MIMO Applications Research Articles

Half‐mode SIW cavity antenna for tri‐band MIMO applications

AbstractA half‐mode (HM) substrate‐integrated‐waveguide (SIW) cavity antenna is designed for tri‐band multiple‐input‐multiple‐output (MIMO) applications. Three cavity edges are shorted by metal posts while one aperture is open to radiate cavity energy into free space. To meet MIMO applications, a T‐shaped slot is etched to split the single HM cavity into two equal SIW subcavities and then they are excited by coaxial feeding ports to realize two antenna elements. To obtain tri‐band operations, four additional rectangle slots are cut, which introduces six quarter modes with different resonating regions. With the cavity size of 0.20λ0 × 0.40λ0, a fabricated prototype exhibits three operating bands with center frequencies of 3.33, 4.09, and 4.72 GHz and peak gain of 4.51, 4.05, and 3.93 dBi. Moreover, the measured port isolation is higher than 18.26 dB and the measured envelope correlation coefficient is below 0.05 within the frequency of interest.

Isolation and Gain Enhancement Using Metamaterial Based Superstrate for MIMO Applications

Isolation and Gain Enhancement Using Metamaterial Based Superstrate for MIMO Applications

Twelve port MIMO antenna with polarisation diversity for cognitive radio applications

In this letter, to overcome the drawbacks in reconfigurable antennas and maintain all the advantages in planar antennas, a compact 12 port integrated UWB and narrow band (NB)/wideband antennas for cognitive radio MIMO applications with polarisation diversity is presented. The proposed system has one pair of UWB antennas for sensing the spectrum and five pairs of NB/wideband antennas for communication. Each pair has two identical antennas, which are orthogonal to each other for polarisation diversity. Sensing antennas linked with ports (P1 and P7) have operating bandwidth of 3–11 GHz, whereas the antennas linked with ports (P2 and P8), (P3 and P9), (P4 and P10), (P5 and P11), and (P6 and P12) have operating bandwidths of 3.5–5.8 GHz, 2.8–3.5 GHz and 5.6–8 GHz (dual band), 8–8.4 GHz and 9–9.8 GHz (dual band), 8.4–9 GHz, and 9.8–11 GHz, respectively. Moreover, the overall volume of the antenna is 58mm × 50mm × 1.6 mm and the entire UWB spectrum is covered by NB/wideband antennas. Also, without any decoupling network, isolation of better than 20 and 15 dB is achieved between every two identical and non-identical antennas, respectively.

Complementary meander‐line‐inspired dielectric resonator multiple‐input‐multiple‐output antenna for dual‐band applications

The communication presents a simple dielectric resonator (DR) multiple-input-multiple-output (MIMO) dual-band antenna. It utilizes two “I”-shaped DR elements to construct an “I”-shaped DR array antenna (IDRAA) for MIMO applications. The ground plane of the antenna is defected by two spiral complementary meander lines and two circular ground slots. In the configuration, two “I”-shaped DR elements are placed with a separation of 0.098λ. The antenna covers dual-band frequency spectra from 3.46 to 5.37 GHz (43.26%) and from 5.89 to 6.49 GHz (9.7%). It ensures the C-band downlink (3.7-4.2 GHz), uplink (5.925-6.425 GHz), and WiMAX (5.15-5.35 GHz) frequency bands. Each DR element is excited with a 50-Ω microstrip line feed with aperture-coupling mechanism. The antenna offers very high port isolation of around 18.5 and 20 dB in the lower band and upper band, respectively. The proposed structure is suitable to operate in the MIMO system because of its very nominal envelope correlation coefficient (<0.015) and high diversity gain (>9.8). The MIMO antenna provides very good mean effective gain value (±0.35 dB) and low channel capacity loss (<0.35 bit/s/Hz) throughout the entire operating bands. Simulated and measured results are in good agreement and they approve the suitability of the proposed IDRAA for C-band uplink and downlink applications and WiMAX band applications.

