Small Antenna Array Research Articles

Electrically Small Platform-Based Antennas for an Unmanned Ground Vehicle

We present a design strategy for platform-based antennas operating on electrically small platforms such as unmanned ground vehicles (UGVs). Specifically, we report the design of a platform-based antenna operating at the lower end of the very-high-frequency (VHF) band for a small UGV with physical dimensions of 99 cm × 67 cm × 39 cm. The antenna is mounted on the bottom of the platform resulting in an extremely low-profile design and generating vertically polarized, monopole-like radiation patterns. Using characteristic-mode theory (CMT), performance metrics of the antenna including its maximum potential bandwidth and radiation patterns are investigated. The performance of the antenna when operating in a realistic operational environment is analyzed using full-wave electromagnetic simulations. A full-scale prototype of the antenna mounted on the bottom of the vehicle was fabricated and experimentally characterized. Finally, the design of this low-profile antenna is extended to a two-element antenna array mounted on the same platform and a prototype of this two-element array was fabricated. Basic experiments were conducted to study impedance matching and mutual coupling effects in this electrically small antenna array. The performance of this array as part of a two-element direction-finding system was investigated through computer simulations.

Design of a Small Array Antenna with an Extended Cavity Structure for Wireless Power Transmission

This paper proposes a design of a small array antenna with an extended cavity structure for wireless power transmission. The proposed array element consists of a square radiating loop, which is designed to resonate at 5.8 GHz, and an extended cavity structure to reduce the mutual coupling between adjacent elements. We derive the optimal element number in a limited space by considering the input power for each element, fabrication cost, and aperture efficiency of the system. To verify the suitability of the proposed a small array with an extended cavity structure, a 2 × 2 downscaled array antenna is fabricated and measured in a full anechoic chamber. The results confirm that the proposed antenna element with an extended cavity structure is suitable for wireless power transmission systems; the proposed array has a transmission efficiency of about 1% at a distance of 2 m when the array is applied to both transmitting and receiving antennas.

Design and analysis of planar wideband monopole antenna using WIPL-D simulator

One of the problems that correspond to the small dimension of an antenna is the bandwidth. In order to overcome the problem from small linear and multiple antenna array systems, the investigation of the antenna elements is needed. The design of planar antennas is to achieve an antenna that is able to match various demands in applications where size, cost, performance, and aerodynamic profiles are very important considerations, a low-profile antenna such as a small. The antenna performance on scattering parameters S11, gain, return loss and impedance input are investigated at obtaining wideband antennas by adjusting antenna design parameters. The substrate thickness needs to be adjusted to 0.813 mm, and the element length at 2 mm and 0.75 mm. The calculation of VSWR, gain, and the radiation pattern is presented using MoM-based WIPL-D. The antenna element when x2 is 2mm in the frequency range 4 GHz – 8 GHz, which this antenna works best on element dimension x2= 1.5mm when the frequency resonance 4.86 GHz and VSWR value is 1. The main advantages of this antenna are the dimension and simple design.

Multi-CubeSat Relative Position and Attitude Determination Based on Array Signal Detection in Formation Flying

High-precision relative position and attitude measurement is crucial for consensus control and collision avoidance in multi-CubeSat formation flying. However, the traditional relative navigation systems comprise many sensors and are not suitable for CubeSats due to large volume, complexity, and cost. In this paper, we propose a new approach, called Multi-CubeSat relative State determination by Array Signal detection (MUSAS). The approach utilizes the existing communication systems and antenna arrays on CubeSats without the need of extra components. In MUSAS, deputy vehicle (DV) CubeSats in a formation broadcast orthogonal spread spectrum signals simultaneously. Two chief vehicle (CV) CubeSats receive and separate the signals and extract the multiple-input multiple-output channel response of each DV CubeSat. Then, by utilizing the bi-directional spatial spectrum estimation, the angles-of-arrival and angles-of-departure of the propagation paths from each DV CubeSat to the CV CubeSats are estimated. Finally, the attitudes and positions of all DV CubeSats relative to the CV CubeSats are determined using the derived rotation matrices. We have theoretically proved the proposed MUSAS algorithm and performed extensive simulations to compare its performance with existing methods. Furthermore, we also developed the testbed of MUSAS and conducted field experiments. The simulation and experiment results have verified that, by exploiting the spread spectrum gain and antenna array gain, MUSAS can achieve high accuracy in relative state determination, even using small antenna arrays and low transmission power.

