Aperture Phase Distribution Research Articles

Out-of-focus holography at the Effelsberg telescope

Context. Out-of-focus (OOF) holography can be used to determine the aperture deformations of radio telescopes that lead to errors in the phase of the complex aperture distribution. In contrast to traditional methods, OOF holography can be performed without a reference antenna, which has a number of practical advantages. Aims. The aim of this work is to develop a standard procedure for OOF holography at the Effelsberg telescope. This includes performing OOF holography observations and the development of dedicated software, the pyoof package, to compute aberrations of the telescope’s optical system. Methods. Based on the OOF holography method developed at the Green Bank telescope, we adapted the approach to the Effelsberg 100 m telescope in order to determine the aberrations of the aperture phase distribution (phase-error maps). Results. The developed OOF holography software is presented as well as the results from observations at Effelsberg. Early results reveal gravitation-related residual deformation not contained in the previously existing aperture and pointing model, and hence we propose changes to the model to counteract aberrations in the telescope’s surface. Conclusions. The OOF holography method (observations and pyoof package) works as expected at the Effelsberg 100 m telescope and is able to validate the good performance of the existing finite element model. Test measurements show that slight improvements of the aperture efficiency and gain elevation dependence are possible but limited in the current configuration.

Mechanical azimuthal beam‐steering Fabry–Perot resonator antenna with large deflection angle

AbstractContinuous beam steering approach with minimal power consumption is highly desirable in modern antenna designs. A simple mechanical method for achieving beam steering in the Fabry–Perot resonator antenna (FPRA) is presented. It involves rotating the upper phase gradient metasurface (PGM) mechanically to change the aperture phase distribution, so the beam is continuously steered in the azimuthal plane while maintaining a large elevation angle. The proposed PGM unit cell comprises a hexagonal ring and patch printed on both sides of the substrate, along with a honeycomb lattice. A prototype antenna operating at 5.65 GHz is fabricated and measured to validate the feasibility. Measurement results show that the FPRA achieves a gain of 14.9 dBi, and can continuously steer its beam in the azimuthal plane with an elevation angle of around θ = 50°. Measured radiation patterns in eight azimuthal directions (φ = 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°) are consistent with the simulated results. Compared with other electrical tuning methods, our design has a compact size and requires lower power for the PGM rotation.

Multibeam Metasurface Antenna Enabled by Orbital Angular Momentum Demultiplexing Feeding for IoT Communication

Multibeam antenna radiations provide linkages to multiple nodes and can bring enhanced communication quality with reduced power consumption for Internet of Things (IoT) applications. In this paper, a novel method providing a low-cost and flexible multibeam antenna solution is proposed. Multiple orbital angular momentum (OAM) modes are used as internal excitations of the antenna, and the generated multiple beams are pencil beams with no OAM mode, which is convenient for IoT nodes connection. First, aperture phase distributions that convert incident vortex beams with different and orthogonal topological orders into designated directional pencil beams are acquired and superimposed to form a metasurface aperture that, under excitations of vortex beams with multiple orders, produces multibeam each with a predefined direction. The proposed multibeam method is then illustrated with a transmissive metasurface design, with four beams pointing at arbitrary half space directions. Techniques such as OAM modes spacing and aperture partitioning are utilized for reducing sidelobe levels (SLLs). Furthermore, a similar multibeam metasurface antenna with additional linear-to-circular polarization conversion function is demonstrated, which opens the possibility of utilizing different polarizations on top of the OAM based multibeam. This paper successfully explores and achieves a novel antenna system with multiple radiations suited for multiple IoT nodes accessing with low cost and low energy consumption, and also provides a new degree-of-freedom for OAM applications.

Multiple Tri-Beam Low Scanning Loss Metasurface Antenna for Wide-Angle Coverage by Superposing Focusing and Periodic Phases

A multiple tri-beam low scanning loss millimeter-wave (mmW) transmissive metasurface antenna for wide-angle coverage is proposed. The aperture phase distribution of the proposed metasurface is the superposition of the focusing phase and the periodic phase. Theoretical studies show that the size of the periodic phase element determines the directions of the three beams, and the periodic phase difference determines the amplitude ratio between the beams. The metasurface is designed according to the calculated phase and five patch antennas are adopted as the integrated linear feed array. A transmissive metasurface antenna prototype is fabricated for measurement verification. Good agreement is observed between the simulation and measurement. The measured results show that the proposed metasurface antenna realizes the tri-beam scanning range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 63 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> , and the scanning loss of 2.9 dBi is within a reasonable range.

