Proposed Multiple-input Multiple-output Antenna Research Articles

Conformal eight‐port dual band antenna with switchable radiation pattern for 5G enabled on‐body wireless communications

AbstractA novel conformal quasi‐yagi antenna and its Multiple Input Multiple Output (MIMO) implementations for wireless body area networks (WBAN) application is reported in this letter. The antenna is developed on a 0.05 mm thin polyimide substrate making the antenna more flexible and conformal. The footprint of the proposed antenna is 35 × 35 mm with a dual dipole arm‐like structure making it resonant at 2.45 and 3.5 GHz covering the industrial scientific and medical and 5G bands for WBAN communications. The antenna is excited using a microstrip‐to‐slotline termination suitably terminated by a circular patch to realize the impedance matching. The ground plane is shaped to maintain good isolation between neighboring antennas during the eight‐element MIMO antenna development. The MIMO antennas are arranged circularly to achieve good antenna coverage along the azimuth directions. The antenna generates a tangential radiation pattern to the plane of the human body making it suitable for on‐body wireless communications. The proposed antenna offers a rotatable radiation pattern by appropriately choosing the antenna port of excitation. The proposed MIMO antenna offers an average gain of 4.5 and 5.2 dBi at 2.45 and 3.5 GHz, respectively. The MIMO antenna parameters are evaluated and presented. The calculated MIMO parameters are within the acceptable limits. Thus, the flexible nature with rotatable directional radiation patterns has made this antenna an attractive choice for on‐body communications in WBAN.

A compact bent microstrip-based wideband millimeter wave MIMO antenna for 5G applications

Abstract This paper proposes a wideband four-element multiple-input multiple-output (MIMO) antenna operating in the millimeter-wave frequency band for 5G communications from 24.37–39.44 and 45.09–50.62 GHz. The antenna design has been realized using Rogers 5880 substrate and consists of a T-shaped strip that is attached to the top of a 50 Ω feeding line. Two microstrip lines are affixed at the terminal points of T-shaped strip and bent toward the feeding structure. These bent strip lines are then extended by joining two additional L-shaped microstrip lines. On the back, there is a partial defective ground plane featuring a rectangular slot and a thin strip line located at its center. The dimensions of the proposed single element and MIMO antenna are 0.933λ × 0.933λ × 0.024λ and 1.865λ × 1.865λ × 0.024λ, respectively (at 28 GHz), while the edge-to-edge distance between the radiation elements of the MIMO antenna is 4.0 mm. The design incorporates an efficient passive fan-shaped decoupling structure to decrease coupling between antenna elements. Simulations and experimental results show good agreement with each other. For all resonant frequencies the measured peak gain is greater than 4.85 dBi, radiation efficiency is over 90%, diversity gain is greater than 9.5, ECC is less than 0.025, TARC is less than -10 dB and CCL is below 0.4 bits/s/Hz. The proposed MIMO antenna, with its wide bandwidth, high gain, high inter-port isolation, and high efficiency characteristics, can be used for 5G wireless communication applications.

A High-Frequency Planar-Configured Millimeter-Wave MIMO Antenna for Fifth-Generation NR Operations

This article presents a simple planar millimeter-wave (mm-wave) multiple input multiple output (MIMO) antenna with four closely spaced radiating elements. The antenna is intended to enhance the bandwidth for 5G new radio (NR) applications and also cover the industrial Ka-band (26.5-40 GHz), Q-band (30-50 GHz), and U-band (40-60 GHz) frequency ranges. The antenna is designed using Rogers RT/duroid 5880 substrate with a size of 25 × 26 × 1.6 mm3. The proposed antenna consists of four identical radiating elements with two of them positioned in a linear configuration facing each other, while the other two elements are placed opposite to the first two, which improves isolation between the elements. Across the entire operating frequency range (26-60 GHz), the antenna demonstrated excellent performance, including 34 GHz wide bandwidth, high isolation of >25 dB, nearly omnidirectional radiation patterns, high gain of 11.1 dB with a high radiation efficiency of 94%, low envelope correlation coefficient (ECC) of 0.0068, and high diversity gain (DG) of 9.967 dB. The simulated findings exhibit a strong positive correlation with the experimental results. The proposed MIMO antenna design is a promising solution for 5G NR applications.

