Isolation enhancement between tightly spaced compact unidirectional patch‐antennas on multilayer EBG surfaces

In this article, ultracompact unidirectional patch antennas are used in different two‐antenna systems for biomedical applications at 5.2 GHz. Multilayer mushroom type electromagnetic bandgap (EBG) structures are designed as slow‐wave medium to reduce the size of the individual patch antennas to 0.1λ₀ by 0.18λ₀. Various techniques are investigated herein to improve antenna isolation for an enhanced Multiple‐Input Multiple‐Output (MIMO) performance. First, the coupling between 0.3λ₀‐spaced antennas is verified to occur dominantly through radiation and near‐field coupling between the patches rather than through substrate‐bound modes. Second, various configurations are proposed to suppress antenna coupling. These approaches include reorientation of the antennas and employment of parasitic radiators between the patches. A novel design is presented in which a unidirectional parasitic slot radiator on an EBG reflector is inserted between the antennas to decouple them. Measurement results confirm efficacy of these approaches in mitigating antenna coupling by more than 11 dB in the operating bandwidth of the antennas. The compact patch antennas maintain efficiency values of higher than 70%. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:30–38, 2015.     

Design of defective electromagnetic band‐gap structures for use in dual‐band patch antennas

Generally, the surface wave of an antenna can be suppressed by integrating the electromagnetic band‐gap (EBG) structures. However, to achieve this effect, the EBG cells must be reasonably designed, otherwise it may lead to performance degradation instead. In this article, a dual‐band pinwheel‐shaped slot EBG structure is proposed. When applied to a patch antenna, defects are introduced into 3 rows of the EBG unit cells. The proposed antenna, incorporating EBGs designed with structural defects, to radiate at 4.9 and 5.4 GHz is simulated and tested. The measured results show that the ?10‐dB bandwidth of the proposed EBG antenna is extended by 41% and 25.4% at low frequency and high frequency, respectively. In addition, the peak gain of the proposed EBG antenna is increased by 2.44 dB at 4.9 GHz and 2.86 dB at 5.4 GHz with >40% efficiency. When compared with the periodic EBG antenna, this antenna is more effective. Thus, these experimental results show that the performance of the EBG antenna can be improved by interrupting the periodicity of the EBGs structures.     

Compact four‐element MIMO SIW cavity backed slot antenna with high front‐to‐back ratio

In this article, a novel design of single layer, compact, multiple input multiple output (MIMO) half‐mode substrate integrated waveguide (HMSIW) cavity backed quad element slot antenna with high front‐to‐back ratio (FTBR) is proposed. The proposed antenna consists of four rectangular SIW cavities with semi‐taper radiating slots. The antenna elements are placed in a fashion to achieve high isolation. This antenna is designed for WLAN vehicular communication system to cover the frequency range of 5.84 GHz to 5.96 GHz. It has high front to back ratio (FTBR) of more than 25 dB without using any external metallic reflector. It has more than 37 dB isolation in between orthogonal elements and more than 24 dB in between parallel elements. The envelop correlation coefficient (ECC) and diversity gain are 0.003 and 9.99 dB respectively in between all the elements. Moreover, the antenna has high gain and efficiency of more than 8 dB and 94%, respectively, in 10 dB impedance bandwidth. It can be tuned in a wide range of frequency.     

A novel substrate integrated waveguide cavity‐backed self‐diplexing antenna array with frequency beam scanning characteristic

This article presented a substrate integrated waveguide (SIW) cavity‐backed self‐diplexing antenna array with frequency beam scanning characteristic. The proposed array consists of 16 SIW cavity‐backed slot antennas. The SIW cavity‐backed slot antenna can be fed by two separate ports to resonate at two different frequencies and achieve high isolation better than 20 dB between two input ports. The proposed element is a typical self‐diplexing antenna. These cavity‐backed slot antennas are shunt‐fed by a compact 1 to 16 SIW power divider and series‐fed by a set of microstrip lines, respectively. As a result, this array achieves an unidirectional radiation pattern at 10.2 GHz with high gain of 15.10 dBi, and a frequency beam scanning characteristic from 7.0 to 9.0 GHz ranging from ?50° to 46°.     