Light-Controlled Large-Scale Wirelessly Reconfigurable Microstrip Reflectarrays

In this article, the concept and design of light-controlled large-scale wirelessly reconfigurable microstrip reflectarrays are proposed. Unlike conventional electrically reconfigurable microstrip reflectarray antennas (RAs) that control the aperture phase distribution by conducting wires for transmitting control signals, the proposed method utilizes light to control the ON- and OFF-state of the integrated positive-intrinsic-negative (p-i-n) diodes wirelessly and binaurally through light-sensitive resistance of photodiodes (PDs). The concept is validated by simulation first, where a 1 bit 32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times32$ </tex-math></inline-formula> wirelessly reconfigurable microstrip RA is designed at 10 GHz with a beam-steering range of ±60° for sidelobe levels < −10 dB, marking a record of 1024 elements with a tri-layer configuration. Experimentally, the light-control scheme is further validated by a smaller porotype of 256 elements, where a light-controlled beam steering from 30° to 45° is demonstrated. Compared with conventional wired reconfigurable microstrip RAs, the proposed method resolves the wire-routing complexity on the RA and offers a new possibility for further improving the maximum directivity, upper operating frequency, and the number of independently controllable polarizations of reconfigurable microstrip reflectarrays, paving the way for developing very-large reconfigurable intelligent surfaces (VRIS). Also, the proposed concept provides a new infrastructure for information exchange between light and microwaves.

Generalized Sequential Rotation Arrays With Full Control of Dual-Circularly-Polarized Aperture-Field Distribution Based on Elliptically-Polarized Elements

In this article, the theory, design, and experimental validation of wideband generalized sequential rotation arrays (GSRAs) are reported. In particular, the GSRA has the ability to provide dual-circularly polarized (dual-CP) beams with different handedness using a single feeding network, whose aperture amplitude and phase distributions can both be independently controlled. Such functionality is achieved by jointly utilizing the dynamic phase and Berry phase, as well as exploiting elliptically polarized (EP) array elements with different axial ratio (AR) values. The proposed technique and the design methodology are verified by two proof-of-concept microstrip GSRAs consisting of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times8$ </tex-math></inline-formula> array of EP stacked-patch elements operating in the K-band. The first prototype exhibits a 3 dB gain difference between the two CP beams, while the other offers a 6 dB gain difference and different sidelobe levels (SLLs) for the generated dual-CP beams. Both arrays are fabricated and measured, experimentally achieving a joint <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11} &lt; -10$ </tex-math></inline-formula> dB, AR < 3 dB, and 3 dB gain bandwidth of more than 28.4% and 20.1% with a beam squinting of less than 3°. In addition, the two GSRAs enable a bandwidth of about 19% and 3% within which the gain difference between the two CP beams of different handedness deviates from the targeted value by less than 1 dB. With the large degree of freedom in aperture field control, the proposed GSRAs could be potential candidates for use in satellite communications, point-to-multipoint communications, and so on.

Arbitrary polarization angle and wavefront manipulation of linearly polarized waves using PB phase

In this paper, a novel method for the manipulation of linearly polarized (LP) electromagnetic waves using Pancharatnam–Berry phase is proposed. By combining polarization synthesis and aperture phase distributions, the polarization angle and wavefront of an LP wave can be arbitrarily manipulated. Four metasurfaces were designed and fabricated to generate pencil, vortex, and Bessel beams with different polarization angels, respectively. Simulation and measurement results consist well and demonstrate the proposed method in both polarization and wavefront manipulation.

Suspended Metasurface for Broadband High-Efficiency Vortex Beam Generation

Electromagnetic (EM) waves carrying orbital angular momentum (OAM) exhibit phase vortex and amplitude singularity. Broadband OAM generation with high efficiency is highly desired with suggested applications such as broadband imaging and communications. In this paper, suspended metasurface structure achieving low-Q factor is proposed to realize broadband phase control and excellent reflection efficiency. Broadband vortex beam generation with OAM order of 1 and 2 are realized using the proposed suspended structure. Furthermore, by analyzing different metasurface aperture phase distribution schemes, the efficiency of the OAM generator is maximally achieved. The designs are validated by simulation and measurement. The proposed OAM generators work across 4–10 GHz with efficiency higher than 82%. This design provides a route to broadband metasurface realization and high efficiency OAM generation.

