Design of small CRPA arrays with circular microstrip loops for electromagnetically coupled feed

This paper proposes a design of small controlled reception pattern antenna (CRPA) arrays using circular microstrip loops with frequencyinsensitive characteristics. The proposed array consists of seven identical upper and lower circular loops that are electromagnetically coupled, which results in a frequency-insensitive behavior. To demonstrate the feasibility of the proposed feeding mechanism, the proposed array is fabricated, and its antenna characteristics are measured in a full-anechoic chamber. The operating principle of the proposed feeding mechanism is then interpreted using an equivalent circuit model, and the effectiveness of the circular loop shape is demonstrated by calculating near electromagnetic fields in proximity to the radiator. The results confirm that the proposed feeding mechanism is suitable to have frequency- insensitive behavior and induces strong electric and magnetic field strengths for higher radiation gain in extremely small antenna arrays

Estimation of Detection Performance for Vehicle FMCW Radars Using EM Simulations

This paper proposes a systematic method for estimating detection performances of a frequency-modulated continuous wave radar using electromagnetic simulations. The proposed systematic method includes a radar system simulator that can obtain range-Doppler images using the electromagnetic (EM) simulations in conjunction with a test setup employed for performance evaluation of multiple targets at different velocities in a traffic environment. This method is then applied for optimizing the half-power beamwidths of the antenna array using an evaluation metric defined to improve the detection strengths for the multiple targets. The optimized antenna has vertical and horizontal half-power beam widths of 10??? and 60???, respectively. The results confirm that that the proposed systematic method is suitable to improve the radar detection performance with the enhanced radar-Doppler images

A Suboptimal Approach to Antenna Design Problem With Kernel Regression

This paper proposes a novel iterative algorithm based on a Kernel regression as a suboptimal approach to reliable and efficient antenna optimization. In our approach, the complex and non-linear cost surface calculated from antenna characteristics is fitted into a simple linear model using Kernels, and an argument that minimizes this Kernel regression model is used as a new input to calculate its cost using numerical simulations. This process is repeated by updating coefficients of the Kernel regression model with new entries until meeting the stopping criteria. At every iteration, existing inputs are partitioned into a limited number of clusters to reduce the computational time and resources and to prevent unexpected over-weighted situations. The proposed approach is validated for the Rastrigins function as well as a real engineering problem using an antipodal Vivaldi antenna in comparison with a genetic algorithm. Furthermore, we explore the most appropriate Kernel that minimizes the least-square error when fitting the antenna cost surface. The results demonstrate that the proposed process is suitable to be used in antenna design problems as a reliable approach with a fast convergence time

Metal Surface Guided-Wireless Power Transfer System for Portable Applications With Multiple Receivers

Recently, research has been actively conducted to overcome various challenges observed in wireless power transfer (WPT) technology. However, as additional techniques are implemented, the complexity and cost of WPT systems increased. Therefore, there is a need for a new WPT method that can overcome the shortcomings of existing technology. This paper presents a metal surface guided-wireless power transfer (MSG-WPT) system for applications with multiple receivers (Rxs). First, a plate-wire propagation enhancer (PWPE) is shown to improve the power transfer efficiency (PTE). However, it is not suitable for portable receiving systems. Based on our analysis of the PWPE characteristics, applying an L-section lumped impedance-matching scheme instead of a PWPE can improve the portability of the Rx. A coil-based propagation enhancer (CPE), or a coil-based inductor (CI), can increase the power received if it replaces the lumped inductor in the L-section scheme. The MSG-WPT system does not experience the co-alignment issues that exist between a pair of transceivers (TRxs) in conventional WPT systems. It can also support multiple Rxs while ensuring that the PTE of each Rx is relatively unaffected. An electromagnetic simulation of the proposed MSG-WPT system is performed using a high-frequency structure simulator (HFSS), and measurements are conducted in a corresponding experimental environment. The system power efficiency is measured at -12 dB in the 4 MHz frequency band. The proposed MSG-WPT system with a CPE is adequately efficient and portable, while also allowing a more liberal arrangement of Rxs compared to other conventional WPT systems

Wideband Flexible/Transparent Connected-Ground MIMO Antennas for Sub-6 GHz 5G and WLAN Applications

A flexible transparent wideband four-element MIMO antenna with a connected ground plane is proposed with numerical computation and experimental measurement studies. The optical transparency is obtained using flexible conductive oxide material AgHT-4 and Melinex substrate. The radiating elements are in the form of circular stub-loaded C-shaped resonators, which are positioned in a carefully structured flexible Melinex substrate with an interconnected partial ground plane structured in the form of an L-shaped resonator, attaining an overall antenna size of 0.33 lambda x 0.48 lambda at the lowest operating frequency. The proposed antenna spans over a -10 dB impedance bandwidth of 2.21-6 GHz (92.32%) with an isolation level greater than 15dB among all elements. The maximum gain is 0.53dBi with a minimum efficiency of 41%, respectively which is satisfactory considering flexible structure and sheet impedance of 4 Omega/sq. MIMO antenna parameters in terms of the envelope correlation coefficient (ECC) and diversity gain (DG) are also extracted where all the values are satisfactory for MIMO applications. The bending analysis of the proposed transparent MIMO antenna along the X and Y axis has revealed good performance in terms of scattering parameters and radiation pattern along with MIMO diversity performance. All of these technical points make the flexible MIMO antenna suitable for smart devices using sub-6 GHz 5G and WLAN band in IoT applications where visual clutter and co-site location issues need to be mitigated with the integration ease of conformal placement on the curved component/device surfaces

Characteristic Impedance Adjustment of Thin-Metal Mesh Transmission Lines for mmWave Display-Integrated Antennas

