Design and Analysis of Rat-Race Coupler for 5G MIMO Antenna System Applications

In this work, design and analysis of a rat race coupler (RRC) for 5G MIMO systems operating at 3.5 GHz. The RRC and rectangular patch array MIMO antenna design are utilized for transmitter and receiver applications. That enables 5G operation. The three components of the proposed antenna are constructed using a traditional rectangular patch antenna and linked in series with a quarter wave feed line and a $50 \Omega$ impedance line. The same array antenna is used to build a two-port MIMO antenna that operates at a frequency of 3.5 GHz. It provides a compact size, excellent isolation, and low insertion loss, making it an ideal solution. The coupler, measuring $32.6\times 33.2 \text{mm}^{2}$, provides a minimum reflection rate of −3 dB, a return loss of over −30 dB, an isolation loss of less than −20 dB, and an excellent coupling coefficient. The antenna has the gain of 5.5 dBi, a return loss of 30 dB, and a bidirectional pattern and isolation of more than −20 dB. The proposed work can be used in 5G MIMO system applications.

I. Introduction

Electrical engineering is advancing rapidly with the onset of 5G technology. This new standard poses unique challenges in terms of designing an efficient, reliable, and high-performance system. One way to tackle these challenges is using rat-race couplers (RRC), which have proven successful in the last two decades. Implementing 5G technology requires high-quality equipment, including antennas and couplers that operate at a frequency range of 3.5GHz. This research paper presents the design of a rat race coupler operating at 3.5GHz for 5G with a Rectangular patch array MIMO antenna. The rat race coupler is a crucial part of a microwave system that splits or combines signals that are 180 degrees out of phase and have equal power. The concept of 5G technology is based on MIMO antennas that can transmit and receive multiple signals simultaneously using beam-forming techniques. This paper aims to provide an overview of the design process, key considerations, and the testing of the rat race coupler in the context of 5G technology. A small dual-band rat race coupler was suggested in [1]. Utilizing the phase-engineerable CRLH TLs and the most effective size miniaturization method shows a 55% size reduction. Two measured orthogonal radiation patterns were used to identify the pattern diversity in MIMO communications. A miniature rat-race coupler having harmonic suppression is suggested in [2]. The lines are exchanged with corresponding stub-loaded transmission lines in traditional Rat race couplers. This research [3] introduced a novel method for creating 3.5 GHz APD circuits employing WPC, WPD, RRC, PS, and HC. In this, all the individual APD blocks have been designed along with an s-parameter analysis to generate the layout. Based on substrate integrated waveguide (SIW) technology rat-race coupler are discussed in [4]. A suitable unit cell of 16-40 GHz band has been selected to get a satisfactory result, which is ideal for 5G applications. Compared to conventional couplers, the suggested coupler has less leakage and loss. [5] describes a new, octave-bandwidth, frequency-independent coplanar waveguide phase inverter used in a small microstrip rat-race hybrid. The design has a frequency of 1.5-3.5GHz with an insertion loss of less than 0.33dB. In order to make parameter optimization simpler, a novel microstrip-to-CPW transition is introduced. The two-element array rectangular microstrip patch antenna has been reported in [6].