A Mechanically Rollable Reflectarray With Beam-Scanning Capabilities

A novel 1-D beam-steerable reflectarray antenna (RA) is proposed for the Ku-band. The RA aperture consists of 24×48 variable size square patch elements printed on a flexible plastic substrate. The aperture is wrapped around two cylinders to create a 12λ×12λ illumination window at the operating frequency of 14 GHz. Beam-steering is achieved by mechanically rolling the aperture. To mitigate antenna pattern degradation, an aperture phase distribution optimization technique is presented. The performance of this RA system is studied analytically using array theory. The effects of aperture size and unit-cell size are also discussed. The performance of the proposed RA is validated using simulations and measurements. The results illustrate that our design achieves 1-D beam-steering from -21∘ to +21∘ in the elevation plane while maintaining towards the broadside direction a maximum realized gain of 25.1 dBi. In this beam-scanning range, the gain variation is less than 1.5 dB, beamwidth variation is less than 1.6∘, and the side lobe level is maintained below -15 dB. In summary, the main advantage of our design is its ability to steer its high gain beam without using complicated feed networks or complex mechanical systems. Such antennas are especially needed in SmallSat and space applications.

A dielectric free near field phase transforming structure for wideband gain enhancement of antennas

The gain of some aperture antennas can be significantly increased by making the antenna near-field phase distribution more uniform, using a phase-transformation structure. A novel dielectric-free phase transforming structure (DF-PTS) is presented in this paper for this purpose, and its ability to correct the aperture phase distribution of a resonant cavity antenna (RCA) over a much wider bandwidth is demonstrated. As opposed to printed multilayered metasurfaces, all the cells in crucial locations of the DF-PTS have a phase response that tracks the phase error of the RCA over a large bandwidth, and in addition have wideband transmission characteristics, resulting in a wideband antenna system. The new DF-PTS, made of three thin metal sheets each containing modified-eight-arm-asterisk-shaped slots, is significantly stronger than the previous DF-PTS, which requires thin and long metal interconnects between metal patches. The third advantage of the new DF-PTS is, all phase transformation cells in it are highly transparent, each with a transmission magnitude greater than − 1 dB at the design frequency, ensuring excellent phase correction with minimal effect on aperture amplitude distribution. With the DF-PTS, RCA gain increases to 20.1 dBi, which is significantly greater than its 10.7 dBi gain without the DF-PTS. The measured 10-dB return loss bandwidth and the 3-dB gain bandwidth of the RCA with DF-PTS are 46% and 12%, respectively.

All-metal wideband metasurface for near-field transformation of medium-to-high gain electromagnetic sources

Electromagnetic (EM) metasurfaces are essential in a wide range of EM engineering applications, from incorporated into antenna designs to separate devices like radome. Near-field manipulators are a class of metasurfaces engineered to tailor an EM source’s radiation patterns by manipulating its near-field components. They can be made of all-dielectric, hybrid, or all-metal materials; however, simultaneously delivering a set of desired specifications by an all-metal structure is more challenging due to limitations of a substrate-less configuration. The existing near-field phase manipulators have at least one of the following limitations; expensive dielectric-based prototyping, subject to ray tracing approximation and conditions, narrowband performance, costly manufacturing, and polarization dependence. In contrast, we propose an all-metal wideband phase correcting structure (AWPCS) with none of these limitations and is designed based on the relative phase error extracted by post-processing the actual near-field distributions of any EM sources. Hence, it is applicable to any antennas, including those that cannot be accurately analyzed with ray-tracing, particularly for near-field analysis. To experimentally verify the wideband performance of the AWPCS, a shortened horn antenna with a large apex angle and a non-uniform near-field phase distribution is used as an EM source for the AWPCS. The measured results verify a significant improvement in the antenna’s aperture phase distribution in a large frequency band of 25%.

Method to Enhance Directional Propagation of Circularly Polarized Antennas by Making Near-Electric Field Phase More Uniform

A new approach to significantly increase the uniformity in aperture phase distribution, through time synchronization in the near-electric field, of circularly polarized (CP) antennas is presented. The method uses the phase of the CP electric field vectors, obtained through full-wave numerical simulations, and does not rely on any approximation such as ray tracing. The near-field data is post-processed to extract the relative phase difference that exists due to the unsynchronized rotations of the electric field vectors in a plane parallel to the antenna aperture. The phase delay is compensated with a thin time-synchronizing metasurface (TSM) that has a 2-D array of time-delay cells. The method is demonstrated with a prototype made of a two-port patch antenna, which is fed through a hybrid junction, and a TSM that is placed at one wavelength spacing above the patch. When TSM is used with patch antenna, its uniform phase area increases manifold thus increasing far-field directivity from 6.8 to 22 dBic.

