On‐board large mesh antenna reflector with high surface accuracy

Experiments on mobile satellite communications are being carried out to determine if they are technically feasible for future domestic satellite services in the Experimental Mobile Satellite System project, which uses Engineering Test Satellite-V. Experimental ISDN (integrated services digital network) basic-rate communications services have also been offered for marine vehicles. The authors describe the configuration of an experimental system for maritime ISDN satellite communications, and the characteristics of ISDN basic-rate interface connections for the digital telephones, G4 facsimiles, and color video-phone terminals of terrestrial ISDN services. This experiment provided much information for designing future mobile satellite communications systems. Moreover, it indicates that forward error correction in a mobile satellite link with poor transmission quality is very effective at improving the communication quality of mobile satellite systems. >

A multibeam digital beamforming (DBF) antenna, developed for a future mobile satellite communications system, is mounted on a vehicle for a receiving experiment in a mobile environment using a satellite signal in the L band. The multibeam is formed by 2-dimensional FFT signal processing. Automatic acquisition and tracking of an arriving signal are achieved by selecting a maximum beam out of the multiple beams in real-time.

[Abstract] This paper proposes dynamic bandwidth/channel access technique using FFT based block signal transmission for future broadband mobile satellite communication systems, which is to supplement next generation terrestrial mobile networks. One of the key issues for next generation mobile satellite communication systems is flexible and scalable access technique in terms of data rate and traffic type, to accommodate various satellite users. OFDMA is a technique to meet the above-mentioned requirements, however it needs large output backoff at HPA. To solve this problem, this paper proposes a new bandwidth/channel access technique using FFT based block signal transmission. The proposed technique uses single carrier modulation suitable for small output backoff operation in HPA, keeping flexibility and scalability as OFDMA has. This paper describes basic principle of the proposed dynamic bandwidth/channel access technique and preliminary performance evaluation results by computer simulation.

A concept for a future advanced mobile satellite communications system using a geostationary satellite is described. In the satellite of this system, a multiple spotbeam antenna, onboard beam interconnection, and millimeter-wave and Ka-band components are required. The configuration of the payloads of Japan's COMETS (Communications and Broadcasting Engineering Test Satellite) for advanced mobile satellite communication experiments is also described. The transponder has an IF filter bank and a SCPC/TDM (signal-carrier-per-channel/time-dimension multiplexing) regenerative modem for beam interconnection. >

As a key technology in future mobile communications system, OFDMA has efficient frequency utilization and strong robustness to frequency selective fading, however it's sensitive to synchronization errors. Although effects of synchronization errors on crossed timeslot's performance have been widely investigated in TDD/CDMA system, little work has done in TDD/OFDMA system. This paper analyzes the effects of synchronization errors on the performance of crossed timeslot in TDD/OFDMA system. It's proved that crossed timeslot is more sensitive to synchronization errors comparing with non-crossed timeslot in TDD/OFDMA system, and even very small frequency synchronization errors or sample clock frequency errors may bring serious degradation to system performance, to which attention should be paid in system design. The downlink user equipment (UE) in crossed timeslot receives strong interference when synchronization errors exist and the main part of the interference is caused by the uplink signal of other UEs in the crossed timeslot.

Cable-network structures are an important part of mesh reflector antennas. The performance of antennas depends greatly on the surface accuracy and tension distribution. However, there are periodic temperature changes in the space environment where the mesh antenna is located. The traditional form-finding and optimization design methods can only guarantee good performance at room temperature, while active adjustment technology is limited by on-orbit measurement technology and control technology. Therefore, it is critical to carefully design the cable-network configuration to reduce the influence of space thermal loads. In this study, a thermal design optimization method for mesh reflector antennas was proposed by considering the deformation compatibility conditions. The length variation of the cable element under thermal loads was analyzed accurately. With the combination of the force density sensitivity matrix and temperature deformation equation, the force density increment equation of the whole cable net was established. By constraining the reflector nodes to the paraboloid and selecting the quadratic sum of the node thermal deformation as the objective function, we obtained a cable-network configuration with better surface shape stability than traditional design methods. Finally, a numerical example is presented to illustrate the effectiveness of the proposed method.