Control of near electric field by topology optimised sub‐wavelength 3D loop antenna

In this Letter, a new method is proposed for the synthesis of the near electric field. This method is based on three-dimensional (3D) small loop antennas with an engineered shape. An arbitrary shape is used as a new degree of freedom. Also, concerns over the implementation of complex shapes are vanished by 3D printing technology. With the help of an array of 3D small loop antennas, complex distribution of electric fields can be realised. To illustrate the functionality of the proposed method, an array of four elements, all of which is connected to a source, is designed to synthesise the desired electric field distribution. The results of design and experimental measurement showed high accuracy and capacity of this method in controlling the electric field.

Microstrip Patch Antenna towards Future of Communication

Objective: The aim of the design will be an antenna with higher gain and low return loss. The antenna is required to operate at 11 GHz. At this frequency there is special satellite communication such as DTH. In future large dish operating at above said frequency may get replaced by a small patch antenna (array). Method: To do this single patch design will not be helpful. Instead of this, array of patches will be required. The array can be of linear type or rectangular type. The best optimum design is to be selected. First a single antenna was prepared and optimized for the highest possible gain and resonating at desired frequency. The same was appended with array of different configurations in order to achieve the goal. Findings: Array design of linear type and rectangular type is proposed in this study. The antenna made is simulated for a wider range of frequencies from 8 GHz to 14 GHz. The antenna was found to resonate at 11 GHz and there is a considerable increase in gain also if the numbers of elements are increased. In this study the dimension of the antenna is diminished in comparison of the conventional one as the existing length and breadth of the substrate is modified and is shown lower section. Along with this in a particular design combination of series feed and corporate feed is shown which in turns improves the impedance matching of the antenna. This helps in better current distribution over all the patches. Application/Improvement: The proposed and designed antenna can be used for communication purpose in X band and further if the gain is improved to meet the gain characteristics of dish antenna (X band) then it can be seen as a replacement of existing dish also. Keywords: Array Antenna, Linear Array, Microstrip Patch Antenna (MPA), Rectangular Array, Return Loss

Compact circularly polarized beam-switching wireless power transfer system for ambient energy harvesting applications

In this work, we propose a circularly polarized (CP) beam-switching wireless power transfer system for ambient energy harvesting applications operating at 2.4 GHz. Beam-switching is achieved using a low profile, electrically small CP antenna array with four elements and a novel miniaturized 4×4 butler matrix. The CP antenna is designed with an e-shaped slot and four antennas. The CP antenna measures 0.32 λ0×0.32 λ0×0.006 λ0 at 2.4 GHz. The antenna has a gain of 3 dBic and an axial ratio less than 3-dB at 2.4 GHz. A linear antenna array consisting of four elements is designed with the CP antenna element with an inter-element distance of 0.29 λ0. A 4×4 butler matrix with miniaturized couplers and crossovers are used to feed the four antenna array elements. Based on the input port of excitation, the main beam of the antenna array is demonstrated to be switched to four directions: −5°, 65°, −55°, and 20°. A CP rectenna is used to demonstrate the wireless power transfer capability of the combination of the butler matrix and the CP-antenna array. The rectenna consists of a Teo-shaped CP antenna and a rectifier. The open circuit voltage at the output of the rectenna is found to peak value of 30 mV at −3°, 61°, −53°, and 17°. Thus a complete system for CP wireless power transfer including the power transmission system as well as the RF energy harvesting sensor is designed and experimentally verified.

