1、 Report ITU-R SA.2166(09/2009)Examples of radiation patterns of large antennas used for space researchand radio astronomySA SeriesSpace applications and meteorologyii Rep. ITU-R SA.2166 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical
2、use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World
3、and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for
4、the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of
5、 ITU-R Reports (Also available online at http:/www.itu.int/publ/R-REP/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amat
6、eur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management Note: This ITU-R Repo
7、rt was approved in English by the Study Group under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2010 ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rep. ITU-R SA.2166 1 REPORT I
8、TU-R SA.2166 Examples of radiation patterns of large antennas used for space research and radio astronomy (2009) TABLE OF CONTENTS Page 1 Introduction 3 2 Model methodology 3 2.1 Guidelines on selecting physical optics-PTD or geometrical optics-GTD . 4 2.2 Analysis of struts 4 3 Example: Deep space
9、research antenna (DSN 34-m) . 5 3.1 Antenna mechanical parameters . 5 3.2 Model results without struts 6 3.2.1 Far-field and near-field of 34-m antenna at 8.425 GHz (no struts) . 6 3.2.2 Far-field and near-field of 34-m antenna at 32.05 GHz (no struts) . 6 3.2.3 Far-field and near-field of 34-m ante
10、nna at 32.05 GHz with statistical surface distortions (no struts) . 9 3.3 Model results with struts . 9 3.3.1 Far-field and near-field of 34-m antenna at 8.425 GHz with struts . 12 3.3.2 Far-field and near-field of 34-m antenna at 32.05 GHz with struts . 14 4 Example: Radio astronomy antenna (Lovell
11、 Mk 1A) 16 4.1 Antenna mechanical parameters . 16 4.2 Model results 16 4.2.1 Far-field and near-field at 150 MHz 16 4.2.2 Far-field at 5 000 MHz, with and without struts 17 4.2.3 Far-field at 5 000 MHz, with and without surface distortions . 18 4.2.4 Far-field and near-field at 5 000 MHz, without st
12、ruts . 18 4.2.5 Comparison of measured pattern with model prediction . 19 5 Conclusions 21 2 Rep. ITU-R SA.2166 FIGURES Page FIGURE 1 34-m antenna radiation pattern at 8.425 GHz with no surface distortion (no struts) 7 FIGURE 2 34-m antenna radiation pattern at 32.05 GHz with no surface distortion (
13、no struts) 8 FIGURE 3 34-m antenna radiation pattern at 32.05 GHz with 0.25-mm (r.m.s.) surface distortion (no struts) . 10 FIGURE 4 34-m antenna radiation pattern at 32.05 GHz with 1-mm (r.m.s.) surface distortion (no struts) . 11 FIGURE 5 34-m antenna radiation pattern at 8.425 GHz with no surface
14、 distortions (with struts) (0 cut) 12 FIGURE 6 34-m antenna radiation pattern at 8.425 GHz with no surface distortions (with struts) (45 cut) 13 FIGURE 7 34-m antenna radiation pattern at 32.05 GHz with no surface distortions (with struts) (0 cut) 14 FIGURE 8 34-m antenna radiation pattern at 32.05
15、GHz with no surface distortions (with struts) (45 cut) 15 FIGURE 9 Far- and near-field of Mk 1A at 150 MHz (no struts) 17 FIGURE 10 Far-field of Mk 1A at 5 000 MHz with and without struts. 17 FIGURE 11 Far-field at 5 000 MHz with and without surface distortion 18 FIGURE 12 Far- and near-field of Mk
16、1A at 5 000 MHz (no struts) . 19 FIGURE 13 Predicted and measured far-field of Mk 1A at 1 420 MHz 20 TABLES TABLE 1 Parameters of 34-m BWG JPL/NASA DSN antenna 5 TABLE 2 Far-field distances for the 34-m BWG JPL/NASA DSN antenna . 6 TABLE 3 Parameters of Mk 1A radio astronomy telescope 16 Rep. ITU-R
17、SA.2166 3 1 Introduction The methodology and guidelines introduced in 2 have been used to model the radiation patterns for large antennas used in deep space research and radio astronomy. These methods are described in detail in Recommendation ITU-R SA.1345 Methods for predicting radiation patterns o
18、f large antennas used for space research and radio astronomy. In predicting the radiation pattern of the NASAs deep space network (DSN) antenna, the latest version of a commercially available software package (GRASP9) has been used. For the radiation pattern of the radio astronomy antenna, an old ve
19、rsion (GRASPC) of the same software has been used. The results illustrate the effect of various parameters on the models predictions and the significance of various mechanical and design features. 2 Model methodology The GRASP9/GRASPC is based on well-established analysis techniques of physical opti
