On the Determination of the Impulse Response of Ultra-Wideband Antennas

On the determination of the impulse response ofOn the determination of the impulse response ofUltra-wideband antennas

S. Sczyslo, G. Armbrecht, H. Thye, S. Dortmund and T. Kaisery , , y ,

Motivation

Each path of the impulse response between two antennas can be separated:

Knowledge of the directional antenna impulse response (IR) allows for:

Derivation of different antenna parameters, e.g. gain, goup delay

more realistic simulations e.g. in a raytracing environmentmore realistic simulations e.g. in a raytracing environment

design of more efficient receivers

On the determination of the impulse response of Ultra-wideband antennasCST User Group Meeting 2010 S.Sczyslo 2

Motivation

Antenna receive IR relates the incident E-field with the signal at the antenna feeding port by:

Antenna transmt IR relates the signal at the feeding port with the transmitted E-Antenna transmt IR relates the signal at the feeding port with the transmitted E-field by:

Antenna transmit and receive IR relation given by Lorentz reciprocity:

=> Transmit Simulation in CST Microwave Studio can be used to characterize a passive antenna


Motivation

A new method, the GTEM method, is presented using an easy setup to determine the receive IR:

Its final equation is very close to the definition equation of the receive IR:


Outline

Introduction of the cone antenna

Simulation of the antenna IR using CST MWS

Simulation Setupp Deconvolution Presentation of the CST / MATLAB framework Results and ComparisonResults and Comparison

Measurement of the antenna IR using the GTEM Method

Pulse propagation in GTEM Cells Method description Results and Comparison

Conclusion


Outline



Simulation Setupp Presentation of the CST / MATLAB framework Results



Conclusion



UWB cone antenna

mechanically simple to guarantee identical antennas

nearly omnidirectional pattern=> single impulse response to characterize azimuth plane

low cross polarization

compact size (20 mm x 20 mm x 20 mm)


Outline



Simulation Setupp Presentation of the CST / MATLAB framework Results and Comparison



Conclusion


Simulation Setup

Determine antenna transmit IR:• Extract E-field component in farfield condition• Extract excitation signal• Extract excitation signal• Deconvolve both signals

E-field probes (farfield) Broadband Farfield Monitor

• Time consuming to define all probes • Check Farfield/RCS• Check Transient farfields


Deconvolution

Applying a Wiener filter in the FD leads to the following deconvolution(see also [1]) :

λ aims to bound in case of low SNR. Identify signal+noise and noise parts of the energy spectral density

λ can be calculated with the “noise“ part which is limited by ωs:

[1] S. Sczyslo, H. Thye, G. Armbrecht, S. Dortmund, and T. Kaiser, “Determination of the impulse response of uwb antennas using gtem cells,” in Ultra-Wideband, 2009. ICUWB 2009. IEEE International Conference on, Sept 2009 pp 753 758


Sept. 2009, pp. 753–758.

CST -> MATLAB Framework Export Farfield

Framework allows for conversion of Antenna Farfield to MATLAB (time & freq dependent)

Extraction of different parameters in MATLAB e.g. antenna impulse response, Gain Macro in CST includes GUI MATLAB script is guided in command line (GUI in next version) Downloadable soon (May 2010 after evaluation) at:Downloadable soon (May 2010 after evaluation) at:

http://www.ikt.uni-hannover.de/software.html


Results

Plane wave to indicate to Lorentz reciprocity

Perfect matching between all three extraction methods


Outline






Conclusion


Pulse propagation in GTEM cell

absorber

septum resistor network

input port


Simulation of pulse propagation in GTEM cell

1.2

Excitation pulse

0.8

1.0

tude

Excitation pulse Simulated Ey in CS1

CS2CS1

0.4

0.6

aliz

ed a

mpl

it

P1 P2

0.0

0.2

nor

ma

• TEM id d l d 20

0 2 4 6 8-0.2

time [ns]

• TEM waveguide developed 20 years ago• frequently used measurement device in EMC for immunity and emission

measurements


Measurement of pulse propagation in GTEM cell

downtime t defines the time intervall until reflections occur at the measurement position downtime tD defines the time intervall until reflections occur at the measurement position

reflections are related to the rear end of the cell

IR of GTEM cell can be modelled by a weighted dirac impulse response (see also [2]) IR of GTEM cell can be modelled by a weighted dirac impulse response (see also [2])

[2] H. Thye, G. Armbrecht, and M. Koch, “Pulse propagation in gigahertz transverse electromagnetic cells,” in IEEE Transactions on Electromagnetic Compatibility, vol. 51, no. 3, Aug. 2009.


g p y, , , g

GTEM method: System Theory Model of the Setup

As has been shown the impulse response of the GTEM cell can be modeled by a weigthed Dirac impulse within downtime tD

=> applying time gating techniques, the IR can be modeled by:

=>


GTEM method: Tradeoff in antenna placement


GTEM method: Measurement Setup

GTEM 5305 Cone antenna inside the GTEM cellPulse Generator

PicoSecond 4015D

S li O illSampling Oscillocope Agilent Infinium 86100B

Pulse Generator: A = -1.9 V t 22tFWHM = 22ps

Oscilloscope: av_cycle = 1024t scale = 500 ps/divt_scale = 500 ps/div Npoints = 405 pts/div (interpolation)


Results using a cutoff frequency fc = 15GHz

nearly perfect match between CST simulation and measurement withGTEM methodGTEM method

slight oscillations for t > 0.3 ns


Outline






Conclusion


Conclusion

• It was shown how to determine the impulse response of an antenna by simulation and measurementsimulation and measurement

• A new framework taking advantage of CST MWS’s farfield monitor and MATLAB t dwas presented

• GTEM method was presented as an efficient method to measure the antenna impulse response

• a nearly perfect match between both methods could have been achieveda nearly perfect match between both methods could have been achieved


Thank you for your attentionThank you for your attention


On the Determination of the Impulse Response of Ultra-Wideband Antennas

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