Wideband DOA estimation with deficient snapshots using low rank Toeplitz structure

In array signal processing, most existing direction-of-arrival (DOA) estimation methods fail to work given deficient snapshots. To solve this problem, this Letter proposes a novel wideband DOA estimation technique by utilising the sparse representation in terms of the low rank Toeplitz structure presented in uniform array geometries, followed by an enhanced MUSIC method. Specifically, each sub-band segment is first focused into the reference frequency band to collect the coherent covariance matrix even in the lack of sufficient samples. Then, the covariance matrix is denoised through a structure-based sparse reconstruction, which exploits the low rank Toeplitz structure. Finally, the DOAs is efficiently estimated via an enhanced MUSIC method. Simulation result confirms the efficacy of the proposed method that works well in MIMO and radar applications.

Compact four‐port MIMO dielectric resonator antenna with pattern diversity

A new compact four-port multi-input-multi-output (MIMO) dielectric resonator (DR) antenna is proposed with pattern diversity. The antenna contains four DR elements, the epsilon-shaped and cylindrical. These four DR elements are placed together such that they resonate at the same frequency. The specific geometry of the DR elements allows to place them at separation which is much smaller than operating wavelength. Hence, the combination of the four DR elements acts as a single DR. This helps in maintaining the compactness of the antenna structure. The antenna operates with the hybrid of modes and excited in epsilon-shaped and cylindrical DR elements, respectively. The excitation of these orthogonal modes helps in obtaining the pattern diversity allowing the antenna for multi-directional coverage. The antenna provides 15.73% overlapping 10 dB impedance bandwidth with the variation of gain within ranges 4–6 and 6–6.5 dBi at port 1/2 and port 3/4, respectively. In addition, the antenna provides the high radiation efficiency >93% at port 1/2 and 97% at port 3/4. Other parameters required for MIMO applications such as envelope correlation coefficient and diversity gain are within the acceptable limits.

Array Antenna Feeding Network Design for 5G MIMO Applications

DOI : 10.26650/electrica.2019.19004 Emerging smart antenna systems require different beam patterns of multiple antennas. Although adjustable phase shifters are mostly used in continuous-beam systems, the Butler matrix is used in switching-beam systems due to its low cost and easy fabrication. In this study, an antenna-array-feeding circuit based on the Butler matrix that can be used for Multiple Input Multiple Output applications is designed for 5G new radio. With the proposed switching system, the control of four beams can be achieved. The Butler circuit, designed to cover the 3.5–4.2 GHz 5G band, has a low complexity and is capable of meeting the need for high data throughput. A simulation of the circuit and circuit sub-elements designed using a 0.508-mm-thick substrate material is performed using the Computer Simulation Technology Microwave Studio computer-aided design tool. Furthermore, a prototype of the Butler circuit is fabricated, and the amplitude and phase variations at the output ports are measured. An average transmission loss of the feed circuit is measured as 1.5 dB, and when the length of the Phase Shifter in the circuit is set to λ/8, with a four-element linear array added to the output of the Butler circuit, the main beam is steered to ±15o and ±35o having maximum gain in the 6.39–8.77 dBi range. Cite this article as : Turker Tokan N. Array Antenna Feeding Network Design for 5G MIMO Applications. Electrica, 2019; 19(2): 120-127.

Millimeter-Wave Continuous-Mode Power Amplifier for 5G MIMO Applications

This paper presents three millimeter-wave (mm-wave) continuous-mode power amplifiers (PAs) for fifth-generation (5G) MIMO applications, including a two-stage differential continuous-mode Class-F−1 PA in 130-nm SiGe process, a single-stage differential continuous-mode hybrid Class-F/F−1 PA in 45-nm SOI CMOS process, and a two-stage differential continuous-mode hybrid Class-F/F−1 PA in 45-nm SOI CMOS process. The first PA design covers 19–29.5 GHz, while the other two designs cover 23–41 GHz, all covering multiple 5G bands (24/28/37/39 GHz). All the presented PA designs are based on a proposed transformer-based continuous-mode harmonically tuned PA output network. This network provides proper harmonic impedance terminations for the fundamental, second-order, and third-order harmonic impedances, which supports continuous-mode Class-F−1 or hybrid Class-F/F−1 PA operations to achieve ultrawide bandwidth yet high efficiency. The first PA design achieves a wide $P_{\mathrm {sat}}~1$ -dB bandwidth of 19–29.5 GHz (43.3%) and high peak power-added efficiency (PAE) (43.5%). The second design achieves an ultrawide $P_{\mathrm {sat}}~1$ -dB bandwidth of 23.5–41 GHz (53.3%) and high peak PAE (46%). Moreover, it achieves 43.4% PAE and 18.6-dBm $P_{\mathrm {sat}}$ at 27 GHz, 40.2% PAE and 18.6-dBm $P_{\mathrm {sat}}$ at 37 GHz, and 41.2% PAE and 18.5-dBm $P_{\mathrm {sat}}$ at 39 GHz, respectively. The third PA design also achieves an ultrawide $P_{\mathrm {sat}}~1$ -dB bandwidth of 23.5–41 GHz (53.3%) and high peak PAE (43.2%). It achieves 43% PAE and 18.9-dBm $P_{\mathrm {sat}}$ at 27 GHz, 37% PAE and 19-dBm $P_{\mathrm {sat}}$ at 37 GHz, and 36% PAE and 18.9-dBm $P_{\mathrm {sat}}$ at 39 GHz, respectively. Extensive 64-/256-QAM modulation tests demonstrate the high PA linearity. Our proposed PA designs outperform the reported mm-wave silicon-based 5G PAs in terms of high efficiency over an ultrawide bandwidth.

