Beam Scanning Angle Research Articles

Non-mydriatic ultra-widefield diffraction-limited retinal imaging.

We demonstrate a new non-mydriatic ultra-widefield optical coherence tomography retinal imaging system, designed with custom optics to improve the imaging field of view, lateral resolution, and patient comfort. The key motivation is to address the challenge with conventional systems that require pupillary dilation, adding time, expense, discomfort, and medical risk to the examination of the retina. Our system provides an ultrawide 100° field of view (beam scanning angle at the scanning pivot point) and maintains a lateral resolution of 20 µm on the center. It also allows a generous working distance of 16 mm, 2-3 times longer than existing ultra-widefield OCT imaging systems. This advanced system was able to avoid iris vignetting artifacts without pharmacological dilation and ensure diffraction-limited ultra-widefield imaging under a generalized eye model. This enables a comprehensive evaluation of retina diseases, especially those affecting the peripheral regions.

Isolation enhancement of compact co‐polarized circular patch antennas using embedded series resonator

AbstractAn embedded series resonator for compact co‐polarized circular patch antenna pairs is presented in this paper. With a compact center spacing (CS) of 0.32λ0 and edge spacing (ES) of 0.03λ0 (λ0 is the free‐space wavelength at the center frequency), strong mutual coupling inevitably arises. However, by introducing a cross‐shaped fence and two quarter‐wavelength open‐ended slots onto a circular patch, port isolation of the first proposed antenna pair is significantly enhanced by 25.2 dB within a bandwidth of 6.2%. Moreover, the effectiveness of the embedded series resonator is demonstrated by achieving a wider 20‐dB decoupling bandwidth of 10.4% for the second proposed compact bandwidth‐enhanced antenna pair. For validation, both proposed prototypes are fabricated and measured, showing good agreement between measurements and simulations. To demonstrate the universality, a 1 × 8 patch array with an embedded series resonator can achieve a beam scanning angle of ±70◦ with a gain attenuation of 2.6 dB. Benefiting from compact size, high isolation, and enhanced decoupling bandwidth, the proposed designs hold promising potential for application in multiple‐input multiple‐output system and antenna array.

Widening Multi‐Beam Scan Angle of Conventional Waveguide Lens Antennas by Increasing Focal Points for Multi‐Feed Excitations

AbstractThis paper presents an alternative approach to improve the achievable beam scan angle of a traditional multi‐beam waveguide lens antenna. Due to the focusing mechanism by manipulating the geometrical curvatures of the waveguide lens, the angular scan range is limited in the conventional waveguide lens design using dual‐focal points of excitations because the geometrical curvatures of the waveguide lens only provide two design freedoms. To overcome this limitation, a solution of treating the waveguide lens as a transmit array consisting of non‐identical elements is proposed so that each element of the antenna array can be well calibrated to improve the maximum scan angular range, where a third focus point of excitation can be created by adding another design freedom from the differentiation between non‐identical elements. Each element of this new transmitting array can be well calibrated with the help of a mathematical expression to improve the maximum angular scan range. Numerical simulations show that the proposed antenna architecture exhibits better radiation characteristics than the traditional waveguide lens antenna. Radiation characteristics are studied and compared for both types of lens antennas to validate the design concept. The proposed triple‐focal point provides a higher gain than the traditional lens antenna with fewer antenna elements. The gains of the beams at ±10°, ±20°, ±30°, and ±40° are found to be 27.78, 26.94, 26.19, and 24.04 dBi, respectively. From the comparison, it is seen that the variation in gain by the proposed triple‐focal array design is more stable than the conventional dual‐focal point design.

Complementary split resonant ring inspired wide-angle frequency-scanning patch array leaky-wave antenna with open-stopband suppression

In this paper, a wide-angle scanning and dual-linearly polarized leaky-wave antenna (LWA) is proposed based on symmetrical complementary split resonant ring (CSRR) feeding lines. The CSRR excites high-dispersed spoof surface plasmon polaritons (SSPPs) and is inspired to enlarge the scanning angle of the circular patch array antenna. The coupling between CSRR and circular patch determines the unit cell dispersion characteristics of LWA, and the coupling between CSRR and circular patch is controlled by designing their respective periods, p/b, to suppress the open-stopband and reduce the grating lobe, The value of p/b controls the frequency range of the open-stopband. Two parallel CSRR feeding lines are located on the bottom layer of the antenna and feed the array antenna of 11 circular patches above the feeding layer with both differential and common modes excitations. The two modes switch with 1-bit phase shifters on the two parallel feeding lines fed with a Wilkinson power splitter and electronically switch dual-linearly polarized radiations. The proposed scenario of the LWA prototype is validated through simulations and experiments. According to the measurements, horizontally polarized radiation achieves large beam scanning angle from −59.5° to +40° in the frequency range from 8 to 11 GHz with common mode excitation. And vertically polarized radiation scanning the main beam from −47° to +41° in the frequency range from 7.8 to 10.8 GHz with differential-mode excitation. The measured peak gains of the two polarizations are 14.4 dBi and 14.2 dBi, respectively, and the cross-polarization ratios are above 21 dB.

