Wideband Antenna Array Research Articles

Low-profile and wide-band RCS-reduction antenna array based on the metasurface polarization converter.

Antenna elements with a low profile and high front-to-back (FB) ratio mean that no additional reflective cavity is required when forming the array, which greatly helps to simplify and lighten the entire array system. In this paper, we enhance the FB ratio of the antenna to 35 dB while maintaining an ultra-low profile of 0.05 λ0 by attaching the broadband polarization conversion metasurfaces (PCMs) as the parasitic patches to the surface of the radiating patch. Meanwhile, the array formed by the proposed antenna is arranged in a checkerboard form, which makes it have a lower radar cross section (RCS) in the X- and Ku- bands. Even with PCMs loaded, the antenna element maintains a small size of 0.58 λ0 × 0.58 λ0, which ensures the proposed array can achieve the ± 45° beam scanning, making it suitable for the phased array. For verification, we propose a low-sidelobe array composed of the proposed antenna elements, which exhibits a low profile, high FB ratio, and broadband RCS reduction through simulation and measurement.

Microwave brain imaging system to detect brain tumor using metamaterial loaded stacked antenna array

In this paper, proposes a microwave brain imaging system to detect brain tumors using a metamaterial (MTM) loaded three-dimensional (3D) stacked wideband antenna array. The antenna is comprised of metamaterial-loaded with three substrate layers, including two air gaps. One 1 × 4 MTM array element is used in the top layer and middle layer, and one 3 × 2 MTM array element is used in the bottom layer. The MTM array elements in layers are utilized to enhance the performance concerning antenna’s efficiency, bandwidth, realized gain, radiation directionality in free space and near the head model. The antenna is fabricated on cost-effective Rogers RT5880 and RO4350B substrate, and the optimized dimension of the antenna is 50 × 40 × 8.66 mm3. The measured results show that the antenna has a fractional bandwidth of 79.20% (1.37–3.16 GHz), 93% radiation efficiency, 98% high fidelity factor, 6.67 dBi gain, and adequate field penetration in the head tissue with a maximum of 0.0018 W/kg specific absorption rate. In addition, a 3D realistic tissue-mimicking head phantom is fabricated and measured to verify the performance of the antenna. Later, a nine-antenna array-based microwave brain imaging (MBI) system is implemented and investigated by using phantom model. After that, the scattering parameters are collected, analyzed, and then processed by the Iteratively Corrected delay-multiply-and-sum algorithm to detect and reconstruct the brain tumor images. The imaging results demonstrated that the implemented MBI system can successfully detect the target benign and malignant tumors with their locations inside the brain.

A high gain wideband array antenna based on metasurface for ETC application

Free flow electronic toll collection (FFETC) has played an important role in building convenient and safe transportation systems in many countries. The most challenging problem when researching and developing this system is shortening the payment cycle so that vehicles passing through the stations do not need to stop or keep going at a speed greater than 60 Km/h. Designing roadside unit (RSU) reader antennas with high gain and suitable radiation pattern is the most feasible and economical solution. This paper proposes a left-handed circularly polarized (LHCP) 2×4 array antenna using sequential phase rotation power dividers at 5.8 GHz band. The element antenna is a square patch antenna with a slit in the middle for better impedance matching, six trapezoidal parasitic patches added to either side of the main patch to create resonance at high frequencies, and a metasurface placed on top of the main patch. The proposed metasurface is a 4×4 array of dual circular unit cells to improve gain and extend axial ratio (AR) bandwidth. The proposed antenna array has a high gain of 17 dBi, -3 dB vertical and horizontal beamwidths of 33.20 and 17.10, which cover over one lane, are expected for any ETC system to avoid interference with other lanes. Impedance bandwidth and AR bandwidth are 2.19 GHz (37.75%) and 2.06 GHz (35.52%), respectively. The overall dimensions of the proposed array antenna are approximately 152×76×6.4 mm3. With the above merits, this antenna is a suitable candidate for the RSU reader antenna in the FFETC

A Wideband Feed Network for Vivaldi Antenna Arrays

A wideband feed network for a Vivaldi antenna array is presented. A limitation of current wideband antenna arrays is the bandwidth of either the feed network or the antenna element. The proposed antenna array consists of four wideband Vivaldi antennas fed with an improved wideband feed network to extend the useable bandwidth of the array. The proposed feed network consists of coplanar waveguide-to-slotline-to-microstrip line transitions. The feed network has a single coplanar waveguide input and four microstrip line output ports. The feed network achieved uniform amplitude and phase balance and an impedance bandwidth of 160% from 1 GHz to 9 GHz. The feed network was used in a uniform linear antenna array to feed four Vivaldi antenna elements. The Vivaldi antenna array achieved stable radiation patterns from 1.3 GHz to 8 GHz, resulting in a useable bandwidth of 144%. The antenna array has a minimum gain of 8 dBi and a maximum of 13.8 dBi within the frequency band. Results for a prototype Vivaldi antenna array, measured in a compact antenna test range, are presented and compared to simulated results from CST Studio Suite.

