Advanced Modelling and Measurement of Wideband Horn Antennas
Dual-ridge horn antennas are commonly used as wideband gain standards for antenna measurements. The example shown in figure 1 is designed by SATIMO. The horn is connectorized and essentially an open, flared ridge waveguide with lateral bars. It is designed to harmonize the gain with the frequency curve. At low frequencies the bars appear as a closed surface and increase the boresight gain of the horn, whereas at high frequencies the bars are electrically transparent and the effective gain decreases. Carefully designed dual ridge horns have excellent return loss, cross polar and flat gain response (typically 7-15 dBi) in a 1:15 frequency range.
Figure 1: Satimo dual ridge horn.
The antenna is modelled and simulated in CST MICROWAVE STUDIO® (CST MWS) using magnetic symmetry condition in the E-plane of the antenna and a rather coarse regular mesh with λ/10 spacing.
The used connectors are approximated with simple structures, and dielectric materials are ignored. For the calculations, perfectly conducting material is assumed for the metallic parts, and PML (Perfect Matching Layer) absorbing boundary conditions are used. The required CPU time for a full analysis is approximately four hours on a Pentium 4, 3 GHz PC.
The dual ridge horn was measured in the Satimo Stargate 64 spherical near field facility in Atlanta, USA as shown in Figure 2 over a frequency range of 800 MHz to 6 GHz.
Figure 2: Wide band horn measurement in the SATIMO spherical near field antenna test range in Atlanta, USA.
The simulated and measured antenna return loss performance for both amplitude and phase components at the antenna reference port is in very good agreement as shown in Figure 3.
Figure 3: Simulated with CST MWS (red) and measured (green) return loss as a function of frequency.
The results of simulated and measured boresight directivity are plotted in Figure 4. A excellent correlation between the two curves can be observed, and the differences fall within the measurement accuracy of the measurement equipment.
Figure 4: Simulated with CST MWS (red) and measured (green) boresight directivity.
Figure 5 shows the comparison of simulated and measured E and H plane radiation patterns at 3.6 GHz. The polarisation definition is Ludwig III. It can be seen that the two curves are very close to each other. The performance CST MWS' Time Domain solver is excellent due to its ability to extract the farfield gain at a large number of frequencies from a single simulation run as opposed to having to carry out a large number of individual simulations at discrete frequencies in the Frequency Domain. The required monitors, 100 in this case, can be defined easily using a dedicate standard macro.
Figure 5: Simulated (red) and measured (green) E and H plane patterns @ 3.6 GHz.
The antenna's back radiated fields are often very difficult to determine with high accuracy due to coupling between the antenna under test and the antenna positioner. The SATIMO Stargate spherical near field system uses a Styrofoam positioner specifically designed for minimum interference with the antenna under test. The excellent agreement between the predicted and measured results for the radiated back lobe of the antenna (Figure 5) confirms the measurement accuracy in this difficult region.
The achieved correlation between the simulated and measured results confirms once again the validity of the numerical modelling of CST MICROWAVE STUDIO®. The ability to extract a high resolution of broadband gain data is a result of the Time Domain Solver ability to define and calculate a large number of farfield monitors in one single simulation run. This rerpesents a significant performance advantage compared to non-Time Domain methods which entail the simulation of a large number of discrete frequencies for the broadband gain extraction.
References:
Lars Foged, A. Giacomini, L. Duchesne, E. Leroux, L. Sassi, J. Mollet; Advanced Modelling And Measurement Of Wideband Horn Antenna; Proceedings of the "11th Internationnal Symposium on Antenna Technology and Apply Electromagnetics (ANTEM 2005)", http://antem2005.ietr.org
CST Article "Advanced Modelling and Measurement of Wideband Horn Antennas"
last modified 12. Dec 2006 11:15
printed 4. Feb 2012 10:36, Article ID 262
URL:
All rights reserved.
Without prior written permission of CST, no part of this publication may be
reproduced by any method, be stored or transferred into an electronic data processing system, neither mechanical or by any other method.
Article ID: 262
Last modified: 12. Dec 2006 11:15
Other Articles
The aim of this article is to emphasize the application of a statistical approach to the analysis of the shielding properties of a real enclosure for radio communication equipment. A model of the enclosure was simulated with the CST MICROWAVE STUDIO® (CST MWS) Transient solver. Excellent agreement between simulation and measured was obtained.
Read full article..
Stefan Prorok, Hamburg University of Technology
We present an overview of our current research activities in silicon photonics and thermal barrier coatings. Doing so, we will comment on how CST Microwave Studio can be used to design strip waveguides, micro ring resonators, as well as 2-D and 3-D photonic crystal structures. Particularly we will concentrate on the discussion of photonic crystal micro cavities which can be used as electro-optic modulators. It will be shown that MWS provides all the functionality to optimize and characterize optical micro cavities. The appearance of resonant modes is adjusted through eigenmode calculation of the photonic crystal waveguide modes. Time domain simulation with discrete port excitation is applied to calculate the intrinsic Q-factor of the cavity. Waveguide ports are used to model experimental conditions of excitation with strip waveguide modes. Field monitors help to understand the mechanism of energy loss from the cavity. The simulation results are compared to measurements on fabricated structures. As possible application we will show a hybrid silicon organic hetero structure cavity for GHz electro-optic modulation.
Read full article..
The article describes the RCS and farfield simulation of a large airplane at a frequency of 4GHz. The simulation is performed with the new Integral Equation solver of CST MICROWAVE STUDIO®. The length and width of the airplane is about 27 meters, and the total height is about 8 meters. The excitation is done by a plane wave from the front. In total, the calculation for the airplane is approximately 350 wavelengths in size. We perform a monostatic RCS calculation and we show the farfield and surface current distributions for the airplane.
Read full article..
This article examines the modelling of lightning strikes using CST MICROWAVE STUDIO® (CST MWS). The surface current distribution due to a double-exponential form lightning strike on the nose of an airplane is calculated by way of example.
Read full article..
CST MICROWAVE STUDIO® (CST MWS) was used to aid in the computational investigation of the transverse B1-field homogeneity and SAR values in a 11.7 T / 500 MHz 4-port driven RF head coil loaded with a high-resolution human model (HUGO based on the Visible Human Project®).
The simulations show the expected enhancement of the B-field in the centre of the head compared with the unloaded case and no significant changes in the maximum 1g SAR values between 2-port linear and circular polarizations.
This work was carried out by CEA Saclay, France and is summarised in this article with the permssion and courtesy of Xavier Hanus and his colleagues.
Read full article..