# Quad-Port Multiservice Diversity Antenna for Automotive Applications
## 1 Introduction  
The quest for high data rates has led to increased research into ultra-wideband (UWB) and multiband antennas. UWB antennas are used for a variety of automotive applications, including keyless entry, security, autonomous driving, vehicle-to-vehicle (V2V) communication, digital keys, and finding a vehicle in crowded parking lots. UWB technology can also be used for vehicle tracking, localization, and parking guidance. The vehicular antenna can be mounted in various locations, such as the back window, windshield, roof, or side mirror. The antenna may be readily fitted with the help of a shark-fin casing and chassis cavity. Modern automobiles are becoming more intelligent, providing comfort and safety to drivers by enabling automated driving assistance and infotainment systems. Vehicle-to-everything (V2X) communication technology provides real-time traffic updates and safer driving by communicating directly with other vehicles. The key technologies for V2X communication in the unlicensed 5.9 GHz band are long-term evolution and wireless access in vehicular environments (WAVE). The notable features of V2X communication include automated driving with optimized fuel consumption, an integrated entertainment system, and the ability to send breakdown prevention information to drivers. In the literature, various antenna configurations have been proposed for automobile applications [1, 2, 3, 4, 5]. In [1], a square patch loaded with an inverted U-slot and a coupled C-slot was reported. In [2], a wheel-shaped fractal antenna was designed on the transparent polyvinyl chloridematerial substrate. In [3], a compact-sized dual-band antenna was presented with left-handed metamaterial. In [4], fractal geometry was used to design a microstrip patch antenna with a small footprint. In [5], a wheel-like fractal antenna was proposed for short-range communication, and the antenna was placed on a virtual car model to test its on-vehicle performance. Signals in the automotive environment are received from multiple paths, resulting in multipath fading and interference. Diversity techniques such as spatial, pattern, and polarization are used to encounter multipath interference. Therefore, a multiple-input-multiple-output (MIMO)/diversity antenna could be advantageous for vehicular communications [6; 7; 8; 9]. But, the main problem with MIMO antennas is high coupling between resonating elements. For improving inter-element coupling in uniplanar wideband MIMO antennas, electromagnetic band-gap (EBG) and other decoupling techniques were proposed in [10; 11; 12; 13]. In [14; 15; 16; 17], dual-port MIMO/diversity antennas with split-ring resonators (SRRs) were presented with improved isolation. In [18], a 3-D UWB MIMO configuration was reported, with the antenna elements positioned orthogonally to each other to reduce mutual coupling. An eight-element UWB MIMO antenna was designed [19], with the antenna elements placed orthogonally to offer dual polarization. A rectangular-shaped patch antenna was proposed in [20], with high inter-element isolation. A multiband dual-polarized antenna was developed in [21], where the antenna elements were placed orthogonally to increase isolation and achieve polarization diversity. An antenna working at multiple frequencies was presented in [22], where the resonating elements were arranged orthogonally to each other to reduce coupling between them. However, the antenna had a larger footprint. A Minkowski MIMO antenna was proposed in [23], where the Minkowski structure was obtained by cutting rectangular slots in the square patch, which helped increase isolation. In [24], a quad-port multiband MIMO antenna with pattern diversity and low inter-element coupling was reported. In [25], a quad-port antenna array was designed for 2G/3G/4G applications with isolation greater than 16.5 dB. In [26], a slotted microstrip antenna was proposed for WLAN applications, with a defected ground plane. In [27], an orthogonal orientation of elements was used to increase isolation in a quad-port triple-band antenna.