A dual‐polarized low‐profile microstrip patch antenna with U‐ or M‐shaped feed network

In this article, a dual‐polarized low‐profile microstrip patch antenna with U‐ or M‐shaped feed network is presented. The U‐ or M‐shaped feed network is printed on the same layer, which can achieve dual bands (5.3 and 5.8 GHz) and low profile (0.06 λ_g). Dual polarizations and high isolation are realized by making use of a quasi‐cross‐shaped slot feeding. Moreover, the port isolation is better than 25 dB, and the antenna gain is above 8.4 dBi for the two ports. And the cross‐polarization levels in both E and H planes are better than ‐30 dB for the two polarization ports, respectively. The design is suitable for array application in MIMO system. Details of the proposed design and experimental results are presented and well agreed.     

A 60‐GHz on‐chip slot‐array antenna in integrated‐passive‐device technology for antenna‐in‐package applications

A new millimeter‐wave antenna structure on a low‐cost, production platform integrated passive device technology is presented. The antenna consists of a 2‐by‐1 array of slot antennas at 60 GHz. An in‐house developed on‐chip antenna measurement setup was used to characterize the fabricated antenna. The measurement results show an antenna gain of more than 5 dBi with a return loss of 18 dB at 60 GHz. The better‐than‐10‐dB impedance bandwidth of the antenna covers the 60‐GHz unlicensed band from 57 to 64 GHz. The 3‐dB beamwidths of the antenna are 105° and 76° at E‐plane and H‐plane at 60 GHz, respectively. The size of the die of the antenna is 2 mm × 4.5 mm. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:155–160, 2014.     

A CPW‐fed band notched wideband circularly polarized ZOR antenna based on CRLH‐TL approach

This article presents design and analysis of three wide band zeroth‐order resonance antennas (antennas I, II, and III) using composite right and left‐handed transmission line (CRLH‐TL) approach. Coplanar waveguide technology, single layer via‐less structures are used to have the design flexibility. The bandwidth characteristics are analyzed by using lumped parameters of CRLH‐TL. By introducing a simple slot in the ground plane of antenna I both bandwidth enhancement and circularly polarization characteristics are achieved in antenna II. Another quarter wave L‐shaped slot has been introduced in the ground plane of antenna II to introduce a notch band in the frequency response of antenna III. Achieved measured 10 dB return loss bandwidth of antenna I and antenna II are 960 (3.3‐4.26 GHz) and 2890 MHz (2.77‐5.66 GHz), respectively. Antenna III offers measured 10 dB return loss bandwidth of 3220 MHz (2.32‐5.54 GHz) with a band notch from 2.39 to 2.99 GHz that isolates the 2.4 GHz WLAN and 3.5 GHz WiMAX band. Antenna II and antenna III have circular polarization property with measured axial ratio bandwidth of 440 MHz. The measured peak realized gain of antennas II and III is around 1.53‐2.9 dBi.     

Millimeter‐wave planar high gain SIW antenna using half elliptic radiation slots

This article reports a high gain millimeter‐wave substrate integrated waveguide (SIW) antenna using low cost printed circuit board technology. The half elliptic slots which can provide small shunt admittance, low cross polarization level and low mutual coupling are etched on the board surface of SIW as radiation slots for large array application. Design procedure for analyzing the characteristics of proposed radiation slot, the beam‐forming structure and the array antenna are presented. As examples, an 8 × 8 and a 32 × 32 SIW slot array antennas are designed and verified by experiments. Good agreements between simulation and measured results are achieved, which shows the 8 × 8 SIW slot array antenna has a gain of 20.8 dBi at 42.5 GHz, the maximum sidelobe level of 42.5 GHz E‐plane and H‐plane radiation patterns are 22.3 dB and 22.1 dB, respectively. The 32 × 32 SIW slot array antenna has a maximum measured gain of 30.05 dBi at 42.5 GHz. At 42.3 GHz, the measured antenna has a gain of 29.6 dBi and a maximum sidelobe level of 19.89 dB and 15.0 dB for the E‐plane and H‐plane radiation patterns. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:709–718, 2015.     

