Hybrid Reflector Research Articles

Refocusing beams of a satellite mirror antenna with moderate deformations of its reflector

Multibeam hybrid reflector antenna (MBHRA) is part of high-performance satellite communication systems. It provides high gain thanks to its large mirror and the use of antenna array to form enough beams covering the working area. Therefore, it is crucial to maintain the needed beams configuration to provide clients with high quality signal. The location of the beams may change because the reflector profile changes under the changeable thermal flux from the Sun, which is not stationary due to orbital motion of the satellite. Although the appearing distortions of the reflector profile are a priori small, but they cause beams to displace from their assigned positions in up to their width of tenth of a degree. Consequently, the level of the signal in coverage areas goes down. Modern MBHRA form their beams with clusters, i.e. groups of elements of the antenna array. Typically, cluster consists out of seven elements: one in the center and others at the vertices of a perfect hexagon. The fact that several antenna elements form a beam opens up the possibility of electronically controlling the beams by adjusting the amplitudes and phases of the exciting distribution, or more precisely, the weighting coefficients of the clusters. To determine which amplitudes and phases to apply, it is necessary to know the current state of the reflector, characterized by either its geometry or its electrodynamic equivalent, such as the best-fit paraboloid (BFP). Laser measurement and photogrammetry are popular solutions for that. A useful alternative to them is reconstruction of the BFP from the signals received by the MBHRA antenna array from a ground-based radio beacon. Emphasizing the dependence of these signals on the state of the reflector, we call them the “signal imprint” of the reflector. The possibility to implement a single ground beacon is due approximation the reflector profile as an equivalent best-fit paraboloid. BFP is uniquely defined by six parameters: change of the focal length, turns in two orthogonal planes and shift of the apex in space {ΔF; αz; αy; Δx; Δy; Δz}. Since some of the parameters are highly correlated in terms of their influence on the signal imprint, the re-construction problem becomes more complicated. So a question whether the set of parameters is overloaded arises reasonably. Maybe it is possible to get rid of some parameters. We considered two options to reduce the number of parameters: focal displacement + turns {ΔF; αz; αy} and apex shift {Δx; Δy; Δz}. Statistical modelling confirms the possibility to reduce the number of sought-for BFP parameters down to the mentioned three instead of six. If the maximum of the focal spot does not shift outside the cluster, then reducing the number of the sought-for BFP parameters to three causes a very small decrease in the gain of beams compared to using the full set of parameters. For the above options, the decrease in gain is 0.03 dB or 0.25 dB. It is interesting to note that in the turns option {ΔF; αz; αy} there is a better correspondence to the reflector surface compared to the displacement option {Δx; Δy; Δz}, but worse matching of the signal imprint, and as a consequence a greater loss in gain. This is due to the higher sensitivity of the beam orientation to the mirror rotations than to the vertex displacement.

Amplitude methods for forming frequency-independent radiation characteristics of multibeam reflector antennas

The trend towards expanding the operating frequency ranges of radio-electronic equipment has led to an increasing interest in recent years in the study of ways to constructing multi-beam frequency-independent reflector antennas, which requires systematization of the principles and methods of their construction. When constructing reflector antennas, methods based on the selection of the directional properties of the feeds and methods based on the selection of the frequency-selective properties of the reflectors are used. Methods based on the choice of directional properties of feeds are divided into methods using horn feeds and methods using feeds in the form of cluster arrays with intersecting apertures. Horn feeds are used to create single-beam reflector antennas. Using cluster arrays, it is possible to form a plurality of beams of frequency-independent partial radiation patterns. Using the example of a hybrid reflector antenna, the possibility of forming nine beams in the azimuthal sector of 20° with a beam width of 3.2° ± 0.45° in the frequency band from 2 to 8 GHz is shown. The level of side lobes outside the working sector in the operating frequency band does not exceed –35 dB, the slope of the direction-finding characteristics varies from 4.8 to 9.8 dB/deg. Among the methods based on the choice of selective properties of reflectors, there are methods using frequency-selective surfaces and methods using corrective coatings on the working surface of the reflector. Frequency-selective surfaces are made in the form of wire meshes with variable pitch, in the form of a set of parabolic plates and in the form of a set of square waveguides with a side size ranging from half-wave at the upper frequency in the middle part of the reflector to half-wave at the lower operating frequency at the edges of the reflector. The disadvantages of using frequency-selective surfaces are the complex and expensive design of the reflector, low antenna efficiency, high side lobes and the need to use a large absorbing screen. When implementing the method using corrective coatings, the separate functions of a frequency-selective surface and a radio-absorbing screen are combined in one structural element – a frequency-dependent corrective coating applied to the working surface of the reflector. Among the advantages of this method, it is worth noting the simple design of the reflector and the possibility of its operation at any polarization, since the reflection characteristics of the coating are practically independent of the type of polarization. A common disadvantage of reflector antennas based on the choice of frequency-selective properties of reflectors is distortion of the shape of the main lobe of partial patterns and a larger range of scatter in the pattern width in the operating frequency band, which prevents the formation of linear direction-finding characteristics and reduces direction-finding accuracy. Due to the low efficiency of multibeam mirror antennas built using amplitude methods for forming frequency-independent radiation characteristics, their use as transmitting antennas is impractical. The completed review and identified features of methods for constructing frequency-independent radiation characteristics can become a methodological basis for the design of broadband multi-beam reflector antenna systems for advanced radio-electronic equipment.