Additively-Manufactured Broadband Metamaterial-Based Luneburg Lens for Flexible Beam Scanning

Multi-beam microwave antennas have attracted enormous attention owing to their wide range of applications in communication systems. Here, we propose a broadband metamaterial-based multi-beam Luneburg lens-antenna with low polarization sensitivity. The lens is constructed from additively manufactured spherical layers, where the effective permittivity of the constituting elements is obtained by adjusting the ratio of dielectric material to air. Flexible microstrip patch antennas operating at different frequencies are used as primary feeds illuminating the lens to validate the radiation features of the lens-antenna system. The proposed Luneburg lens-antenna achieves ±72° beam scanning angle over a broad frequency range spanning from 2 GHz to 8 GHz and presents a gain between 15.3 dBi and 22 dBi, suggesting potential applications in microwave- and millimeter-wave mobile communications, radar detection and remote sensing.

A Circularly Polarized Non-Resonant Slotted Waveguide Antenna Array for Wide-Angle Scanning.

A compact circularly polarized non-resonant slotted waveguide antenna array is proposed with the aim of achieving wide-angle scanning, circular polarization, and low side-lobe levels. The designed antenna demonstrates a scanning range of +11° to +13° in the frequency domain and a beam scanning range of -45° to +45° in the phase domain. This design exhibits significant advantages for low-cost two-dimensional electronic scanning circularly polarized arrays. It employs a compact element that reduces the aperture area by 50% compared to traditional circular polarization cavities. Additionally, the staggered array method is employed to achieve an element spacing of 0.57λ within the azimuth plane. Isolation gaps were introduced into the array to enhance the circular polarization performance of non-resonant arrays. The Taylor synthesis method was employed to reduce the side-lobe levels. A prototype was designed, fabricated, and measured. The results indicate superior radiation efficiency, favorable VSWR levels, and an axis ratio maintenance below 3 dB across the scanning range. The proposed antenna and methodology effectively broaden the beam scanning angle of circularly polarized slotted waveguide array antennas.

Liquid Crystal Materials for Electronically Reconfigurable Antennas: Overview Toward 5G Applications

This paper discusses the use of Liquid Crystal (LC) technology for Electronically Reconfigurable Antennas (ERAs) that are essential for future-based 5G communication systems and satellite platforms. This comprehensive study covers the development of liquid crystal performance metrics and the deployment of LC technology for RF front-end antenna systems, ranging from GHz to THz frequency bands. Here, low profile LC varactor with phase shifter-based antenna systems is investigated for beam steering, enabling to scan a wide range with minimum scan time of operation. The LC phase shifter-based antenna has shown an insertion loss of ≪3[Formula: see text]dB for 5G frequency bands and a high figure-of-merit over a bandwidth of 2.5[Formula: see text]GHz with minimum time response of 30[Formula: see text]ms. These LC-based ERAs can feature wide beam scanning angles with high power-handling capability, better efficiency, high linearity with low power consumption for satellite ground terminals and 5G communication systems.

CRLH Leaky-Wave Antenna with High Gain and Wide Beam-Scanning Angle for 5G mmWave Applications

In this paper, a novel composite right-/left-handed (CRLH) leaky-wave antenna with a simple structure, low cost, high gain, and wide beam-scanning range performance for the millimeter wave (mmWave) band. The proposed antenna comprises a series-fed array of asymmetrically slotted elliptical CRLH unit cells loaded with a short-circuit stub. By optimizing the length of the stub, the condition of the CRLH structure is balanced to enable beam scanning from the backward to the forward direction within the mmWave band. The proposed antenna exhibits a wide beam-scanning angle of 112° (-60° to 52°), coupled with high gain and radiation efficiency at the designated band. Furthermore, it is fabricated on a traditional microwave substrate, Rogers RT/duroid 5880, thus offering a cost-effective approach to streamlining the manufacturing process. The measurement results confirmed a peak realized gain of 16.8 dBi. The excellent performance achieved using a low-cost design makes the proposed antenna attractive for 5G mmWave applications.

