Mutual Coupling Reduction Research Articles

Wideband, High-Density Circularly Polarized Array With Reduced Mutual Coupling and Enhanced Realized Gain

A planar single-layer parasitic swastika-shaped structure, which serves as an effective isolator, is developed for mutual coupling reduction in wideband, high-density circularly polarized (CP) arrays. A closely spaced two-element CP antenna array demonstrates the efficacy of the approach. The currents induced by the CP coupling are effectively canceled out when this isolator is integrated into it. The antenna elements are co-planar. They are arranged with a center-to-center distance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.4\lambda _{\mathrm {L}}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{\mathrm {L}}$ </tex-math></inline-formula> being the wavelength of the lower bound of the array’s operational bandwidth) and have an extremely small edge-to-edge distance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 0.024\lambda _{\mathrm {L}}$ </tex-math></inline-formula> . The parasitic element yields an increase of the isolation level between the antenna elements of more than 9.4 dB over the entire operational band, with a maximum improvement of 20.4 dB. Moreover, the antenna elements realize a modest maximum gain improvement of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.2$ </tex-math></inline-formula> dB in the boresight direction over the same band. The overlapped impedance matching and 3 dB axial ratio (AR) bandwidths cover the range of 1.7–2.7 GHz, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 45$ </tex-math></inline-formula> % fractional bandwidth. A prototype was fabricated and measured; the measured results are in good agreement with their simulated values.

A non-uniform strip-array decoupling structure of the MIMO antenna-arrays for the DSRC application

ABSTRACT In this paper, a non-uniform strip-array decoupling structure (SADS) of the MIMO antenna-arrays for the dedicated short-range communication (DSRC) applications in intelligent transportation systems (ITS) is presented. The SADS is composed of metal strips with non-uniform longitudinal layout, which has a simple strip-array geometry, low design and fabrication complexity, and easy to be applied to the design domain without destroying the original antenna-array. The design of the strip thickness, strip-array layout and number of strips is realised by the proposed simple and effective optimisation method. The mutual coupling between the elements can be effectively suppressed to less than −32 dB by the proposed structure in the required bandwidth (5.795 GHz~5.815 GHz). The results show that, compared with the no-strip and uniform SADS, the non-uniform SADS can improve the maximum mutual coupling reduction by 23 dB and 13 dB, respectively. Both the simulated and measured results verify the effectiveness of the proposed SADS, which makes it very suitable for the large-scale MIMO antenna-arrays.

Mutual Coupling Reduction in Closely Spaced MIMO Dielectric Resonator Antenna in H-Plane Using Closed Metallic Loop

In this study, the mutual coupling in multiple-input-multiple-output (MIMO) dielectric resonator antenna (DRA) is reduced by employing closed metallic loops. The loops are wrapped around the adjacent edges of the dielectric resonators (DR) where magnetic coupling is significant. The proposed method employs only the conductive metallic strips for mutual coupling reduction and this makes the entire design very simple and compact. The impedance bandwidth varies from 4.73 to 5.1 GHz, covering the Sub&#x2013;6 GHz 5G band. The realized MIMO DRA has an isolation of 28 dB at the resonant frequency with a measured peak gain at each port of 3.5 dBi and a peak radiation efficiency of 93%. The obtained measured results yield a low correlation coefficient (&#x003C;0.05) mostly at the entire band that contribute to diversity gain (&#x003E; 9.8 dB) to increase the capacity of communication system, is reported in this paper. The proposed antenna was fabricated and the closed loop strip is wrapped around using in house facility. Furthermore, some issues related to the fabrications tolerance have been investigated to justify the difference between some simulated and measured results.

