Symmetric Reflector Research Articles

An Efficient Ring-Shaped Phase Center Calculation Method Based on a New Phase Efficiency Calculation Model

Axially symmetric circular aperture reflector antennas fed with back-fire feeds such as the hat feed have a ring-shaped phase center. This communication presents an efficient method for calculating location of the ring-shaped phase center. First a phase efficiency calculation model (PECM) for a feed with a ring-shaped phase center is constructed. To facilitate the phase center calculation, an approximate PECM with a simpler form is also proposed. Detailed numerical results show that the model is more accurate than the existing one in the literature. Based on the proposed approximate PECM and the Newton–Raphson’s iterative method, a novel ring-shaped phase center calculation method is then developed. Phase center calculation results for two types of hat feeds show that the proposed method is accurate and efficient. Moreover, the method is easy to implement and does not rely on a good initial point.

Compact Dual Circularly Polarized Primary Feeds for Symmetric Parabolic Reflector Antennas

Four-arm Archimedean spiral antennas, capable of generating both senses of circular polarization with broadside radiation patterns, are investigated as a primary feed in symmetrical parabolic reflector antennas with circular rims. Unidirectional, center-fed, and compact spiral antennas are studied, backed by a planar reflector as a ground plane. Both right- and left-handed circularly polarized fields with broadside radiation patterns, according to the first and third modes of the spiral, are realized by confining the radiation zone to less than a three-wavelength circumference. The proposed feed exhibits excellent pattern symmetry and axial ratios well below 0.5 dB at the boresight direction for both senses of polarization. In this letter, the performance of the proposed spiral antenna is fully addressed as primary feeds in symmetrical parabolic reflector antennas. Different antenna parameters such as gain, cross polarization, and efficiency are studied for paraboloids, having different focal-length-to-diameter ratios, for both senses of circular polarization. Efficiencies of 70% and higher are obtained over a frequency band of 2.5-5.0 GHz.

Design of Symmetrical Beam Triple-Aperture Waveguide Antenna for Primary Feed of Reflector

This research presents a triple-aperture waveguide antenna as the primary feed of parabolic reflectors. The proposed antenna is able to rectify the asymmetry and also achieve a symmetrical unidirectional beam through the application of two parasitic coupling apertures. The design of the antenna is that of a rectangular waveguide (radiating aperture) vertically jointed to the two coupling apertures of the same measurement widthwise (i.e., one stacked on top and the other underneath) to achieve the symmetrical beam. The rectangular waveguide is 97.60 mm and 46.80 mm in width (a) and height (b), respectively, to propagate the WLAN frequency band of 2.412–2.484 GHz. Simulations were carried out to determine the optimal antenna parameters and an antenna prototype was subsequently fabricated and tested. The simulated beamwidths in theE- andH-planes at-3 dB were equally 67° (i.e., 67° for both theE- andH-planes) and at-10 dB also equally 137°, while the measured results at-3 dB were equally 65° and at-10 dB equally 135°. The simulation and measured results are thus in good agreement. The simulated and measured antenna gains are, respectively, 8.25 dBi and 9.17 dBi. The findings validate the applicability of the antenna as the prime feed for rotationally symmetric parabolic reflectors.

Parametric Study of Cylindrical Dielectric Resonator Antenna (CDRA) Feeder with Symmetric Parabolic Reflector

In this study a parabolic reflector antenna is designed and fabricated for IEEE 802.11a WLAN application. Initially, a single element circular tuning slot coupled Cylindrical Dielectric Resonator Antenna (CDRA) feeder is designed and fabricated for a symmetric parabolic reflector. Subsequently, the designed feeder is integrated at the focal point of the parabolic reflector to provide unidirectional radiation pattern with improved gain and sidelobe levels. The measured fractional impedance bandwidth achieved for the proposed antenna is 1.8% for S₁₁<-10 dB from 5.32 to 5.52 GHz. A radiation pattern with broadside radiation and low back radiation has been obtained. A good measurement gain of approximately 13 dB is achieved over the bandwidth by placing CDRA feeder at the focal point of the parabolic reflector. In addition, a comprehensive parametric study has been conducted to realize the effect of slot size and position on the resonance frequency of the designed feeder. Furthermore, a parametric study of various reflector parameters has also been performed to study the effect of size, depth and focal point of the parabolic reflector on gain of the antenna. Important design factors have been identified from the parametric study of the antenna. The experimental and measured results show that the designed antenna is suitable for IEEE WLAN 802.11a wireless application.