Design and analysis of a compact 6-port microstrip MIMO antenna for 2.4-GHz WLAN applications

A compact 6-port MIMO antenna consisting of equilateral triangle elements have demonstrated in order to miniaturize the size and reduce the mutual coupling of antenna elements due to its geometrical shape. The antenna is designed on FR4 material and simulated results by HFSS software are provided. The simulated results show that the proposed MIMO antenna achieves the return loss of less than -10 dB and the mutual coupling of less than -12.5 dB between elements in a bandwidth ranging from 2329 to 2495 MHz, which entirely covers WLAN frequency band allocated from 2400 MHz to 2480 MHz. The obtained results indicate that the proposed antenna is a good candidate for MIMO applications.

High inter-port isolation dual circularly polarized slot antenna with split-ring resonator based novel metasurface

In this paper, a Dual Circularly Polarized (DCP) full-duplex planar slot antenna suitable for C-band applications is presented. The antenna has a single slot with a T-shaped stub that is shared by both the transmitting (TX) and receiving (RX) ports which operate at two mutually orthogonal circular polarizations. A metasurface made up of 4 pairs of face-to-face Split Ring Resonators (SRRs) acts as a decoupling network to enhance the isolation between TX and RX ports. The designed antenna has an impedance bandwidth of 1340 MHz which is 28.52% of centre frequency f0=4.71 GHz. The 3 dB axial ratio (AR) bandwidth is 8.97% centred at fAR=4.44 GHz whereas inter-port isolation is better than 27 dB and reaches up to 36 dB within the usable band. The proposed design also exhibits characteristics suitable for MIMO applications.

Isolation improvement of UWB MIMO antenna utilising molecule fractal structure

A compact four-element UWB MIMO antenna is proposed and its characteristics are investigated. The proposed antenna has a hexagon molecule-shaped fractal structure as its radiating element. The antenna elements are placed orthogonally to each other in order to yield good isolation, without any additional decoupling structure. The band rejection in WLAN band is attained by etching a C-shaped slot on each radiating element. The antenna has a compact size of 40 × 40 × 1.6 mm 3 and exhibits stable omni-directional radiation pattern. In addition, it shows an acceptable impedance bandwidth ( S 11 <; -10 dB) in the range 2.4-10.6 GHz with an isolation better than -20 dB over the UWB range. The performance of the proposed antenna is calculated in terms of antenna characteristics and MIMO parameters. The isolation level in-between the elements is found to be reasonable for MIMO application. The simulated and measured results are in good accord which makes the antenna a suitable candidate for massive MIMO and high-density packaging applications.