Space Efficient Meta-Grid Lines for Mutual Coupling Reduction in Two-Port Planar Monopole and DRA Array

Traditionally used mutual coupling (MC) reduction techniques such as electromagnetic bandgap structures, isolators and neutralization lines require extra space between radiators. Besides, metamaterial-based techniques require multi-layer arrangements. However, the proposed meta-grid lines overcomes the above demerits by integrating meta-grid lines in the ground plane itself. As a proof-of-concept, two-port CPW-fed monopole antenna array (TPCFMAA) and two-port DRA array (TPDRAA) are designed, fabricated and tested. It has been observed that the TPCFMAA has mutual coupling below −20 dB for frequency between 2.6 to 4.4 GHz. The envelope correlation coefficient reduces from 0.072 to 0.026 by integrating meta-grid lines in the ground plane of the TPCFMAA. At 3.5 GHz, the inter-element distance between the antennas is noted to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${0.015}\lambda _{\mathrm {h}}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{\mathrm {h}}\,\,=$ </tex-math></inline-formula> highest operating wavelength). The TPDRAA’s operating frequency can be tuned by changing the parameters of the annular ring slot in the excitation patch. The bandwidth of TPDRAA can be further increased by merging the two resonances of the two annular ring slots in the excitation patch. For TPDRAA, the measured −10 dB impedance bandwidth is from 5.65 to 6.55 GHz. The mutual coupling between the antenna elements is seen to be below −16 dB for an inter-element spacing of 4.8 mm, which is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.090\lambda _{\mathrm {h}}$ </tex-math></inline-formula> . The measured gain of TPDRAA within the bandwidth is from 4.17 dBi to 5.2 dBi. The TPCFMAA can be used in 3.5 GHz Internet of Vehicles (IoV) multi-user MIMO service, whereas the TPDRAA can be used for satellite communication in the 5.925 to 6.425 GHz frequency band, WiMAX in the 5.7 to 5.85 GHz band, ISM in the 5.725 to 5.85 GHz band, and WLAN in the 5.8 GHz band.

Mutual Coupling Reduction in Antenna Arrays using Circular Complementary Split Ring Resonator Metamaterial Structure in Comparison with Non-Metamaterial Antenna Array

Mutual Coupling Reduction in Antenna Arrays using Circular Complementary Split Ring Resonator Metamaterial Structure in Comparison with Non-Metamaterial Antenna Array

Compact Multibeam Array with Miniaturized Butler Matrix for 5G Applications

This paper presents the design and implementation of a miniaturized beam steering network that produces broadside beams when it is fed with a compact antenna array. Butler Matrix (BM) was used as the beam steering network. It was completely built from a miniaturized 3 dB hybrid-couplers in planar microstrip technology. It was configured by feeding the BM with a Planar Inverted-E Antenna (PIEA) array separated at 0.3 λ as against the 0.5 λ separation. This makes the BM produce a major radiation pattern at the broadside. Apart from the miniaturization, no modification was made from the BM side. However, employing effective mutual coupling reduction techniques helped to design the compact PIEA array. The validity of this BM based multibeam PIEA array was demonstrated by comparing the simulation results of the reflection coefficients, transmissions coefficients and the radiation pattern with measurements. The measurement results showed good agreement with simulations.

Enhanced 4-Port MIMO Antenna Based on Electromagnetic Mutual Coupling Reduction Using CSRRs Metamaterials for Sub-6 GHz 5G Applications

Enhanced 4-Port MIMO Antenna Based on Electromagnetic Mutual Coupling Reduction Using CSRRs Metamaterials for Sub-6 GHz 5G Applications

Mutual Coupling Reduction of a Circularly Polarized MIMO Antenna Using Parasitic Elements and DGS for V2X Communications

In this article, a 4-port circularly polarized (CP) multiple-input multiple-output (MIMO) antenna at 5.9 GHz is presented for the vehicle to everything (V2X) communications. A novel hybrid decoupling structure consisting of circular ring parasites and defected ground structure (DGS) is used to reduce the mutual coupling between the MIMO elements. The circular ring parasites are incorporated between the antennas to reduce the mutual coupling between perpendicular antennas. Whereas, the DGS significantly reduces the mutual coupling between adjacent antennas. These circular ring parasites and DGS affect the electromagnetic field distribution and consequently reduce the mutual coupling. The effectiveness of the decoupling structure is explained through transmission coefficient and surface current distribution. The simulated and measured results show that the proposed MIMO antenna provides overlapping S11 (&#x2013;10 dB) and axial ratio (3-dB) bandwidth of 2.04% (5.82 &#x2013; 5.94 GHz) with a peak gain of 7.68 dBic. Moreover, the fabricated MIMO antenna offers excellent diversity performance, isolation between antenna elements is very high (&#x003E;34dB), envelope correlation coefficient (ECC) is lower than 0.001, and diversity gain is 9.99 dB, very close to the ideal value of 10 dB. Furthermore, the link budget for the proposed MIMO system is calculated to check the suitability for V2X communications which shows that the antenna can communicate between them over a distance of 1.5 kilometers with a 21 dBm of transmit power. Owing to these qualities, the proposed MIMO antenna can be an excellent choice for V2X MIMO communications.