Direction of Arrival Estimation Using Amplitude and Phase Information in Low-Profile MIMO Arrays

Accurate direction of arrival (DOA) estimation in compact terminal devices using small antenna arrays is challenging due to their limited radiating apertures. In this communication, we employ both the amplitude and the phase information to improve the estimation accuracy and eliminate phase ambiguity without increasing the size of the antenna array. The optimal amplitude ratio between the antenna patterns is theoretically studied using the theories of the Fisher information, Cramer–Rao bound, and ambiguity function. Criteria of proper amplitude ratio are summarized from the theoretical investigations. Following the guidelines, two antenna arrays are modified to build effective antenna patterns and improve the estimation accuracy. Specifically, the compact monopole-patch array and the dual-monopole array reduce the DOA estimation errors by over 60% and 20%–40%, respectively, under a medium SNR of 10 dB. The phase ambiguity has been eliminated in both arrays as well. The monopole-patch array requires phase calibration in the measurement, whereas the dual-monopole array does not. Experiments were carried out for the dual-monopole array in the anechoic chamber, achieving the estimation accuracy of 0.67° averaged over 360°.

A Miniature Microstrip Antenna Array using Circular Shaped Dumbbell for ISM Band Applications

The aim of this work is the achievement, and the validation of a small microstrip patch antenna array using a circular shaped dumbbell defected ground structure. This work has been dividing into two stages: The first step is to miniaturize a microstrip patch antenna resonating at 5.8GHz, which operate in the Industrial Scientific Medical band (ISM) and the second is to use a circular defected ground structure to shift the resonance frequency of the antenna array from 5.8GHz to 2.45GHz. At last, a miniaturization up to 74.47%, relative to the original microstrip antenna array has accomplished. The antenna structure has designed, optimized and miniaturized using CST MW Studio. The obtained results have compared with Ansoft’s HFSS electromagnetic solver. The antenna array has fabricated on FR-4 substrate, and its reflection coefficient is measured.

Comparison of Plane Wave and Spherical Vector Wave Channel Modeling for Characterizing Non-Specular Rough-Surface Wave Scattering

This letter demonstrates advantages of modeling the nonspecular wave scattering from surfaces of a multiple-input multiple-output (MIMO) channel in terms of the spherical vector wave (SVW) mode expansion. We propose the SVW mode coupling matrix $\boldsymbol {M}$ as a more efficient alternative to the commonly used set of distinct plane waves. $\boldsymbol {M}$ incorporates the scattered field components through the limited number of modes due to the cutoff property. A planar surface with random roughness is used to simulate the nonspecular scattering contribution to the radio channel, which is computed using physical optics. The matrix $\boldsymbol {M}$ and the plane wave channel model parameters are estimated from simulated radio channels. The estimates are used to compare the contribution of the nonspecular scattering to the radio channel reproduced from these two approaches. The comparison is performed for a small array antenna arrangement. Compared are the error of the magnitudes of MIMO channel transfer matrix, the narrowband channel eigenvalues, the correlation matrix distance, and the mutual information. It is found that $\boldsymbol {M}$ from the SVW channel modeling performs better in reproducing the radio channel of nonspecular scattering from the studied rough surface.

Capacity‐enhancement in MIMO systems using biomimetic electrically small antenna arrays

The authors investigate the performance of multi-input-multi-output (MIMO) communications systems that exploit biomimetic antenna arrays (BMAAs) with electrically small-aperture dimensions. By exploiting the mutual coupling between closely spaced radiating elements and extracting the maximum available power from all excitation modes of the array, BMAAs can significantly outperform conventional antenna arrays with similar aperture sizes. As a proof of concept demonstration, they examine the use of two-element BMAAs consisting of two $\lambda /4$λ/4 monopole antennas with variable element spacing in an MIMO system. The capacity of MIMO systems using such BMAAs is compared with those that use conventional antenna arrays with the same element types and spacing. Their simulation results demonstrate that using BMAAs can offer considerable capacity enhancements in an MIMO system. To experimentally verify these results, a prototype of a two-element BMAA operating at 615 MHz with element spacing of $\lambda /10$λ/10 and a regular array prototype with similar antenna elements and dimensions are fabricated and characterised. The performance of MIMO systems using these two antennas is modelled using numerical channel modelling using the measured antenna responses. These results are found to be in good agreement with theoretical predictions.