Not half bad

Researchers from the Samsung Electronics Network R&D Center in Shenzhen, China, have fabricated and tested a prototype compact substrate-integrated-waveguide (SIW) cavity multiple-input-multiple-output (MIMO) antenna with potential applications in 5G communications. The triangular half mode design achieves an enhanced bandwidth by merging together two coupled modes in the required operating band and boasts high isolation and radiation efficiency. Since it was first introduced a decade ago, SIW technology has drawn significant attention from researchers, with particular appeal in the antenna community. It can be fabricated in planar form using periodic metallic vias and has the advantages of high-Q factor and high-power capacity. In addition to this, cavity antennas resonating at cavity modes and radiating energy through opened cavity edges or etched slots are well-known for good radiation performance. The SIW cavity antenna is an antenna type created by introducing SIW technology into a cavity antenna design. Antennas transmitting and receiving wireless signals are important components in communication systems. The SIW cavity antenna can not only combine the attractive characteristics of conventional cavity antennas, such as good radiation performance and unidirectional radiation pattern, and but also offers the advantages of planar SIW technology, such as low profile, convenient fabrication, and easy integration with planar circuits. Author Bing-Jian Niu in anechoic chamber holding the proposed antenna. Analytical model of the proposed SIW cavity antenna. The SIW cavity antenna reported in the teams published Letter is designed for MIMO applications. By etching three slots, a half-mode SIW cavity was divided into four eighth-mode sub-cavities. Two large sub-cavities are excited by two coaxial ports to construct two antenna elements and cavity energy is coupled from the excited sub-cavities to the unexcited sub-cavities to enhance bandwidth. Thus, a compact two-element MIMO antenna with enhanced bandwidth can be designed and achieved. As is well-known, MIMO antennas have been widely adopted in modern wireless systems. Co-author Bing-Jing Niu, however, notes that: “Two major challenges faced in the design are narrow bandwidth and poor isolation among antenna elements. In our proposed design, three slots are etched in the half-mode SIW cavity. The width, length, and position of these slots are carefully selected in our Letter.” To meet the stringent requirements on antenna fabrication for wearable and portable devices, antenna designs are becoming more and more complex. Compact two-element MIMO antennas with enhanced bandwidth and high isolation are in great demand. With an enhanced bandwidth of 160 MHz, high isolation of 19.5 dB, antenna gain of 4.9 dBi, and radiation efficiency of 72.8%, the proposed SIW cavity MIMO antenna has good specifications and properties, making it suitable for potential applications for forthcoming fifth-generation wireless communications. Etched slots in the antenna provide new perspectives and opportunities for designing SIW cavity antennas, which not only radiate cavity energy into free space but also control the coupling between adjacent sub-cavities. The challenges the group overcome were the ideal selection of slot width, length, and position to optimise their prototype for its intended applications. In the proposed design, a wide rectangle slot is considered as the de-coupler to enhance the antenna isolation while two narrow T-shaped slot are utilised as the coupler to enhance the impedance bandwidth. The novel design makes it possible to increase the channel capacity and link reliability in wireless communication channels. In the short term, this work is expected to be utilised in the sub-6 GHz band. In the longer term, massive MIMO antenna based on SIW cavities will likely be successfully developed and integrated successfully into communication networks. Mr Niu discusses the groups upcoming work and views on the future of the field: “To improve the conformal performance of planar antennas, we are considering liquid crystal polymers (LCP) as a manufacturing substrate. It has the ability to support 3D integration and low tangents up to and including millimetre-wave (MMW) applications. In addition, to improve the MIMO performance, multiple-element MIMO antennas such as four-element and eight-element, have been developed in our own research group. As one of the most pervasive core technologies, massive MIMO antennas will lead to an accelerated pace of research and development in wireless communication with the promise of significant new breakthroughs over the next decade. An unprecedented number of antennas result in major technical challenges as well as new opportunities in antenna design, channel propagation, electronic components and circuit design, and communication theory. We hope the SIW cavity antenna is a good candidate to address this issue.”

Highly compact GaN-based all-digital transmitter chain including SPDT T/Rx switch for massive MIMO applications

AbstractThis paper presents a fully digital transmitter chain from baseband to antenna, including a modulator, two truly digital (i.e. fully switched) microwave power amplifiers and a transmit/receive switch. Both, amplifier and switch monolithic microwave integrated circuits were implemented in a GaN HEMT process. The novel amplifier design provides greatly reduced complexity, needing only three voltage sources. Measurements were conducted using 5, 20, and 100 MHz wide baseband signals. Carrier frequencies cover the 900 and 2000 MHz bands. For the 5 MHz BB signal an ACLR of over 52 dB is reached, fulfilling the 3GPP specs for base station use while still maintaining a final-stage drain efficiency of 46% at 6.5 dB peak to average power ratio. Full-scale output power at 30 V supply voltage was measured to exceed 3 W at 80% drain efficiency. Further features of this digital amplifier approach include small form factor and frequency agility, making it an ideal candidate for software defined radio.