Integration of the modified Butler matrix and decoupling network for beam‐steering antenna array

In this article, the design and realization of a planar microstrip array antenna with a 4 × 4 modified Butler matrix is presented. The proposed switched-beam smart antenna operates at 4.95 GHz. The significant purpose of this research is mutual coupling reduction between antennas of the array. Therefore, the microstrip array antenna is arranged as E-plane mode and the novel decoupling network is used to reduce the mutual coupling. The mutual coupling of the proposed structure is measured −35 dB at 4.95 GHz frequency. The mutual coupling reduction of 17 dB is achieved by using the decoupling network. Also, the impedance bandwidth of the proposed structure with |S11| < −10 dB is about 300 MHz (6%) operating at the center frequency of 5.05 GHz and the average gain of 10.6 dB is obtained.

Cross-Band Mutual Coupling Reduction in Dual-Band Base-Station Antennas With a Novel Grid Frequency Selective Surface

In this communication, a grid frequency selective surface (GFSS) is developed for cross-band near-field mutual coupling suppression. The unit cell of the GFSS consists of a break metal strip and a parallel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonator. The GFSS realizes low-stop property at 1.7–2.4 GHz (B1 band) and high-pass property at 3.3–3.8 GHz (B2 band). The novel GFSS is applied in a 5G dual-band antenna array with one B1 band antenna and four B2 band antennas. The cross-band mutual coupling coefficients are reduced from −14 dB to lower than −35 dB at the B1 band. Meanwhile, the radiation patterns of the B2 band antenna element are not affected due to the nonscattering feature of the GFSS. The dual-band base-station antenna array prototype is fabricated and measured to demonstrate the effectiveness of the proposed design in cross-band mutual coupling reduction.

Mutual coupling reduction in wideband dielectric resonator antennas

Mutual coupling reduction in wideband dielectric resonator antennas

Wideband MIMO Antenna Mutual Coupling Reduction with Electromagnetic Band-Gap Structure

This communication presents a small size, planar, and two-port wideband multiple-input-multiple-output (MIMO) antenna operating from 2.08 GHz to 5.81 GHz with 94.55% fractional bandwidth. It satisfies the bandwidth requirements of multiple wireless applications in both 5G (sub-6 GHz band) and 4G bands namely Bluetooth (2.4 GHz), LTE (2.5 GHz), WLAN (2.4/5.2/5.8 GHz), and WiMAX (3.5/5.5 GHz). An electromagnetic band-gap (EBG) structure is embedded in the ground plane to reduce the resulting mutual coupling between the antenna elements. As a result, more than 18 dB port isolation is obtained over the entire working band. The important MIMO antenna performance parameters such as envelope correlation coefficient (ECC < 0.05), diversity gain (DG > 9.95 dB), and channel capacity loss (CCL < 0.345 bits/s/Hz) are within the acceptable ranges. Measurement is done on the fabricated antenna. A reasonable agreement is observed between the simulated and measured results.

