Azimuth Beamwidth Research Articles

2D sectorial dipole‐enabled planar endfire circularly polarized antenna with widened azimuth half‐power beamwidth

AbstractThis letter proposes a novel planar endfire circularly polarized antenna with widened half‐power beamwidth. Widened azimuth beamwidth mechanism of 2D sectorial electric dipole is theoretically revealed, thus it is able to combine with a rectangular magnetic dipole to yield a half‐power beamwidth widened planar endfire circularly polarized antenna. Finally, a prototype planar endfire circularly polarized antenna with sectorial flared angle of α = 270° is fabricated, simulated, and implemented to validate the design approach. As investigated, the antenna exhibits broadened azimuth half‐power beamwidth of 150° over a frequency range of 2.40–2.45 GHz.

A novel optimization method for attenuating multi‐interferences in satellite communication earth station

SummaryThe study of multi‐interferences plays a pivotal role in advancing the development of next‐generation, high‐performance communication devices. In this paper, we propose a design approach for auxiliary antennas aimed at mitigating multi‐interference challenges within satellite communication earth stations. We introduce an eight‐element auxiliary antenna with an elliptical beam comprising dual radiation patches and a T‐shaped power divider, to attenuate interferences originating from three distinct directions. To enhance the azimuthal beamwidth, we adjust the dimensions of the ground plane and extend the substrate. At a frequency of 12.5 GHz, the antenna exhibits a 3‐dB beam spacing of 38° and an azimuthal width of 162°, with a maximum gain of 7.9 dBi. We employ a sidelobe canceller to optimize the antenna's performance, and both simulations and measurements affirm that the auxiliary antenna achieves an extinction interference cancelation ratio exceeding 27 dB under all circumstances.

An Applied Frequency Scaling Algorithm Based on Local Stretch Factor for Near-Field Miniature Millimeter-Wave Radar Imaging

The frequency scaling algorithm (FSA) is a popular imaging algorithm for dechirped SAR data. To obtain a large azimuth detection area, the miniature millimeter-wave (mmW) linear-frequency-modulated continuous-wave (LFMCW) surveillance radar requires a wider azimuth beamwidth, which leads to additional range frequency aliasing in FSA. Because of the adoption of the dechirp-on-receive technique, the sampling frequency is much smaller than the range bandwidth during near-field imaging, which further aggravates the aliasing effects. The target cannot be well focused, and it makes the weak targets submerged in the background. To acquire high-quality SAR images, an improved FSA using the local stretch operation is proposed. The aliasing bandwidth properties introduced by the FS operation and the desired objective range cell migration (RCM) factor are used in this proposed local-stretch FSA (LSFSA). The initial RCM factor is adjusted by the stretch operation to eliminate the frequency aliasing to a certain level without increasing the computing load. The LSFSA is suitable for solving the problem of range frequency aliasing in near-field side-looking SAR and high squint SAR with wide azimuth beamwidth. The proposed method is validated using reasonable simulations and convincing experiments.

A Novel Time-Domain Frequency Diverse Array HRWS Imaging Scheme for Spotlight SAR

The frequency diverse array (FDA) technique is a novel scheme for high resolution wide swath synthetic aperture radar (SAR) imaging, which employs a frequency increment across the array elements. This introduces a range-angle-dependence to the transmission steering vector, which is exploited for range ambiguity resolution in strip-map SAR. Generally in spotlight mode, scatterers dispersively distributed in azimuth have different Doppler histories, in which the range ambiguity resolution for strip-map SAR fails. To extend the flexibility of FDA, in this paper a novel FDA imaging scheme for spotlight mode SAR is proposed. Exploiting the property of the same illuminated period of all scatterers in spotlight mode, the proposed scheme is carried out entirely in the azimuth time domain, which allows for higher processing efficiency and real-time implementations. Still, excessive Doppler history differences among scatterers deteriorate the scheme performance for azimuth-edge scatterers. Aiming at this situation, a residual angle phase compensation in time domain is considered for the cases of a large azimuth beam width, improving the applicability of the proposed scheme. Compared with existing methods, the proposed spotlight FDA-SAR offers the possibility of achieving simultaneously high azimuth resolution and wide swath performance with high efficiency. Simulations and analyses are performed to demonstrate the effectiveness of the proposed spotlight FDA-SAR scheme.

