Composite Antenna Research Articles

Compact loop‐dipole composite antenna with wideband operation and dual polarization

AbstractA design of the antenna with dual diagonal polarizations for 2G/3G/LTE base station applications is first described in this paper. The antenna has a compact size, and its structure is mainly composed of two orthogonally situated dipoles fed with coaxial baluns, a cross strip mounted on the dipoles, and a planar reflector. The cross strip can be regarded as dual orthogonal loop antennas. By embedding thin slots into the loop‐dipole composite antenna, the impedance bandwidth for return loss less than 15 dB can cover the frequency band from 1.7 to 2.7 GHz. Because the adopted balun also serves as an impedance transformer, the cross polarization level at the broadside is lower than −30 dB for all operation frequencies. Then, we found that by varying the dimensions of the slot, the loop‐dipole composite antenna can also deliver a 70% impedance bandwidth for return loss less than 10 dB, and the cross polarization level is lower than −25 dB in whole E‐plane and H‐plane. Antenna prototypes are constructed, and experimental and simulated results have good agreements.

Improving Channel Capacity in Indoor $4 \times 4$ MIMO Base Station Utilizing Small Bidirectional Antenna

Preparing toward the new-generation communication by improving the capacity in the channel can be achieved by employing a MIMO system with polarization diversity means. This paper presents a low-profile $4 \times 4$ MIMO bidirectional antenna consisting of two composite antennas mounted on a ground plane. The composite antenna is constructed by stacking a notch antenna and a loop antenna on top of each other and each antenna is fed independently. This antenna is capable of dual-polarized radiation patterns pointing in two different directions, where the notch antenna produces a horizontally polarized wave in the ${x}$ -axis direction while the loop antenna gives a vertically polarized wave in the ${y}$ -axis direction. The combination of two composite antennas has good isolation between the elements and is capable of improving the channel capacity for indoor MIMO base station applications. This paper includes the validation of both the fabrication of the proposed antenna design and the channel propagation measurement using the proposed antenna, confirming the excellent antenna performance for long term evolution application at a frequency of 3.5 GHz.

Compact Broadband Omnidirectional Radiation Pattern Printed Dipole Antenna Incorporated With Split-Ring Resonators

A broadband, low-profile, compact, and cost-effective antenna consisting of a printed dipole loaded with split-ring resonators (SRRs) is presented. The antenna consists of two identical printed SRRs, each enclosing an arm of a printed dipole element. Each SRR and the center-fed half-wavelength dipole element are printed on the top and bottom sides of a thin dielectric substrate. The dipole is excited by a coaxial feed, while the SRRs are electromagnetically coupled to the dipole. The dipole, in conjunction with the SRRs, generates three resonant modes with stable omnidirectional radiation patterns. These resonances interact to provide broadband characteristics, that is, a measured impedance bandwidth covering 1.32–2.46 GHz for a reflection coefficient of less than −10 dB. The functionalities, mechanisms, and modes of operation of the composite antenna structure are discussed in relation to both the dipole and the SRRs. A prototype is fabricated and measured in order to validate the antenna design. It is computationally and experimentally confirmed that the antenna demonstrates broadband characteristics as well as a stable gain with non-deteriorating omnidirectional radiation patterns. The compact antenna, which has the overall dimensions of 9.6 mm $\times$ 74.4 mm $\times$ 0.508 mm ( $0.06\lambda \times 0.469\lambda \times 0.0032\lambda$ at 1.895 GHz), has a measured fractional bandwidth of 60.31%, an omnidirectional radiation pattern with a gain greater than 1.8 dBi, and a radiation efficiency greater than 88% within a broad impedance bandwidth. The compact size, simple structure, and stable radiation properties of the antenna render it suitable for many wireless communication applications.

