Two-element Array Research Articles

Co-Circularly Polarized Van Atta Array Enabled by Quasi-Monostatic STAR Antennas

A true in-band full-duplex (IBFD) co-circularly polarized (CP) Van Atta array with the active enhancement of the radar cross section (RCS) at 2.45 GHz is demonstrated for the first time. This operation is enabled by a quasi-monostatic simultaneous transmit and receive (STAR) element consisting of two quadrifilar helix antennas (QHAs) counter wound with respect to each other and placed coaxially. Co-CP operation is realized by operating one helix in the forward mode and the other in the backward mode, which increases the isolation between the transmit (Tx) and receive (Rx) layers at the antenna level. To further enhance the isolation, the Van Atta array beamforming network (BFN) is formed from a reduced complexity CP configuration featuring only 90° hybrids and amplification. The concept of operation is verified through measurement of a two-element array and simulated eight-element array with aid from a novel method for the synthesis of Van Atta array performance from conventional range and bench measurements. The effect of mutual coupling in the array is examined along with the role of the phase delay in the BFN.

Chaos Time Delay Signature Suppression Assisted by a Phased Array With Four Different Waveguide Structures

We propose and demonstrate a chaos generation scheme that conceals the time-delay signature (TDS) by injecting the output of an external-cavity semiconductor laser (ECSL) into a two-element phased array (ECSL-TPA). We consider the case of the ECSL output with obvious TDS, and evaluate the performance of the ECSL-TPA with four waveguide structures in TDS suppression. The numerical results demonstrate that the ECSL-TPA allows for desired TDS suppression in wide parameter space regardless of the waveguide structures considered. However, different TDS behavior exists for these structures, which provides guidance for future design and optimization of the proposed ECSL-TPA. Additionally, the influence of some key parameters including the injection rate, frequency detuning, laser separation ratio, pump rate, linewidth enhancement factor, and frequency offset on TDS is systematically studied. Appropriate settings of these key parameters are beneficial for TDS suppression and thus optimizing optical chaos. The phased array can be extended to include a large number of elements and thus generates multiple independent chaotic signals with indistinguishable TDS in parallel, paying the way for chaos-based applications that require independent, high-quality chaos simultaneously.

A UWB Antenna Array Integrated with Multimode Resonator Bandpass Filter

This paper presents a novel design of a modified ultrawideband (UWB) antenna array integrated with a multimode resonator bandpass filter. First, a single UWB antenna is modified and studied, using a P-shape radiated patch instead of a full elliptical patch, for wide impedance bandwidth and high realized gain. Then, a two-element UWB antenna array is developed based on this modified UWB antenna with an inter-element spacing of 0.35 λL, in which λL is the free space wavelength at the lower UWB band edge of 3.1 GHz, compared to 0.27 λL of a reference UWB antenna array designed using a traditional elliptical patch shape. The partial ground plane is designed with a trapezoidal angle to enhance matching throughout the UWB frequency range. The mutual coupling reduction of a modified UWB antenna array enhances the reflection coefficient, bandwidth, and realized gain, maintaining the same size of 1.08 λ0 × 1.08 λ0 × 0.035 λ0 at 6.5 GHz center frequency as that of the reference UWB antenna array. The UWB antenna array performance is investigated at different inter-element spacing distances between the radiated elements. To add filtering capability to the UWB antenna array and eliminate interference from the out-of-band frequencies, a multimode resonator (MMR) bandpass filter (BPF) is incorporated in the feedline while maintaining a compact size. The measurement results showed a close agreement with simulated results. The proposed UWB filtering antenna array design achieved a wide fractional bandwidth of more than 109.87%, a high realized gain of more than 7.4 dBi, and a compact size of 1.08 λ0 × 1.08 λ0 × 0.035 λ0 at 6.5 GHz center frequency. These advantages make the proposed antenna suitable for UWB applications such as indoor tracking, radar systems and positioning applications.