Four-Arm Log-Periodic Toothed Antenna With Hybrid Reflector Composed of Inhomogeneous Metamatarial Elements for Electronic Support Measures

Four-Arm Log-Periodic Toothed Antenna With Hybrid Reflector Composed of Inhomogeneous Metamatarial Elements for Electronic Support Measures

Use of heavy dielectric materials in solidly mounted A1 mode resonators based on lithium niobate

This paper discusses the applicability of dielectric materials with high acoustic impedance Z a for use in A1 Lamb mode solidly mounted resonator (SMR) with large electromechanical coupling coefficient k 2 . The study first shows that the use of metal as a reflector creates parasitic capacitance C p, which reduces k 2 significantly. Then, A1 Lamb mode SMRs are designed using HfN, HfO2, WN, WO3 etc., and achievable performances are compared. When either HfN, HfO2, WN, or WO3 is employed, relative large k 2 up to 25% is achievable. For further k 2 enhancement, a hybrid reflector configuration is also examined, wherein HfN is applied only to the top high Z a layer and W is applied to the others. The result indicates that C p caused by the W layers is still significant, and k 2 becomes worse in total.

Searchless algorithm for reconstruction of the reflector profile of a hybrid reflector antenna from antenna array signals

Searchless algorithm for reconstruction of the reflector profile of a hybrid reflector antenna from antenna array signals

Reconstruction of the reflector geometry of a satellite multibeam hybrid reflector antenna by processing antenna array signals

Reconstruction of the reflector geometry of a satellite multibeam hybrid reflector antenna by processing antenna array signals

Ku-Band Dual Linear-Polarized 1-D Beam Steering Antenna Using Parabolic-Cylindrical Reflector Fed by a Phased Array Antenna

We propose a 1D beam steering high gain hybrid reflector-phased array antenna system for enhanced data rate wireless communication at Ku -band (12 - 14 GHz). The proposed hybrid antenna system consists of a ${D}$ = 50 cm offset parabolic-cylindrical reflector with ${f}/{D} = 0.4$ fed by an $8\times4$ dual linear-polarized stacked patch phased array antenna placed along the focal line of the reflector. The parabolic-cylindrical reflector has the property of a wide-angle beam steering along the cylindrical axis as compared to a conventional parabolic reflector. A complete implementation of the dual linear-polarized phased array antenna with the silicon RFIC chipset based beamforming network and integrated with aluminum offset parabolic-cylindrical reflector is reported. Cavity model and physical optics approximations are used to analyze the radiation characteristics of the phased array and the induced currents on the parabolic-cylindrical reflector surface, respectively. Furthermore, the multilevel fast multipole method (MLFMM) is used along with the method of moments (MoM) in TICRA GRASP for a comprehensive analysis of the proposed hybrid reflector system. The peak directivity of the reflector pattern is around 27 dBi for both the X-polarization and Y-polarization, and a beam scanning of ±30° is achieved along the cylindrical axis of the reflector for 3 dB reduction in the gain. The analytical and computed results of the proposed hybrid reflector-phased array antenna system are experimentally verified.

Performance enhancement of shorted polygonal archimedean spiral antenna using hybrid reflector

In this paper, performance enhancement in a shorted polygonal archimedean spiral antenna has been proposed by backing it with a hybrid reflector. In the proposed work, two arms of the polygonal spiral antenna are shorted at an outer octagonal conductive ring aiding in size reduction of the polygonal spiral. The shorted polygonal spiral antenna with the advantages of low profile and the good axial ratio at lowest frequencies of operation is backed by a hybrid reflector that utilizes combination ferrite layer which tapers towards the center to a PEC layer. The hybrid reflector helps to improve the gain of the antenna significantly at low frequencies without compromising the gain of the antenna at high frequencies. The antenna operates from 0.6 GHz to 6.5 GHz with a minimum boresight gain of 0.2 dBic at 0.6 GHz and an average gain of 6 dBic from 2.2 GHz. The antenna also demonstrates a good axial ratio of ≤3 dB over the VSWR bandwidth in a low-profile dimension of 0.13 λ0 × 0.13 λ0 × 0.04 λ0. The proposed work thus presents a novel idea to develop a compact high-performance spiral by shorting the arms of a polygonal spiral with a conductive ring and backing the same by a hybrid reflector and cavity.