Compact UWB MIMO antenna with cross‐shaped unconnected ground stub using characteristic mode analysis

AbstractIn this letter, a compact ultrawideband (UWB) multi‐input‐multi‐output (MIMO) antenna with cross‐shaped unconnected Ground stub using characteristic mode analysis (CMA) is presented. The proposed work consists of two elliptical shape monopole UWB antenna with a cross‐shaped stub in the ground plane. The compact MIMO antenna has the dimension of 25 × 25 × 1.6 mm3. These monopoles are able to excite several characteristic modes (CMs), which support to wideband resonance, and cross‐shaped stub support CM at lower frequency band in the ground plane and reduces mutual coupling between monopoles. The UWB MIMO antenna is resonating in frequency bands from 2.97 to 13.8 GHz bandwidth with a good mutual coupling (&lt;−15 dB). The diversity performance envelop correlation coefficient (ECC) and diversity gain (DG) of the antenna are less than 0.05 and more than 9.97, respectively. The experimental result confirming a good treaty with the simulated ones, so that the proposed antenna is suitable for compact UWB MIMO applications.

Dual-Polarized, High-Gain, and Low-Profile Magnetic Current Array Antenna

In this communication, a dual-polarized 36-element (3 × 6 × 2) magnetic current array antenna is designed without using complex feeding network. Instead, a pair of differential feeds is adopted to excite the overall dual-polarized array within a low profile. Such a simple feeding strategy is achieved by using the TM90 mode of a microstrip antenna, which is loaded by 3 × 4 identical half-wavelength slots for each polarization. In this configuration, an in-phase 3 × 6 element singlepolarized magnetic current array is achieved for high gain, but with narrow bandwidth due to the high-order mode. By trivially 90° rotating and combining, the proposed dual-polarized, high-gain, and low-profile magnetic current array is designed, constructed, and measured. Within a total size of 2.92λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 2.92λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.085λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at the center frequency), the measured maximum gain is 15.5 dBi, also with the merits of low profile, low sidelobes, simple feeding, and high port isolation, exhibiting promising usage in MIMO and diversity applications.

A Symmetrical Dual-Beam Bowtie Antenna With Gain Enhancement Using Metamaterial for 5G MIMO Applications

A symmetrical dual-beam end-fire bowtie antenna with gain enhancement is achieved by integrating three pairs of metamaterial (MTM) arrays for 5G MIMO applications. The first pair of MTM array with high refractive index (HRI) are deployed to form a wide beam antenna. The second pair of HRI MTM array are arranged along the end-fire direction (x-direction) in front of the radiators in order to split the single wide beam into dual beam. Besides, the third pair of anisotropic MTM array with HRI along x-direction and near zero refractive along y-direction are incorporated in front of the second pair of MTM array to improve the gain performance. The proposed technique is verified by both the full-wave electromagnetic simulation and experiment, and the simulated and measured results agree very well with each other. Moreover, the measured results reveal that the main beam directions of the proposed antenna point to ±30° with respect to the end-fire direction (0°) over 24.25-27.5 GHz, with a maximum gain of 7.4 dBi at 26 GHz and a 4.2 dB gain improvement compared to the wide beam antenna.

A Low-Profile, Dual-Polarized Patch Antenna for 5G MIMO Application

A dual-polarized patch antenna with an extremely low profile is proposed in this communication. It consists of a main radiator, an annulus, and a reflector. The main radiator contains two pairs of differentially driven feedlines and an irregular patch. These differentially driven feedlines are utilized to coupled feed the irregular patch through a small gap, which has distinguished feature compared with other designs. It turns out that a resonance at 3.55 GHz is generated. Then, an annulus is set above the main radiator to compensate the inductive component induced by the main radiator and generate the other resonant point. As a result, the dual-polarized antenna could work from 3.3 to 3.6 GHz with the extremely compact size of 0.29λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.29λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.06λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at 3.45 GHz.) The simulated isolation and cross-polarization discrimination at 0° of the antenna element reach more than 35 and 44 dB. The simulated front-to-back ratio of co-polarization and cross-polarization is larger than 44 and 22 dB, separately. To verify the design, a prototype of the 2 × 2 array based on the element is fabricated and measured. The results show that the antenna has high potential in the fifth-generation (5G) massive multiple-input multiple-output application.

