# Glueless Multiple Input Multiple Output Dielectric Resonator Antenna with Improved Isolation
## 1 Introduction  
We cannot think of a world without modern wireless communication technologies today. An antenna plays an important role in making communication systems wireless and efficient. Microstrip patch antennas were the preferred choice for major wireless communication applications before the advent of dielectric resonator antennas (DRA). In the current times, the application of dielectric resonator antennas (DRAs) increased in emerging wireless standards because of their inherent advantages, such as no surface wave losses, high radiation efficiency, compact size, nearly constant gain, high impedance bandwidth (IBW), and ease of excitation [1; 2; 3]. Hence, they are good candidates for various applications across the spectrum, from microwaves to optical frequency bands. The current state of the art of DRAs in the microwave regime includes filtering DRAs [4; 5], compact DRAs with omnidirectional radiation patterns [6], RF energy harvesting [7], microwave image sensing [8], directional radiation pattern [9], frequency tunable DRAs [10], X-Band DRA arrays [11], DRAs for 5G communications [12; 13], tunable characteristics of DRA [14], DRA in X-band applications [15], and DRA for mm-wave applications [16; 17]. Multiple-input multiple-output (MIMO) technology allows us to achieve higher data rates during wireless communication. In MIMO systems, a number of transmitters and receivers are utilized simultaneously to transfer more data, which increases data rates. For this, multiple port antennas are required to act as transmitters and receivers in the wireless system. In [18; 19], initial designs of MIMO antenna using DRA, which combines advantages of both MIMO and DRA technology, were presented in 1983. In [20], recent MIMO DRAs have been reviewed comprehensively. Generally, adhesive or glue is used to stick the DRA on the substrate, which gives rise to performance degradation due to an extra layer of glue dielectric between DR and substrate. Radiation properties, impedance matching, and gain of the antenna are also affected due to the application of adhesive [21; 22]. Some general-purpose adhesives are Loctite 499 (CyanoAcrylic (CA) type), Loctite 4212, and Araldite, which are used to glue DR with substrates but when high heat is intentionally used for disassembly, the ceramic often cracks before the bond, possibly due to excessive mismatch in the effective expansion rates. These bonds are not very flexible to accommodate differential thermal expansion rates. The bond line has to be carefully process-controlled to minimize RF losses while still preserving mechanical strength. In recent times, researchers are heading towards achieving glueless techniques in DRA to remove the drawbacks of glue. Compound substrate, grooved ground plane, hooks, and side pins are proposed instead of glue for fixing DRA on the substrate in [23; 24; 25; 26], respectively. As per the knowledge of authors, first time, a novel glueless technique in dual-port MIMO DRA, which not only supports the DRA, but improves its performance, is presented in this dissemination. Here, an aperture-coupled fed glueless dual port MIMO DRA is presented for X-band applications. Ring shaped cylindrical DRA is taken due to ease of design. Major highlights of proposed antenna are following: (i) compactness; (ii) novel glueless technique; (iii) symmetric structure; and (iv) first glueless dual-port MIMO DRA. The proposed antenna is much more compact than state of art configurations, with net volume of DRA and substrate, which are approximately 3.5 cm\({}^{3}\) and 2.88 cm\({}^{3}\), respectively. Novel glueless technique with four metallic cylinders are used, which not only provide mechanical strength to the antenna, but improves it performance characteristics also. The antenna demonstrates simulated IBW of 10.37% in X-band with maximum simulated gain of 6.2 dBi. Antenna structure is symmetric, which is a desirable feature in the MIMO antenna for easier installation without any ambiguity regarding ports.