure (CDGS) is designed in the partial ground plane of the proposed MLM-MIMO. The CDGS aims to mitigate the coupling effects by perturbing the surface current distributions in the partial ground plane. At the same time, it also contributes to the overall array design by reducing the weight, increasing the compactness, enhancing the gain, and improving other MIMO parameters. The axial ratio (AR) below 3 dB, envelope correlation coefficient (ECC) less than 0.005, and a MIMO diversity gain (DG) near 10 is also aimed with the proposed design along with the suppression of mutual coupling below -30 dB and return loss below -25 dB for high standard MIMO applications. The proposed antenna prototype, having an aperture size of 40 mm by 48 mm, is fabricated in an FR4 substrate and investigated to validate the simulated results. The CST microwave studio (CST-MWS) based simulation outcomes are found to be in close agreement with the measurement outcomes reported as -25.27 dB S11, -30.96 dB S21, 2.55 dBi gain, and 76.64% efficiency. The aimed targets for radiation properties, isolation characteristics, antenna parameters, and other diversity metrics such as mean effective gain (MEG), channel capacity loss (CCL), and total active reflection coefficient (TARC) values have met the standard MIMO needs. The AR for circular polarization (CP) is also achieved, which shows that the proposed design is suitable for satellite communication, where challenges like better coverage area, multipath and interference mitigation, antenna positioning flexibility, and signal degradation are addressed through circularly polarized design. Furthermore, the performance analysis and a detailed comparison with other works in this domain show the superiority of the proposed design.