Millimetre‐wave dielectric resonator antenna array based on directive LTCC elements

The study deals with the application of low-temperature co-fired ceramic (LTCC) technology for design of a higher-order mode dielectric resonator antenna element operating at centre frequency 25.7 GHz. The LTCC material that the authors use provides very low dielectric losses and enables us to design an antenna element with very high radiation efficiency. The authors follow by examining the mutual coupling between two resonators and the authors propose a small (1 × 4) one-dimensional antenna array composed of such elements. In order to minimise the dimensions of the ground plane and to place the connector at a convenient location, the authors design a parallel feed network in substrate integrated waveguide technology, thus reducing the radiation losses of the feeding structure. The experiments verify the four-element antenna array concept with maximum measured gain of 16.3 dBi.

Trade-Off Analysis of Mutual Coupling Effect on MIMO Antenna Multiplexing Efficiency in Three-Dimensional Space

We analyzed the relation between two opposite effects of mutual coupling (MC), correlation reduction and gain loss, on the MIMO antenna performance in three-dimensional (3D) space. In the antenna level, those MC effects can be represented in terms of two main MIMO antenna parameters: the antenna correlation and radiation efficiency. The main contribution of this paper is the derivation of MC-related effects only on the antenna parameters, which then can be plugged into multiplexing efficiency, a realistic antenna-level MIMO performance metric, to evaluate the trade-off between two opposite MC effects. Uniform linear arrays with and without polarization diversity are used to analyze the MC effects, and to clarify the ambiguities of their contributions on the MIMO performance. The impacts of azimuth and elevation angular spreads to the MC and MIMO antenna performance are also investigated. Results show that the MC, contrary to common intuition, has a positive contribution to the MIMO performance relative to when MC is not considered in the system, especially at small antenna spacing. It implies that the correlation reduction dominates the gain loss from the MC effects. So, we can infer that the MC actually is not the reason for performance degradation in small spacing antenna arrays.

Direction-of-Arrival Estimation Enhancement for Closely Spaced Electrically Small Antenna Array

In this paper, compact direction finding systems using a scatterer of a high dielectric constant in between adjacent closely spaced electrically small antennas are examined. By adding a high-permittivity scatterer, the directional sensitivity can be enhanced. However, due to limited physical dimension, an electrically small antenna has highly reactive impedance. To enhance the received power level, a matching network is included. The highest directional sensitivity satisfying a given power constraint is compared for with and without scatterer cases. In addition, widely used matching approaches such as multiport-conjugate matching (MCM), self-conjugate matching (SCM), and eigenmode decoupling matching are investigated to increase the received power. The impact of these matching networks on the directional sensitivity is studied. The power and the directional-sensitivity bandwidth after matching are also analyzed. Finally, the two-monopole and a high-permittivity scatterer system with SCM and MCM circuits is fabricated and tested.

Experimental Study of Electrically Compact Retrodirective Monopole Antenna Arrays

Auto-pointing and angular super-resolution properties of the radiation patterns generated by an electrically compact retrodirective monopole antenna array are demonstrated experimentally for the first time. The operation of electrically compact (element spacings less than one-fifth of the radiation wavelength) retrodirective antenna arrays that were theoretically considered in our previous work is confirmed by measurement. Particularly, it is shown that the direction-of-arrival information carried by an incident electromagnetic wave can be encoded into the evanescent near field of an electrically small resonant antenna array with a spatial rate higher than the spatial oscillation rate of the incident field in free space. This observation is supported by the near-field measurements, demonstrating that the magnitude of the scattered (evanescent) field in the array environment can exceed the magnitude of the incident field in free space by at least 6 dB. Retrodirective array antenna matching and the feasibility of a frequency-division full-duplex communication link based on the proposed antenna arrays are also discussed.

