Conventional Reflector Research Articles

Resistance frequency selection surface framed reflector antenna for 5G OTA measurement

AbstractIndirect far field (IFF) over‐the‐air (OTA) test could be one of the most applicable test methods for 5G mmWave devices. The compact antenna test range (CATR) method has been introduced to the OTA test by 3GPP. Conventional metallic parabolic reflectors without edge treatment can lead to serious edge diffraction which results in high noise and low accuracy. The serrated reflector improves edge diffraction but performs poorly at low frequencies. Reflector antenna with a resistance frequency selection surface (RFSS) frame is proposed for 5G OTA CATR measurement at millimeter frequency, which collimates spherical incident waves into quasi‐plane waves in a relatively short distance, thus forming a quiet zone (QZ) in which large devices under test can be measured in small chamber. In this paper, the reflector with RFSS is investigated through the numerical and experimental methods, it is found that serrated RFSS frame with low edge diffraction could achieve the excellent QZ, which could be helpful in miniaturing CATR chambers for 5G OTA measurement.

Colored reflectors to improve coincidence timing resolution of BGO-based time-of-flight PET detectors

Time-of-flight (TOF) positron emission tomography (PET) detectors improve the signal-to-noise ratio of PET images by limiting the position of the generation of two 511 keV gamma-rays in space using the arrival time difference between the two photons. Unfortunately, bismuth germanate (BGO), widely used in conventional PET detectors, was limited as a TOF PET scintillator due to the relatively slow decay time of the scintillation photons. However, prompt Cerenkov light in BGO has been identified in addition to scintillation photons. Using Cerenkov photons for timing has significantly improved the coincidence timing resolution (CTR) of BGO. Based on this, further research on improving the CTR for a BGO-based TOF PET system is being actively conducted. Wrapping materials for BGO pixels have primarily employed white reflectors to most efficiently collect scintillation light. White reflectors have customarily been used as reflectors for BGO pixels even after Cerenkov light began to be utilized for timing calculations in pixel-level experiments. However, when the arrival-time differences of the two 511 keV annihilations photons were measured with pure Cerenkov radiators, painting the lateral sides of the radiators black can improve CTR by suppressing the reflection of Cerenkov photons. The use of BGO for TOF PET detectors requires simultaneously minimizing scintillation loss for good energy information and suppressing reflected Cerenkov photons for better timing performance. Thus, reflectors for BGO pixels should be optimized for better timing and energy performance. In this study, colored polytetrafluoroethylene (PTFE) tapes with discontinuous reflectance values at specific wavelengths were applied as a BGO reflector. We hypothesized that CTR could be enhanced by selectively suppressing reflected Cerenkov photons with an optimum colored reflector on the BGO pixel while minimizing scintillation photon loss. CTRs were investigated utilizing white and three colors (yellow, red, and green) PTFE tapes as a reflector. In addition, black-painted PTFE tape and enhanced specular reflector film were investigated as reference reflector materials. When 3 × 3 × 20 mm3 BGO pixels were wrapped with the yellow PTFE reflector, the CTR was significantly improved to 365 ± 5 ps from 403 ± 14 ps measured with the conventional white PTFE reflector. Adequate energy information was still obtained with only 4.1% degradation in light collection compared to the white reflector. Colored reflectors show the possibility to further improve CTR for BGO pixels with optimum reflectance design.