The Influence of the Azimuth RCS Pattern of Calibrator on SAR Absolute Calibration

The realization of radiometric calibration relies on the known artificial point targets as the reference, such as corner reflectors. One of the criteria of the calibrator is that the 3 dB-beamwidth of the azimuth radar cross section (RCS) pattern needs to be larger than the synthetic aperture radar (SAR) antenna 3-dB beamwidth to ensure the SAR antenna, which has a narrow azimuth beamwidth, can align to the calibrator while also making the nominal RCS value of the calibrator approximately constant during the radiometric calibration. However, the RCS of the calibrator is actually inconstant within a synthetic aperture period, especially when the SAR antenna beamwidth is wide. The simplified treatment will introduce errors to calibration. In this letter, the azimuth RCS pattern is taken into account. The error caused by the constant RCS is modeled. Based on the error model, an improved criterion of the calibrator is discussed. The experiments use the known SAR system parameters for numerical simulation based on dihedral corner reflectors (DCRs) with different sizes. The results verify the error model and indicate that when the SAR beamwidth is larger than the beamwidth of the calibrator, and the introduced error cannot be ignored. The relationship between the size of the calibrator and the SAR beamwidth is further analyzed through the experiments.

Broadband Circularly Polarized Microstrip Array Antenna With Curved-Truncation and Circle-Slotted Parasitic

This article presents a novel broadband circularly polarized microstrip array antenna for synthetic aperture radar system onboard Cessna 172 Aircraft. The antenna employs an 8×8 matrix formation with uniform element separation of 0.5λ and single-proximity-coupled strip-line feeding. The circular polarization wave generation uses a curved-truncation patch and a circle-slotted parasitic patch above it to realize the broadband circularly polarized antenna. The broadening of the axial ratio bandwidth (ARBW) applies a fully serial sequential rotation on the array feeding network. Meanwhile, the gain is improved using a circle-slotted parasitic patch with a floating cover on the top layer. The prototype antenna has a physical aperture of 270 mm × 300 mm with 1.1-kg weight. The prototype produces an impedance bandwidth of 1.5 GHz (29.3%), ARBW of 1.62 GHz (30.6%), a gain of 18.17 dBic, and aperture efficiency of 26%. The azimuth and elevation beamwidth achieved 12.7° and 13.0° at the center frequency, respectively.

Robust Maritime Target Detector in Short Dwell Time

Detection of small-sized maritime targets is an important task for a marine surveillance radar. Recently, with the emergence of a marine surveillance radar system that has a narrow azimuth beamwidth and rapidly rotating antennas, the available dwell time for detecting a maritime target is usually very short. This short dwell time considerably degrades the performance of conventional detectors, especially those focusing on small-sized targets. In this paper, we propose an efficient detector for small-sized maritime targets to provide a reliable detection performance, even in short dwell times. The proposed scheme is based on a new joint metric, which results from the product of the magnitude and difference features in the Doppler spectra. We discriminate the target bins from sea clutter bins using a statistical discriminator based on the joint metric, whose probability density function follows the product distribution of standard gamma distributions. Compared to conventional detectors, the proposed scheme can provide a robust performance in terms of the average signal-to-clutter ratio as well as the detection rate, especially in shorter dwell times.

Fan‐beam antenna design based on metasurface lenses

A fan-beam antenna system based on metasurface lenses is proposed for backhaul antenna applications at 10.4 GHz. The planar metasurface lens is composed of three pairs of subwavelength unit cells with high transmission and opposite phase. These phase shifters are arranged to transform the Gaussian distributed near field from a linear patch antenna array into the sin c-function distributed aperture field, which in turn brings a sector radiation pattern in the azimuth plane and a pencil beam in the elevation plane. The simulated and measured results demonstrate that the presented lens antenna offers a sharp roll-off fan beam with the azimuth beamwidth 60°, elevation beamwidth 10°, and the gain 18.2 dB with the flat-top ripple less than 2.0 dB.