Applications of trimode waveguide feeds in adaptive virtual array antennas

AbstractThis paper presents the formation of an adaptive virtual array antenna in a symmetric parabolic reflector antenna illuminated by trimode circular waveguide feeds with different mode alignments. The modes of interest are the TE11, TE21, and TM01 type modes. The terms TE and TM stand for the transverse electric and transverse magnetic modes, respectively. By appropriately exciting these modes and varying the mode orientations inside the primary feed, the effective source of radiation is displaced on the reflector aperture, while the resulting secondary patterns remain axial. Different antenna parameters such as gain, cross polarization, and phase center locations are investigated. It is demonstrated that the extra third mode facilitates the formation of symmetric virtual array antennas with reasonable cross polarization discriminations at the diagonal plane.

Design of Radiation-Pattern-Reconfigurable Antenna With Four Beams

This letter presents a novel radiation-pattern-reconfigurable antenna that could operate in four directions without any antenna servo system. This is achieved by changing the wave director and wave reflector via appropriate p-i-n diodes. The reconfigurable antenna is incorporated within the four symmetrical wave detectors or wave reflectors to form the structure. The antenna can cover all directions in the azimuth plane ( $xy$ -plane) by controlling the states (on or off) of four p-i-n diodes. The achieved maximum gain of the antenna is 5.08 dB. A good agreement is found between the simulated and the measured results. Further advantages of the introduced antenna design are its easy fabrication process and its low cost.

Estimation Method of Temperature Field of Large Axial Symmetric Reflector Antenna in Real-time

For the irregular temperature field caused by the multiple conditions of reflector antenna and the change of solar directon, temperature field can be described as a function of the angle between sunlight and aperture plane, based on which, a method of estimating temperature field in real-time is presented. A thermal analysis model is founded and a temperature data sheet is built by calculating the temperature fields under different angles between sunlight and antenna aperture plane. According to current working condition, corresponding temperature field can be obtained by looking-up the temperature data sheet, performing rotation, and being corrected by the measuring temperature values. For this engineering problem, one 7.3 m reflector antenna operated in Ka band is considered as a research object, and the simulation temperature and the measuring temperature are estimated both with good agreement with the estimated temperatures. The analysis results show that the proposed method is simple, fast and effective, and can be used for the real-time compensation for the thermal distortion. There is also reference value for the antenna structure design.

Achromatic orbital angular momentum generator

We describe a novel approach for generating light beams that carry orbital angular momentum (OAM) by means of total internal reflection in an isotropic medium. A continuous space-varying cylindrically symmetric reflector, in the form of two glued hollow axicons, is used to introduce a nonuniform rotation of polarization into a linearly polarized input beam. This device acts as a full spin-to-orbital angular momentum convertor. It functions by switching the helicity of the incoming beamʼs polarization, and by conservation of total angular momentum thereby generates a well-defined value of OAM. Our device is broadband, since the phase shift due to total internal reflection is nearly independent of wavelength. We verify the broad-band behaviour by measuring the conversion efficiency of the device for three different wavelengths corresponding to the RGB colours, red, green and blue. An average conversion efficiency of 95% for these three different wavelengths is observed. This device may find applications in imaging from micro- to astronomical systems where a white vortex beam is needed.

Antenna reflector emulation by simplified metamaterial-coated plates

The optical transformation has been found to be an exceptional tool for determining the permittivity and permeability tensors ε and μ that are required to provide desired patterns of electromagnetic energy flow. In a previous application of the optical transformation, a planar metamaterial-coated plate (MMCP) was designed which will scatter waves in the same manner as a three-dimensional parabolic reflector. The required ε and μ, however, were not diagonal. A new method is proposed which can be applied to cylindrically symmetric reflectors of general geometry, and which results in ε and μ tensors which are diagonal. This is accomplished (a) by dividing the original region into two sub-regions and performing the transformation on each one separately, and (b) by performing the transformation along orthogonal surfaces that include the reflector boundaries. The method is applied to conical, parabolic, and spherical reflectors. The MMCP that is equivalent to each of these geometries is numerically validated for wave guide and plane wave radiation sources.

Analysis of Omnidirectional Dual-Reflector Antenna and Feeding Horn Using Method of Moments

A hybrid numerical technique is applied for the analysis of circularly symmetric dual reflector antenna fed by TEM coaxial horn to generate an omnidirectional radiation pattern. By following the steps of a technique developed for the analysis of horn antennas, it employs a stepped-waveguide method to analyze the interior surfaces of the TEM coaxial horn transition and the electric field integral equation (EFIE) is applied on the outer surfaces of the TEM coaxial horn including the radiating aperture and the reflectors. Simultaneously, the magnetic field integral equation (MFIE) is employed on the aperture to relate the aperture fields and those in the horn transition. Method of moments (MoM) is employed to numerically solve the resultant hybrid field integral equation. The technique is applied for electromagnetic analysis of a coaxial TEM horn antenna and an omnidirectional dual reflector antenna. Results for the antenna return loss at the input port and for the vertical radiation pattern are given and compared with measurements and with commercial software results.