Compact eight-element MIMO antenna array for sub 6 GHz Mobile applications

A compact eight-element multiple-input multiple-output (MIMO) antenna array operating at the sub-6-GHz (LTE band 52) for the 5G handheld applications is proposed. The antenna array is realized by employing eight couple-fed slots etched on the ground plane of the MIMO antenna system. The size of the slot radiators excites the required operating bandwidth. A parametric analysis study of the effect of varying the size of the slot radiators on the ground plane is provided to give some insight into the operation of the proposed antenna system. The radiators are excited by 50-Ω strip lines. Rectangular-shaped slits are used as isolation structures to mitigate the mutual coupling effect between elements, resulting in a low Envelope Correlation Coefficient (ECC) of less than 0.1 at the operating bandwidth. The proposed MIMO antenna was fabricated and experimentally validated. The measured and simulated results are in good agreement. Other MIMO performance indicators, such as radiation patterns, Mean Effective Gain (MEG), and the proposed MIMO antenna system’s total efficiencies, are being analyzed. Measurements and simulation results are consistent, which shows that the proposed antenna is a good candidate for 5G applications in the LTE band 52.

A planar UWB-MIMO antenna with high isolation and reconfigurable single band-elimination characteristics

A compact ultra-wideband (UWB) triple mode frequency reconfigurable multiple-input multiple-output (MIMO) antenna with electronically controllable single band elimination properties is presented in this work. The reported antenna comprises of two rotationally symmetric identical modified circular radiators each having tapered microstrip feed lines and separate partial defected ground structures (DGS). The slotted radiating patches consist of C-shaped parasitic strips placed at their centers. Two PIN diode switches were utilized to join and detach the C-shaped strip and slotted circular radiator, and thus total four PIN diodes are employed in the dual-port MIMO configuration to achieve switchable operation between UWB and single band-notched UWB characteristics. The recommended antenna possesses ultrawide bandwidth with Snn ≤ −10 dB except at the rejected bands and attains isolation better than −21 dB in all reconfigurable modes. The proposed MIMO antenna shows good diversity behavior which has been proved through the study of various parameters, such as envelope correlation coefficient (ECC), CCL and diversity gain with values fulfilling the acceptable standard for practical usage. High diversity gain and ECC value below 0.0006 are obtained for all the modes. The suggested antenna structure is ideally suited for ultrawideband MIMO systems with on-demand suppression of WiMAX or WLAN signals.

Higher Order MIMO Antenna Design Using Capacitively Coupled Meandered Loop Element for 5G Smartphone Applications

In this paper, a compact 10-element multiple-input multiple-output (MIMO) antenna system for fifth generation (5G) wireless communication system is presented. The antenna structure has a T-shaped feeding element and a reduced size capacitively coupled meandered loop radiating element. The proposed MIMO antenna system is operating at 3.5 GHz. The MIMO antenna element is self-isolated and it has a compact size of 13.45×6 mm2. It exhibits very good isolation of more than 15 dB without using any external decoupling structure like a neutralization line or slot technique. Furthermore, performance parameters like total efficiency are around 40-64%, envelope correlation coefficient (ECC) is below 0.02, while gain of all antennas is between 3-3.4dBi. The performance of the proposed MIMO antenna is also verified through the measurement of its fabricated prototype. In this paper, a compact 10-element multiple-input multiple-output (MIMO) antenna system for fifth generation (5G) wireless communication system is presented.