A wideband circularly polarized CPW-fed substrate integrated waveguide based antenna array for ISM band applications

This article presents a compact size circularly polarized substrate integrated waveguide (SIW) based wideband antenna array that serves industrial, scientific, and medical (ISM) band applications. A coplanar waveguide (CPW) technique is used to ensure the antenna size compactness. The proposed antenna is fabricated on a low-profile Rogers RT6002 substrate with a dielectric constant of 2.94, tanδ of 0.0012 and an approximate height of 0.76mm. The proposed design covers the frequency range from 2.15 GHz to 3.63 GHz (60.4%) while the axial ratio has a 3 dB bandwidth covering from 2.19 GHz to 2.51 GHz (13%) at the operating band of 2.45 GHz. The antenna is miniaturized and has a size of about 46.50 × 29 × 0.76 mm3. The simulation and experimental results are taken into consideration and there is a good promise between them. Hence, the antenna is a suitable applicant to be utilized for the applications in the ISM band.

A Wideband High-Gain Microstrip Array Antenna Integrated with Frequency-Selective Surface for Sub-6 GHz 5G Applications.

This paper presents a wideband and high-gain rectangular microstrip array antenna with a new frequency-selective surface (FSS) designed as a reflector for the sub-6 5G applications. The proposed antenna is designed to meet the US Federal Communications Commission (FCC) standard for 5G in the mid-band (3.5–5 GHz) applications. The designed antenna configuration consists of 1 × 4 rectangular microstrip array antenna with an FSS reflector to produce a semi-stable high radiation gain. The modeled FSS delivered a wide stopband transmission coefficient from 3.3 to 5.6 GHz and promised a linearly declining phase over the mid-band frequencies. An equivalent circuit (EC) model is additionally performed to verify the transmission coefficient of the proposed FSS structure for wideband signal propagation. A low-cost FR-4 substrate material was used to fabricate the antenna prototype. The proposed wideband array antenna with an FSS reflector attained a bandwidth of 2.3 GHz within the operating frequency range of 3.5–5.8 GHz, with a fractional bandwidth of 51.12%. A high gain of 12.4 dBi was obtained at 4.1 GHz with an improvement of 4.4 dBi compared to the antenna alone. The gain variation was only 1.0 dBi during the entire mid-band. The total dimension of the fabricated antenna prototype is 10.32 λo × 4.25 λo ×1.295 λo at a resonance frequency of 4.5 GHz. These results make the presented antenna appropriate for 5G sub-6 GHz applications.

Wideband mm-wave high-gain multibeam antenna array fed by 4 × 4 groove gap waveguide butler matrix with modified crossover

This paper presents a wideband millimeter wave (mm-Wave) high-gain multibeam antenna array fed by Butler Matrix (BM) based on groove gap waveguide (GGW) technology. First, the components of 4 × 4 GGW BM have been designed and analyzed, especially the proposed modified crossover, which greatly improves the performance of BM as feeding network. Then a 2 × 2-element subarray with three layers has been proposed, combined with the 4 × 4 GGW BM to form a 1 × 4 broadside antenna array. Finally, the prototype of high-gain wideband four-beam antenna array has been manufactured and measured. The measured results verify the superior performance of the multibeam antenna array between 26.3-29.7 GHz. The return loss (RL) can reach 15 dB and isolation between ports is also less than 15 dB, and the measured maximum gain of radiation patterns and the maximum radiation efficiency can also reach 19.05 dBi and 86.8%, respectively. The measured results have a good agreement with the simulated results.