Wideband Small Aperture Endfire Antenna Based on Spoof Surface Plasmon Polaritons

This communication presents a wideband endfire antenna based on odd mode spoof surface plasmon polaritons (SSPPs). The odd mode SSPPs is supported by dipole-shaped unit cells. Since the introduction of phase reversal crossover, the ordinary antenna is segment to two sections of SSPPs with half-length that make up a two-element array. The endfire directivity of the proposed modified SSPPs antenna is enhanced due to the extra phase added by the phase reversal crossover. It achieves 67% relative bandwidth from 4 to 8 GHz. The maximum measured endfire gain attains 7.9 dBi. The simulated and measured results are in good agreement over the operating band. The proposed antenna is wideband, low-profile, small aperture, and low-cost.

A Compact, Low-Profile, Broadside Radiating Two-Element Huygens Dipole Array Facilitated by a Custom-Designed Decoupling Element

A compact, low-profile, broadside radiating, two-element Huygens dipole array is developed for in-band full-duplex (IBFD) applications. Each radiating element is a multilayer near-field resonant parasitic (NFRP) design that is electrically small with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ka=0.76$ </tex-math></inline-formula> at its resonance frequency, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{0} = 1.511$ </tex-math></inline-formula> GHz. The center-to-center distance between the elements is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.3\lambda _{0}$ </tex-math></inline-formula> . The array’s outstanding performance is facilitated by a custom-designed decoupling element. This specially engineered scatterer is printed on an additional layer and consists of a pair of meander-line resonators connected by a metallic strip. The overall height of the entire system is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}/20.3$ </tex-math></inline-formula> . The passive decoupling element operates as several electrically small electric dipoles whose scattered fields mitigate the interactions between the two radiators. It provides very high isolation levels between them and improves the overall directivity of the array. The optimized array was fabricated, assembled, and tested. The measured results, in good agreement with their simulated values, confirm that the developed decoupling structure not only increases the peak isolation level from 14.4 to 50.4 dB but it also improves the peak realized gain in the broadside direction by 0.5 dB and the corresponding front-to-back ratio (FTBR) value by 14.4 dB.

Joint estimation of frequency and angle-of-arrival for two element antenna array using Eigen-approach

ABSTRACT An Eigen-approach method using a two-element antenna array for estimating the frequencies of source signals jointly with the angle-of-arrival (AOA) was proposed. The eigenvector corresponding to the minimum eigenvalue of the autocorrelation matrix was used initially to find the frequencies of the source signals. By moving the roots produced from the eigenvector one-by-one and finding the power of the output, the frequencies of the source signal were estimated. Finally, using the eigenvector of the autocorrelation for each output signals from the first stage produced the AOA for the source signal. The results presented validate the use of the Eigen-approach with the two-element antenna array method in finding an accurate estimation of frequencies and the AOA for the source signals at different noise power levels even when multiple source signals have the same AOA.

Four-Node Antenna Feeding Network for Interfacing With Differential Front-End Electronics

A novel concept of a differential feeding network for four-node antenna/antenna arrays is proposed. The network is constructed out of a four-strip coupled-line directional coupler operating in a mixed differential-nodal mode enabling direct interfacing of differential front-ends with single-ended antennas. It is shown, that such a configuration provides at the outputs of the proposed feeding network four signals, which are equal in amplitude and with phase progression of 90°. Thus, such a network can be utilized for generating either dual-circular polarization from a 2× 2 antenna array or can constitute simultaneously two out-of-phase power dividers and a directional coupler resulting in a two-beam antenna array in one cut-plane and two-element array in the other one. The dual-circular excitation is of particular interest for modern-day transceivers as it enables polarization-division-duplex communication. The presented concept is confirmed by measurements of two different antenna arrays operating at 2.5 GHz frequency range featuring dual-circular and dual-beam properties, respectively.

Reduction of Mutual Coupling between Radiating Elements of an Array Antenna Using EBG Electromagnetic Band Structures

In this paper, a new array antenna configuration based on Electromagnetic Band Gap (EBG) structures has been proposed for 3.5GHz wireless communication systems. The proposed slotted EBG structure, high impedance surface (SHI), consists of three squares and a square ring deposited on a substrate (Rogers RO4350) which has a relative permittivity of 10.2 and a thickness of 1.27mm. Initially a matrix of 3×7 unit cells of EBG structures is introduced between two patches of an array and then a matrix of 3×14 unit cell of EBG structures is integrated between eight patches, which resonate around 3.5GHz (Wi MAX). The insertion of these structures between the radiating elements of an array antenna reduces the mutual coupling and antenna dimensions by approximately (8dB, 11%) and (12 dB, 5%) respectively for two, eight elements array antenna. In addition, the directivity has been slightly improved in the presence of EBG structures, from 4.52dB to 6.09dB for a two-element array antenna, and from 8.18dB to 8.4dB for an eight-element antenna.