Development of C-Shaped Parasitic MIMO Antennas for Mutual Coupling Reduction

In the 5G system, multiple-input multiple-output (MIMO) antennas for both transmitting and receiving ends are required. However, the design of MIMO antennas at the 5G upper band is challenging due to the mutual coupling issues. Many techniques have been proposed to improve antenna isolation; however, some of the designs have impacts on the antenna performance, especially on the gain and bandwidth reduction, or an increase in the overall size. Thus, a design with a detailed trade-off study must be implemented. This article proposes a new C-shaped parasitic structure around a main circular radiating patch of a MIMO antenna at 16 GHz with enhanced isolation features. The proposed antenna comprises two elements with a separation of 0.32λ edge to edge between radiation parts placed in a linear configuration with an overall dimension of 15 mm × 26 mm. The C-shaped parasitic element was introduced around the main radiating antenna for better isolation. Based on the measurement results, the proposed structure significantly improved the isolation from −23.86 dB to −32.32 dB and increased the bandwidth from 1150 MHz to 1400 MHz. For validation, the envelope correlation coefficient (ECC) and the diversity gain (DG) were also measuredas 0.148 dB and 9.89 dB, respectively. Other parameters, such as the radiation pattern, the total average reflection coefficient and the mean effective gain, were also calculated to ensure the validity of the proposed structure. Based on the design work and analysis, the proposed structure was proven to improve the antenna isolation and increase the bandwidth, while maintaining the small overall dimension.

Mutual coupling reduction in tri-band MIMO antenna using spikes loaded asymmetric loop resonator for WLAN and Wi-MAX band

Mutual coupling reduction in tri-band MIMO antenna using spikes loaded asymmetric loop resonator for WLAN and Wi-MAX band

Decoupling of a Wideband Dual-Polarized Large-Scale Antenna Array With Dielectric Stubs

A technique of decoupling dielectric stubs (DDS) is proposed for mutual coupling reduction of wideband, dual-polarized, and large-scale antenna arrays in this paper, where a low dielectric constant DDS is mounting on a dual-polarized and wideband antenna array seamlessly. The decoupling mechanism of the proposed DDS is qualitatively explained. By properly optimizing the dielectric constant and dimensions of the dielectric stubs, the DDS can reduce the mutual couplings between array elements efficiently. The dielectric stubs are considered as perturbations to slightly localize the electromagnetic fields emitted from the antenna element to lower the space wave coupling. The advantages of the proposed decoupling technique are wideband, low cost, high efficiency, and suitable for large-scale antenna arrays. For demonstration, 4 × 4 dual-polarized and wideband antenna arrays with and without the DDS are simulated, measured, and compared. The simulated results show that the antenna array with the DDS can achieve all port-to-port isolations over 25 dB from 4.4 to 5.0 GHz for all the coupling paths, which are 7 dB higher than the counterparts without the DDS. Moreover, the total efficiencies of the antenna elements with the proposed DDS are also improved. The measured results agree well with the simulated, verifying the effectiveness of the proposed method of DDS for decoupling of large-scale antenna arrays.

Multiple input multiple output (MIMO) and fifth generation (5G): an indispensable technology for sub-6 GHz and millimeter wave future generation mobile terminal applications

AbstractThe in-depth exploration in the future 5G technology symbolizes a revolution in technology for antenna designers to encounter the all time increasing need as well as demand for higher data rate wireless communications. The paper gives out an exhaustive review of the evolution and characteristics of the 5G spectrum allocations, the MIMO antenna design with regard to mutual coupling reduction techniques and safer user applications. It precisely covers almost all the aspects of 5G which mainly include the types of antenna designs and their performance parameters related to MIMO design. The paper also presents a brief description of massive MIMO technology for base station applications. The main aim of the paper is: (1) to emphasize the frequencies allocated for the 5G including sub-6 Ghz and mm-wave bands; (2) to underline the suitable antenna designs for MIMO applications for mobile devices and base stations; (3) to highlight the mutual coupling effects in MIMO designs and its reduction techniques; (4) to consider the gaps in the literature and the challenges for reducing SAR effects for the safety of the users. This review paper has been an attempt to explore the evolution of 5G bands and antenna designs for 5G applications, comparison based on the literature, and the techniques implemented for enhancing the MIMO antenna performances.