A 45° Polarized Wideband and Wide-Coverage Patch Antenna Array for Millimeter-Wave Communication

A 45° polarized millimeter-wave (mmWave) patch antenna and arrays with wide impedance and gain bandwidth are proposed in this article. The compact antenna consists of stacked patches, one substrate integrated waveguide (SIW) back cavity, one SIW square cavity, and a feeding line. The patches and the SIW back cavity rotate 45° with respect to the SIW square cavity. For the antenna, the −10 dB impedance bandwidth is from 22.31 to 29.65 GHz, and the peak gain is greater than 5 dBi in the bandwidth from 22 to 30.5 GHz. Based on the proposed antenna, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times16$ </tex-math></inline-formula> linear array is designed, fabricated, and measured. According to the experimental results, all antenna elements can realize the −10 dB impedance bandwidth from 21.7 to 27 GHz. Within 3 dB gain fluctuation, the scanning coverage of the linear array can achieve 116° in the frequency band from 22 to 26 GHz and 110° at 27 GHz. Then, an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> planar array with wide bandwidth and wide scanning coverage is proposed. The reflection coefficient can achieve less than −10 dB from 21.82 to 27.22 GHz. The main beam of the radiation pattern can be widely spatially scanned. In the bandwidth from 22 to 26 GHz, the scanning coverage within 3 dB gain fluctuation can achieve 107°. Also, at 27 GHz, the coverage can achieve 90°. Due to the outstanding performance, reliable multilayer printed circuit board (PCB) fabrication technology, and easy integration with circuits, the proposed antenna and arrays are good candidates for the fifth-generation (5G) mmWave communication systems, satellite communication systems, and so on.

Optimizing the Mutual Information of Frequency-Selective Multi-Port Antenna Arrays in the Presence of Mutual Coupling

As larger bandwidths are used in multiple antenna wireless systems, the frequency selectivity of the antenna arrays starts to impact rate. Motivated by optimizing the achievable rate in compact antenna arrays, we present a system model that incorporates the effects of mutual coupling (MC) of wideband physically realizable single-input multiple-output (SIMO) and multiple-input single-output (MISO) antenna systems. For the SIMO system setup, we extract the noise correlation matrices for two different antenna array configurations (parallel and co-linear). We optimize the inter-element spacing in each alignment while maximizing the achievable rate and fixing the transmit power. Then, we compare the two compact antenna designs to a perfectly matched single omni-directional antenna while accounting for MC. Likewise, for the MISO antenna system, we derive the optimal beamformer that maximizes the achievable rate using the same antenna configurations as the SIMO system. Then, we study the impact of MC and develop a new single-port matching technique for wideband antenna arrays. Finally, we provide reciprocity plots to compare the performance of the SIMO-MISO systems using different channel models.

On the Relation Between Beam Coupling and Feed Coupling in Wideband Antenna Arrays

We present a study on beam coupling in radiating structures that support multiple simultaneous beams. The formation of multiple beams is relevant in modern wireless communication applications when diverse data streams can be sent from a single transmitter to users located in different directions. General expressions are provided that relate the coupling between radiated beams to the associated current distributions on the radiating aperture. When expanding the currents in terms of basis functions, the beam coupling can be also written in terms of coupling contributions due to each pair of basis functions. The analysis is applied to antenna arrays with different levels of mutual coupling between the array elements. More specifically, arrays of resonant elements, characterized by very low mutual coupling, are compared with arrays of connected elements, which are strongly coupled. We show that, even for a very high level of mutual coupling between individual array elements, it is possible to obtain orthogonal beams if the total current distributions associated with the beams are uncoupled.

A Dual Slant-Polarized Cylindrical Array of Tightly Coupled Dipole Antennas

This study proposes a design of a low-profile ultra wide-band cylindrical antenna array with plus/minus 45-degree dual polarization. The proposed compact cylindrical antenna array produces an omnidirectional radiation pattern in the azimuth plane to cover all directions. It consists of <inline-formula> <tex-math notation="LaTeX">$20\times 4$ </tex-math></inline-formula> dual-polarized elements within a diameter of 131 mm and a height of 116 mm. The array elements are tightly coupled slant-polarized wideband dipole antennas, and hence, rotational symmetry of radiation patterns in the horizontal plane is achieved for the two orthogonal polarizations. Furthermore, a metasurface structure has been designed and placed over the interconnected array elements to achieve ultrawideband capabilities. The proposed array provides less than &#x2212;10 dB reflection coefficient over a frequency band between 1.7 GHz and 5.9 GHz. The cross-polarization discrimination (XPD) is 15 dB at boresight in the azimuth plane. The electromagnetic characteristics of the cylindrical array and its corresponding planar array before bending have been evaluated and compared via simulations, and verified by measurements. The compact size, lightweight, and printable design of the proposed antenna array enable low-cost manufacturing and ease of installation. The proposed array design overcomes many challenges encountered in wide-band MIMO systems by covering the entire sub-6 GHz band while providing wide 360-degree coverage in the azimuth plane, hence, supporting multibeam applications.