Magnetoelectric Antenna Array

The paper is devoted to the theoretical and practical research of a magnetoelectric antenna array with control by electric potential. Magnetoelectric multiferroic structures have been of great scientific interest in recent years, since they have allowed the creation of new types of microwave devices with advantages such as high speed, small dimensions, and energy efficiency. The paper demonstrates experimentally and theoretically that such structures can simultaneously contain the effects previously consider in earlier theories. These are the dependences on the magnitude of the applied electric field: the frequency of ferromagnetic resonance considered in the theory of magnetoelectric interaction, and the spectrum of reciprocal electromagnetic-spin waives due to the dependence of the dielectric constant of the ferroelectric on the applied electric field. In order to confirm this idea, a two-element antenna array that includes a magnetoelectric composite structure as a control element has been developed. The magnetoelectric composite material is formed by an yttrium-iron garnet film and piezoelectric PZT. In this work, a comparative analysis of the results of simulation and experiment has been carried out. For this, an experimental setup and a model of a two-element antenna array have been designed, and an electromagnetic simulation has been carried out. The experimental and the simulation results have showed a high degree of convergence. At a frequency of about 2.4 GHz, the experiment has observed a shift in the radiation pattern by 12 degrees, and the simulation has showed a shift of 10 degrees. The frequency dependences of the reflection coefficient obtained both during simulation and during the experiment for two values of the applied electric field, 0 kV/cm and 20 kV/cm, have showed a certain degree of similarity. These results, as well as the mathematical description of the processes in magnetoelectric multiferroics, confirm the hypothesis about the need to consider these effects simultaneously when designing microwave devices.

An mm-Wave Scalable PLL-Coupled Array for Phased-Array Applications in 65-nm CMOS

A new two-element phase-locked loop (PLL)-coupled array for the implementation of millimeter-wave (mm-wave) and subterahertz (sub-THz) phased arrays is presented. This architecture avoids using lossy phase shifter to create the required phase shift between the adjacent elements in a phased-array system. The required phase shift is generated by utilizing a dual nested loop PLL. The two PLL loops work together to stabilize the frequency and create the required phase shift. Moreover, it can be scaled simply by adding more unit cells to the architecture. A 112-121-GHz two-element phased array is designed and fabricated in a standard 65-nm CMOS process. It consumes 147-mW power and provides a phase shift of 46.7° ranging from 58.53° to 105.2° at 117 GHz.

Single-Antenna-Based GPS Antijamming Method Exploiting Polarization Diversity

The vulnerability of Global Positioning System (GPS) receivers to jammers is a major concern owing to the extremely weak received signal power of GPS. Researches have been conducted on a variety of antenna array techniques to be used as countermeasures to GPS jammers, and their antijamming performance is known to be greater than that of single antenna methods. However, the application of antenna arrays remains limited because of their size, cost, and computational complexity. This study proposes and experimentally validates a novel space-time-polarization domain adaptive processing for a single-element dual-polarized antenna (STPAPS) by focusing on the polarization diversity of a dual-polarized antenna. The mathematical models of arbitrarily polarized signals received by dual-polarized antenna are derived, and an appropriate constraint matrix for dual-polarized-antenna-based GPS antijam is suggested. To reduce the computational complexity of the constraint matrix approach, the eigenvector constraint design scheme is adopted. The performance of STPAPS is quantitively and qualitatively evaluated through experiments as follows. 1) The carrier-to-noise-density ratio (C/N0) of STPAPS under synthetic jamming is demonstrated to be higher than that of the previous minimum mean squared error (MMSE) or minimum variance distortionless response (MVDR) based dual-polarized antenna methods. 2) The strengths and weaknesses of STPAPS are qualitatively compared with those of the previous single-element dual-polarized antenna methods that are not based on the MMSE or MVDR algorithms. 3) The characteristics of STPAPS (in terms of the directions and polarizations of the GPS and jamming signals) are compared with those of the conventional two-element single-polarized antenna array method, which has the same degree of freedom as that of STPAPS.