A Broadband Circularly Polarized Fabry-Perot Resonant Antenna Using A Single-Layered PRS for 5G MIMO Applications

This paper presents the design and the realization of broadband circularly polarized (CP) Fabry-Perot resonant antenna using a single superstrate for the fifth-generation (5G) wireless multiple-input-multiple-output (MIMO) applications. The antenna consists of a corner cut patch with a diagonal slot and a superstrate. The individual resonances of the corner cut patch and patch with diagonal slot are overlapped to improve the intrinsic narrow impedance and axial ratio (AR) bandwidths of the single-fed patch antennas. A half-wavelength spaced superstrate having a half-wavelength thickness is employed as a partially reflecting surface (PRS) for high gain and wide AR as well as impedance bandwidths. The design procedure and mechanisms of the PRS are discussed in detail through the equivalent circuit and ray tracing analysis. Simulated and measured results show that the proposed antennas have a wide operational bandwidth of 25-33 GHz (27.6%) for |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -10 dB with a stable gain achieving a maximum value of 14.1 dBiC and a wide 3-dB AR bandwidth ranging from 26-31.3 GHz (17%). This operational bandwidth of the antenna covers the proposed entire global 5G millimeter wave (mmWave) spectrum (26-29.5 GHz). Moreover, a 2 × 2 MIMO antenna is designed using the proposed antenna in such a way that the polarization diversity of the adjacent radiator is exploited, resulting in high isolation between antenna elements and low-envelope correlation coefficient, which makes it a suitable candidate for future 5G MIMO applications.

A Fully Integrated C-Band GaN MMIC Doherty Power Amplifier With High Efficiency and Compact Size for 5G Application

This paper presents a fully integrated C-band Doherty power amplifier (DPA) based on a 0.25-μm GaN-HEMT process for the 5G massive MIMO application. The performance degradation caused by nonlinear output capacitance is analyzed, and a novel compensation technique is proposed. A low-Q output network is employed to broaden the bandwidth, and its insertion loss in the back-off region is demonstrated to be mainly decided by the Q-factor of the drain bias inductor of the main PA. Hence, by adopting on-chip transmission lines with high Q-factors for drain biasing, a full integration, and a low loss can be achieved simultaneously. Reversed uneven power splitting and back-off input matching are proposed for gain enhancement. The fabricated DPA demonstrates a small-signal gain of 8.6-11.6 dB, an output power of 40.4-41.2 dBm, a 6-dB back-off drain efficiency (DE) of 47% - 50%, and a saturation DE of 55%-63% across a wide bandwidth from 4.5 to 5.2 GHz, with an ultra-compact size of 2.2 mm × 2.1 mm. Using a 40-MHz LTE signal with a 7.7-dB peak-to-average power ratio at the carrier frequency of 4.9 GHz, the measured average output power and efficiency are 33 dBm and 43%, respectively. The raw adjacent channel power ratio is -29 dBc and is improved to -46 dBc by applying digital predistortion.

Mutual Coupling Reduction in an Array of Patch Antennas Using CLL Metamaterial Superstrate for MIMO Applications

The capability of a magnetodielectric superstrate to suppress the surface wave propagation is investigated. It is shown that the capacitively loaded loop (CLL) metamaterial (MTM) superstrate exhibits a high degree of surface wave attenuation. One of the important applications of such structure is to reduce the mutual coupling between the microstrip patch elements in array antennas. The results of numerical simulations show a significant reduction in the mutual coupling between the antenna elements. To verify and confirm the simulation results, a prototype of the CLL-MTM superstrate incorporating an array of rectangular patch antennas are fabricated and tested. The proposed two-element array antenna has a dimension of approximately $1.6\lambda \times 0.9\lambda \times 0.16\lambda $ while achieving a gain and an efficiency of 8.2 dB and 97%, respectively. Measurement shows the mutual coupling reduction of over 55 dB. The CLL-MTM superstrate provides the gain and efficiency almost the same of unloaded array antennas with 0.1 dB and 2% changes, respectively.