Decoupling and Cloaking of Rectangular and Circular Patch Antennas and Interleaved Antenna Arrays with Planar Coated Metasurfaces at C-Band Frequencies-Design and Simulation Study.

An electromagnetic cloaking approach is employed with the intention to curb the destructive effects of mutual interference for rectangular and circularly shaped patch antennas situated in a tight spacing. Primarily, we show that by coating the top surface of each patch with an appropriately designed metasurface, the mutual coupling is considerably reduced between the antennas. Furthermore, the cloak construct is extended to a tightly spaced, interleaved linear patch antenna array configuration and it is shown that the coated metasurfaces successfully enhance the performance of each array in terms of their matching characteristics, total efficiencies and far-field realized gain patterns for a broad range of beam-scan angles. For rectangular patches, the cloaked Array I and II achieve corresponding peak total efficiencies of 93% and 90%, in contrast to the total efficiencies of 57% and 21% for uncloaked Array I and II, respectively, at their operating frequencies. Moreover, cloaked rectangular Array I and II exhibit main lobe gains of 13.2 dB and 13.8 dB, whereas uncloaked Array I and II only accomplish main lobe gains of 10 dB and 5.5 dB, respectively. Likewise, for the cloaked circular patches, corresponding total efficiencies of 91% and 89% are recorded for Array I and II, at their operating frequencies (uncloaked Array I and II show peak efficiencies of 71% and 55%, respectively). The main lobe gain for each cloaked circular patch array is approximately 14.2 dB, whereas the uncloaked Array I and II only achieve maximum gains of 10.5 dB and 7.5 dB, respectively.

Analysis of tightly-coupled dipole phased array antennas with metasurface superstrate

Tightly coupled dipole arrays, including connected arrays, and capacitively coupled arrays, are one of the best solutions for wideband phased array antenna designs. However, to increase bandwidth and maximum scan angle, we can use a metasurface superstrate. We propose an analytical model to compute the scan impedance of a tightly coupled dipole array loaded with a metasurface. This analytical model helps us to simplify the calculation of the scan impedance of the array and speeds up the design process of these array antennas. It is shown that the metasurface superstrate improves the bandwidth and beam scanning angles of the array. Using the proposed general transmission line model, the computation of the scan impedance of tightly coupled dipole arrays is done very fast with minimum error. The semi-analytical model is about 7 times faster than a full-wave simulation.

Wide-Angle Scanning Microstrip Patch Antenna Array for mmWave Applications with High Gain

This paper presents a modified rectangular microstrip patch antenna (MRMPA) array conforming to the hemisphere for wide-angle beam scanning. Two different conformal antenna array designs are presented in this work. The first of these designs, a 13-element MRMPA array conformal to the surface of a circular arc, and the second one, a 9-element array conformal to the surface of a hemisphere, are designed and optimized. The geometrical approach of calculating the phase value is used to calculate the phase value of each antenna. The simulated results show that the 13-element conformal MRMPA array is achieving a beam scanning angle of ±84° with a gain of 13.89 dBi with low side lobe levels, and further, the gain of the array is enhanced by a dielectric superstrate that improved the gain by ∼2 dBi at all the scanning angles. Second, an MRMPA array conformal to a hemisphere with nine elements is designed with beam scanning ability from φ = 0°−360° and θ = ±30° with a gain of 15.69 dBi, and further, the gain is enhanced by ∼3 dBi with the dielectric superstrate. Full-wave simulations have proven both designs to be accurate and aligned with theoretical calculations.

A Parallel Folded Dipole Antenna With an Enhanced Bandwidth for 5G Millimeter-Wave Applications

In this communication, a planar folded dipole antenna array with wide operating bandwidth and compact size is proposed for 5G millimeter-wave (mmWave) applications. The basic antenna element is a pair of parallel folded dipoles (PFDs) connected at the terminals. Compared with a single half-wavelength dipole, the PFD can achieve a flatter impedance curve in the working frequency band, and it is easier to achieve broadband impedance matching with 50Ω feeding line. Moreover, a coupling slot feeding method is adopted to feed the proposed antenna element. The capacitance provided by the coupling slot can counteract the inductance caused by the PFD, thus improving the impedance matching at the low frequency band. Benefiting from the innovative design, the proposed antenna element can achieve an ultra-wide impedance bandwidth of 64% and a compact size of 0.26λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.28λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Furthermore, a wide scanning angle with ±50° over wide bandwidth is testified by a 1×8 array using active simulation. For verification, a 4×4 full corporate-fed array is designed based on the proposed element. The measured results prove that the proposed 4×4 array has a -10 dB impedance bandwidth of 65% covering 17 to 33.75 GHz and a peak gain of 17.5 dBi. The measured total efficiency is from 69% to 82% over the working frequency band. With the merits of compact size, wide working bandwidth, and wide beam scanning angle, the proposed antenna is a good candidate for mmWave wireless communications.