Controlling Elevation and Azimuth Beamwidths With Concentric Circular Microphone Arrays

Solutions for frequency-invariant or constant-beamwidth beamforming with concentric circular arrays (CCAs) generally control only the azimuth-beampattern. This work introduces a beamforming methodology, which instead of designing a fixed beamwidth across the spectrum, maximizes the directivity-factor under the constraint that the beamwidth is greater than or equal to a pre-defined target-beamwidth, in both the elevation and the azimuth. The principal idea lies in dynamically weighting the microphones of the CCA based on two factors - (i) their corresponding ring number or radius, and (ii) their alignment with the signal-path. The parameters controlling the weights are determined using a modified gradient-descent algorithm. Experimental results show the flexibility and advantage of the proposed methodology over state-of-the-art methods.

An E-Band Beam Sharpening Antenna Based on Monopulse Comparator

An E-band antenna module and corresponding beam sharpening method is proposed to achieve high azimuth resolution for front-looking real aperture radar application. To achieve high angular resolution with a small antenna aperture size, a solution involving real beam and super-resolution is investigated. A monopulse antenna is developed to produce two coprime channels, which are essential for the subsequent beam sharpening in digital domain. A dual-aperture horn antenna and a monopulse comparator that make up the monopulse antenna are designed respectively, and the experimental prototypes are fabricated and tested. Experimental results show the antenna module can operate in the 75 to 80 GHz band, more than 20 dBi gain and 12° half power azimuth beamwidth can be maintained in the sum-patterns, and the null-depths are lower than -20 dB in the difference-patterns. Based on the measured sum and difference patterns, an azimuth super-resolution processing based on two-channel deconvolution is implemented. The simulation results show the sharpening ratio can achieve 12 dB with 0 dB signal-noise-ratio and truncated half power beamwidth. Theoretically, the azimuth super-resolution of 0.8° can be achieved with 20 mm aperture size. The corresponding achievements are valuable in the follow-up E-band civil front-looking imaging system.

Cascaded Fresnel Lens Antenna for Scan Loss Mitigation in Millimeter-Wave Access Points

Millimeter-wave lens antennas will be essential for future wireless access. Conventionally, they increase the gain in the boresight direction only. In this article, cascaded Fresnel zone plate lenses are combined with a phased array to increase the gain at wide steering angles of ±52°. The side lenses are tilted to align with the maximum steering angle and cascaded to increase the focusing gain. The inner lenses increase the gain by 2.45 dB at boresight, and by 3.19 dB at the maximum steering angle. When the side lenses are repositioned, the simulated focusing gain increases to 4.69 dB. Asymmetric amplitude distributions are proposed to prevent the main lobe from splitting. An eight-element seven-lens prototype operating at 28 GHz achieved a gain from 12.96 to 15.35 dBi with a bandwidth of at least 1.3 GHz for all measured beam directions. The maximum measured azimuthal beamwidth was 27°. A design procedure and a theoretical analysis of diffraction through the lenses are provided. By increasing the SNR, this beamforming antenna could improve the coverage of three-sector 5G microcell base stations, and support gigabit wireless links for vehicular, rail, and satellite communications.

PO-Based Automatic Design and Optimization of a Millimeter-Wave Sectoral Beam Shaped Reflector

In this article, we present a ray optics-based iterative procedure for the design and optimization of a shaped reflector able to achieve a high roll-off sectoral pattern in the azimuthal plane and a very narrow beam in the elevation plane, as required in a surveillance application at 76–77 GHz. Three prototypes of such kind of reflector with different azimuthal half-power beamwidths were fabricated and measured, showing a fair agreement with numerical simulations.