Origami-inspired self-deployable reflectarray antenna

Reflector antennas, operating at high frequencies, require a high surface accuracy: deviations from the target geometry accuracy result in a loss of RF performance (e.g., antenna gain and efficiency). As a result, the aperture may need to be larger, or a more complex backing structure must be engineered to achieve the reflector surface accuracy to deliver the equivalent gain of an efficient solid reflector. This would typically increase the mass, the stowed volume, and the design complexity. The design of larger aperture deployable antennas (e.g., Cassegrain, Offset) for SAR (Synthetic Aperture Radar) applications can be challenging for missions where platform size and payload mass are limited.Inspired by the Origami based techniques, Oxford Space Systems (OSS) is currently developing an innovative SAR Reflectarray antenna, targeting the X-Band frequency range, with the aim of achieving a relatively large aperture from a small, stowed volume suitable for a small satellite. The Reflectarray antenna architecture has several potential advantages over other antenna designs. It is a cost-competitive technology with excellent stowage efficiency, which can be further improved with origami-based folding mechanisms/kinematics. It requires a simplified deployment mechanism and in contrast to conventional parabolic reflectors, it does not need a separate backing structure.Until now, work on space deployable Reflectarray antennas (e.g., MARCO, OMERA and ISSARA missions from NASA) have focused on multi-degree of freedom structures, i.e., independent self-actuated hinge driven architectures. This paper presents an elegant single degree of freedom, origami-inspired Reflectarray architecture that does not require actuation on all the hinges. Thanks to its Hold-Down Release Mechanism (HDRM) and spring-loaded hinges, the OSS Reflectarray antenna is self-deployable. It maintains the required flatness accuracy achieved through its novel hinge integrated latching system.The OSS Reflectarray antenna has an 8:1 footprint stowage ratio, which enables installation on small satellite platforms (between 50 kg and 100 kg). The reflectarray has been designed to work in the X-band frequency with dual linear polarization for the concept study. However, the architecture can be scaled up or down to suit other frequency bands, making the OSS Reflectarray compatible with many applications and platforms.

Quantum Inspired Broadband Photonic Absorber: Potential Application as Solar Sail along with Mobility Analysis

Electromagnetic wideband absorption is still perceived as a critical and formidable challenge to address with an unambiguous photonic absorber. Subwavelength metamaterial (MM) unit cells with unique and controlled features have recently gained considerable interest. However, meta‐atoms, generated using a quantum‐inspired pattern distribution, are underwhelming in existing literature to design photonic absorbers and their potential application to manufacture solar sails is still quite uncommon. In this article, to create a flexible, polarization‐insensitive, ultrathin, and broadband MM absorber, quantum interference pattern‐inspired design is utilized. Herein, a novel approach to fabricating solar sails for the space exploration incorporates the proposed broadband photonic absorber rather than conventional reflectors. The quantum‐inspired meta‐absorber (QIMA) exhibits an absorption of over 91% for the visible domain, i.e., 380–800 nm under a conventional plane‐polarized source. It is shown in the study that broadband absorbers are almost equivalent to excellent reflectors to design the solar sails in terms of the time‐averaged force calculated by utilizing the Maxwell stress tensor method. Thus, the QIMA has the potential to be a viable alternative to reflectors in the design of futuristic solar sails for space exploration. The interference theory model is also utilized to assure the dependability of calculated data, and additionally, the standard AM1.5 solar spectrum is utilized to demonstrate the QIMA's solar‐harvesting potentiality.

Experimental comparison of evacuated tube solar air heater based on energy and exergy analyses with environmental and economic (4‐E) study

AbstractFor the purpose of low‐medium air heating applications like timber seasoning, HVAC, agricultural & food drying, space heating and desalination, there is requirement of hot air. Solar air heaters are the promising systems to satisfy these requirements in a very inexpensive manner. Due to higher efficiency at higher operating temperature and lower cost, evacuated tube collectors (ETCs) are preferred for solar air heating. In this manuscript, the comparative parametric study of two similar sets of evacuated tube solar air heater (ETSAH) is performed. The comparison is based on energy & exergy analyses, and also presents the environmental and economic study (4E analyses). Each set is fabricated using mild steel (M.S.) along with 50 evacuated tubes with total collector area of 8.46 m2. The experimental investigations are made at diverse flow rates, with and without using conventional reflectors. Without incorporating any additional heat storage unit, the system provides average hot air temperature of 76.13°C when average solar intensity was 502.68 W/m2 during 11 h of operation from 09:00 to 20:00 h. ETC's absorber glass and the M.S. material was observed to have significant energy storage and discharge. The single set of ETSAH has mitigation of 89.20 tons with 2.05 years of energy payback period, which is significantly low as compared to its 20 years of lifespan. For the optimum system performance the cost of generated hot air is 0.00048 $/kg, which is considerably low.