A Dual-Band Orthogonally Polarized Contour Beam Transmitarray Design

A dual-band (12.5/14.25 GHz) orthogonally polarized contour beam transmitarray has been designed to accomplish the contour beam pattern for a European coverage region in both transmit and receive frequency bands. A quad-layer transmitarray unit cell configuration is optimized theoretically for an efficient dual-band operation. An orthogonally polarized 3-dipole unit cell with 360° phase range is used to control transmission phases at both frequencies independently. A modified intersection approach with a fast Fourier transform algorithm is used to optimize the aperture phase distribution of transmitarray at each frequency independently. An antenna prototype has been fabricated and tested. The measured contour beam patterns are in good agreement with the calculated patterns in both frequency bands. The measured minimum gains in the required coverage region are 25 and 25.3 dBi at 12.5 and 14.25 GHz, respectively.

3-D Printed Terahertz Lens to Generate Higher Order Bessel Beams Carrying OAM

Conventional vortex beams carrying orbital angular momentum (OAM) suffer from the limitation of beam divergence in wireless communications applications. This article proposes novel 3-dimensional (3-D) printed discrete dielectric lenses (DDLs) for generation of nondiffractive OAM beams operating at 300 GHz. By virtue of its arbitrary aperture phase control capability, a terahertz (THz) DDL combining the functionalities of three conventional bulky refractive hyperbolic, spiral phase plane, and aixcon lenses is proposed to generate nondiffractive Bessel vortex beam carrying OAM. An aperture field analysis method is also developed to evaluate the radiation performance of the DDL antennas. Furthermore, to cover the OAM signal in an intended longitudinal region, two DDL synthesis methods are explored to generate extended higher order Bessel beams carrying OAM. The first approach is based on geometric optics, while the second uses the alternating projection method (APM) to optimize the aperture phase distribution of the DDL. Two THz DDLs are conveniently fabricated by 3-D printing technology. Measured results demonstrate that THz nondiffractive OAM beams can be successfully generated by the designed DDLs. The generated THz OAM beam with attractive nondiffractive characteristic may open new opportunities for next-generation ultra-high-speed wireless communications.

A 2-D Beam-Scanning Bessel Launcher for Terahertz Applications

This article proposes a novel nondiffractive Bessel beam launcher based on discrete dielectric lens (DDL) antenna with 2-D beam-scanning capability operating at 300 GHz. The terahertz (THz) Bessel beam launcher consists of two identical in-plane rotatable DDLs fed by a commercially available pyramid horn. First, the two thin and lightweight DDLs can transform the quasi-Gaussian beam with spherical phase front from the feed horn into a well-collimated and confined pseudo-Bessel beam. Second, we demonstrate that simultaneous in-plane rotation of the two DLLs in the same and opposite directions can steer the generated Bessel beam in the azimuth and elevation, respectively. Hexagonal dielectric post is employed as the element of the DDL, whose height is tuned from pixel to pixel to realize the required aperture phase distribution. 3-D printing technology was utilized to fabricate the two DDLs aiming at simplifying the manufacturing process and reducing the cost. The theoretically calculated, simulated, and measured results reveal that the designed THz DDL can generate 2-D scanning nondiffractive Bessel beam with a large field of view (FoV) of 86.2° and full azimuth coverage. The proposed 2-D scanning THz Bessel beam launcher can find widespread applications in THz fast noncontact detection, tracking, and imaging systems.

Low-Cost Ultrawideband High-Gain Compact Resonant Cavity Antenna

A 3-D printed planar permittivity-gradient superstrate (PGS) is used to improve the directive radiation characteristics of a waveguide-fed compact resonant cavity antenna (CRCA). Far-field directivity of classical uniform superstrate-based RCAs is limited due to nonuniform aperture phase distribution caused by even transmission through the superstrate. Transverse PGS has been used here to remarkably improve aperture phase distribution and hence directive radiation performance of RCAs. Furthermore, the PGS was rapidly prototyped in one hour and 43 min using a low-cost acrylo-butadiene styrene (ABS) filament without using traditional multistep milling and machining. Single step fabrication was performed and effective dielectric constant of the ABS was varied through controlled infill percentage in different regions of the PGS. Measurements of a prototype indicate unrivaled results, from a smaller footprint, which includes peak directivity of 16.048 dB, 3 dB directivity bandwidth of 49.65% and sidelobe levels lower than -10.4 dB throughout the operating frequency band. The 3-D printed PGS thus outperforms all previously reported superstrates, for RCAs, by demonstrating similar radiation performance with an equivalent material cost of only 0.41 USD.