An Extremely Large Ka-Band Reflectarray Antenna for Interferometric Synthetic Aperture Radar: Enabling Next-Generation Satellite Remote Sensing

The Surface-Water Ocean Topography (SWOT) mission, currently in development at NASA?s Jet Propulsion Laboratory (JPL), will employ the Ka-band radar interferometer (KaRIn) to characterize the ocean's height at the unprecedented spatial resolution of 2 km and is designed to provide a global inventory of significant terrestrial water bodies [area g(250 m)2] and rivers (width g50-100 m). The key enabling technology for this instrument is a pair of large, deployable antennas that form the interferometer. This article describes the development of the largest reflectarray antenna currently in process for a spaceflight application: a 5 ? 0.26-m offset-fed reflectarray antenna with a 4.37-m focal length. It details critical aspects of the development, including the radio-frequency (RF) design and analysis, fabrication, and measurement, and discusses unique requirements imposed by the interferometer that resulted in significant design and verification challenges. Flight-hardware measurements demonstrated a gain of approximately 49.5 dB, corresponding to an efficiency of 52%, and an azimuth beamwidth of 0.105?, with a beam-pointing knowledge of 5 millidegrees. Accurate characterization of these antenna-performance parameters is critical to the success of the KaRIn instrument.

A Planar Differential Wide Fan-Beam Antenna Array Architecture: Modular high-gain array for 79-GHz multiple-input, multiple-output radar applications

This article proposes a planar, wide fan-beam differential, corporate-fed patch antenna array architecture for automotive radar applications that mitigates the multipath and multiple reflections effects of its conventional series-fed counterpart. The proposed array architecture offers the merits of wide beamwidth in azimuth, high gain, yet, is applicable in multiple-input, multiple-output (MIMO) configurations. Two 8 × 1 arrays were developed, built, and measured at the 77-81-GHz band. In design 1, the width of driven 50-Ω patch is optimized for the widest beamwidth and the array feeding network employs impedance transformers for matching. The experimental verification showed an azimuthal half-power beamwidth (HPBW) of 70° with a 15-dBi gain. In design 2, the interelement spacing is increased for wider beamwidth and less mutual coupling, and the feeding network transformers were eliminated to mitigate scattering and radar cross section (RCS) in turn. A 130° azimuthal HPBW was measured. A 2 × 2 MIMO radar hardware was built, employing the proposed array architecture on a scalable radar platform to validate its applicability in MIMO radars. For the sake of comparison, another reference demonstrator with conventional series-fed arrays was built. Frequency-modulated continuous-wave (FMCW) radar range and angle measurements were performed where multiple reflections and multipath effects were mitigated.

A Wideband Beamforming Antenna Array for 802.11ac and 4.9 GHz in Modern Transportation Market

In this work, a novel antenna structure has been proposed, which consists of multiple sub-array features i.e., a field selectable beam (90°, 180°, 270°, and 360°) and the choice of gain (11.16, 14.59 and 17.25 dBi) that can be easily adapted to cater for the dynamic scenarios in the transportation environment. The sub-arrays were designed using the microstrip patch antenna (MPA) concept with capacitive feed and dual substrate stacked up configuration for superior operating bandwidth covering the entire 802.11ac (5.17 to 5.85 GHz Industrial Scientific and Medical (ISM) band), in addition to the extended coverage for 4.92 to 4.98 GHz licensed band with narrow azimuth beamwidth of 24°. The sub-array was designed, simulated and experimentally evaluated and the beamforming results revealed that the antenna structure can be integrated with beamforming concepts to provide an enhanced wireless link between the ground base station and the mobile terminals that allows beam steering to focus on the targeted direction and null the interference directions with small beam width. It is expected that the proposed configurable gain/beam beamforming antenna array will further reduce the deployment cost and enhance the anti-interference performance by two-fold, and shall bring the user experience in the transportation market to the next level.

Pattern synthesize of a cylindrical conformal array antenna by PSO algorithm

Pattern synthesize of conformal array antennas is often a challenging problem. Various optimization algorithms such as genetic, particle swarm optimization (PSO), and invasive weed optimization have already been used for pattern synthesizing of conformal arrays. In this paper, a focused beam is synthesized for a quarter cylindrical conformal array antenna using the PSO algorithm with small computations. The desired pattern is a focused beam at θ = 90° and ϕ = 45° with 10° beamwidth in elevation and 15° beamwidth in azimuth with −20 dB side-lobe level. This method can be used in general for synthesizing arbitrary desired patterns and array geometries.