A Dual Ka/Q-Band Reflectarray

Introduction. Duplex satellite communication is commonly arranged using two spaced frequency bands, with one band receiving and the other band transmitting signals to a satellite. The main task of a communications satellite antenna system consists in providing an identical coverage area across all involved frequency bands, which is often a challenging task for conventional parabolic reflector antennas. Reflectarrays allow an independent control of the reradiated wave phase in spaced frequency bands, which can be used to create efficient multi-band antenna systems for modern communication satellites.Aim. To develop a Ka/Q-frequency range phase-correcting element and to create on its basis a dual-band reflectarray for operation with orthogonal circular polarizations and identical gains in a given sector of angles in significantly spaced frequency ranges.Materials and methods. Numerical studies were carried out using the finite element analysis method. Radiation patterns were measured using the near field scanning method.Results. A single-layer dual-band phase-correcting reflectarray element was developed for operation with orthogonal circular polarizations with low losses and a weak dependence of the relative position of the elements on the phase characteristic. On the basis of the proposed element, a reflectarray consisting of 24 465 two-frequency elements was synthesized and manufactured. The developed prototype of a single-layer dual-band reflectarray demonstrated good characteristics, with the efficiency reaching 56 and 36 % in the Ka- and Q-frequency ranges, respectively, and an almost identical minimum gain in the ±0.75° angle sector.Conclusion. The research results confirm the potential of the developed reflectarray to successfully replace conventional parabolic reflectors installed both on modern communication satellites and as part of ground-based satellite terminals in the millimeter wavelength range.

Experimental analysis of evacuated tube solar air heater (ETSAH) with inbuilt sensible thermal energy storage

AbstractIn the present work, an evacuated tube solar air heater (ETSAH) with inbuilt sensible heat storage material (SHSM) is experimentally evaluated. The system comprises two sets each having 50 evacuated tubes with an H‐type arrangement and a total collector area of 16.92 m2. For the purpose of hot air generation, ETSAH is simultaneously connected in series and in parallel with and without the use of reflectors. Three different mass flow rates of 122.90, 164.87, and 212.83 kg/h were fixed to get 12 diverse cases of ETSAH operation. The highest hot air temperature reported by the system is 121.7°C when it was connected in series with conventional reflectors at 212.83 kg/h of flow rate and 469 W/m2 average solar intensity. The system reported an overall average energy efficiency of 49.76% and an exergy efficiency of 17.97% with the highest average hot air temperature difference of 56.12°C from 09:00 to 20:00 h. Without the incorporation of any additional SHSM, the average hot air temperature delivered by ETSAH (when under the neighbor building shadow) is 49.73°C logged from 17:00 to 20:00 h. The economic analysis is also carried out to ensure its practical application and feasibility. For the best system performance, the annual cost of hot air generation is 0.0194 Rs./kg (0.0002433 $/kg).

Development of a solar device for jute filling based humidification dehumidification desalination

ABSTRACT It is predicted that the ground water sources which are currently termed as sustainable will also begin to deteriorate, and this may lead to the degradation of the cropland and may severely affect food production, smooth colonial expansion and also damage the balance of ecosystem. Since 2011, much of the interest has been laid upon the concepts of Ecohydrology, which dwells upon the interconnectivity of ecosystem and hydrology. This study emphasises on the recycling of waste water and desalination of sea water. Among various desalination techniques, humidification–dehumidification (HDH) technique, using solar energy as the heat source for evaporation of salt water, has gathered attention in recent years. A conventional solar reflector HDH desalination plant requires a humidifier, where saline water is fed and made to evaporate in running air, when drizzled through nozzles and passed through the jute surface, which will be further reduced due to a fan which will be installed at the end of a humidifier region. Therefore, there will be enhancement in vapour formation and then sent to a dehumidifier where pure water is separated from moist air through condensation. The proposed unit in which latent heat can be recovered, which may yield 20 L/day on floor area of 2 m2 and adopting jute as filling in humidifier. The latent heat that is extracted from the moist air may be further utilised in the preheating of the saline water. Here, a prediction model was developed over data collected for 25 days and net gain obtained from the experimentation will be used to calculate gained output ratio. A preliminary parametric study to explore the technical feasibility of the HDH reveals that a fixed bed column filled with EDTA provides a longer working duration to assure the overall system’s performance and to remove surplus salt.