High-Performance Green Flip-Chip LEDs with Double-Layer Electrode and Hybrid Reflector

High-performance green flip-chip light-emitting diode (FC-LED) was realized by combining double-layer electrode and highly reflective hybrid reflector. The introduction of double-layer electrode improved uniformity of current spreading over the entire active region. The highly reflective hybrid reflector, composed of SiO2 total internal reflection (TIR) layer and Nb2O5/SiO2 distributed Bragg reflector (DBR), offer higher reflectance and wider bandwidth compared to conventional DBR. Numerical simulation and experimental results indicated that the green FC-LED has advantages of uniform current spreading and high light extraction efficiency (LEE) compared to green top-emitting LED (TE-LED). Due to uniform current spreading, the forward voltage of the green FC-LED is 0.28 V lower than that of the TE-LED at 20 mA. Compared to TE-LED, the light emission intensity of the green FC-LED at 20 mA is enhanced by 18% due to the higher reflectance of hybrid reflector and increased utilization ratio of active region area caused by double-layer electrode structure.

A Hybrid Reflector Antenna for Two Contoured Beams With Different Shapes

A hybrid reflector antenna is presented in this letter to generate two contoured beams with different sizes and shapes using a single feed for each beam. This antenna is a dual offset Gregorian design with the Mizuguchi condition and is fed with two horns. One horn illuminates the main reflector and the other one illuminates the subreflector. In this antenna configuration, the main reflector aperture is shared by two contoured beams and the shapes of these two contoured beams are determined by main reflector surface and subreflector surface, respectively, and the electrical performances can be optimized independently. There is, therefore, minimal loss of gain in this dual coverage antenna as compared with a single/dual reflector dedicated to a single coverage. This method has many advantages such as providing two different shaped beams, good aperture efficiency, simple mechanical structure, light weight, and low complexity. The antenna design procedures are described in detail. The Ku-band Earth deck antenna prototype with dual shaped beams is designed, fabricated, and measured. A good gain performance is demonstrated for two different shaped regions. The difference between the predicted edge-of-coverage gain results and the measured results is less than 0.2 dB.

Simulation modeling of functional adaptive interference nulling for multibeam hybrid reflector antenna systems

This paper considers the simulation of adaptive nulling mechanism patterns in hybrid reflector antenna systems with a 19-element feed element, in which the radiation pattern is formed as a cluster. Incidents of broadband and narrowband interference are studied in the article.

Specialized software for the adaptive nulling unit of a hybrid reflector antenna

This paper considers the development of specialized software for a hybrid reflector antenna adaptive nulling unit; it conducts the calculation of a desired amplitude and phase distribution of the feed array in counter service area formation and interference cancelling.

Methods of Assessing the Characteristics of the Multiprocessor Computer System Adaptation Unit

Currently, a growing number of satellite communication systems developers and manufacturers pay attention to the adaptive multibeam antenna systems. These systems allow you to implement flexible traffic management by forming a multi-beam patterns within the service area. In addition, they have such an important property, as the high noise immunity when exposed as a deliberate and industrial noise provided by the use of spatial filtering methods for interference. The adaptive multibeam antenna can be built on the basis of a phased antenna arrays with scanning beams and multibeam antennas are constructed on the basis of hybrid reflector antennas [1]. The main control element of such antennas is a block adaptation that implements control algorithms and individual beams beamforming. A block adaptation is a processor based on the adaptive signal processor, and the adaptation is made on the program level. In [2] made

Enhanced Broadside Gain of an Ultrawideband Diamond Dipole Antenna Using a Hybrid Reflector

This communication studies the effect of a hybrid reflector on the radiation pattern of an ultrawideband diamond dipole antenna. The cause of a split radiation pattern in the broadside direction appearing when using a uniform artificial-magnetic-conductor-based reflector is investigated and is found to be due to destructive interference in the broadside direction produced by surface currents localized in certain areas of the reflector. A hybrid reflector is then proposed to mitigate this problem using both electrical and magnetic conductors. This solution enhances the gain in the broadside direction of the ultrawideband antenna. A complete antenna with a feeding system and a hybrid reflector has been fabricated and the measurement results are presented.