Wideband and High Gain Array Antenna for 5G Smart Phone Applications Using Frequency Selective Surface

This work presents an eight element array antenna with single layer frequency selective surface (FSS) to obtain high gain. The eight elements are fed by single port. The FSS consists of 14x6 unit cells with one unit cell size is 5&#x00D7;5 <i>mm</i>² having wideband behavior. The antenna uses Rogers RT Duroid 5880 substrate and giving very wide bandwidth from 20 GHz to 65 GHz, covering mm-wave 5G bands (including 28 GHz, 38 GHz and 60 GHz). The designed FSS is showing stop band transmission characteristics below -10 dB threshold from 25 GHz to 42 GHz and 59 GHz to 61 GHz. The eight element antenna integrated with the FSS reflector, which results an improvement in the gain level from 12 dB to 15 dB at 28 GHz, from 10 dB to 12 dB at 38 GHz, and from 9.5 to 11 dB at 60 GHz. The dimensions of the antenna are 33&#x00D7;27&#x00D7;0.787 <i>mm</i>³. The proposed antenna shows stable gain and directional radiation patterns. The simulation findings are experimentally confirmed, by testing the fabricated prototypes of the proposed antenna system.

Bandwidth Enhancement of Millimeter-Wave Large-Scale Antenna Arrays Using X-Type Full-Corporate Waveguide Feed Networks

A one-time-reflection equivalent model of the full-corporate waveguide feed networks is investigated to propose a novel approach to bandwidth enhancement of millimeter-wave large-scale antenna arrays. Theoretical analysis reveals that the in-phase superposition phenomenon of multiple small reflections at specific frequencies caused by the topology of the feed network is also a significant factor to affect the achievable bandwidth of the large-scale arrays, apart from the bandwidth performance of the individual power dividers and radiators composing the array. In order to weaken the undesirable effects on bandwidths caused by the small reflections, a full-corporate waveguide feed network with an X-type topology is then presented. Air-filled waveguide X-junctions and waveguide-fed horn sub-arrays are designed to fulfill new threedimensional (3D) printed V-band antenna arrays. Excellent performance, including an improved bandwidth of about 40%, a gain of up to 27.8 dBi, and stable unidirectional radiation patterns with cross polarization of less than –32 dB, are confirmed experimentally by an 8 × 8 prototype. The theoretical model and the bandwidth enhancement scheme in this paper are valuable to realize the high-gain wideband antenna arrays for emerging millimeter-wave applications.

Light-weight wideband antenna array with low sidelobes for SAR applications

PurposeThe purpose of this study is to achieve the low-cost, light-weight and compact antenna array with wide bandwidth and low side lobe levels for synthetic aperture radar (SAR) applications in Ku frequency band.Design/methodology/approachA compact design of a rectangular microstrip patch antenna array using multilayered dielectric structure is presented in Ku-band for advanced broadband SAR systems. In this design, stepped pins are used to connect the microstrip feed lines to the radiating patches.FindingsThe simulation and fabrication results of the multilayered antenna and a 1×16-element linear array of the antenna with Taylor amplitude distribution in the feeding network are presented. The antenna element has a 10-dB impedance bandwidth of more than 26%, and the linear array shows reduction in bandwidth percentage (about 15.4%). Thanks to Taylor amplitude tapering, the side lobe level (SLL) of the array is lower than −24 dB. The maximum measured gains of the antenna element and the linear array are 7 and 19.2 dBi at the center frequency, respectively.Originality/valueIn the communication systems, a high gain narrow beamwidth radiation pattern achieved by an array of multiple antenna elements with optimized spacing is a solution to overcome the path loss, atmospheric loss, polarization loss, etc. Also, wideband characteristics and compact size are desirable in satellite and SAR systems. This paper provides the combination of these features by microstrip structures.