Polarization discrimination and surface sensing with a near-IR nanostructured hybrid mirror

We demonstrate experimentally how to turn a conventional distributed Bragg reflector into a polarization selecting mirror operating in the near-IR at normal incidence without diffraction and with high extinction ratio. Our approach involves combining a dielectric multilayer composite with a sub-wavelength metal wire-grid nanograting, which can be routinely fabricated using well-established planar fabrication techniques. Moreover, the design and working principle of our nanostructured hybrid mirror enable it to operate as a surface sensor and allow straightforward integration of the mirror with functional materials for tuning its wavelength/polarization extinction ratio.

Intelligence Enabled by 2D Metastructures in Antennas and Wireless Propagation Systems

The development of the next generation of wireless systems is bringing renewed attention to the physical layer of the communication link. Indeed, the new low-latency requirements cannot be satisfied relying only upon the extreme virtualization of the hardware functions. Moreover, conventional wireless systems with fixed characteristics and functionalities are not appropriate to modern electromagnetic environments, which undergo continuous and fast variations. Embedded smartness is a required feature for widening the range of the possible electromagnetic responses to support advanced and novel functionalities. In this paper, we show how the combination of 2D metastructures with conventional antennas and reflectors enables an unprecedented electromagnetic behavior, which is at the basis of new properties, capabilities, and applications. In particular, we propose an emerging design approach based on the shifting of the reconfigurability, adaptivity, sensing, and power management of a wireless system at the physical level, thanks to the use of properly designed 2D metastructures to be coupled with standard antennas and reflectors.

The Effect of the OMT in Electromagnetic Simulations of MeerKAT Primary Beams

Until recently, full-wave electromagnetic (EM) primary beam simulation results for MeerKAT’s offset-Gregorian reflector antennas in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> -band (856–1711 MHz) differed systematically and inexplicably from high-precision field measurements. The measured beam patterns exhibit unexpected frequency- and polarization-dependent pointing offsets (squint) in both horizontal (H) and vertical (V) directions for the copolarization patterns, as well as distinctive asymmetries in the horizontal direction for the cross-polarization patterns in the upper half of the band. These effects were not predicted by design stage simulations that are based on the excitation of the fundamental waveguide mode only. Conventional large reflector simulation strategies used in the literature idealize the orthomode transducer (OMT) and waveguide and exclude this module from primary beam simulations entirely. This research shows that the inclusion of MeerKAT’s wide-bandwidth OMT and waveguide in the simulation is critical to the excitation of the TE21 mode, which results in the asymmetric features observed in the measurements. It is found that the characteristic frequency-dependent asymmetries of the primary beams are a consequence of the design of the OMT and cannot be attributed to manufacturing tolerances, reflector collimation errors, nor the coupling to conductive structures near the feed horn.

Beam Divergence Reduction of Vortex Waves With a Tailored Lens and a Tailored Reflector

In this paper, we present a tailored lens and a tailored reflector in order to reduce the large beam divergence inherent to Orbital Angular Momentum waves (OAM waves-Vortex waves) that are generated by an Uniform Circular Patch Antenna Array (UCA) at 10 GHz. The tailored lens and the tailored reflector are designed by the shape function (5) and (9) around the antenna s center axis, respectively. The tailored lens is compared to UCA without and with conventional lens. The simulated and measured results show a significant improvement when using the tailored lens. Following, a tailored reflector is implemented and compared to UCA without and with conventional reflector. Firstly, the two reflectors are simulated with an impressed field source to neglect the influence of the UCA. The simulated results of the two reflectors show that the tailored reflector has a better performance than the conventional reflector when the height of the reflector $r_0$ is less than around 1.5 $\lambda$ and when the opening angle of the reflector theta is less than 38{\deg} (for UCA with $d$ of $\lambda/2$). In addition, the reflectors are simulated with real UCA with different shapes of PCB, which can disturb the reflected waves from the reflector. Two lenses and two reflectors are manufactured and measured in an anechoic chamber and compared to the simulation results. This paper shows that the vortex waves needs a special lens or a special reflector to reduce effictively the beam divergence especially when the radius of the UCA is very large.