Scalable Near-Field Fed Far-Field RAIN RFID Reader Antenna for Retail Checkout Counters

This article presents a scalable ultra-high-frequency (UHF) radio frequency identification (RFID) reader antenna for retail checkout counters. The antenna’s simultaneous near-field and far-field operation enable effortless and reliable asset identification. Two meandered microstrip lines that are 90° out-of-phase form the near-field antenna rim around a far-field patch antenna. The patch antenna is fed by those meandered lines along the vertices on its orthogonal points, resulting in circular polarization. The near-field radiation is evenly distributed with no surface dead zones, and the far-field radiation pattern is symmetrical with a 90° half-power beam-width in both azimuth and elevation planes. The antenna operates in the North American UHF RFID band (902-928 MHz) with a 50 MHz impedance bandwidth. Fabricated antenna’s gain and axial ratio at the band’s center frequency of 915 MHz is 3.3 dBi, and 1.4 dB, respectively. This antenna is low-profile, low-cost and recyclable as it is constructed from polyolefin substrate and copper foils. The antenna is pragmatic, scalable with increasing checkout counter sizes and insusceptible to proximity assets and metal frames.

Linear array of dual‐polarised slot‐coupled dielectric‐rod elements for wireless applications

The design of a dual-polarised series-fed microstrip array antenna for wireless applications, especially in the 5150–5750 MHz band, is delineated in this study, which consists of 12 dielectric rods, fed by circular slots. The rod height can be exploited to improve antenna gain and control its azimuth beamwidth. Using circular slot elements with a central crossing point improves port isolation and cross polarisation. The array elements are fed via two series-fed six-element arms having 25 dB Taylor distribution in each polarisation. The given arms are fed from the centre. Regarding H-polarisation, the arms are fed with a 180° phase shift to improve isolation between the ports as well as the cross polarisation. Additionally, a reflector plane is placed behind the array to suppress back-lobe radiation. A prototype of the array antenna is fabricated and measured. The return loss of the antenna is over 10 dB, varying from 5.1 to 5.8 GHz, and the isolation exceeds 30 dB over the bandwidth. The measured and simulated patterns are presented for both polarisations.

Enforcement of Dynamic Sector Division for Massive MIMO Using Code Fed Antenna Arrays

A PAT code fed arrays are utilized to implement a dynamic sector division in a simple way to enforce following the sectors’ varying data traffic in modern multiple access environment. However, the previous solutions include hardware installations which are complex, expensive, and difficult to adjust for changing requirements throughout different time periods of day. This paper presents a novel idea to perform sector division using uniform PAT code-fed linear antenna arrays which simplified the implementation of such a dynamic system. These arrays are fed with fixed polyphase codes with optimum correlation properties. Only linear phase shifts of antenna elements in the array sub-groups of the different users are necessary to simply implement the needed division. The radiated pattern for each user’s data set is controlled by selecting the corresponding active sub-group of antenna elements to transmit through. The azimuth beamwidth can be adjusted by selecting a combination of different sub-groups. The simulation results proved that a dynamic sector division can be simply and efficiently implemented by using the proposed linear phase code fed arrays within the base station.

Systems Analysis of a Pattern Reconfigurable Antenna for Capacity Improvement of Cell Edge Users in Cellular Networks

An evaluation of a beam reconfigurable base station transceiver for cellular applications is presented from both systems and antenna design perspective. The proposed technique uses an azimuth beam switching method, which incorporates PIN diodes to provide a fast switching reflecting ground plane for a three sector antenna. Numerical systems analysis has been carried out on a hexagonal homogeneous cellular network to evaluate how the reconfigurable antenna can be used to tradeoff the mean and cell edge capacity by reconfiguring the azimuth beamwidth. The systems analysis shows that a mean cell edge improvement from 15 to 18 Mbit/s is achievable and this improvement is consistent for cell sizes ranging from 500 to 1500 m. The proposed reconfigurable antenna has been designed, manufactured, and characterized, and the measured results are shown to be similar to simulations.