Dual‐band CPW fed MIMO antenna with polarization diversity and improved gain

A dual‐band MIMO slot antenna with polarization diversity and improved gain is proposed in this article. The antenna is composed of two C‐type back‐to‐back connected slot resonators and offers resonances at 3.5 and 5.2 GHz. This antenna element is further used to design a MIMO antenna. By introducing one U‐shaped slot between two antenna elements, isolation between the ports of this MIMO antenna is improved further. Finally, an artificial magnetic conductor (AMC) is placed below the MIMO antenna to enhance its gain. Gain enhancement of 1.5 and 2.2 dB is achieved at lower and upper band, respectively. S‐parameters, radiation patterns, gain, envelope correlation coefficient, and channel capacity loss are investigated to conclude about its performances in MIMO applications. Dual band dual polarization (circular and linear), improved isolation, polarization diversity (right‐hand circular polarization and left‐hand circular polarization), gain enhancement all are presented in a simple design represents the novelty of the proposed MIMO antenna.     

UWB MIMO antenna implemented with orthogonal quasi‐circular slot dipole radiators

In this paper, a very low‐profile two‐port ultra‐wideband antenna for multiple input‐multiple output applications is proposed. The antenna is implemented by using two orthogonal quasi‐circular slot dipole radiators fed by coaxial lines. The antenna performs from 2 to 10 GHz, with an average peak‐gain of 4 dB, and high port isolation, with values around S₂₁ = ?20 dB and below. The radiation patterns of both antennas are opposite to each other and hence, the diversity gain reaches values around 20 dB. The low inter‐port coupling and low correlation are verified by obtaining the envelope correlation coefficient, which is lower than 0.003. These calculations were made by the S‐parameter and far‐field methods. The total active reflection coefficient shows that the antenna operative bandwidth does not change for different input signals with random phases, preserving the operation from 2 to 10 GHz. The antenna performance is compared to different state of the art slot configurations, showing advantages to previously published work.     

High‐gain dual‐polarized antenna for ultrawideband applications

In this article, a high‐gain and dual‐polarized antenna with UWB operation is proposed. The antenna is composed of two tapered dipoles as radiating elements, which are arranged orthogonally and fed perpendicularly to achieve polarization diversity. A metallic cavity reflector is placed behind the radiator for high gain radiation entire the operating bandwidth. To validate the design method, an antenna prototype is designed, fabricated, and measured. The measured results demonstrate that the proposed design has good performance with |S₁₁| ≤ ?10 dB and isolation ≥20 dB over a frequency band 3.2‐8.8 GHz, equivalently to about 93.3%. In addition, unidirectional radiation pattern and broadside gain of from 8.1 to 11.8 dBi are obtained across the operating bandwidth.     

Compact planar frequency reconfigurable multiple‐input‐multiple‐output antenna with pattern and polarization diversity characteristics for WiFi and WiMAX standards

A compact planar frequency reconfigurable dual‐band multiple‐input‐multiple‐output (MIMO) antenna with high isolation and pattern/polarization diversity characteristics is presented in this article for WiFi and WiMAX standards. The MIMO configuration incorporates two symmetrically placed identical antenna elements and covers overall size of 24 mm × 24 mm × 0.762 mm. Reconfiguration of each antenna element is achieved by using a PIN diode which allows antennas to switch from state‐1 (2.3‐2.4 GHz and 4.6‐5.5 GHz) to state‐2 (3.3‐3.5 GHz and 4.6‐5.5 GHz). In state‐1, the configuration offers isolation ≥18 dB and 20 dB in lower band (LB) and upper band (UB) respectively; whereas, in state‐2, isolation ≥21 dB and 20 dB in LB and UB respectively is achieved. The same decoupling circuit provides high isolation in dual‐band of two states, which makes overall size of the proposed design further compact. The antennas are characterized in terms of envelope correlation coefficient, radiation pattern, gain, and efficiency. From measured and simulated results, it is verified that the proposed frequency reconfigurable dual‐band multi‐standard MIMO antenna design shows desirable performance in both operating bands of each state and compact size of the design makes it suitable for small form factor devices used in future wireless communication systems.     