A stroke detection and discrimination framework using broadband microwave scattering on stochastic models with deep learning

Stroke poses an immense public health burden and remains among the primary causes of death and disability worldwide. Emergent therapy is often precluded by late or indeterminate times of onset before initial clinical presentation. Rapid, mobile, safe and low-cost stroke detection technology remains a deeply unmet clinical need. Past studies have explored the use of microwave and other small form-factor strategies for rapid stroke detection; however, widespread clinical adoption remains unrealized. Here, we investigated the use of microwave scattering perturbations from ultra wide-band antenna arrays to learn dielectric signatures of disease. Two deep neural networks (DNNs) were used for: (1) stroke detection (“classification network”), and (2) characterization of the hemorrhage location and size (“discrimination network”). Dielectric signatures were learned on a simulated cohort of 666 hemorrhagic stroke and control subjects using 2D stochastic head models. The classification network yielded a stratified K-fold stroke detection accuracy > 94% with an AUC of 0.996, while the discrimination network resulted in a mean squared error of < 0.004 cm and < 0.02 cm, for the stroke localization and size estimation, respectively. We report a novel approach to intelligent diagnostics using microwave wide-band scattering information thus circumventing conventional image-formation.

Design of an S-Band Phased Array with Modified Dipoles

A wideband, low cross-polarization, high-gain, and wide-angle scanning antenna array is presented in this paper. The antenna array contains 8 subarrays in the horizontal dimension, and each subarray contains 4 unit cells. A two-side printed dipole with an amendatory equivalent circuit model is adopted, and the metal vias are introduced in the element design to ameliorate the cross-polarization level. A radome, acting as the wide-angle impedance matching layer, is introduced to achieve wide-angle scanning. A prototype of a 4 × 8 array is fabricated and measured. The results show that the operating bandwidth of aperture efficiency (BWAE) above 60% is about 26.7% from 2.6 GHz to 3.4 GHz. The measured scanning loss in the H-plane is 2.7 dB when scanning up to 60° with active voltage standing wave ratio (VSWR) &lt;3, and the gain can achieve 21 dB at 3 GHz with a cross-polarization level below −30 dB at all angles.

A Wide-Band High-Efficiency Hybrid-Feed Antenna Array for mm-Wave Wireless Systems

A wide-band and high-efficiency planar antenna array with a novel hybrid-feed structure is proposed in this article. By combing the coaxial-line feed magneto-electric (ME) dipoles with the aperture coupled dielectric cavity, a hybrid-feed 2 × 2-unit ME-dipole sub-array is invented. The low-loss ridge gap waveguide (RGWG) corporate-feed network is used to replace the high-loss substrate-based feed networks and high-cost RWG feed networks. New forms of RGWG H-plane divider are designed to build the RGWG feed network. An 8 × 8-unit ME-dipole antenna array is designed and fabricated to verify the validity of the array. The radiation part consists of two layers of a low-cost printed circuit board (PCB), and the feeding part consists of two copper plates manufactured by computer numerical control (CNC) milling. Measured results show that a relative bandwidth of 16.4% with |S11| &lt; −10 dB is achieved, with a maximum radiation efficiency of 85%. The stable symmetric radiation patterns are observed in both the E-plane and H-plane, covering the operation band. Based on the measured results, a 16 × 16-unit ME-dipole antenna array is simulated. Results indicate that the proposed array has wide-band and high-efficiency features, which is suitable for large-scale array design in mm-wave wireless systems.

Wideband and High-Gain Wearable Antenna Array with Specific Absorption Rate Suppression

In this paper, a wideband and high-gain antenna array with specific absorption rate suppression is presented. By adopting the wideband monopole antenna array and the uniplanar compact electromagnetic band gap (UC-EBG) structure, the proposed wearable antenna array can realize a high gain of 11.8–13.6 dBi within the operating band of 4.5–6.5 GHz. The sidelobe level of the proposed wearable antenna array is less than −12 dB, and the cross polarization in the main radiation direction is less than −35 dB. Benefiting from the UC-EBG design, the specific absorption rate is suppressed effectively, guaranteeing the safety of the proposed antenna array to the human body. The proposed antenna array is processed and tested, and the measurement results show good agreement with the simulation results.

Design of Wideband Antenna Array with Dielectric Lens and Defected Ground Structure

In order to increase the gain of an end-fire antenna array and improve its broadband characteristics, techniques using a dielectric lens and defected ground structure have been investigated in this paper. The element of the array was constructed using an antipodal tapered slot, and two pairs of U-slots were symmetrically cut on the edges of the two antipodal fins to obtain better performance regarding impedance and radiation in the wider band. While loading an ellipse dielectric lens onto each element, the direction and gain were enhanced at the higher frequency. Meanwhile, a defected ground structure was added on the ground plane to decline the mutual coupling of adjacent radiation arms. This design method was verified by a four-element array and a four-way Wilkinson power divider was used as a feed network. Finally, a fabricated sample was tested. Experimental results showed the designed array was available.

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.