In the design of a large deployable mesh reflector, high surface accuracy is one of ultimate goals since it directly determines overall performance of the reflector. Therefore, evaluation of surface accuracy is needed in many cases of design and analysis of large deployable mesh reflectors. The surface accuracy is usually specified as root-mean-square error, which measures deviation of a mesh geometry from a desired working surface. In this paper, methods of root-mean-square error calculation for large deployable mesh reflectors are reviewed. Concept of reflector gain, which describes reflector performance, and its relationship with the root-mean-square error is presented. Approaches to prediction or estimation of root-mean-square error in preliminary design of a large deployable mesh reflector are shown. Three methods of root-mean-square error calculation for large deployable mesh reflectors, namely, the nodal deviation root-mean-square error, the best-fit surface root-mean-square error, and the direct root-mean-square error, are presented. Concept of effective region is introduced. An adjusted calculation of root-mean-square error is suggested when the concept of effective region is involved. Finally, these reviewed methods of root-mean-square error calculation are applied to surface accuracy evaluation of a two-facet mesh geometry, a center-feed mesh reflector, and an offset-feed mesh reflector for demonstration and comparison.

Ultra-thin shell foldable and self-deploying composite reflectors are being developed for space antennas to meet low cost, low mass and high surface accuracy. For Ku-band missions a full-scale offset parabolic reflector antenna is designed by considering different concepts of monolithic and nonmonolithic structures, different stiffening schemes, manufacturing ease, and lower cost. The resulting reflector is based on stiffened spring back reflector concept but it provides much simpler design, significantly lower mass and lower cost. It is a simple monolithic structure, and consists of a reflector surface and a flat skirt. The skirt is an integral part of the reflector and is used to stiffen the reflector. The full size version is an offset parabolic reflector with a diameter of 6 m, a focal length of 4.8 m, and an offset of 0.3 m. In order to demonstrate the concept, 1/3-scaled version is designed, manufactured, and tested. Experiments of the demonstrator are conducted for quasi-static folding, dynamic deployment behavior, stiffness measurements, modal analysis, and surface accuracy in deployed configuration; the experimental results are compared with the results of finite elements solutions where applicable.

Form-finding methods for deployable mesh reflector antennas

To meet the high gain requirement, a 2×2 a microstrip patch antenna array is designed and used as a feed source to illuminate a symmetric parabolic reflector antenna at 300 GHz. The effect of the substrate and conductor material properties on the performance of the microstrip array antenna is discussed. Resulting reflector antenna performance is discussed using this feed. Another application of this array is to excite dielectric lens antennas for high gain. These high gain antennas can find application in future THz communications.

The high-frequency performance of the reflector antennas is mainly limited by the surface. It has been shown that distortions on different regions of the reflector surface can have different effects on the radiation performance. In other words, degradation of the radiation pattern due to the presence of surface distortions is sensitive to the location and behavior of the surface distortion profile. In this paper, the concept of “sensitivity of the radiation pattern to the surface distortion” has been introduced and quantified. It can be used in the design of different reflector antennas to prevent radiation degradations due to surface distortion. Based on the Physical Optics and variational analysis, the first-order variational of the far-fields with respect to the surface profile is formulated to present the concept of sensitivity. The variational amplitude can be modified to show the concept of sensitivity of the radiation pattern to the distortions on the surface. Reflector antennas with different geometries and feeding methods have different sensitivity plots. Both co- and cross-polarization fields for feed antenna are considered ti be used in the symmetric and offset reflectors, and sensitivity plots are extracted. Sensitivity plots show areas on the surface that have stronger effects on the radiation pattern variations in the region of the main-lobe and the first few side-lobes.