Wideband linear microstrip array antenna with high efficiency and low side lobe level

In this letter, the design and fabrication of the linear microstrip array antenna by series fed are presented. The array antenna consists of 16 reflector slot‐strip‐foam‐inverted patch (RSSFIP) antennas. The gain and efficiency of the linear array antenna is 16.6 dBi and 61% at 10 GHz, respectively. The antenna has a bandwidth (BW) of 45% from 8.1 to 12.8 GHz (S₁₁ < ?10 dB) and side lobe level (SLL) of ?25.6 dB across the BW of 19.2% from 9.4 to 10.4 GHz. These are achieved by using a microstrip series fed with defected ground structure (DGS) to feed the patch array antenna. Good agreement is achieved between measurement and simulation results.     

Low‐profile substrate integrated waveguide (SIW) cavity‐backed self‐triplexed slot antenna

A low‐profile self‐triplexed slot antenna is proposed for multiple system integrations. The antenna comprises of hybrid substrate integrated waveguide (SIW) cavity (a combination of a half‐mode circular and half‐mode rectangular SIW), radiating slot, and feeding network. A slot is imprinted on the upper metal‐layer of the SIW which splits the cavity into three radiating sections. It offers tri‐frequency bands when each section is excited separately. By finely tuning the antenna dimensions, it produces three frequency‐bands around 5.57, 7.17, and 7.65 GHz simultaneously utilizes a single slot with maintaining the intrinsic input‐port isolation better than 20 dB. This property helps to introduce the self‐triplexing phenomenon. Compared with the conventional multiband antennas that use an extra circuitry to ensure the port isolations, this design preserves compactness and easy to integrate with planar circuits Moreover, the proposed antenna is fabricated and the measured results mutually agreed with the simulated counterparts. The proposed design can be a feasible option for mobile transceiver applications.     

Compact 2 × 2/4 × 4 tapered microstrip feed MIMO antenna configuration for high‐speed wireless applications with band stop filters

In this research, compact tapered feed 2 × 2/4 × 4 MIMO antenna are presented and investigated. The proposed MIMO antenna consists of a square patch and modified rectangular ground, which is chamfered at edges and etched with two semicircular slots. Likewise, obstruction caused by WiMAX and WLAN interfering bands is also taken care of by introducing notched filters. WiMAX is removed by embedding an rotated T‐type stub and a C‐type slot eliminates the WLAN band. The proposed antenna configuration covers the usable bandwidth of 3.07 to 11.25 GHz for 2 × 2 MIMO and 2.97 to 11.28 GHz for 4 × 4 MIMO. Also, both the MIMO antennas provide isolation <–20 dB. Proposed MIMO antennas are fabricated and characterized in near, far‐field, and diversity performance where envelope correlation coefficient, directive gain (DG), total active reflection coefficient (TARC), and channel capacity loss are simulated and measured. 4 × 4 MIMO antenna configuration provides stable gain with a maximum radiation efficiency of 91% and monopole radiation patterns.     

Millimeter‐wave antenna with wide‐scan angle radiation characteristics for MIMO applications

A three‐element quasi Yagi‐Uda antenna array with printed metamaterial surface generated from the array of uniplanar capacitively loaded loop (CLL) unit‐cells printed on the substrate operating in the band 25‐30 GHz is proposed. The metamaterial surface is configured to provide a high‐refractive index to tilt the electromagnetic (EM) beam from the two dipole antennas placed opposite to each other. The metamaterial region focuses the rays from the dipole antenna and hence increases the gain of the individual antennas by about 5 dBi. The antenna elements are printed on a 10 mil substrate with a center to center separation of about 0.5 λ ₀ at 28 GHz. The three‐element antenna covers 25‐30 GHz band with measured return loss of 10 dB and isolation greater than 15 dB between all the three ports. The measured gain of about 11 dBi is achieved for all the antenna elements. The three antenna elements radiate in three different directions and cover a radiation scan angle of 64°.     