Delay Insensitive Signal-Injection Calibration for Large Antenna Arrays Using Passive Hierarchical Networks

Efficient beamforming of phased-array antennas requires that the phase delay of each channel is accurately known. One technique for achieving this is to distribute a calibration or local-oscillator reference signal through a delay-insensitive signal distribution network. In this paper, we propose using passive hierarchical signal distribution networks to distribute such signals, a method that scales significantly better with the size of the array than existing signal distribution methods. We analyze the impact of impedance variations within the network on the phase accuracy and propose a calibration front-end architecture. This front end also enables the return loss and coupling between antennas to be monitored for diagnostic purposes. We present an implementation of this front end that was applied to a small prototype antenna array, and show that this implementation exhibited low sensitivity to delays within the calibration network, reduced the temperature-dependent phase error of the front ends substantially, and can be used for performing antenna return-loss measurements.

Ultracompact Retrodirective Antenna Arrays With Superdirective Radiation Patterns

It is shown that the direction-of-arrival (DoA) information carried by an incident electromagnetic (EM) wave can be encoded into the evanescent near field of an electrically small resonance antenna array with a spatial rate higher than that of the incident field oscillation rate in free space. Phase conjugation of the received signal leads to the retrodirection of the near field in the antenna array environment, which in turn generates a retrodirected far-field beam toward the original DoA. This EM phenomenon enables electrically small retrodirective antenna arrays with superdirective, angular super-resolution, auto-pointing properties for an arbitrary DoA. A theoretical explanation of the phenomenon based on first principal observations is given and full-wave simulations demonstrate a realizability route for the proposed retrodirective terminal that is comprised of resonance dipole antenna elements. Specifically, it is shown that a three-element disk-loaded retrodirective dipole array with $0.15\lambda $ spacings can achieve a 3.4-dBi maximal gain, 3-dBi front-to-back ratio, and 13% return loss fractional bandwidth (at the 10-dB level). Then, it is demonstrated that the radiation gain of a three-element array can be improved to approximately 6 dBi at the expense of the return loss fractional bandwidth reduction (2%).

Design of a Small Arc-Shaped Antenna Array with High Isolation for Applications of Controlled Reception Pattern Antennas

This communication proposes the design of an arc-shaped antenna array with high isolation to increase the null depth for controlled reception pattern antenna applications. The array is composed of three identical antennas, and each array element is transformed from a rectangular shape to an arc shape to maximize the distance between antenna edges for isolation improvement. The proposed array is fabricated on a 5.5-inch circular substrate to measure antenna characteristics in a full anechoic chamber and is further evaluated by estimating its null depth in conjunction with the conventional power inversion method. The results prove that the array is suitable to effectively improve the isolation and the null depth at low-elevation angles.

Application of Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS) for Sea-State Detection

To combine the advantages of long detection range and small antenna array, the newly designed Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS) transmits radio waves by ionospheric reflection and receives oceanic backscattered ground waves. To combine the functions of operating frequency selection and sea-state detection, WIOBSS can transmit the interpulse coding wave and frequency-modulated continuous wave waveforms in one hardware platform. The hardware and software of the radio system are introduced. A sky-wave over-the-horizon sea-state detection experiment was carried out in Chongyang and Longhai, China, on January 28, 2015. The observations of the oceanic surface echoes 130–300 km from the coastline are also presented.

Measuring superdirective electrically small antenna arrays mounted on PCBs

ABSTRACTThis article addresses the problem of measuring superdirective electrically small antennas mounted on printed circuit broads (PCBs). Different configurations for connecting the excitation system (SMA connector and coaxial cable) to an array of 31 × 25 mm2 integrated in a PCB of 110 × 70 mm2 are studied. This configurations are evaluated based on the cable effect on the array's input reflection coefficient and radiation pattern. Obtained results show that properly connecting the cable with the array mitigates its effect, and hence, it can be measured. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2269–2274, 2015