Wide-Angle Beam-Scanning Leaky-Wave Antenna Array Based on Hole Array SSPPs

In this letter, a leaky-wave antenna (LWA) array based on hole array spoof surface plasmon polaritons (SSPPs) is proposed, which can realize wide frequency beam scanning angle. By etching periodic hole arrays on the upper metal of the defective ground structure, the SSPP structure is formed and the frequency scanning beam is generated by using its higher-order radiation mode characteristics. The radiation mechanisms of the design are explained by using the dispersion relationship, electric field distributions, and space harmonics. The LWA array is fed by a 1 to 4 power divider and achieves good impedance matching within 6-16 GHz bandwidth. The average peak gain value of the proposed LWA antenna array is about 16.86 dBi and the frequency beam scanning range is 91°. The antenna array has the characteristics of easy fabrication, low cost, and high gain performance, which provides a new design concept for wide-scanning-angle LWA Array and can meet the demand of high gain requirements in radar and other related fields.

Design of Leaky-Wave Antenna With Wide-Angle Backfire-to-Forward Beam Scanning Based on Generalized Pattern Synthesis

Frequency-scanning antenna has been extensively explored in radar and vehicle communication systems, but it is a challenge to provide methodological guidance to achieve a wide scanning angle. Here, a generalized pattern synthesis method is proposed and a leaky-wave antenna with wide scanning range is designed to verify the technique. First, a generalized antenna element (GAE) is presented, whose main beam can steer continuously with frequency. Meanwhile, the phase constant of the leaky wave determines the beam direction of the array factor. Then, a leaky-wave antenna can steer with a large beam scanning angle and stable gain as patterns of the array factor and the GAE are manipulated simultaneously. To verify, a prototype SIW LWA with double-layer transverse slots is fabricated and measured. Experimental results show this antenna achieves continuous dual-beam scanning from backfire (-90∘) to forward (±20∘) from 12.4 GHz to 19.9 GHz with a total coverage range of 220∘ and the realized gain varying from 8.3 dBi to 12.8 dBi.

Cloaking of Equilateral Triangle Patch Antennas and Antenna Arrays with Planar Coated Metasurfaces

We have proposed an effective metasurface design to accomplish the cloaking of equilateral patch antennas and their array configuration. As such, we have exploited the concept of electromagnetic invisibility, employing the mantle cloaking technique with the intention to eliminate the destructive interference ensuing between two distinct triangular patches situated in a very congested arrangement (sub-wavelength separation is maintained between the patch elements). Based on the numerous simulation results, we demonstrate that the implementation of the planar coated metasurface cloaks onto the patch antenna surfaces compels them to become invisible to each other, at the intended frequencies. In effect, an individual antenna element does not sense the presence of the other, in spite of being in a rather close vicinity. We also exhibit that the cloaks successfully reinstate the radiation attributes of each antenna in such a way that it emulates its respective performance in an isolated environment. Moreover, we have extended the cloak design to an interleaved one-dimensional array of the two patch antennas, and it is shown that the coated metasurfaces assure the efficient performance of each array in terms of their matching as well as radiation characteristics, which in turn, enables them to radiate independently for various beam-scanning angles.

Ultrawide-Angle and Compact Leaky-Wave Antenna Based on Complex Periodic Structure

A compact antenna with the characteristic of wide-angle frequency beam scanning based on complex periodic structure is proposed. A double gradient spoof surface plasmon polaritons (SSPPs) structure is added to the standard microstrip line for reducing the antenna size. The miniaturization of the proposed antenna is analyzed with the method of dispersion curves and electric field distribution. Periodic changes of the groove depth and trapezoidal gradient structure increase the beam scanning angle from backward to forward and suppress the open stopband effect. The proposed structure is printed on the FR-4 substrate with a compact size of 0.23λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 3.71λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength of the lowest operating frequency), and has a working frequency band from 12.5 to 42.5 GHz for |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> |< –10 dB. Meanwhile, a wide beam-scanning angle of 142° (–52° to +90°) and an average gain of 7.9 dBi are obtained by simulation and measurement. The proposed leaky-wave antenna has a potential application in wireless communication system due to its small size, broad frequency band, wide beam scanning angle and low cost.