Preparation and Analysis of the Deployment Behavior of Shape Memory Polymer Composite Antennas

Preparation and Analysis of the Deployment Behavior of Shape Memory Polymer Composite Antennas

Surface enhancement of THz wave by coupling a subwavelength LiNbO3 slab waveguide with a composite antenna structure

Highly intense terahertz electromagnetic field and efficiently surface localized terahertz field in subwavelength volumes are of vital importance for terahertz photonics integration, also will greatly accelerate the development for integrated applications in biochemical sensing, imaging, terahertz spectroscopy, enhancement of nonlinear effects and even quantum research. In this paper, we achieved large terahertz field enhancement and surface field localization through depositing a pair of Au composite antennas on a LiNbO3 subwavelength slab waveguide, which can serve as an excellent on-chip platform for terahertz research and application. The antennas consist of two opposing tip-to-tip triangles separated by a gap, and each triangle combines with a strip antenna. Time-resolved imaging and finite-difference time-domain method were used to resolve the characteristics of the designed antennas experimentally and simulatively. Through these methods, we demonstrated outstanding abilities of the platform: leading to a large electric field enhancement, concentrating almost full terahertz energy on the waveguide’s surface when they are resonant with the terahertz waves and tunable resonant frequency. These abilities make the subwavelength waveguide coupling with the composite antennas be able to sever as a good integrated device to identify terahertz-sensitive small objects, or an excellent platform to terahertz spectroscopy and quantum research.

Design and Development of Compact Microstrip Patch Antenna for Wireless Applications

In this paper, a novel dual band microstrip patch antenna based on composite patch antenna and radiating part. By selecting a suitable offset feed position, it is feasible to provide 50Ω characteristic impedance and thus making better impedance matching. The proposed antenna has been improved broader bandwidth by using RT Duroid substrate. The radiating part is plays a important role in creating a lower operating band (2.45 GHz) in addition to achieve miniaturization. The proposed antenna has to be fabricated with RT / Duroid substrate and dimensions of 19 × 22 × 0.8 mm. The measured -10 dB bandwidth of 200 MHz at 2.45 GHz and 990 MHz at 5.45 GHz, which is quite useful for Industrial, Scientific and Medical (ISM) and WLAN applications.

Tri-band composite cylindrical dielectric resonator antenna with hybrid mode excitation and cross-polarization suppression

This communication investigates composite cylindrical dielectric resonator antenna (CDRA) for various wireless applications. Three important features of proposed antenna design are (i) realization of two different hybrid modes, that is, HEM11δ and HEM12δ mode in CDRA with the help of modified annular ring printed line (work as both magnetic dipole and electric dipole), both the hybrid modes support broadside radiation characteristics (ii) suppression of HEM21δ mode, in order to reduce the cross-polarization level in H-plane of other hybrid modes (HEM11δ and HEM12δ mode) by an amount of 8-10 dB (iii) creation of triple-band attribute using the concept of composite antenna. The proposed antenna design has been fabricated and practically tested. Simulated outcomes show good agreement with measured outcomes. It works in three frequency bands, that is, 2.25-2.79 GHz, 3.1-4.0 GHz, and 5.05-5.6 GHz. The designed antenna structure is appropriate for WLAN and WiMAX applications.

Deformation analysis and experiments for functional surface of composite antenna structure

Composite structure with embedded microstrip antenna array is a multifunctional structure that can provide the capabilities of a panel skin structure and a radar antenna simultaneously, and it is usually installed in the structural surface of the air, water, and ground vehicles. The environmental load under in-service conditions leads to structural deformations of the composite antenna structure. In this paper, theoretical analysis and experimental validations were presented to investigate the deformations of the functional surface in the composite antenna structure. An electromechanical coupling analysis method was proposed to evaluate the performance of the deformed composite antenna structure subjected to external loads. Composite antenna structure specimens were designed, fabricated, and measured. Using the specimens, experimental systems were built to investigate the deformation. The results show that structural deformation decreases the electromagnetic performance of the composite antenna. The coupling analysis method can be applied to evaluate the performance of the deformed composite antenna structure at the design stage.