The performance of a cylindrical reflector antenna of approximately parabolic profile is investigated. The theoretical simulations implement both rigorous method of regularization and physical optics approaches. The complex-point source concept is used to simulate the tapered illumination. The ideal parabolic profile is approximated by a set of 27V straight line segments. A long electric dipole may be moveable from focal line to allow us to examine the impact of focal shifts on the overall performance of the reflector antennas. The methods may be applied to various geometrical and electrical parameters for reflector antennas (D//spl lambda/ /spl les/500, p = F/D /spl ges/ 0.1) but they have been mainly used to perform analysis of the giant cylindrical reflector antenna (Molonglo Observatory Synthesis Telescope, MOST) of the University of Sydney, which is located in Australia near Canberra. It was shown that the design of this antenna is potentially capable of increasing its operating frequency from the present 843 MHz to 2 GHz, without significant loss in forward gain or distortion of the radiation pattern.

The antenna is a critical component of the communication system. The antenna is used in wireless communication for signal transmission and reception over long distances. There are numerous sorts of antennas, such as wire antennas, traveling wave antennas, reflector antennas, microstrip antennas, and so on. The application of antennas is determined by the antenna's attributes as well as the frequency range of operation. As a result, it is vital to understand the behavior of antennas over a wide range of operations and select the optimum antenna for the application. The performance parameters of the antenna determines its efficiency. VSWR, Return Loss, Directivity, Bandwidth, and more parameters are available. As a result, one of the primary areas of focus is antenna analysis. In this study, we simulate various antenna types and derive performance parameters such as return loss, directivity, and so on. MATLAB will be used to simulate the antenna at various frequencies. When all of the parameters are taken into account, the analysis becomes quite tough. In this case of ambiguity, we use fuzzy logic to calculate the antenna's performance index. A variety of antenna parameters will be fed into the fuzzy inference system, which will make a judgment based on a set of rules. The crisp numbers are turned into fuzzy values using the fuzzification process, then evaluated and defuzzied to obtain the antenna's performance index. The fuzzy inference system will be developed in MATLAB, and the overall system will be modeled in Simulink.

Due to the continuous enhancement of pointing accuracy, detection range, and other performance metrics, reflector antennas are evolving toward high-frequency bands, increased gain, and overall improved performance. In this context, the influence of structural uncertainties, such as antenna feed and main reflector accuracy, on performance has become notably prominent. The inherent interdependence between structure and electromagnetic properties accentuates the impact of structural and electromagnetic uncertainties on electrical properties like gain and pointing of reflector antennas. Addressing the challenge of analyzing the impact of uncertainty on antenna performance and ensuring optimal functionality, this paper derives the phase interval resulting from feed position deviations in the aperture plane. Additionally, it investigates the influence of feed direction uncertainty on the amplitude of the aperture plane and provides an expression for the pattern under main reflector shape uncertainty. Building upon these analyses, an electromechanical coupling model for the structural uncertainty of the reflector antenna is established, unveiling the influence mechanism of key structural uncertainty factors on electrical performance. To illustrate these concepts, a calculation example is presented using the 110 m antenna design model from Qitai. The discussion delves into the profound impact mechanisms of feed and main reflector uncertainties on antenna gain, side lobes, pointing, and other performance aspects.

To research the deformation of the net surface of the mesh antennas under the gravity, a calculating model of a large hoop truss mesh antenna was studied using the whole coordinates interaction method (WCIM). The influence of the gravity and the initial tensions in the networks on the surface accuracy of the mesh antennas was discussed. To calculate the surface shape in the agravic environment, a cup-up and cup down procedure was developed. The influence of the gravity on the surface accuracy decrease when the initial tensions in the networks increase. When the angle between the antenna and the horizontal plane (AAHP) varies, the nodes of the net surface fluctuate in the certain ranges respectively in the local coordinates fixed on the antennas. The conclusions are useful for the adjustment for the net surface accuracy on the ground.