Dual-Band Dual-Circularly Polarized Fabry-Pérot Cavity MIMO Antenna Using CMM-Based Polarization Converter and MMA for Vehicular Satellite Communications

A 2 × 2 dual-band dual-circularly polarized (CP) Fabry-Pérot cavity (FPC) multiple input multiple output (MIMO) antenna is proposed in this paper. It is formed by arranging four identical FPC antenna elements with 90° rotation. The FPC antenna element is composed of a single linearly polarized (LP) feeder and a chiral metamaterial (CMM)-based partially reflective surface (PRS), which acts as a polarization converter. The feeder is with a hybrid structure of a slot radiator operating in the low band and a patch radiator in the high band. As the orthogonal currents on the end and center arms of the H-shaped patch break the degeneracy of two CP waves at different frequencies, the PRS simultaneously realizes left-hand CP (LHCP) and right-hand CP (RHCP) features at two different bands, respectively. To enhance the port isolation between two adjacent antenna elements, a broadband, wide-angle, polarization-independent metamaterial absorber (MMA) is introduced to suppress the space wave coupling. To verify the design concept, the proposed MIMO antenna prototype is fabricated and measured. The measured bandwidth with a voltage standing wave ratio (VSWR) of less than 2 covers 3.32-3.42 GHz and 6.23-6.93 GHz, and the LHCP pattern and RHCP pattern are realized at 3.33-3.42 GHz (2.7%) and 6.59-6.75 GHz (2.4%), respectively. A maximum gain enhancement is up to 5.31 dBi in the low band and up to 4.3 dBi in the high band. In addition, the port isolation is better than 42 dB, and the ECC is less than -40 dB. With these performances, the proposed MIMO antenna is suitable for vehicular satellite communication applications.

A Novel Shaped Four Port MIMO Antenna for Wireless Communication

This paper presents a compact novel shaped micro strip line fed four element Multiple Input Multiple Output (MIMO) antenna for wireless application at 2.4 GHz. Four vertically oriented identical rectangular patch antennas are used to form a hollow cylinder of rectangular cross section. The direction of radiation of each antenna is thus oriented at 900 with respect to its two adjacent antennas providing good isolation between adjacent antennas in this compact MIMO system. Each antenna element has the dimensions of 0.30λx0.38λx0.012λ. The whole MIMO antenna has the outer dimensions of 0.38λx0.38λx0.30λ. The uniqueness of the proposed MIMO antenna is that the inner space of the hollow cylindrical structure can be used for hosting the associated signal processing unit of the whole system. Performance parameters of the proposed MIMO antenna are investigated using Computer Simulation Technology (CST). Envelope Correlation Coefficient (ECC) less than 0.033 and almost 10dB Diversity Gain (DG) are obtained at 2.4 GHz for this simple and compact antenna system. Ratio of Mean Effective Gain (MEG) of any two antennas is less than 0.02dB. Performance parameters of the proposed MIMO antenna system are compared with similar types of antennas found in recent literature.

Modeling of quasi-tapered microstrip antenna based on expansion-exponential tapered method and its application for wideband MIMO structure

In this paper, a quasi-tapered wideband antenna using a circular-shaped with an inverted-omega ground structure is presented. A tapered antenna is usually developed based on linear-shape, exponential-shape, or Klopfenstein-shape tapper. Here, we proposed an expansion of the exponential tapered model to investigate the circular-shaped tapered structure. In detail, the proposed antenna is divided into circular divergent and circular convergent-tapered sections. Then, the impedance ratio is utilized to analyze the tapered structure. Moreover, the ABCD parameter based on the transmission line model is used to investigate the overall antenna structure. The proposed model was verified by finite element method and also step impedance resonance evaluation. Furthermore, the proposed wideband antenna is also developed with multiple input multiple output (MIMO) and mutual coupling reduction structure. The antenna was fabricated on a Rogers RT/Duroid 5880 substrate with εr = 2.2, thickness of h = 1.6 mm, and dielectric loss tan d = 0.0009. As a result, the proposed MIMO antenna can successfully cover the 4G (3.3 GHz), mid-band 5G (3.4–3.8 GHz), WLAN (5.8 GHz), X-band (10–11 GHz), and high-band 5G (24.5–26 GHz) communications. A good agreement between the simulated and measured results validates the proposed method.