Electromagnetic absorption properties of spacecraft and space debris

Aim of the work is to present a method to evaluate the electromagnetic absorption properties of spacecraft and space debris. For these objects, the radar detection ability depends mainly on volume, shape, materials type and other electromagnetic reflecting behaviour of spacecraft surface components, such as antennas or thermal blankets, and of metallic components in space debris. The higher the electromagnetic reflection coefficient of such parts, the greater the radar detection possibility. In this research an electromagnetic reverberation chamber is used to measure the absorption cross section (ACS) of four objects which may represent space structure operating components as well as examples of space debris: a small satellite, a composite antenna dish, a Thermal Protection System (TPS) tile and a carbon-based composite missile shell. The ACS mainly depends on geometrical characteristics like apertures, face numbers and bulk porosity, as well as on the type of the material itself. The ACS, which is an electromagnetic measurement, is expressed in squared meters and thus can be compared with the objects geometrical cross section. A small ACS means a quite electromagnetic reflective tendency, which is beneficial for radar observations; on the contrary, high values of ACS indicate a strong absorption of the electromagnetic field, which in turn can result a critical hindering of radar tracking.

Loop-Dipole Composite Antenna for Wideband Microwave-Based Medical Diagnostic Systems With Verification on Pulmonary Edema Detection

A unidirectional and compact antenna for wideband microwave-based medical diagnostic applications is presented. The main part of the antenna is formed from the combination of loop and dipole interleaved structures. To enable the antenna to resonate at a low frequency within a compact substrate area, a pair of slots is created on the loop’s vertical arms, whereas the dipole’s structure is tapered to compensate for the negative effect of the capacitively loaded slots. With the proposed configuration, the antenna acts as an array of two dipoles and a quasi-Yagi antenna at lower and higher frequencies, respectively, and thus radiates mainly in one direction. The antenna has a compact size (with respect to the wavelength at the lowest operating frequency) of $0.23 \times 0.23$ , making it 50% smaller than similar designs. It has a measured fractional bandwidth of 55% at 0.65–1.15 GHz and peak gain and front-to-back ratio of 3.8 dBi and 11 dB, respectively. To verify the practicality of the antenna, it is applied in an array configuration and successfully tested in detecting pulmonary edema in realistic simulation and experimental environments.

In situ non-destructive evaluation of an aircraft UHF antenna radome based on pulse-echo ultrasonic propagation imaging

Most aircraft antennas are protected by radomes made of composite materials. However, antenna radome structures are easily damaged by external forces and internal manufacturing defects. To detect damage in the composite antenna radomes while in service, a full-field pulse-echo ultrasonic propagation imaging (PE UPI) system is proposed as an in situ non-destructive inspection technique, which is mobile inside a hangar. The radome is generally a double-curvature structure, and thus, a curvature compensation algorithm is also developed to increase damage visibility. The proposed hardware and software have been tested by detecting a resin rich region formed between the E-glass/epoxy plies. To visualize the damage, PE ultrasonic wave propagation imaging has been performed, and ultrasonic energy mapping has also been applied. A curvature compensating algorithm has been newly developed and compared for its performance in damage visibility improvement. To verify the size of the real defects of a UHF antenna radome, destructive testing has been performed by cutting the defect area, polishing the cross section and investigating the section using a 50× microscope. The results have shown the feasibility of the proposed PE UPI system and the inspection strategy as an in situ non-destructive evaluation technique for radome structures.

Defect visualization of aircraft UHF antenna radome using full-field pulse-echo ultrasonic propagation imaging system

Most of aircraft antennas usually have various types of radome made of composite materials for protecting antenna structures. However, these antenna radome structures, which are installed on the outside of airplane, are easy to be damaged by external forces such as drag, foreign object, bird strike and others. In this study, full-field pulse-echo ultrasonic propagation imaging (PE UPI) system is proposed as the non-destructive inspection technique to visualize manufacturing defects in composite antenna radome. Based on the results of the sample case study, it is shown that the ultrasonic wave propagation imaging (UWPI) that is generated by the proposed full-field PE UPI system is able to highlight the intact internal condition of antenna structure and its defect area. Additional damage visualization techniques like ultrasonic energy mapping (UEM), variable time window amplitude map (VTWAM) and also ultrasonic spectral imaging (USI) algorithms are applied to improve the reliability of the damage visualization. It can be concluded that the proposed PE UPI system is an effective non-destructive inspection technique for the composite radome structures.