Novel dual-band EBG structure to reduce mutual coupling of air gap based MIMO antenna for 5G application

A novel variable band gap center frequency and dual band gap stacked electromagnetic band gap (VBS-EBG) structure for multiple input multiple output (MIMO) antenna system used for the fifth-generation (5G) technology is presented in this paper. Proposed VBS-EBG is mathematically analyzed using transmission line model. Variation in band gap center frequency of VBS-EBG is simulated using eigenmode solution of high frequency structure simulator (HFSS) for different air gap and experimentally validated. It is observed from simulated and experimental results that proposed VBS-EBG gives more than 29.2 % and 39.13 % broader variation in first band gap and second band gap center frequency respectively, compared to reported variable band gap center frequency EBG structures. Application of the proposed EBG structure to reduced the mutual coupling of MIMO antenna system is carried out. 16.16 dB and 6.05 dB reduction in mutual coupling is observed at first and second resonance respectively of MIMO antenna with proposed EBG structure.

Hybrid metasurface loaded tri‐port compact antenna with gain enhancement and pattern diversity

A tri-port compact antenna loaded on hybrid metasurface (MS) with gain enhancement and pattern diversity is proposed in this article. The antenna consists of three analytically designed contorted radiators (Ant-1, Ant-2, and Ant-3). A koch-fed fractal aperture ground plane is used to improve impedance matching and port isolation, thus eliminating supplementary decoupling networks. Ant-1 is 45° tilted, operating in wideband mode. Ant-2 is one-fourth, Ant-3 is one-half in electrical lengths with L-shaped metallic contortions to achieve good matching characteristics and asserts pattern diversity. A hybrid MS (combination of conventional customized MS's) structure is loaded for gain enhancement of ≈ 8.93 dBi. Ant-1 operates at (4.97-10.63) GHz with 72.56% frequency bandwidth (FBW), Ant-2 operates at (8.5-10.4) GHz with 20.1% (FBW) and Ant-3 operates at (7.2-9.6) GHz with 28.57% (FBW). The differentiation in antenna electrical size assists compactness, reduction in mutual coupling (>17 dB), has uncorrelated radiation patterns at each port delivering far-field diversity with low ECC < 0.1. A prototype antenna of size 28.6 mm × 28.6 mm is fabricated and experimented, which are in good agreements with EM simulation and equivalent circuit model response. The proposed tri-port antenna can be a promising candidate for MIMO diversity applications.

Investigation on The Mutual Coupling Reduction in MIMO Antenna using Dual Split CSRR EBG

In many applications, it is now desirable to prevent a device from being affected by an external electromagnetic field or prevent the device’s intrusion into the electromagnetic field. The elimination or reduction of coupling between neighbouring systems is desired, and this is achieved through the use of electromagnetic shields and absorbers. This project focuses on an investigation that analysed the band-gap region for unit cell EBG simulation and unit cell array simulation. It is revealed that unit cell simulation provides an accurate result where the band-gap region is from 2 GHz to 3.5 GHz. The performance of the EBG is validated using a microstrip MIMO antenna. Using EBG, the S21 is reduced from -18.63 dB to -28.80 dB. Meanwhile, the MIMO antenna gain with the proposed EBG is 2.78 dBi, greater than MIMO antenna without EBG (2.47 dBi).

Reduction of Mutual Coupling in UWB/MIMO Antenna Using Stub Loading Technique

Abstract The research presents mutual coupling reduction between UWB-MIMO antenna elements using stub loading technique. The proposed 2 × 2 UWB antenna geometry consists of two circular-shaped monopole radiators with a partial ground for perfect impedance matching. Stubs of 20 mm × 0.2 mm are inserted between the two antenna elements in the ground plane to improve the isolation. The decoupling stub leads to a mutual coupling reduction of less than 20 dB. The farfield measurement at a selected frequency of 10 GHz confirms an omnidirectional radiation pattern. Different MIMO antenna metric such as channel capacity loss (CCL), mean effective gain (MEG), total active reflection coefficient (TARC), envelope correlation coefficient (ECC), and surface current are presented. Details of the design considerations and the simulation and measurement results are presented and discussed. The proposed MIMO antenna array can be well suited for UWB applications.