20、cs (PO), supplemented with physical theory of diffraction (PTD), geometrical optics (GO), and uniform geometrical theory of diffraction (GTD). Geometrical optics and GTD are ray-based analysis methods which can only be applied to one single reflector at a time to limit the complexity of the associat
21、ed ray-tracing problem. Physical optics and PTD can be applied to any number of reflector analyses in arbitrary order, where the induced currents obtained by a physical optics analysis on one reflector can be used as a source illuminating a second reflector. For the physical optics calculations, the
22、 surface of the reflector is divided into a grid of surface elements. The radiated field is found by integration of the surface currents at each point on the grid. To simulate the effect of aperture blockage, the surface currents are set to zero in the shadow of the feed on the reflector surface. Th
23、e GTD approach follows three steps: Step 1: selection of significant rays; Step 2: ray tracing; Step 3: field calculation. A simple caustic correction procedure is applied which smoothes the diffracted field for angles close to the caustic direction. It cannot, however, accurately predict the field
24、close to the caustic in the boresight direction. The GTD method, in general, requires less computation time than the physical optics approach. Therefore, GTD is used for all angles except where GTD is inaccurate. Due to the caustic on boresight, the physical optics method is used for angles in this
25、sector. The scattering effects from supporting struts are determined by means of physical optics. For thick struts the conventional physical optics approach is used, and for thin struts a special technique is developed which makes it possible to calculate the surface currents on both the illuminated
26、 and the shadow side of the strut. Two important effects from struts are typical for reflector antennas: 1 they may block the field from the main reflector travelling towards the far field; 2 they may shadow the field from the feed illuminating the reflector. Both of these effects may be calculated
27、in GRASP9. Random surface distortions can be imposed on the surface of the main reflector. The distortions are correlated over a distance consistent with the size of the individual panels of the reflector surface. 4 Rep. ITU-R SA.2166 2.1 Guidelines on selecting physical optics-PTD or geometrical op
28、tics-GTD Physical optics-PTD and geometrical optics-GTD can be used as alternative analysis methods, except for the main-beam direction of a focusing aperture where GTD fails. The analysis method applied to a particular problem depends on many factors. Typically, physical optics should be used in th
29、e following cases: 1 the field is calculated at or near a caustic of the reflected field, i.e. in the focusing region of a reflector; 2 the reflector is in the near field of the feed, (in contrast, GTD always assumes far-field conditions); 3 the antenna is a dual-reflector system with low cross-pola
30、rization requirement, since physical optics is more accurate in predicting the cross-polarization due to the sub-reflector curvature; 4 the reflector is shaped, (in this case the GTD algorithm may not find all diffraction points and there may be more reflection points for one field point); 5 the ref
31、lector has an irregular edge, (in this case the GTD ray tracing algorithm may fail in finding all diffraction points, just as the inclusion of a corner-diffracted field may be necessary to obtain satisfactory accuracy, an option which is not included in GRASP9). On the other hand, GTD may be more ap
32、propriate for the following cases: 1 the antenna has a single electrically large reflector, and the radiation pattern is calculated for a wide range of angles, since the physical optics analysis may take substantially longer than the GTD analysis, especially for higher frequencies (larger antenna si
33、ze in terms of wavelength). This is due to the fact that many more field point calculations are necessary to sample the far-field sufficiently and accurately, and each field point calculation would require substantially higher number of current integration points. A GTD analysis does not suffer from
34、 the second factor since it is almost independent of the antenna size; 2 the near-field pattern needs to be calculated quickly, and where it can provide insight into a particular scattering problem if the edge-diffracted and reflected ray fields are observed independently. 2.2 Analysis of struts In
35、single and dual reflector antennas, struts are used to support the feed system and sub-reflector in rotationally symmetric or near-symmetric systems. These struts may have a serious impact on the antenna performance. The efficiency and cross-polarization are degraded and the side-lobe level is incre
