Impact of the Coordinate System s Orientation

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1 April 25th 2016 Impact of the Coordinate System s Orientation Susanne Kürschner, KATHREIN-Werke KG Rosenheim

2 Impact of the Coordinate System s Orientation Overview Simulation Settings Results Conclusion 2

3 1. Overview 3

Overview In most mobile telephone applications, the base station antennas are dual polarised The two polarisations are not orientated horizontally and vertically, but in a 45 angle (+45 and -45 ) Due

4 Overview In most mobile telephone applications, the base station antennas are dual polarised The two polarisations are not orientated horizontally and vertically, but in a 45 angle (+45 and -45 ) Due to the common three sector deployment of the base stations, the main beam of the arrays should be broad in the horizontal direction and relatively small in the vertical direction Vertical cut through the main beam of a mobile telephone base station antenna (orange) with outlines of buildings on the ground (black) Top view of the horizontal cuts in three sector deployment of base station antennas 4

Overview This is usually achieved by arranging the dipoles in a line to focus the main beam vertically and using the geometry of the reflector to produce the desired horizontal beam width For the

5 Overview This is usually achieved by arranging the dipoles in a line to focus the main beam vertically and using the geometry of the reflector to produce the desired horizontal beam width For the simulation this leads to a model in which the polarisations (and therefore the feeds of the radiating elements) are oriented in a 45 angle to the radiating structures and their reflectors feeding structure of the dipole 5

the coordinate system, boundary approximation, mesh type and CST Studio version As reference the structure was also

6 Overview It s not obvious which orientation the model should have in the coordinate system to obtain accurate results for both S-Parameters and farfields To test this, a number of simulations have been made with various settings for the coordinate system, boundary approximation, mesh type and CST Studio version As reference the structure was also simulated using the Frequency Domain Solver and a Tetrahedral Mesh, thus obviating the influence of the coordinate system 6

7 Overview 7

8 2. Simulation Settings 8

9 Simulation Settings The analysed structure is a simplified model of a commonly used dipole for frequency bands between 1.71 GHz and 2.69 GHz The dipole s head is quadratic with an edge length of 51 mm, it s height is 37 mm It is fed via two crossed inner conductors The red material is a dielectric with an ε r of 3.4 All metallic components are defined as PEC 9

10 Simulation Settings Frequency The simulation frequency was set to 1.6 GHz to 2.8 GHz, with 1.71 GHz to 2.69 GHz being the operation band of the dipole Farfield monitors were set from 1.7 GHz to 2.7 GHz in 100 MHz steps Template Based Post Processing To evaluate the farfields, post processing templates were used The evaluated farfield parameters (as defined by NGMN Alliance) are Directivity Horizontal Half Power Beam Width H HPBW Horizontal 10 db Beam Width H 10 db BW Cross Polar Ratio (in boresight) CPR 10

11 Simulation Settings Time Domain Solver (Transient) In the transient time domain solver environment two types of mesh were used: The Hexahedral (Legacy) Mesh, which was the standard mesh until CST Microwave Studio Version 2013, creates a mesh based on fixpoints of the structure The Hexahedral Mesh, which was introduced in CST Microwave Studio Version 2014, creates a mesh based on edges of the structure The settings for both types were chosen in a manner so that the resulting number of mesh cells were similar (450,000 to 500,000) For hexahedral mesh types there are also various types of boundary approximations, which define how mesh cells with more than one material are treated For complex structures the FPBA (Fast Perfect Boundary Approximation), either with the enhanced accuracy or not, is advisable, so both were used 11

12 Simulation Settings Hexahedral Mesh Hexahedral Mesh (Legacy) Standard Coordinates Rotated Coordinates Standard Coordinates Rotated Coordinates The new Hexahedral Mesh has more evenly spread mesh lines The Legacy Mesh generates a much more refined mesh for the feeding structure of the dipole 12

13 3. Results 13

14 Results Frequency Domain Solver The results for the frequency solver are nearly the same for CST Studio Versions 2015 and 2016, both for the S-Parameters as well as the farfield results 14

15 Results Time Domain Solver (Transient) Very little differences in the evaluated farfield results for all simulation setups between CST Versions 2015 und 2016 FPBA boundary approximation: For both mesh types the results with a rotated coordinate system are slightly more accurate EFPBA boundary approximation: The results for the Hexahedral Legacy Mesh are similar for both coordinate systems The new Hexahedral Mesh is more accurate for the high frequencies if the coordinate system is rotated In general the results generated with the Hexahedral Legacy Mesh are more similar to those generated with the Tetrahedral Mesh, at least in this example This is probably due to the fact that while the structure is complex, it has no crucial curved edges (which is the main advantage of the new Hexahedral Legacy Mesh) 15

16 Rotated Coordinates Standard Coordinates Results Time Domain Solver (Transient) 2015 / Hex Legacy / FPBA 2016 / Hex Legacy / EFPBA 2015 / Hex / FPBA 2016 / Hex / EFPBA 16

17 4. Conclusion 17

18 Conclusion In a time domain solver environment, the influence of four basic settings have been analysed: The Mesh Type should be chosen according to the structure, in this example the Legacy Mesh yields better results. However this might not be true if the basic components are not straight The Coordinate System had no definite positive or negative impact on the simulation results* The Boundary Approximation was an important factor in all simulations, the enhanced accuracy mode improved the results significantly The difference between the CST Studio Versions is nearly negligible *For a whole array of antennas, the rotated coordinate system is not advisable anyway since it generates a great number of mesh cells in the corners of the bounding box. 18

Sources Recommendation on Base Station Antenna Standards (by NGMN Alliance): http://www.

19 Sources Recommendation on Base Station Antenna Standards (by NGMN Alliance): Thank you for your attention! 19

Antenna Simulation Overview

Antenna Simulation Overview Marc Rütschlin, Senior Application Engineer 2011 CST European UGM 18-19 May 2011 1 Antenna Choice Analysis Optimisation Environment Antenna Design Flow 2011 CST European UGM