Spatial suppression of interference in hybrid reflector antennas*

The article describes a 7-beam hybrid reflector antenna with a 19-element feed element which forms a radiation pattern in the form of a cluster. During the research the synthesis of the amplitude-phase distribution of the antenna feed element has been conducted. A radiation pattern for three situations of interference: along the first side lobe, along the ramp of the main lobe, along the main lobe.

Adaptation algorithms for satellite communication systems equipped with hybrid reflector antennas

This paper reviews adaptation algorithms influenced by active interferences in satellite communication systems. A multi-beam antenna is suggested as an adaptive system; it is built on the basis of a hybrid reflector antenna with a 19-element array feed element, which incorporates a modified algorithm for radiation pattern synthesis used for suppressing targeted interferences. As a criterion for this synthesis, antenna gains are used at fixed points. As a result, the size of the objective function and time required for the synthesis can be significantly limited.

Enhanced luminous efficiency of phosphor-converted LEDs by using back reflector to increase reflectivity for yellow light.

To obtain high reflectivity over a broad range of green, yellow, and red light as well as blue light incidents from a particular angular range and further increase the luminous efficiency of a phosphor-converted white LED packaging module, a novel back hybrid reflector including a SiO(2) total internal reflection layer (TIR), five-pair SiO(2)/TiO(2) double distributed Bragg reflector (DBR) stacks, and a gold (Au) metallic mirror was designed and fabricated. The double DBR stacks have layers configured to reflect green, yellow, and red light as well as blue light, which includes a first portion where the thickness of the layers are relatively larger, and also includes a second portion where the thickness of the layers is relatively smaller. Light that is passing toward the hybrid reflector at angles greater than the critical angle (56°) is reflected by the SiO(2) TIR layer at the sapphire/SiO(2) interface, whereas the light that passes through the SiO(2) TIR layer with incident angles between 0° and 56° is reflected by the double DBR stacks. The overall hybrid reflector can ensure a reflectivity of more than 95% in both the blue light wavelength region and the yellow light wavelength region. The obtained higher reflectivity in the yellow light wavelength region will benefit the phosphor-converted LEDs because yellow light backscattered by phosphor particles is reflected upward.

GaN-based high-voltage light-emitting diodes with backside reflector

High-voltage light-emitting diodes (HV-LED) withbackside reflector, including Ti3O5/SiO2 distributed Bragg reflector (DBR) or hybrid reflector combining DBR and Al or Ag metal layer, are investigated using Monte Carlo ray tracing method. The hybrid reflector leads to more enhancement of light-extraction efficiency (LEE). Moreover, the LEE can also be improved by redesigning the thicknesses of DBR. HV-LED with four redesigned DBR pairs (4-MDBR), and those with a hybrid reflector combining 4-MDBR and Al metal layer (4-MDBR-Al), are fabricated. Compared to 4-MDBR, the enhancement of light-output power induced by 4-MDBR-Al is 4.6%, which is consistent with the simulated value of 4.9%.

Improved Light Extraction Efficiency of a High-Power GaN-Based Light-Emitting Diode With a Three-Dimensional-Photonic Crystal (3-D-PhC) Backside Reflector

An interesting approach to improving the light extraction efficiency of high-power GaN-based light-emitting diodes (LEDs) by the use of a 3-D-photonic crystal (3-D-PhC) backside reflector is studied. A 3-D-PhC backside reflector is formed by coating a self-assembled SiO2 nanosphere monolayer between the hybrid reflector and backside of a sapphire substrate. The 3-D-PhC structure is used to enhance light scattering. At 350 mA, as compared with a conventional LED (with a hybrid reflector while only without the 3-D-PhC structure), the studied device exhibits 23.6% enhancement in the light output power without the degradation of electrical properties. Therefore, the performance of high-power GaN-based LEDs could be further improved by using a 3-D-PhC backside reflector.

Enhancement in light output power of LEDs with reflective current blocking layer and backside hybrid reflector

A GaN-based light-emitting diode (LED) with reflective current blocking layer (CBL) underneath p-electrode pad and backside hybrid reflector was fabricated and investigated. With a 20 mA injection current, the LED with SiO2/ITO/Al reflective CBL deposited on naturally textured p-InGaN/p-GaN surface exhibited a light output power that was 7.6% and 18.5% higher than those of the textured LEDs with SiO2 CBL and without SiO2 CBL, respectively. The LED with backside hybrid reflector exhibited a light output power that was 30% higher than that of LED without the hybrid reflector. The enhancement in light output power is attributed to the improved current spreading performance via the SiO2 CBL, the Al omnidirectional metal reflector to prevent the light absorption by the opaque p-electrode pad, and the backside hybrid reflector to extract bottom-emitting light.