# Compact Four-Port Circularly Polarized MIMO X-Band DRA
###### Abstract  
A circularly polarized (CP) multi-input multioutput (MIMO) dielectric resonator (DR) antenna (DRA) with compact size and four ports is implemented. CP radiation was achieved using the deformed DR geometry excited with aperture coupled feeding. A CPDRA with a single and two ports is investigated. The defected ground structure (DGS) was incorporated into the antenna for improving the isolation between the ports. The DGS was incorporated in such a way that the required phase difference between the generated orthogonal degenerate modes is preserved. This concept could be utilized in implementing a compact four-port CP antenna. The MIMO antenna provides a 10 dB impedance bandwidth of 38% (8.5-12.5 GHz) and a 3 dB AR bandwidth of 9.32% (9.2-10.1 GHz). The gain of the implemented antenna was around 6 dBi in the band where CP radiation was achieved. The MIMO performance parameters were calculated, and their values remained within the acceptable limits. The implemented antenna could suitably be used in X-band applications. antenna; circular polarization; dielectric resonator; MIMO; X-band +
Footnote †: journal: Sensors  
plus 0.3 em minus 0.3 em minus 0.  
technique in a single-port antenna, and (ii) implementing the compact multiport antenna structure with high isolation along with the desired phase difference between the generated orthogonal modes, so that CP field can be obtained. A traditional cross-slot is investigated for fulfilling the aim of achieving the CP response in MIMO DRA with two ports [7]. A multiport DRA with two ports used metal strips to achieve a CP field [10]. A CP multiport DRA was reported with the deformed geometry of the DR [16]. Moreover, a research work was reported with the usage of a quarter modified feedline is a two-port CP MIMO DRA [12]. Another research work utilized a traditional stair-shaped slot for excitation in implementing a four-port MIMO antenna [13]. These research works utilized the techniques of obtaining the CP response in DRA, which had earlier been reported in the case of a single-port antenna; here, the MIMO antenna was implemented with the said objective. Still, most of all these recently reported antenna structures can provide the facility up to only two ports. To find a solution to the stated research issues, a compact four-port CP MIMO DRA was designed and implemented in this research work. Utilizing a deformed geometry of the DR in implementing the CP antenna or antenna array is always reliable over deforming the feeding line from the point of structural stability [17; 18; 19]. So, a deformed geometry of the DR is used for obtaining the CP field. T\(\alpha\)antenna analysis with a single radiating element was conducted to obtain the radiation behavior of the antenna. This study was utilized in the implementation of a two-port MIMO antenna with CP response by the appropriate incorporation of DGS. The concept of a two-port MIMO antenna is utilized in implanting a four-port CP MIMO DRA. The four radiating elements are arranged with the simple aperture coupled feeding into a compact space. The defected ground structure was incorporated into the antenna structure to enhance the isolation between the radiators, so that the phase differences between the orthogonal modes required to achieve the CP response are preserved. The suggested antenna could suitably be used in X-band applications with 38% (8.5-12.5 GHz) and 9.32% (9.2-10.1 GHz) impedance bandwidth and AR bandwidth, respectively. The deformed geometries of the DR with a single port were previously reported [20; 21; 22; 23]. However, implementing the four-port MIMO antenna with CP response has not been investigated till now, and this is the novelty of this research work. Providing the CP response in a compact antenna structure with an increased number of ports is the advantage of the implemented antenna. The novelty and advantages of the reported research work can be summarized in the following points.