Enabling Spherical Beam Coverage for Millimeter-Wave Stationary and Mobile Applications: A stackable patch antenna

The limited beam-scanning angles of planar phased arrays are one of the most critical challenges for millimeter-wave (mm-wave) wireless communication systems. This article proposes a new class of antenna topology, denoted as a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">stackable patch antenna</i> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SPA</i> ), that achieves near-spherical beam-steering coverage for mm-wave applications. The proposed SPA consists of two identical rectangular patch antenna elements. By separately controlling the magnitude and phase of the excitation ports, the proposed antenna can radiate in multiple directions that are normal or parallel to the patch elements. In addition, the proposed structure has the advantage of enabling end-fire radiation when the structure is encompassed by the full metallic frame of a device. This is accomplished without any deformation or modification of the metal frame.

A Dual-Band Planar Antenna Array With High-Frequency Ratio for Both Sub-6 Band and mm-Waveband

In the 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> Generation Partnership Project (3GPP), the major carrier frequency bands of the 5G communication are assigned in the Sub-6 band and the millimeter wave (MMW) band. The frequency ratio between the two bands is more than 4. Due to the contradiction between large element size in Sub-6 band and narrow element spacing in the MMW band, it is hard to design one antenna array to be used in both of the two carrier frequency bands especially for a miniaturized communication system. In this article, a novel dual-band planar antenna array is proposed to solve the contradiction by using recombining technology. The measured results show that the antenna array is able to satisfy the requirements of the two carrier bands. In the Sub-6 band, the antenna array scale is 4×4. The antenna array has an operating band of 4.5-6GHz with the array gain more than 12.9dBi. In ±40° beam scanning angle, the sidelobe level (SLL) is lower than -12dB and the gain variation is less than ±0.9dBi. The isolation between the adjacent elements is more than 20 dB. In the MMW band, the array scale is 4×8. The antenna array has an operating band of 24.5-26GHz with the array gain more than 20dBi. In ±40° beam scanning angle, the SLL is lower than -10dB and the gain variation is less than ±1.9dBi. The isolation between the adjacent elements is more than 20dB. The antenna array has also shown good performance in an actual over air communication test in the two carrier bands by using 16-QAM modulation.

An Interpolation-Based Time-Modulated Antenna Array for Beam Scanning at Carrier Frequency

The formula of the Fourier series for a periodic function indicates that traditional periodic time modulation only provides amplitude weighting at the carrier frequency of a time-modulated array (TMA). Therefore, beam scanning through time modulation technique could only be realized at harmonic frequencies. In order to achieve low sideband levels (SBLs) in harmonic beam scanning, a large number of modulation statuses are required in TMAs, which significantly increases the cost and complexity of the entire system. The intent of this work is to develop a novel TMA with array-interpolation aperture and ON–OFF time modulation to achieve beam scanning at the carrier frequency. By performing interpolation computation at the antenna array level, high-precision beam scanning with low SBLs can be realized with pseudorandom ON–OFF time modulation and a static 1-bit phase control. As compared with the state-of-the-art designs, the proposed TMA requires much fewer modulation statuses, and it significantly facilitates beam-scanning control. A forward design strategy is presented to analytically determine the time modulation sequences and the static 1-bit phase statuses for specified beam scanning angles and sidelobe levels (SLLs). Numerical and experimental results well demonstrate the effectiveness of the proposed TMA.

Reconfigurable Folded Transmitarray Antenna With Low-Profile Based on Metasurfaces

A reconfigurable folded transmitarray antenna (RFTA) with fully planar structure is presented in this letter. It consists of an electronically reconfigurable metasurface and a polarization rotating metasurface (PRMS). A pair of PIN diode switches is integrated on the reconfigurable meta-atom to realize the 1-bit transmission phase manipulating, and a patch antenna is integrated on the center of the PRMS to feed the RFTA. Through twice reflecting, polarization rotating, and transmission phase compensation, the spherical wave from the feed is transformed into the scannable pencil-shaped beam. Meanwhile, the antenna profile is reduced to about 1/3 compared to the traditional reconfigurable transmitarray antenna (RTA). The RFTA prototype with 12 × 12 elements is designed, fabricated, and measured. Experimental results show that the gain of 13.4 dBi at 5.8 GHz is obtained and the two-dimensional beam scanning angle covers ±60°. This work significantly reduces the profile of traditional RTA, making it a promising candidate for the wireless communication system with limited space.