EBG design and analysis for wideband isolation improvement between aircraft blade monopoles

A new lightweight multilayer mushroom EBG is proposed to significantly improve the isolation between collocated aircraft L‐band blade monopole antennas. Isolation improvement between two L‐bands (960‐1220 MHz) blade monopoles of nearly 20 dB is obtained with a three‐layer EBG design without requiring any redesigning or tuning of the antennas. Since the proposed EBG structure only contains very thin dielectric sheets and foam substrates it would be a lightweight structure. Moreover, the EBG being a stand‐alone structure from the antenna it can be designed, built, and placed between the antennas as an add‐on device to significantly improve antenna isolation over a relatively wide bandwidth (25%). An experimental EBG structure was built and tested demonstrating wideband isolation improvement performance.     

A triple‐band antenna for MIMO WLAN applications

A novel triple‐band antenna element by etching parasitic slot on ground plane is presented. A three‐element antenna system for WLAN MIMO communications is fabricated by using the proposed antenna element. The triple‐band antenna element is designed for the WLAN standard frequency ranges (2.4‐2.485, 5.15‐5.35, and 5.475‐5.725 GHz). The three identical antenna elements are rotationally symmetric on the substrate, isolated by using metal‐vias cavity. The measured average peak gain within the operational bandwidth is about 2.7 dBi. The isolation between the antenna elements can achieve better than 17 dB at the lower band (2.25‐2.65 GHz), while more than 32 dB at the higher bands (5.20‐5.35 and 5.47‐5.73 GHz) is obtained.     

Compact high isolation wideband 4G and 5G multi‐input multi‐output antenna system for handheld and internet of things applications

This article presents a compact wideband multi‐input multi‐output (MIMO) antenna with a high port‐to‐port isolation, having a height h = 3.5 mm for 4G, 5G, and Internet of things (IoT) applications. Two identical planar inverted‐F antennas (PIFA) are used in this antenna system. For achieving wideband characteristics, closed‐ended and open‐ended rectangular slots are etched out on top plate of each PIFA, whereas a slot is etched in ground plane under the top plate of each PIFA. For achieving high isolation, a rectangular slot is etched out in the center of ground plane between two PIFAs. For further reduction in mutual coupling, a small rectangular strip is connected between the top plates of two PIFAs that introduce an antiresonance for enhancing isolation between two PIFA elements. The minimum isolation obtained between the ports of the two PIFAs is about ?20 dB. The minimum impedance bandwidth obtained by the two PIFAs is from 2 to around 3.6 GHz, thus become a wide band antenna covering WLAN band (2.45GHz), 4G‐LTE bands, WiMAX bands (IMT‐2.1 GHz, IMT‐2.3 GHz, and IMT‐E 2.6 GHz), and a sub‐6 GHz 5G band (3.4‐3.6 GHz). The simulated results are compared with the measured ones that are generally found in good agreement. Being low profile and compact, this antenna can be used for advanced 5G communication systems and IoT devices.     

Study of miniaturized E‐patch antenna loaded with novel E‐shape SRR metamaterial for RFID applications

A new design of compact micro strip antenna, based on a newly structure "E"SRR of metamaterial is proposed and designed using CST Microwave Studio. It has been found that the characteristics of new micro strip antenna with novel designed metamaterials placed in the same plane as the radiating element are comparable to the conventional patch antennas, whereas its gain, directivity, and radiating efficiency are remarkably improved. For the design and fabricated antenna, it shows that with the addition of split ring resonator, the frequency has been shifted from 2.38 GHz to 2.4 GHz. The return loss of this antenna increased from ?60 dB to ?70 dB. The realized gain increased from 7.1 dbi for the antenna alone to 7.31 dbi for the meta‐material antenna. Prototype for all antennas are fabricated and measured. Good agreement between the measured and simulated results is achieved.