This paper proposes four methods and empirical formulas of adjusting characteristic impedances for thin-metal mesh transmission lines. The characteristic impedances are discretely adjusted by changing the number and the size of unit meshes, which provides macro-tuning capability, and the discrete values can be tuned more precisely by varying the thin-metal line width and the aspect ratio of mesh geometry. The validity of proposed methods is confirmed by full-wave numerical simulations, and the simulated impedance variations are well-described by our empirical formulas. For further verifications, 26 distinguished samples of thin-metal mesh transmission lines and a 28-GHz thin-metal mesh antenna are fabricated, and their characteristics are measured in millimeter-wave spectrums. The measured results confirm that the proposed methods and empirical formulas can provide accurate and more flexible design rules for impedance adjustment, which allows potential advances in display-integrated antenna applications

Design of a Compact Indirect Slot-Fed Wideband Patch Array with an Air SIW Cavity for a High Directivity in Missile Seeker Applications

This research proposes a compact indirect slot-fed wideband patch array antenna for a missile seeker application. The proposed single antenna consists of three dielectric layers for a radiator, an air substrate-integrated waveguide (SIW) cavity, and an indirect feeding network. The rectangular patch is used as a radiator on the first substrate layer, and the air SIW cavity (ASIWC) is employed to obtain high directivity and low mutual coupling characteristics in the second substrate layer. In the third layer, an indirect feeding structure is used to achieve the wideband characteristics in the Ka-band. The single element is extended to a 4 x 1 linear array with fabrication, and the fabricated array characteristics are measured in a full anechoic chamber. The measured operating fractional frequency bandwidth is 9.2%, and the measured array gain is 11.7 dBi at the bore-sight direction (theta(0) = 0 degrees)

Compact Wideband Four Element Optically Transparent MIMO Antenna for mm-Wave 5G Applications

A four-element compact wide-band optically transparent MIMO antenna with a full ground plane is proposed. The four elements transparent MIMO system has a compact size of 24x20 mm(2) with the undivided ground plane as most of the real-time systems demand a common reference. The complete antenna system achieves around 85% transparency due to a combination of AgHT-8 and Plexiglas which forms the transparent conductive patch/ground and substrate, respectively. The antenna geometry leads dual-band operation ranging from 24.10 - 27.18 GHz (Impedance bandwidth D 12%) and 33 - 44.13 GHz (Impedance bandwidth D 28.86%) targeting the mm-wave 5G applications. The 4-element antenna system achieves isolation between inter-elements > 16 dB and maximum gain value of greater than 3 dBi with more than 75% efficiency. The proposed transparent MIMO antenna is evaluated in terms of diversity gain (DG), envelope correlation coefficient (ECC), total active reflection coefficient (TARC), and mean effective gain (MEG) where decent MIMO performance with isolation more than >16 dB between the adjacent and other elements is achieved. Transparent MIMO antenna achieves directional patterns for the operating band with the value of DG > 9, ECC < 0.1, TARC value less than and the ratio of MEG within the agreed limit of +/- 3 dB conforming acceptable MIMO/diversity performance

Multipole resonance and Vernier effect in compact and flexible plasmonic structures

Spoof surface plasmons in corrugated metal surfaces allow tight field confinement and guiding even at low frequencies and are promising for compact microwave photonic devices. Here, we use metal-ink printing on flexible substrates to construct compact spoof plasmon resonators. We clearly observe multipole resonances in the microwave frequencies and demonstrate that they are still maintained even under significant bending. Moreover, by combining two resonators of slightly different sizes, we demonstrate spectral filtering via the Vernier effect. We selectively address a target higher-order resonance while suppressing the other modes. Finally, we investigate the index-sensing capability of printed plasmonic resonators. In the Vernier structure, we can control the resonance amplitude and frequency by adjusting a resonance overlap between two coupled resonators. The transmission amplitude can be maximized at a target refractive index, and this can provide more functionalities and increased design flexibility. The metal-ink printing of microwave photonic structures can be applied to various flexible devices. Therefore, we expect that the compact, flexible plasmonic structures demonstrated in this study may be useful for highly functional elements that can enable tight field confinement and manipulation

Aperture-Fed Quad-Port Dual-Band Dielectric Resonator-MIMO Antenna for Sub-6 GHz 5G and WLAN Application

A four-port dielectric resonator-based connected ground multiple-input multiple-output (MIMO) antenna is designed. The presented antenna was excited through the aperture feeding technique. The dual bands are achieved by optimally feeding the rectangular dielectric resonator through engineered triangular slots. The antenna has operating modes of TE111X and TE111Y at 4.5 GHz and 5 GHz, respectively. It presents a 2 : 1 VSWR bandwidth of 2.64% (4.48 GHz-4.60 GHz) and 1.2% (4.96 GHz-5.04 GHz) in the lower and upper bands, respectively. The edge-to-edge distance between array elements is around 7.5 mm. The single antenna dimension is 30 mm x 30 mm, whereas the four-port antenna dimension is 60 mm x 60 mm. The optimum isolation was achieved by carefully placing the antenna elements on the substrate through multiple iterations. The antenna provides port isolation better than 20 dB at both resonances with full ground profile. The advantage of the antenna is that it provides fair antenna and MIMO parameters without additional isolation techniques. The antenna has efficiency in order of 88.02% and 86.31%. The peak gain is 7.67 dBi and 8.32 dBi at 4.5 GHz and 5 GHz, respectively. The optimum envelope correlation coefficient (ECC) is 0.037, channel capacity coss (CCL) is 0.2 bits/sec/Hz, diversity gain (DG) is 9.99 dB, and total active reflection coefficient (TARC) is -18.87. The antenna elements are orthogonally placed with adequate separation to achieve polarization diversity and spatial diversity. The antenna provides the utilization in Sub-6 GHz 5G and WLAN communication applications