Ultra-Wideband Metamaterial-Loaded Microstrip Array Antennas using Fibonacci &amp; Fractal Geometric Patterns, Design and Modelling

In this study; theory, design and modeling of a new topology of ultra-wideband (UWB) metamaterial (MTM) loaded microstrip array antenna using Fibonacci &amp; fractal geometric patterns are analyzed. This antenna is made basically from many monopole elements which are loaded by complementary metamaterial transmission line (CMTL) unit cells. The distributed CMTL element, contains a Koch-shaped expanded complementary single split ring resonator (CSRR) pair. At first step, the UWB microstrip array antenna designed with two CMTL-loaded monopole element. So, using an iterative method based on the Fibonacci and fractal geometry patterns, the array antenna is expanded. As the order of iteration increases, the impedance bandwidth of the proposed array antennas improve more, and the radar cross section (RCS) decreases. the impedance bandwidth of the proposed third-order Fibonacci and fractal CMTL-loaded array antennas are 250 MHz and 539 MHz more than the two-element CMTL-loaded array antenna, respectively. Finally, this paper presents an improved method to extract the parameters of an equivalent circuit model of the proposed MTM-loaded array antenna. Verification of the equivalent model have been validated utilizing ADS software. The obtained model, in addition to numerically efficient in comparison with the full wave analysis utilizing the moment method, gives a good physical insight to the mutual coupling mechanism of the array antenna.

Characterization and Optimization of a Collinear Array of Circularly Polarized Side-Mounted Elements

This paper presents the radiation characteristics of a two-element collinear array of shunt-fed, slanted dipoles side-mounted to a metallic tower. It presents the radiation characteristics of the array as commonly implemented by FM broadcasters and suggests methods on how to optimize these characteristics such as the power gain, pattern circularity, side-lobe reduction, and horizontal-vertical polarization component ratio for the array to better conform to broadcast standards. By determining these characteristics using an advance antenna simulation software, optimization variables are identified, and their optimized values are determined. The optimized values lead to improved radiation characteristics of the array in conforming with broadcast requirements. Results show that adjusting the distance between the dipoles to less than one wavelength reduces the sidelobe of the array radiation pattern; varying the dipole physical specifications improves the polarization component ratio and the circularity of the radiation pattern. However, varying the dipole specifications also reduces the gain of the array. For applications requiring higher gains, other methods of realizing high collinear array gains are recommended.

Characterization and Optimization of a Collinear Array of Circularly Polarized Side-Mounted Elements

This paper presents the radiation characteristics of a two-element collinear array of shunt-fed, slanted dipoles side-mounted to a metallic tower. It presents the radiation characteristics of the array as commonly implemented by FM broadcasters and suggests methods on how to optimize these characteristics such as the power gain, pattern circularity, side-lobe reduction, and horizontal-vertical polarization component ratio for the array to better conform to broadcast standards. By determining these characteristics using an advance antenna simulation software, optimization variables are identified, and their optimized values are determined. The optimized values lead to improved radiation characteristics of the array in conforming with broadcast requirements. Results show that adjusting the distance between the dipoles to less than one wavelength reduces the sidelobe of the array radiation pattern; varying the dipole physical specifications improves the polarization component ratio and the circularity of the radiation pattern. However, varying the dipole specifications also reduces the gain of the array. For applications requiring higher gains, other methods of realizing high collinear array gains are recommended.

Design of dual mode wideband SIW slot antenna for 5G applications

A compact dual mode wideband antenna is presented in this paper which operates from 24.8 to 31.6 GHz (suitable for 5G applications). The antenna is based on substrate integrated waveguide (SIW) and consists of a two-element array of half-bow-tie slots. Each slot excites two modes (slot mode and half patch mode) in the antenna due to its geometry. The resonant frequencies in these modes are optimized to achieve wide impedance bandwidth using Ansys HFSS. A prototype is fabricated and its measured impedance bandwidth is 6.8 GHz, which is in close agreement with the simulated one. It also has a peak gain of 8.5 dBi at 30.4 GHz and its physical size is 2.4λg × λg, where λg is the guide wavelength at center frequency.