A Car Logo Design-Inspired CPW-Fed Semitransparent Antenna for Vehicular Applications

In this paper, a quad-port multiple-input multiple-output (MIMO) semitransparent antenna is designed for automotive applications. The transparent soda lime glass substrate is used in the prototype antenna for windshield applications, and the radiator is nontransparent copper metal. The unit cell radiator of the MIMO antenna is similar to the “NISSAN automobile-like” logo. The proposed MIMO antenna has a −10 dB impedance bandwidth of 3.4 to 11 GHz. The edge-to-edge distance between the elements in the MIMO configuration is 6 mm. The antenna elements are perpendicularly oriented to offer dual (horizontal and vertical) polarization, which aids in providing better isolation and good signal reception in all directions. The isolation between the resonating elements is greater than 15 dB without the use of any decoupling structure. The diversity metrics are examined in order to gain a better understanding of the MIMO antenna performance. The envelope correlation coefficient (ECC) is less than 0.01, diversity gain (DG) is greater than 9.98 dB, and the total active reflection coefficient (TARC) and channel capacity loss (CCL) are less than −10 dB and 0.07 bits/s/Hz, respectively. The quad-port MIMO antenna offers transparency of 52.26% over the entire area. The proposed antenna could be suitable for automotive applications such as intelligent transportation systems (ITS), vehicular communications, and the automatic vehicle identifier (AVI).

An Isolation Improvement for Closely Spaced MIMO Antenna Using λ/4 Distance for WLAN Applications

An isolation improvement for a closely spaced quad port multiple-input multiple-output (MIMO) antenna for WLAN applications is presented. The proposed antenna consists of four L-shaped monopole microstrip patch antennas with a rectangular slot at the center and truncated edges at the corner of each patch element. Interelement isolation is improved by more than 12 dB by considering the patch size, ground size, and distance between the patch elements. The designed antenna uses λ/4 distance between the patch elements. The slot in each patch improves the bandwidth, and truncated edges at the corner of the patch improve the impedance matching of the antenna. The proposed MIMO antenna is designed with the overall dimensions of 45.5 mm × 45.5 mm × 1.96 mm. The MIMO parameters for the proposed technique, which include envelope correlation coefficient (E.C.C.) are less than 0.5, and the diversity gain (D.G.) is 10 dB, suggesting this antenna’s suitability for MIMO operations. The average peak realized gain (A.P.R.G.) and radiation efficiency (RE) is 2.8 dBi and greater than 80% for the prescribed band of interest. The antenna element is fabricated and tested using microwave analyzer N9917A. The measured result seems to be in good contact with the simulation. The proposed MIMO antenna is well-suitable for WLAN applications.

A Compact Planar Monopole UWB MIMO Antenna for Short-Range Indoor Applications.

A compact, four-element planar MIMO (Multiple Input, Multiple Output) antenna that operates in an ultra-wideband is presented for diversity application. The orthogonal position of the unit cells replicates the single antenna thrice, thereby decreasing mutual coupling. A UWB MIMO antenna measuring 35 × 35 × 1.6 mm3 is built using a microstrip line (50 Ω impedance) on an FR4 substrate having a thickness of 1.6 mm. The ground plane and radiator of this antenna are adjusted in several ways to bring it within its operating constraints between the frequencies of 3.1 GHz and 10.6 GHz. This technique makes the antenna small and covers the entire ultra-wideband (UWB) frequency range. The NI USRP was used to test the proposed MIMO antenna to determine its real-time performance. Based on the computed results, we conclude that this proposed antenna has outstanding characteristics in terms of performance and is suitable for wireless ultra-wideband indoor communication and diversity utilization with a small size.

