Cst an Antenna Simulation

Antenna Simulation Application Note CST STUDIO SUITE™

Kra, Jeb / v1.0 / 02. July 2012 CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

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Antenna Examples Simulation Setup Post Processing Co/Cross Polarization Phase Center Ludwig 3 Antenna Array Tips & Tricks

Antenna Examples Ready-to-simulate antennas are available here: Online Help -> Examples and Tutorials  CST MWS Examples -> Transient Analysis Examples -> Antennas -> Overview

 CST MWS Examples -> Integral Solver Examples -> Antennas -> Overview

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Construct simple Antenna Examples

Please note: Simulation settings in these macros are optimal for fast simulation runtime. CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Antenna Examples Overview Category

Examples

Typical Applications  Communication  Radar  Radio astronomy

Reflector

 Parabolic dish  Corner reflector

Aperture

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Rectangular horn Circular horn Ridged horn Waveguide array

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Radar Reflector feed Calibration standards Measurement

Wire (Slot)

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Dipole LPDA, Yagi-Uda Helix Printed antennas Discone

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Communication GPS EMC measurement RFID Almost anything else…

Patch

 Rectangular patch  Circular patch  Patch arrays

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Radar Communication GPS Imaging

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Solvers

How to generate Farfield Results I  Define boundaries as open (add space)  Define a farfield monitor at the frequency of interest  Make sure that the antenna radiates at the farfield monitor frequency CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

How to generate Farfield Results II  Define a farfield monitor at several frequencies (macro is available)

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Definition of Farfield Probes Farfield monitors record the radiation in all directions for one frequency. Farfield probes record the radiation in one direction for all frequencies.

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Farfield Definitions Approximation: EAbs (enabled) EAbs (disabled)

E1 E1

2

2

E2 E2

2

2

ER

2

Radiation efficiency: erad

radiated power accepted (input) power

Total efficiency: etotal

radiated power stimulated power

Directivity: D( , )

4

power radiated per unit solid angle radiated power

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Component definition:

Total Radiated Power (TRP) There are three possibilities to calculate the TRP value:  Macros -> Results -> Farfield -> Show Total Radiated Power (TRP) Specify power level in Watt or dBm. Choose linear or logarithmic TRP output (in farfield plot).

 Results -> Combine Results  Template Based Postprocessing (TBP) -> Farfield and Antenna Properties -> Farfield Result -> Evaluation Range: 3D -> Result value: TRP CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Total Isotropic Sensitivity (TIS) TIS handling is very similar to TRP. Specify receiver sensitivity in Watt or dBm. Specify linear or logarithmic TIS output.

 Only one (TIS or TRP) can be displayed at the time.  TIS can also be applied to CST Design Studio full system or multi-port combined results (similar to TRP).

TIS far-field monitors are created. TIS is also displayed in far-field plot. CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

SAR Results 2D or 3D plot including information about the position of the maximum. Opens logfile containing all results. Visualization of max. SAR cube Macros -> Results -> 2D 3D Results -> Plot Averaging Volume for maximum SAR value CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Diversity / MIMO Antennas Multiple antennas (antenna diversity) may overcome problem of fading dips. Antenna 1

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TBP -> Farfield Result -> MIMO Select from: • Diversity Gain • Envelope Correlation Coefficient • Multiplexing Efficiency

Antenna 2

Load farfield of second antenna

„best of“ (diversity gain)

Set XPR and power distribution

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For lossless antennas in isotropic environment the correlation and diversity gain can also be calculated from S-Parameters

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Co- / Cross-Polarization

The co-polarized far field component has the same polarization as the excitation (y-oriented in above case). The cross-polarized far field component is orthogonal to the copolarized component and main lobe direction. In order to use different polarizations for transmitting/receiving, an antenna design goal might be to maximize the co-polarized and minimize the cross-polarized component. CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Co- / Cross-Polarization 1. Select the tab “Axes“. 2. Click “Main lobe alignment“. 3. Choose the “Ludwig 3“ coordinate system. Polarization vector direction (arbitrary user input possible). If “Main lobe ... “ is not selected, the user can enter arbitrary directions for:  polarization plane normal (z‘) (= theta axis),  cross-polarized component (x‘) (= phi axis). CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Phase Center Calculation = y‘z‘ plane = x‘z‘ plane

Finding the best location to place the horn inside a parabolic antenna. The best position is to match the focal point of the dish with the phase center of the horn.

? CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Circular Polarization Left and right polarized field components are calculated from the tangential components: Eleft Eright

1 E1 iE 2 2 1 E1 iE 2 2

There are two different ways to calculate the circular polarization:  Combine Results  Simultaneous excitation (only TD-Solver ) CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Ludwig 3 Ludwig 3 vertical

Ehorizontal E cos Evertical E sin

E sin E cos

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Ludwig 3 horizontal

Antenna Array The total farfield of an antenna array can be calculated in four different ways:    

Complete simulation of the array Array Factor Periodic Cells (TD-Solver , FD-Solver Unit Cells (FD-Solver ) + Array Factor

) + Array Factor

More information can be found in the Online Help. CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Tips & Tricks for an Accurate Farfield Tip 1: Choose sufficient accuracy.

The accuracy level in the TD-Solver should be -40 dB. For larger frequency bands (e.g. 0-3 GHz) or poor radiation it is recommended to use -60 dB so that the E- and H-fields on the bounding box do not suffer from FFT/DFT truncation errors. CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Tips & Tricks for an Accurate Farfield Tip 2: Set appropriate boundary conditions.

The ”open (add space)“ boundary condition ensures λ/8 space at the center frequency. For lower frequencies (bigger λ) increase the bounding box size or adjust the center frequency. CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com

Tips & Tricks for an Accurate Farfield Tip 3: Check the energy balance.

At 4.5 GHz the far field may be inaccurate.

Far field values become inaccurate, if S-parameter balance ≈1 (no power is radiated). In this case directivity and gain are calculated from dividing ≈0/0, which is numerically critical. A good measure for total radiated power is: (1 - balance). CST – COMPUTER SIMULATION TECHNOLOGY | www.cst.com