A Decoupling and Matching Network Design for Single- and Dual-Band Two-Element Antenna Arrays

This article presents a new decoupling and matching network (DMN) design for symmetric, single- and dual-band two-element antenna arrays. The DMNs use parallel-line-based coupling elements. The decoupling between the output ports of the proposed DMN and the reflection coefficients at these ports is obtained using the scattering parameters of the coupled antenna array and those of the DMN. These are clearly expressed as functions of the DMN's design parameters. These design parameters are determined using a simple numerical method to provide high inter-element isolation and good impedance matching for the array. To verify the proposed synthesis procedure, three DMN example designs are considered. These include one for a single-band array and two for dual-band arrays having different frequency ratios. Prototypes of these antennas along with their DMNs were designed, fabricated, and experimentally characterized. In each case, a good agreement between the measured and theoretical results is achieved. Simulation and measurement results show that the proposed DMN design and its associated synthesis procedure can be employed to significantly improve the interelement isolation of single- and dual-band, two-element arrays in various scenarios.

Mesoporous silica nanoparticles-based fluorescent mini sensor array with dual emission for discrimination of biothiols

Development of novel functional silica nanoparticles has drawing great attention in the field of fluorescent sensing as they provide advantages in term of versatile functionalization, high stability, and good biocompatibility. In the present work, a dual-fluorophore-functionalized mesoporous silica nanoparticle was designed and fabricated, where two silanized fluorophores, NAA and RB-2, were chemically bound to the nanoparticle surface. A series of measurements including TEM, BET, FT-IR, TGA and XPS were carried out to characterize the morphology variation and verify the surface functionalization. Fluorescence measurements revealed that the fluorescent nanoparticle displayed typical naphthalene and rhodamine emission bands, where the naphthalene units exhibited weak fluorescence emission due to the modification of 2,4-dinitrobenzenesulfonyl group (DNBS). The reaction with biothiols led to departure of DNBS group and thereby recovered the fluorescence of naphthalene unit. The presence of different biothiols resulted in different extents of fluorescence changes of naphthalene and rhodamine. Moreover, the dual-fluorophore functionalized nanoparticle at different concentration showed different responses to the same biothiol and was used as sensing element to construct a two-element sensor array. By collecting the four signals, the mini sensor array could provide distinct recognition pattern and can realize fingerprint discrimination of the four biothiols (H2S, Cys, Hcy, GSH) in aqueous solution and human serum.

Gain and isolation enhancement of patch antenna using L‐slotted mushroom electromagnetic bandgap

In this paper, the application of the L-slotted mushroom electromagnetic bandgap (LMEBG) structure to patch antenna and antenna array is investigated. A coaxial fed patch antenna and antenna array are designed at 5.8 GHz, center frequency for ISM band (5.725-5.875 GHz). Two layers of LMEBG are placed around the patch to achieve a gain enhancement of 1.9 dB. Measured results show a bandwidth enhancement of 300 MHz with an additional resonant frequency at 5.6 GHz with 4.5 dB of gain. A 5 × 2 array of LMEBG is used to achieve a 2 dB mutual coupling reduction and 2 dB gain enhancement for a two-element H-coupled patch antenna array.

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.

A Novel High Gain Monopole Antenna Array for 60 GHz Millimeter-Wave Communications

This paper presented the design and implementation of a 60 GHz single element monopole antenna as well as a two-element array made of two 60 GHz monopole antennas. The proposed antenna array was used for 5G applications with radiation characteristics that conformed to the requirements of wireless communication systems. The proposed single element was designed and optimized to work at 60 GHz with a bandwidth of 6.6 GHz (57.2–63.8 GHz) and a maximum gain of 11.6 dB. The design was optimized by double T-shaped structures that were added in the rectangular slots, as well as two external stubs in order to achieve a highly directed radiation pattern. Moreover, ring and circular slots were made in the partial ground plane at an optimized distance as a defected ground structure (DGS) to improve the impedance bandwidth in the desired band. The two-element array was fed by a feed network, thus improving both the impedance bandwidth and gain. The single element and array were fabricated, and the measured and simulated results mimicked each other in both return loss and antenna gain.