A Dual Port Hybrid Super-wideband MIMO Antenna with Diminished CCL and High BDR for IoT Applications

In this work, a simple hybrid dual port skull-shaped super wideband Multiple Input Multiple Output (MIMO) antenna with improved isolation is designed and analyzed. Each antenna element consists of a skull-shaped radiator along with a rectangular notched chamfered Defective Ground Plane structure (DGS). The proposed antenna’s impedance bandwidth and radiation characteristics are improved by the triple elliptical inclined slot and DGS together. To accomplish the proposed MIMO configuration, the antenna elements are further organized in a linear arrangement. Deteriorated isolation characteristics, which are the key bottleneck for such MIMO schemes, are significantly improved in the proposed design by using a corrugated T-shaped strip decoupling plane. This 2-port MIMO antenna is placed on top of a glass epoxy FR4 substrate and has an overall dimension of 45 × 50 × 0.787 mm3 (0.20λ × 0.19λ × 0.003λ). The proposed MIMO antenna is fabricated and the experimental results are verified with the simulation results. The results indicate that the proposed antenna covers an operational bandwidth of 48.75 GHz (1.25–50 GHz) with a fractional bandwidth of 190.24% and offers an isolation of less than −20 dB throughout the frequency range of operation. The proposed MIMO has an extremely high bandwidth dimension ratio (BDR) of 5092 among the reported antennas. An optimal performance has been achieved with a lower value of Envelope Correlation Coefficient (ECC) ≤ 0.02, high multiplexing efficiency, extremely lower Channel Capacity Loss (CCL) of 0.2, and omnidirectional radiation characteristics. These design metrics show the potential of our antenna to operate for eMBB (Enhanced Mobile Broadband) applications which includes 5G, Augmented reality, and etc.

Dual-Band Millimeter Wave 2 × 2 MIMO Slot Antenna with Low Mutual Coupling for 5G Networks

A dual-band 28/38 GHz multiple-input multiple-output (MIMO) two elements antenna for the next 5G network is proposed in this paper. The single element is composed of a slot monopole antenna loaded with stub and a small crescent with an entire size of 15 × 15 mm2. The two elements are added to compose the suggested configuration. One of the antennas is printed on the upper layer while the other is located on it's back of the substrate to improve the coupling between elements without using any decoupling structures. The innovative antenna of dual-band works at 28/38 GHz and is achieved by adjusting the stub length and the crescent radius. The introduced MIMO antenna system has been experimented and the results have the same compatible trace with the simulated outcomes. The proposed two ports MIMO achieved a reasonable gain that reaches 5.7 and 6.9 dBi in the 28/38 GHz bands, respectively. The proposed MIMO antenna performance is also analyzed and achieved the envelope correlation coefficient, a diversity gain, and channel capacity Loss of about 10–4, 10 dB, and less than 0.3 bit/s/Hz, respectively over the 28/38 GHz bands. Finally, from the simulated and measured outcomes, it can be confirmed that the suggested MIMO antenna system can be applied to 5G wireless telecommunication applications.

Compact UWB MIMO Antenna for 5G Millimeter-Wave Applications.

This paper presents a printed multiple-input multiple-output (MIMO) antenna with the advantages of compact size, good MIMO diversity performance and simple geometry for fifth-generation (5G) millimeter-wave (mm-Wave) applications. The antenna offers a novel Ultra-Wide Band (UWB) operation from 25 to 50 GHz, using a Defective Ground Structure (DGS) technology. Firstly, its compact size makes it suitable for integrating different telecommunication devices for various applications, with a prototype fabricated having a total size of 33 mm × 33 mm × 0.233 mm. Second, the mutual coupling between the individual elements severely impacts the diversity properties of the MIMO antenna system. An effective technique of orthogonally positioning the antenna elements to each other increased their isolation; thus, the MIMO system provides the best diversity performance. The performance of the proposed MIMO antenna was investigated in terms of S-parameters and MIMO diversity parameters to ensure its suitability for future 5G mm-Wave applications. Finally, the proposed work was verified by measurements and exhibited a good match between simulated and measured results. It achieves UWB, high isolation, low mutual coupling, and good MIMO diversity performance, making it a good candidate and seamlessly housed in 5G mm-Wave applications.