36、ased. The three most important mechanisms by which the strut scattering influences the antenna radiation are: 1 shadowing and changes of the main reflector currents caused by direct feed illumination of the struts; 2 shadowing and changes of the main reflector field by the struts and consequent refl
37、ector field blockage effects; 3 reflected field from the main reflector by the scattered field from the struts, which originated from the incident field on the strut from the main reflector. The degradation of the peak gain (efficiency) is mainly due to the effects (1) and (2) of which (1) is only i
38、mportant in a system where the struts are not supported by the outer edge of the main reflector. The side-lobes will mainly be affected by the strut scattering (2) and (3) where (3) is rarely significant and occurs in very special cases. Rep. ITU-R SA.2166 5 For circular struts, two types of analyse
39、s can be used depending on the size of the struts: 1 a simple physical optics approach, which is especially useful for struts which are thick relative to the wavelength; 2 a canonical solution for struts with diameters in the order of the wavelength. An accurate prediction of the effects of the stru
40、ts both on the main lobe and on the side-lobes can be achieved by taking the current distribution along the circumference of the strut into account. This is relatively simple for a circular strut, because the canonical problem (plane wave incidence on an infinite circular cylinder) has a simple solu
41、tion in series form. For thick struts the current distribution can alternatively be found by the simple physical optics approximation. To include the precise effect of the struts in the radiation pattern requires elaborate and time consuming computation. 3 Example: Deep space research antenna (DSN 3
42、4-m) 3.1 Antenna mechanical parameters The major parameters of the 34-m beam-waveguide (BWG) antenna of the DSN, are given in Table 1. TABLE 1 Parameters of 34-m BWG JPL/NASA DSN antenna 34-m BWG antenna Main reflector diameter 34 m, circular aperture, shaped Subreflector diameter 3.429 m, shaped Fo
43、cal length 11.8 m, primary focus Frequency range 8.400-8.450 GHz (rcv) 7.145-7.190 GHz (tmt) 25.5-27 GHz (rcv) 31.8-32.3 GHz (rcv) 34.2-34.7 GHz (tmt) Feed gain pattern Pattern equivalent to a 31 dB gain horn Surface distortions 0.25 mm (r.m.s.) Surface distortion correlation distance 1-2 m A number
44、 of these antennas are located in several places around the world; specifically, in Goldstone, California; near Madrid, Spain; and near Canberra, Australia. The far-field distances defined for these antennas at various frequencies of operation are given in Table 2. 6 Rep. ITU-R SA.2166 TABLE 2 Far-f
45、ield distances for the 34-m BWG JPL/NASA DSN antenna Mode Frequency (GHz) Wavelength(mm) 34-m antenna Mid (km) Far (km) Tmt 2.115 141.75 0.106 16 Rcv 2.295 130.63 0.109 18 Tmt 7.1675 41.83 0.159 55 Rcv 8.425 35.58 0.167 65 Tmt 34.45 8.70 0.268 266 Rcv 32.05 9.35 0.261 247 3.2 Model results without s
46、truts The 34-m beam-waveguide antenna was modelled at both 8.425 GHz and 32.05 GHz receive frequencies in the far-field and near-field without struts. The effects of varying the observation distance within the near-field were examined as well as the effects of surface distortions. All the results ar
47、e for the antenna assumed to be transmitting with linear polarization. All patterns are for 0 azimuth plane cut with antenna pointing in 90 elevation direction. The effects of gravity, wind, etc. are ignored. 3.2.1 Far-field and near-field of 34-m antenna at 8.425 GHz (no struts) Figures 1a) and 1b)
48、 show the gain pattern at 8.425 GHz with no surface errors and no struts in both linear and logarithmic scales. The physical optics-PTD method was used from 0 to 0.1 (less than 2 beamwidths). The GTD-PO (GTD on subreflector, physical optics from main) was used from 0.1 to 4. Then, geometrical optics
49、-GTD method was used at all other angles. The three curves in the figures show the changing gain pattern as the observation point moves from far-field to successively shorter near-field distances. It should be noted that, the curve spike at around 10 is due to the feed to subreflector edge diffraction, while the spike at around 100-110 is due to the subreflector to the main reflector edge diffraction in back field region. 3.2.2 Far-field and near-field of 34-m antenna at 32.05 GHz (no struts) Figures 2a) and 2b) show the g
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