A Corrugated Printed Dipole Antenna With Equal Beamwidths

A corrugated printed dipole antenna with equal beamwidths in the principal planes is proposed, designed, and evaluated. Orthogonal stubs are added to the dipole arms to equalize its radiation patterns. They also reduce the size of the dipole arms. The antenna is designed to operate at 3 GHz, and has dimension of 36 × 80 × 1.58 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The -10 dB S 11 bandwidth of the antenna is from 2.75 to 3.62 GHz, i.e., 27.3%. The E- and H-plane radiation patterns of the antenna are nearly equal up to 135 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> from the boresight. To confirm the simulation results, the antenna is fabricated and tested, showing good agreement between simulation and measurement results. Its performance as a feed on a deep reflector, with f/D = 0.25 and D = 45 cm is also studied, where f is the focal length of the reflector and D is its diameter. It provides an enhanced bandwidth of 29.6%, equal E- and H-plane radiation patterns of the reflector, and a gain of 21.4 dBi or an efficiency of 69%. The reflector is only 4.5 λ0 in diameter and would suffer significant blockage losses with conventional waveguide feeds. The proposed feed causes negligible blockage, and provides a respectable efficiency. It is a suitable feed for small symmetric reflectors.

Improved Cross-Polarization Performance of a Multi-Phase-Center Parabolic Reflector Antenna

This letter addresses the cross-polarization properties of electronically controlled multi-phase-center parabolic reflector antennas, illuminated by over-moded primary feeds. Due to the presence of the higher-order modes in the primary feed, the secondary cross-polarization levels deteriorate in the case of symmetric reflector antennas. As for the offset reflectors, the primary multimode feed required to displace the phase-center location may produce a significant crosstalk in the orthogonal polarization. It is shown how one can improve the cross-polarization performances of aforementioned adaptive antennas, which are capable of providing axial beams while their phase-center locations are displaced. The conventional array technique with a simple signal processing is used for the symmetric case, whereas a trimode primary feed is employed for the offset case.

A discontinuous surface reflector for high-power integrated LEDs

High-power integrated LEDs usually have a bright square surface. When the rays emitted from them are collected to project a round spot at a very short distance using a rotationally symmetrical reflector, there will be a dark spot in the centre. This problem can be avoided in advanced lighting systems. A discontinuous surface reflector is designed by a simple method based on the three-dimensional form of compound parabolic concentrators. The dark spot is removed, and the uniformity is better.

Experimental Demonstration of Reflectarrays Acting as Conic Section Subreflectors in a Dual Reflector System

This paper experimentally demonstrates the use of a microstrip reflectarray as a low-profile planar substitute to a conic section subreflector (hyperboloidal type) in a symmetric dual reflector system at Ku-band. At first, a brief discussion on the simulation and measurement techniques utilized in the paper is provided. A nominal dual reflector Cassegrain system is synthesized through simulations where a feed horn is used to illuminate the hyperboloidal subreflector. Next, a flat metallic subreflector is placed at the subreflector location. This is a critical task as it shows the importance of phase compensation. Due to the flat subreflector, the feed is defocused from the image of the focus and creates phase aberration, leading to beam bifurcation, pattern degradation, and performance deterioration of the dual reflector system. A planar microstrip patch-type subreflectarray is then designed to mimic a hyperboloidal subreflector. Ray tracing is applied to the subreflector-feed system to calculate the phase needed to compensate for the axial defocusing of the feed. A prototype subreflectarray based on the ray-optics approach is fabricated. Radiation pattern measurements and back-projection holographic diagnostics demonstrate that the subreflectarray acts as a hyperboloidal subreflector and restores the antenna performance with a well-defined main beam and low side lobes.

Computational Photography with Panoramic Sensors that Have Uniform Resolution with Respect to Unwarping Transformations

We address the problem of designing a computational photographic system for panoramic imaging, which employs a rotationally symmetric reflector and yet produces uniform resolution images. Our design is a catadiotpric sensor, whose key component is a rotationally symmetric mirror. Catadioptric sensors have already been designed that are equiresolution with respect to solid angle, but such sensors do not take into account the effect of unwarping transformations that are typically applied to the initially recorded images. The family of catadioptric sensors that we describe may be considered as realizing area preserving/scaling cylindrical projections. We present the derivations of the equations that describe such sensors and demonstrate in simulation their properties with respect to unwarping.

