## 1 Introduction  
Ultra-wideband (UWB) antennas have sparked a lot of current research interest as they are an essential element in wireless communication systems. Of late, UWB communication technologies have been studied to fulfill the demand for high data speed, low cost, and low power [1]. The planar antennas are turning out to be more popular for UWB applications after the Federal Communications Commission (FCC) assigned UWB an unlicensed frequency range from 3.1 GHz to 10.6 GHz [2]. For emerging UWB wireless applications, printed slots and monopole-type antennas are used because of their simple realization, satisfactory frequency response, and easy integration with other active devices [3]. UWB antennas are widely used in radar imaging, radio frequency identification [4], public security, and device positioning. Some smart applications of UWB antennas include vehicular radar systems, surveillance systems, software-defined radios, spectrum analysis, and proximity fuses [4]. Some research problems in UWB antennas include wide impedance matching, radiation stability, low profile, small size, and reasonable cost [5]. Multiple-input-multiple-output (MIMO) is a multiplexing technology with multiple antennas both on the transmitter and receiver, which can enhance the channel capacity by making full use of the rich scattering environment without sacrificing additional spectrum or power [6; 7; 8]. MIMO antennas are used to achieve a high capacity and throughput [9]. In the last decade, many research papers that investigated the performance of MIMO systems for satellite-terrestrial networks have been published. In article [10], a secrecy-energy efficient hybrid beamforming (BF) scheme was investigated, wherein a multibeam satellite (MS) system shared the mm-wave spectrum with a cellular system. Under the assumption of imperfect angles of departure for the wiretap channels, the hybrid beamformer at the base station and digital beamformers at the satellite were jointly designed. In [11], a joint beamforming design and optimization for reconfigurable intelligent surface-aided hybrid satellite-terrestrial relay networks were reported, where the links from the satellite and base station (BS) to multiple users were blocked. In [12], a low-complexity optimization framework in terms of secrecy-energy efficiency beamforming for MS systems was developed. An alternating optimization scheme using the signal-to-leakage-plus-noise ratio criterion and successive convex approximation method to iteratively obtain closed-form beamforming weight and power allocation factors was presented. In [13], the physical layer security of a satellite network was investigated, whose downlink spectral resource was shared with a terrestrial cellular network. A multi-antenna BS was proposed as a source of green interference to enhance secure transmission, with the assumption that imperfect channel state information (CSI) and statistical CSI of the link between the BS and satellite user are available at the BS. In multi-antenna wireless communication systems, precoding has to be studied to simultaneously support data transmission to multiple users to reduce the interference prior to transmission and achieve the channel capacity [14]. The antenna system with a beam scanning capability can filter the interference of other channels by targeting the radiation pattern in a specific direction to obtain more stable data transmission [15]. For secure MIMO transmission in a mobile vehicular network, a wireless-powered communication with integrated MIMO technology for radio frequency energy harvesting was presented [16]. Massive MIMO and mm-wave MIMO are considered to be the key enablers for fifth-generation (5G) wireless networks. By exploiting the sparsity of mm-wave channels, the corresponding channel estimation can significantly reduce the required pilot overhead. It is particularly beneficial to mm-wave MIMO systems, where the number of pilot symbols increases linearly with the number of reflecting elements and transmit antennas [17].