On Increasing the Slow-Fading Channel Diversity Using Block-Coded MIMO-OFDM With Reconfigurable Antennas

In this paper, we propose a new block coding scheme to increase the diversity gain of multiple-input–multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems over slow-fading wireless channels. We assume that the antenna elements at the transmitter are reconfigurable and capable of independently changing the physical characteristics of their radiation patterns. The composite right-left handed leaky-wave antenna is an example of reconfigurable antennas with such characteristics. We use this feature of the antennas and develop a block coding scheme that exploits, in addition to the spatial and frequency diversity, a new additional degree of diversity, which is called state diversity. We determine the maximum achievable diversity order of the proposed coding scheme in spatially correlated frequency-selective channels. To demonstrate the performance of the proposed block coding technique, we provide numerical results and compare them with those of the previously developed coding schemes for MIMO-OFDM systems. The results indicate that the proposed code achieves significantly higher diversity and coding gain, even in spatially correlated channels, compared with the existing counterparts.

AMC‐based broadband bowtie antenna for WIMAX application

ABSTRACTA broadband bowtie antenna with artificial magnetic conductor (AMC) ground is proposed for WIMAX application. Loaded with two parallel open stubs in the upper layer, the proposed bowtie antenna has the merit of broad band. An AMC surface composed of 6 × 9 Jerusalem cross slot unit cells is designed under the bowtie antenna with a distance of 0.1λ, where λ denotes the free space wavelength at 3.0 GHz, for gain enhancement and wide bandwidth on the basis of low profile. Measured results show that, with maintaining a low profile, the composite antenna has a wide bandwidth (return loss 10 dB) from 2.48 to 3.8 GHz (42.04%). The measured peak gain is up to 7.94 dBi, and the maximum cross‐polarization level is −17 dB for both E and H plane. And the measured front‐to‐back ratios are <−19 dB. Both the bowtie antenna and the AMC surface are fabricated and measured. The simulated and the measured results are in good agreement. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2657–2661, 2016

Compact Planar Loop–Dipole Composite Antenna With Director for Bandwidth Enhancement and Back Radiation Suppression

A wideband and unidirectional loop-dipole composite antenna with a planar structure is proposed. The antenna includes a half-wavelength dipole and a one-wavelength loop that are printed on different sides of a substrate. To control the radiation characteristics of each element separately, the dipole is fed using a coaxial cable, whereas the loop is fed using offset broad-side coupling. To overcome the low front-to-back ratio (FBR) at lower and upper frequencies of the band, where the loop-dipole mode is not dominant, while maintaining a compact size, a parasitic strip is located in the vicinity of the loop. The strip acts as a director for the dipole at the low frequencies and for the loop at the high frequencies and thus significantly improves the FBR at those frequencies. The antenna achieves a wide fractional operating bandwidth of 49% at 0.7-1.15 GHz, a size reduction of more than 50% compared with recent similar designs, stable gain with a peak value of 4.8 dBi, and a minimum FBR of 11 dB across the operating bandwidth. Owing to its compact and planar structure, lightweight, simple fabrication, and stable radiation characteristic, it can be utilized in various wireless applications operating at the ultrahigh-frequency band.

Bandwidth and Directivity Enhancement of Loop Antenna by Nonperiodic Distribution of Mu-Negative Metamaterial Unit Cells

The theory, design, analysis, and verification of a wideband and unidirectional loop antenna loaded with mu-negative (MNG) metamaterial unit cells is presented. It is shown that by nonperiodic positioning of MNG unit cells on the loop structure, the amplitude of the surface current can be modified in a desired section of the loop, and hence, unidirectional radiation is achievable at the mu-zero resonance frequency. Moreover, it is demonstrated that as a result of the capacitive MNG loading, a 90° phase difference occurs between the vertical arms of the loop. Therefore, its radiation mechanism can be characterized as an array of two dipole antennas positioned a quarter wavelength apart, thus creating unidirectional radiation. To further improve the performance of the antennas, a quarter-wavelength strip is located in the vicinity of the loop to act as a resonator and director at higher frequencies. With the proposed structure, the final design is at least 50% smaller, in terms of the occupied area, than recent antenna designs of conventional loops, MNG loaded loops, and loop–dipole composite antennas. It also achieves a wide fractional bandwidth of 52% from 0.64 to 1.1 GHz, which is 50% wider than recent MNG metamaterial unit cell loaded loops, with a measured peak front-to-back-ratio and gain of 13 dB and 4.8 dBi, respectively.