Quasi-Optical Multi-Beam Antenna Technologies for B5G and 6G mmWave and THz Networks: A Review

Multi-beam antennas are critical components in future terrestrial and non-terrestrial wireless communications networks. The multiple beams produced by these antennas will enable dynamic interconnection of various terrestrial, airborne and space-borne network nodes. As the operating frequency increases to the high millimeter wave (mmWave) and terahertz (THz) bands for beyond 5G (B5G) and sixth-generation (6G) systems, quasi-optical techniques are expected to become dominant in the design of high gain multi-beam antennas. This paper presents a timely overview of the mainstream quasi-optical techniques employed in current and future multi-beam antennas. Their operating principles and design techniques along with those of various quasi-optical beamformers are presented. These include both conventional and advanced lens and reflector based configurations to realize high gain multiple beams at low cost and in small form factors. New research challenges and industry trends in the field, such as planar lenses based on transformation optics and metasurface-based transmitarrays, are discussed to foster further innovations in the microwave and antenna research community.

Planar focusing reflectors based on monolithic high contrast gratings: design procedure and comparison with parabolic mirrors.

Here, we describe in detail a procedure for the numerical design of planar focusing mirrors based on monolithic high contrast gratings. We put a special emphasis on the reconstruction of the hyperbolic phase of these mirrors and we conclude that the phase does not have to be perfectly mimicked to obtain a focusing reflector. We consider here the grating mirrors that focus light not in the air but in the GaAs substrate and we compare them with conventional parabolic reflectors of corresponding dimensions. The light intensity at the focal point of the focusing grating mirrors was found to be comparable to that of the parabolic reflector. Moreover, the reflectivity of the focusing grating mirrors is almost as high as that of parabolic mirrors covered with an additional reflecting structure, if the ratio of the reflector width to the focal length is less than 0.6. Planar focusing grating mirrors offer a good alternative to parabolic mirrors, especially considering the complexity of fabricating three-dimensional structures compared to planar structures.

Extreme Scanning Double Shaped-Reflector Antenna With Multiple Interactions for Focal Plane Array Applications

A new type of focal plane array (FPA) reflector antenna concept is proposed with a very wide field-of-view over a wide bandwidth (20–40 GHz) for ground terminals for Ka -band satellite communication and multifunction radars. The proposed concept maximizes the percentage of active array elements up to 90% within the required scanning range of ±10° along the azimuthal plane. It combines the advantages of phased arrays in terms of wide-angle scanning and of FPA systems in terms of high antenna gain. This FPA system achieves a 15 dB higher antenna gain as compared to a phased array with a size equal to the feed array of the proposed reflector system. Based on a minimum required 80% aperture efficiency at 30 GHz, the illuminated array region is increased by a factor of 200 as compared to traditional prime-focus configurations. In addition, the FPA configuration significantly reduces the required overall array size by a factor of 1.5 as compared to conventional double-parabolic reflector configurations. Moreover, the scanning capabilities have been significantly improved as compared to classical prime-focus and double-parabolic reflectors. Since a large part of the array is active, we can obtain high effective isotropic radiated power (EIRP).

A technique based on the quasi-actual feed for suppressing sidelobe levels of reflector antenna

ABSTRACT A sidelobe-suppression technique for the reflector antenna is proposed. Compared to the conventional reflector antenna analysis technique, the proposed technique adopts the novel quasi-actual feed instead of the traditional imaginary feed to calculate and optimize the radiation pattern of the reflector antenna. The calculated and the optimized radiation results obtained by the proposed technique are more accurate since the quasi-actual feed data is closer to that of the practical feed. In the proposed technique, the sidelobes are suppressed by optimizing the shape of the reflector illuminated by the quasi-actual feed. The reflector shape is smoothly transformed by the non-uniform rational B-spline technique and the scatter of the reflector is efficiently calculated by the physical optics and the Gauss-Legendre quadrature algorithms. The pattern result of this proposed technique is compared with the result simulated by FEKO software, a good agreement is achieved and has a higher efficiency. As an example of applying the proposed technique, an unshaped and a shaped reflector antennas with the same feed and the same size are designed, fabricated and tested, and the measured results agree well with the expectations on the low sidelobe characteristic.