A Compact High-Isolation Four-Element MIMO Antenna with Asymptote-Shaped Structure

The demand for high-speed wireless communication systems has led to the development of ultrawide-band (UWB) antennas with a compact size and high performance. In this paper, we propose a novel four-port multiple-input multiple-output (MIMO) antenna with an asymptote-shaped structure that overcomes the limitations of existing designs for UWB applications. The antenna elements are placed orthogonally to each other for polarization diversity, and each element features a stepped rectangular patch with a tapered microstrip feedline. The unique structure of the antenna significantly reduces its dimensions to 42 × 42 mm2 (0.43λ×0.43λ@ 3.09GHz), making it highly desirable for use in small wireless devices. To further enhance the antenna's performance, we use two parasitic tapes on the ground plane at the back as decoupling structures between adjacent elements. The tapes are designed in a windmill shape and a rotating extended cross shape, respectively, to further improve the isolation. We fabricated and measured the proposed antenna design on a single-layer substrate (FR4) with a dielectric constant of 4.4 and a thickness of 1 mm. The measured results show that the impedance bandwidth of the antenna is 3.09-12 GHz, with an isolation of -16.4 dB, an envelope correlation coefficient (ECC) of 0.02, a diversity gain (DG) of 9.991 dB, an average total effective reflection coefficient (TARC) of -20 dB, an overall group delay value less than 1.4 ns, and a peak gain of 5.1 dBi. Although there may be some antennas that have better performance in one or two specific aspects, our proposed antenna has an excellent trade-off among all the antenna characteristics including bandwidth, size, and isolation. The proposed antenna also exhibits good quasi-omnidirectional radiation properties, making it well-suited for a range of emerging UWB-MIMO communication systems, particularly in small wireless devices. In summary, the compact size and ultrawide-band capabilities of the proposed MIMO antenna design, coupled with its improved performance compared to other recent UWB-MIMO designs, make it a promising candidate for 5G and next-generation wireless communication systems.

28/38 GHz dual-band MIMO antenna with wideband and high gain properties for 5G applications

In this paper, a novel high gain 4-element dual-band multiple-input multiple-output (MIMO) antenna is proposed for fifth generation (5G) wireless applications. A crescent shape is created initially from a circular structure and then the proposed antenna is formed by using slots and Defected Ground Structures (DGS) to set resonances at the desired frequencies. The proposed MIMO antenna operates both at 28 GHz and 38 GHz frequencies. In addition, the MIMO antenna has 3.05 GHz and 2.41 GHz bandwidth at those frequencies, respectively. The antenna elements are orthogonally placed to each other as a design concept to enhance the isolation between the elements up to 30 dB. Moreover, the MIMO antenna has maximum measured gains of 8.14 dB and 8.04 dB at 28 GHz and 38 GHz, respectively. The antenna size achieves compactness with the total size of 60 × 60 × 0.508 mm3. The designed MIMO antenna is also evaluated in terms of important MIMO parameters such as diversity gain (DG), envelope correlation coefficient (ECC), mean effective gain (MEG), and channel capacity loss (CCL). The proposed antenna is a great candidate for modern 5G applications that require both wideband and high gain properties with its MIMO antenna parameters of DG, ECC , MEG and CCL.