Performance Comparison of Symmetric and Offset Reflector Antennas Adaptively Illuminated by Novel Triple Mode Feedhorn

Parabolic symmetric and offset reflector antennas adaptively illuminated using a novel triple-mode feedhorn (TE11+TM01+TE21) with different mode combinations and impedance and radiation performances are presented. The combination of the radiating modes in a feedhorn with proper amplitude and fixed phase values helps in electronically pointing the main beam of the radiating patterns such as that obtained in a beam-steering antenna with limited beam-scan range. This type of radiation performance virtually creates a displaced phase center location for the feedhorn, which, consequently, adaptively illuminates the reflector antenna surface. Impedance-matching bandwidths are preserved for both reflector antennas similar to the case of feedhorn alone. The copolarization gain and peak cross-polarization levels are far better with the offset reflector antenna than the symmetric reflector antenna. Such reflector antennas find applications in ground moving target indicator (GMTI) and space based radars. The investigation results are solely computed using FEKO full-wave analysis tool.

A Review On Designing Of The Dual Reflector Axially Symmetric Cassegrain Antenna

Dual reflector antennas are considered as pencil beam antennas that can produce radiation identical to searchlight. Cassegrain Reflector Antenna Design consists of various effects caused by blockage by primary feed or by the subreflector and its effect on overall performance. The objective of the paper is to provide the overview of the designing approach that is used to design the axially symmetric cassegrain antenna. This paper also provides the reader the overview of the various challenges and limitation that are faced by the designer while designing the axially symmetric dual reflector cassegrain system.

A Novel Beam Squint Compensation Technique for Circularly Polarized Conic-Section Reflector Antennas

Beam squint generally exists in offset reflector antennas with circularly polarized feeds. It is manifested by a small beam shift of the radiation pattern in the plane perpendicular to the principal offset plane, which can significantly affect the beam pointing accuracy. In this paper a practical and widely applicable compensation technique for the beam squint is proposed. Simulation results show that a small lateral feed displacement in the perpendicular plane can effectively minimize or eliminate the linear phase shift caused by the depolarization effect, thus compensating for the beam squint effect. This is in practice very useful for offset reflector antennas where the previously suggested method based on feed tilting may not be proper. A simple formula is derived to quickly estimate the optimal feed displacement for both right- and left-hand circularly polarized feeds. Three representative examples: a single offset parabolic reflector, a suboptimal offset Cassegrain reflector, and an axially symmetric Cassegrain reflector with an off-focus feed, are presented to validate the proposed method. Satisfactory results are achieved for all three examples.

Design of a novel gas sensor structure based on mid-infrared absorption spectrum

A new type of light-collecting structure that can greatly improve signal-to-noise ratio for gas test was designed on the basis of mid-infrared absorption spectrum principle. A rotational symmetric ellipsoid reflector was employed to collect the mid-infrared radiation with the light source and detector on two focuses, and Beer–Lambert law was applied to construct related math models. Theoretical analysis showed that this structure could perfectly enhance the gains of signals by 648 times. Experimental analysis of methane gas was carried out by using principle of differential absorption, 3.31 μm mid-infrared absorption wavelength and double PbSe detectors. The detection limit of this system was 50 ppm and the test precision was as high as 3%. Due to the attenuation and imprecise ellipsoid reflector, the experimental gain of differential signal was 220 times.

A Lower-Cost High-Resolution LYSO Detector Development for Positron Emission Mammography (PEM).

In photomultiplier-quadrant-sharing (PQS) geometry for positron emission tomography applications, each PMT is shared by four blocks and each detector block is optically coupled to four round PMTs. Although this design reduces the cost of high-resolution PET systems, when the camera consists of detector panels that are made up of square blocks, half of the PMT's sensitive window remains unused at the detector panel edge. Our goal was to develop a LYSO detector panel which minimizes the unused portion of the PMTs for a low-cost, high-resolution, and high-sensitivity positron emission mammography (PEM) camera. We modified the PQS design by using elongated blocks at panel edges and square blocks in the inner area. For elongated blocks, symmetric and asymmetrical reflector patterns were developed and PQS and PMT-half-sharing (PHS) arrangements were implemented in order to obtain a suitable decoding. The packing fraction was 96.3% for asymmetric block and 95.5% for symmetric block. Both of the blocks have excellent decoding capability with all crystals clearly identified, 156 for asymmetric and 144 for symmetric and peak-to-valley ratio of 3.0 and 2.3 respectively. The average energy resolution was 14.2% for the asymmetric block and 13.1% for the symmetric block. Using a modified PQS geometry and asymmetric block design, we reduced the unused PMT region at detector panel edges, thereby increased the field-of-view and the overall detection sensitivity and minimized the undetected breast region near the chest wall. This detector design and using regular round PMT allowed building a lower-cost, high-resolution and high-sensitivity PEM camera.