Segmented quarter cylindrical dielectric resonator antenna: simulation and experimental investigation in composite form for wideband applications

A probe feed wideband multi-element dual segments quarter cylindrical dielectric resonator antenna (q-CDRA) in composite forms have been proposed. The q-CDRA has been introduced by splitting CDRA into four uniform quarters and multi-segmentation approach has been castoff for further improvement in bandwidth of q-CDRA. The dual segments q-CDRA has been designed and analyzed using theoretical analysis and Ansoft HFSS simulation software. Further the dual segment multi-element q-CDRAs in composite form have been designed. A coaxial probe has been placed at the center of the ground plane for the excitation of proposed multi-element and multi-segmented composite form of q-CDRA, which excite TM01δ mode in the proposed antenna. The input characteristics and radiation patterns of the proposed composite antennas have been studied and their results are compared with corresponding experimental results. Prototype of single, two, and four elements dual-segment composite q-CDRAs have been fabricated and input characteristics of the proposed composite antennas have been compared with each other. Four elements dual-segment composite q-CDRA has shown wide impedance bandwidth (|S11| ≤ −10 dB) of 85.13% with monopole-like radiation pattern. The peak gain of 4.85 dBi with 98.5% radiation efficiency has been achieved for dual-segment four elements composite q-CDRA. The proposed multi-element dual-segment composite q-CDRAs may find suitable applications in C and X-band with complete covering of the 5.0 GHZ wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) band.

Composite GPS Patch Antenna for the AR Bandwidth Enhancement

A composite Global Positioning System (GPS) patch antenna with a quadrature 3 dB hybrid coupler was designed and implemented for working RHCP and had a broadband axial ratio (AR) bandwidth. We designed two patches as a FR-4 patch and 1.5 mm thickness thin ceramic patch with a quadrature 3 dB hybrid coupler. A CP radiation pattern was achieved, and the AR bandwidth improved by incorporating a quadrature 3 dB hybrid coupler feed structure in a micro-strip patch antenna. SMD by chip elements was applied to the quadrature 3 dB hybrid coupler. For the composite FR-4 and ceramic patch antennas, the VSWR measurement showed a 2 : 1 ratio over the entire design band, and the 3 dB AR bandwidth was 295 and 580 MHz for the FR-4 patch and ceramic patch antennas, respectively. The antenna gains for the composite FR-4 and ceramic patch antennas were measured as 1.36–2.75 and 1.47–2.71 dBi with 15.11–25.3% and 19.25–28.45% efficiency, respectively.

Dual-Band Operation of a Circularly Polarized Four-Arm Curl Antenna with Asymmetric Arm Length

This paper presents dual-band operation of a single-feed composite cavity-backed four-arm curl antenna. Dual-band operation is achieved with the presence of the asymmetrical arm structure. A pair of vacant-quarter printed rings is used in the feed structure to produce a good circular polarization (CP) at both bands. The cavity-backed reflector is employed to improve the CP radiation characteristics in terms of the 3-dB axial ratio beamwidth and broadside gain. The proposed antenna is widely applicable in dual-band communication systems that have a small frequency ratio. Examples of such a system are global positioning systems.

Slim planar composite antenna with two orthogonal polarisations for WLAN router applications

A slim planar composite antenna for WLAN router applications is presented. A J-antenna and a dipole antenna are proposed as components antennas for the vertical and the horizontal polarisations, respectively. The arms of the dipole adopt a bent structure for size miniaturisation. For tuning the impedance matching, a matching stub is introduced working as a parallel inductor on the upper part of the dipole. The antenna is made by copper and fed by coaxial lines. The final antenna achieves two orthogonal polarisations with a low cross-polarisation level <−18 dB, a return loss better than 10 dB, and port isolation in excess of 19.3 dB from 2.38 to 2.51 GHz, thus making it suitable for use in 2.45 GHz WLAN router polarisation diversity applications. The slim planar structure with 25.5 mm width and light weight makes it easy to install on WLAN routers.