The effect of changing the formation of multiple input multiple output antennas on the gain

In this paper, different 2×1 and 2×2 multiple input multiple output (MIMO) antennas were investigated with changing substrate shapes and changing the placing of the patches on the substrate, all the investigated antennas based on FR-4 substrate are characterized by , and loss , with a partial ground. The original antenna covered 3.4 to 13.5 GHz. The best simulation results of the proposed 2×1 MIMO antenna received for 2×1 inverted with high ultra-wideband (UWB) with bandwidth up to 40 GHz, the received maximum gain was up to 6.51 dB, with an average gain of more than the original single antenna at about +1.27 dB. The best of eight 2×2 MIMO antennas configurations that give good results were shown. The best-received gain compared with a single antenna gain were at 4.2 GHz about +2.73, +1.17, and +0.92 dB for plus-shaped, loop, and chair-shaped respectively. A comparison between the proposed MIMO antennas and other reported works were done. The proposed MIMO antennas give a good maximum gain and are suitable for different narrow bands within the UWB such as wireless local area network (WLAN), worldwide interoperability for microwave access (WiMAX), aeronautical radio navigation (ARN), International Telecommunication Union 8-GHz (ITU-8), and X-Band applications with the ability to give high gain without the need to increase the radiated power of the transmitter antenna.

Circularly polarized three-element MIMO antenna with diversity and polarization reconfigurability techniques

This paper proposes a circularly polarized (CP) three-element multiple-input multiple-output (MIMO) antenna system with diversity and polarization reconfigurability techniques for wireless local-area network (WLAN) applications. The proposed MIMO antenna system employs two CP antennas with endfire characteristics and a broadside slot antenna. The polarization reconfigurability technique is achieved using pin diodes in all three antenna elements. Additionally, the three antennas have distinct directional radiation patterns, improving the MIMO antenna system's diversity performance. The three-element MIMO antenna system is fabricated for validation, and antenna parameters are measured. For all the states, the proposed antenna provides good antenna characteristics for the WLAN frequency band (5.15 GHz − 5.35 GHz). The three-element MIMO antenna exhibits good port-to-port isolation, and MIMO parameters like total active reflection coefficient (TARC), channel capacity loss (CCL), envelope correlation coefficient (ECC) and diversity gain (DG) are within the acceptable range.

Wideband Gain Enhancement of MIMO Antenna and Its Application in FMCW Radar Sensor Integrated With CMOS-Based Transceiver Chip for Human Respiratory Monitoring

A novel compact multiple-input multiple-output (MIMO) antenna is proposed with wideband gain enhancement. It consists of two identical antenna elements spacing about half wavelength. First, a 1-to-2 Y-shaped power divider with wideband anti-phase outputs is designed to feed two modified Vivaldi radiators. The currents on the two radiating surfaces keep the same direction in a wideband to increase radiation without being canceled. Second, the square-ring unit cell is analyzed to form metasurface, placed in the front of the radiator. It can guide the forward electromagnetic (EM) radiation while reducing the backward radiation. Third, a U-shaped slot is etched between the two modified Vivaldi radiators. It is approximated as an effective electrically small dipole radiator. Such arrangement further effectively enhances the radiation performance in the direction of the main lobe and destructively interferes with the sidelobe radiation. These features make the antenna far-field radiation pattern reshaped. Thereby, the gain is improved in a wide bandwidth. Meanwhile, the MIMO antenna diversity performance is analyzed with low mutual coupling. Wideband gain enhancement contributes to improve the detection capability of the frequency modulated continuous wave (FMCW) radar sensor. As a proof of concept, the proposed MIMO antenna prototype is fabricated. The measured impedance bandwidth ranges from 11.5 to 21.3 GHz [59.76% fractional bandwidth (FBW)] with isolation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\ge 24.92$ </tex-math></inline-formula> dB. The gain is up to 10.6 dBi, the radiation efficiency is 88.01%–90.02%, and the envelope correlation coefficient (ECC) is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\le 0.00122$ </tex-math></inline-formula> . Integrated with the transceiver chip fabricated on the 65 nm CMOS process, the proposed MIMO antenna is applied in the FMCW radar sensor. The test system is built up, and the experiments on different breathing conditions are conducted for different human subjects. The proposed MIMO antenna could reduce measurement error, thereby improving measurement accuracy for human respiratory monitoring.