A Dual-Band Dual-Circularly Polarized Reflectarray for K/Ka-Band Space Applications

Reflectarrays (RAs) offer low-cost and low-profile solutions for reflector antennas that are polarization and frequency selective. These features augment their capabilities for point-to-point communications compared to conventional reflectors. Here, a dual-band dual-circularly polarized (CP) RA that can radiate independently shaped beams in the desired directions for each polarization in each band is proposed. The RA is composed of a dual-band dual-linearly polarized (LP) RA and a dual-band LP-to-CP polarizer. The proposed RA can be employed to reduce the number of the required apertures for a four-color multiple spot beam coverage implemented using a single-feed-per-beam configuration from four to two. The underlying unit cell of the proposed RA is designed for 18.3–18.8 GHz and 27.0–27.5 GHz. It provides a 323° phase shift in the lower band and 381° phase shift in the higher band while maintaining a cross-polarization level better than 15 dB in both bands and excellent decoupling between the two bands. An offset-fed RA is designed, fabricated, and measured.

New Design of a Solar Collector Reflector

In this research paper, a new theoretical approach for designing and simulating the optical performance of a solar reflector is presented, increasing its intercept factor and hence its efficiency. In order to achieve this, a special computer code was developed using MATLAB. After that, the result of this approach is to be compared with conventional reflectors (flat and circular shaped reflectors). In comparison, the new r at the specified dimensions has showed a huge improvement over the flat reflector where the maximum intercept factor has been around 97% for the designed reflector and about 84% for the flat one, while it has slightly exceeded the elliptical reflector by 4%. On the other hand, the max intercept factor for both the circular and the designed reflector has been almost the same. If the reflector width range falls within the range 5-11 cm, the designed reflector shows a larger intercept value than the circular one and above 11 cm the contrary occurs, noticing that the elliptical reflector intercept value significantly falls below those values for those two reflectors.

Improvement of reflectron time-of-flight mass spectrometer for better convergence of ion beam

Reflectron time-of-flight mass spectrometer (RTOF-MS) is a powerful tool to achieve high resolution in mass analysis of various ions. As it is often supposed that analyte ions are generated in a small volume in the ion-extraction region, its performance is not optimized for ions spread over a large volume. Not only the mass resolution is degraded due to incomplete space and energy focusing, but also the ion beam is subject to significant divergence of ion trajectories after it is reflected from an ion reflector. Here we present a novel design of RTOF-MS equipped with an additional electrostatic lens in front of a conventional grid-less ion reflector for improving convergence of an ion beam. The performance is examined by mass analysis of Ag3+ ions extracted from a volume of 6.3 cm3, i.e., a cylinder with 20-mm length and 20-mm diameter. The improved convergence of an ion beam is demonstrated by a two-dimensional image of ions on the ion detector. Mass resolution is evaluated as well.

Perfect Absorption Efficiency Circular Nanodisk Array Integrated with a Reactive Impedance Surface with High Field Enhancement.

Infrared (IR) absorbers based on a metal–insulator–metal (MIM) have been widely investigated due to their high absorption performance and simple structure. However, MIM absorbers based on ultrathin spacers suffer from low field enhancement. In this study, we propose a new MIM absorber structure to overcome this drawback. The proposed absorber utilizes a reactive impedance surface (RIS) to boost field enhancement without an ultrathin spacer and maintains near-perfect absorption by impedance matching with the vacuum. The RIS is a metallic patch array on a grounded dielectric substrate that can change its surface impedance, unlike conventional metallic reflectors. The final circular nanodisk array mounted on the optimum RIS offers an electric field enhancement factor of 180 with nearly perfect absorption of 98% at 230 THz. The proposed absorber exhibits robust performance even with a change in polarization of the incident wave. The RIS-integrated MIM absorber can be used to enhance the sensitivity of a local surface plasmon resonance (LSPR) sensor and surface-enhanced IR spectroscopy.