A Radial Line Slot-Array Antenna With Low Side Lobes and a Uniform-Phase, Tapered-Amplitude Aperture Field Distribution

The paper presents a circularly polarized radial line slot array (CP RLSA) antenna with a nearly optimal monotonic variation of slot length with radius, in order to simultaneously reduce antenna side-lobe levels and to make the aperture phase distribution nearly uniform. It has additional advantages of excellent radiation efficiency, high gain and good overall bandwidth. The antenna comprises a single-layer radial transverse electromagnetic quasi-TEM waveguide with radiating slots on the aperture. The amplitude tapering is implemented by gradually varying slot lengths on the antenna aperture as a function of radial distance, utilizing a slot coupling analysis. Several antenna designs were investigated, each having a physical diameter of 345 mm ( $23\lambda _{0}$ ) and a thickness of 4.6 mm ( $0.3\lambda _{0}$ ), where $\lambda _{0}$ is the free-space wavelength at the operating frequency of 20 GHz. A prototype was fabricated and measured, showing a good agreement between the predicted and measured results. The sidelobe levels at the operating frequency are less than −20 dB due to tapering in the near-field amplitude distribution. The measured magnitude of the input reflection coefficient ( $S_{11}$ ) of the antenna is below −10 dB within the frequency range of 19 GHz to 21 GHz. The antenna has a measured peak directivity and a peak gain of 34.3 dBic and 33.8 dBic, respectively. Both the measured 3dB directivity bandwidth and 3dB gain bandwidth are 5.4%. Aperture efficiency is 48% and radiation efficiency is 94.2% at the operating frequency. The fabricated antenna also successfully fulfilled the condition of circular polarization with an axial ratio bandwidth exceeding 5%.

3-D-Printed Phase-Rectifying Transparent Superstrate for Resonant-Cavity Antenna

A three-dimensional (3-D)-printed nonplanar highly transmitting superstrate is presented to improve the directive radiation characteristics of a resonant-cavity antenna (RCA). Classical RCAs are reported with nonuniform aperture-field distribution that compromises their far-field directivity. The concept of near-field phase correction has been used here to design a phase-rectifying transparent superstrate (PRTS), which was fabricated using the 3-D printing technology. The PRTS is printed using easily accessible polylactic acid filament. It has a significantly lower cost and weight compared to its recently published counterparts, while its performance is comparable. The 3-D printing technology yielded the prototype in less than 4 h, which is considerably less compared to the traditional machining methods. Measurements of the prototype indicated close correspondence between the predicted and the measured results. Significant increase in the antenna performance has been achieved, due to the rectification of the aperture phase distribution. Notable aspects encompass 7.3 dB increase in the antenna peak directivity (from 13–20.3 dBi), significant sidelobe level suppression, and an improvement of aperture efficiency by 36.1%, with a PRTS that costs less than 2.5 USD.

Electromagnetic-wave beam-scanning antenna using near-field rotatable graded-dielectric plates

The paper proposes an electromagnetic-wave beam-scanning antenna system using a simple rotation of a pair of near-field graded-dielectric plates (GDPs). The antenna system requires an electromagnetic (EM) illuminator, with nearly symmetric aperture field distribution, as the base antenna and two types of GDPs: one radially graded dielectric (RGD) and two linearly graded dielectric (LGD) plates. The RGD first focuses the beam of the base antenna in the broadside direction, and the LGD then tilts the focused beam at an offset angle. For some types of base antennas, having fairly uniform aperture phase distributions, an RGD may not be required and only a pair of LGDs are sufficient. Irrespective of the antenna configuration, using a simple rotation of the two LGDs, the beam can be scanned to any position within a large conical region. The antenna system presented as a proof of concept has a resonant-cavity antenna as the base antenna and three graded-dielectric plates. The aperture length of the antenna system is 6λ0 and its height is 2.2λ0. The results predicted by numerical simulations indicate that the antenna system has highest peak directivity of 21 dBi. The beam can be scanned to any direction within a cone having an apex angle of 20°.

Improved design of a SIW long slot leaky wave antenna with low SLL

This study presents a new design for the substrate integrated waveguide (SIW) long slot leaky wave antenna (LWA) with narrow beam, low side lobe level (SLL) and low cross-polarisation. To meet these specifications, the changes of phase constant, β, along the structure are compensated, the required leakage constant, α r , is determined more accurately by considering the loss and a straight slot along the antenna is used. In order to calculate the leakage constant of the leaky-mode more accurately, thru-reflect-line method along with HFSS simulations is used. By properly determining the shape of SIW walls, the amount of leakage along the slot and the phase constant can be controlled. This results in a desired aperture amplitude and phase distribution. The presented LWA realises a Taylor distribution with a predefined SLL of -25 dB. Such a design also leads to a low cross-polarisation level and narrow beam at centre frequency of 17 GHz. The measurement results are consistent with the simulation results.