WIPL-D Model and Simulation Results for a
46cm Diameter Impulse Radiating Antenna (IRA)
Mary Cannella Taylor* and Tapan K. Sarkar
Computational Electromagnetics (CEM) Lab, Syracuse University
Syracuse, New York, 13244-1240, USA
cannella@syr.edu; tksarkara-syr.edu
WIPL-D was used to model and simulate an Impulse Radiating Antenna (IRA) with a
46cm diameter paraboloidal reflector and 45 degree feed arms. Model views are shown
and the results of frequency domain simulation up to 20GHz are shown to agree with
results from published measurements. Beam pattems at three frequencies show the highly
directional behavior of this antenna. The simulated frequency domain data is inverse
Fourier transformed to obtain the time domain response to a Gaussian pulse input. This
response is integrated to obtain the response to a step input, which compares well with
the theorized step input response of the IRA.
Introduction
The Impulse Radiating Antenna (IRA) was first theorized by Carl Baum in 1989 [1].
Since that time, additional papers have filled out the knowledge of the IRA [2-5] and
several versions of the IRA have been built and tested by Everett Farr and others with the
goal of optimizing the structure [6-9]. The objective of this document is to show the
model and simulation results both in the time and frequency domain of the electrical
characteristics of the antenna using the electromagnetic analysis code WIPL-D [11].
Since this code uses entire domain basis functions over large subsectional patches it is
possible to analyze electrically large structures and configurations on a desktop pc using
modest computational resources. In this paper, we introduce a WIPL-D model which is
based on design information provided by E. Farr for an IRA-2 [9], which has 30 degree
feed arms. However, instead we built the model with the basic 45 degree feed arms from
the IRA-1 [6]. We show the frequency domain results of the simulation along with
simulated beam pattems at three frequencies. The frequency domain data are transformed
to time domain and the transient response is also shown. The modeled results are
compared to published IRA measurements [6].
WIPL-D Model of 46cm Diameter Impulse Radiating Antenna (IRA)
The IRA structure modeled consists of a 46cm diameter paraboloidal reflector and four
feed arms with 45 degree spacing. Figure 1 shows the front and side views of the IRA
modeled in WIPL-D. The segmentation for the paraboloidal reflector is set by a
parameter n = 16 which defines 16 segments per quarter circumference of the reflector.
The plates which make up the feed arms are automatically discretized by WIPL-D into
appropriate meshing for a maximum firequency of 20GHz.
0-7803-8883-6/05/$20.00 ©2005 IEEE
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Fig. 1. Front view showing quarter symmetry and side view with feed arm discretization.
WIPL-D Simulation Results
The frequency domain results of the WIPL-D simulation are shown in Figs. 2, 3 and 4a.
The Fig. 2 shows the far-field radiation, EB vs. frequency and Fig. 3 overlays the beam
pattern at I GHz, I OGHz and 20GHz, showing the high directivity of the IRA. Figure 4
compares the simulated vs. measured results. Fig. 4a shows the dB gain vs. frequency
from WIPL-D which agrees well to the general shape and peak gain found in the
measurements documented by Bowen et al [6, Fig. 3.5] for the IRA-I with 300 feed arms
and the IRA-2 with 450 feed arms, shown in Fig. 4b.
1 IRAPAG E
sbs(66)M
15 -
_1ta 14-,J
1612
f[Rnidol0
-1IR
_ 2 IPAG
23 8
i
<~~~~~~~~~~~~~~~~~~~~~~~~~, 2IRAH
I
187
OGH
J
X20GH2
10
0
2
1
5
A
12
IA
5
a
2
5 .5
Fig. 2. Far-Field Radiation vs. Frequency.
554
O0
16 5 2
Fig. 3. Beam Pattern at three frequencies.
Er G.n [,B]
Rq0
^ 2 eRXq2OG
I 461
,
3
E"ftdwr G*u onB-ai,q
_
611
I R-A
-
~~~~~~~~~~~~~~~~~~~~~~~~~~---- c166s0I
n
20
,
Peak Gain 29.3 dB at 17.7 GHz
-30
Gain
fO
0
2
4
6
d
10
12
14
16
20
16
GH
10
20
2
4
6
8
12
10
Fleq-ry GH4
14
16
16
0
Fig. 4. a) WIPL-D dB Gain vs. Frequency, b) Published Measurements [6, Fig. 3.5]
Time Domain Response
The time domain response is obtained from the radiation field calculated in WIPL-D. The
frequency domain data is weighted by a Gaussian window of approximnately 16GHz
bandwidth and the results are inverse Fourier transformed to generate the time domain
response. Table I summarizes the paraicters used in the analysis.
Parameter
Af
N
ts
At
To
Description
Value
20 MHz
2 = 2048
40.96 GHz
24 psec
set by simulation
select
calc: f,= NAf
cale: At = 1/ f,
calc: To = 1/Af
frequency resolution
sequence period
sampling frequency
sampling interval
record length
50 nsec
TABLE 1: List of signal processing parameters
Figure 5a shows the time domain response of the IRA to a Gaussian input pulse. The IRA
acts as a differentiator on transmit and will differentiate the input impulse, producing a
pulse doublet in the far field.
MD IRA46cm: TIm, domain response,T.025ns
(16GHz),%t6ns
o1011 TD IRA46cm: Timedomainresponseintegrated
1.5
.0.5 .---
.1~~~~~~~~-----
-1
4
s
7
.me Isecondsl
8
9
4
6
x 10Sm.
6
7
[second]
8
x 10
9
Fig. 5. a) Time Domain Response to Gaussian Pulse Input, b) Response to Step Input
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The designed operation of the IRA is to produce an impulse in the far field. This is
achieved with a step input to the transmitter, which the IRA differentiates on transmit. To
generate the response of the IRA to a step input, we recognize that the desired step input
is the integral of the pulse, and therefore take the integral of the simulated far-field
radiation response due to the pulse input. This results in the far-field transient response
due to a step input and is shown in Fig. Sb. The shape of this plot agrees with the
theoretical shape of the IRA transmit pulse [3,4]. The pre-pulse extends from
approximately 4.3ns to 5.Sns, which corresponds to the time 2F/c = 1.22nsec, or the time
for the excitation to travel from the source at the focal point F to the reflector and back to
the circular aperture of the paraboloidal reflector, from which it radiates as a plane wave.
Conclusions
In this paper, we have presented a model and simulation of an IRA using the
electromagnetic analysis code WIPL-D. The frequency domain results from WIPL-D
have been shown along with the antenna pattern at three frequencies. The WIPL-D data
have been transformed to time domain using a Gaussian window and inverse Fourier
transform, and the resulting plot shows the transient response due to a Gaussian pulse as
the input. Integration of this result gives the transient response due to a step input, which
is the radiated impulse for which the antenna was designed. Future work includes using
the IRA in scattering scenes with other antennas and various configurations of targets and
ground planes.
References
[1] C. E. Baum, "Radiation of Impulse-Like Transient Fields", Sensor and Simulation
Note 321, November 1989.
[2] C. E. Baum, E. G. Farr and D. V. Giri, "Review of Impulse-Radiating Antennas",
Chapter 12 in Review ofRadio Science 1996-1999, W. S. Stone, ed., Oxford
University Press, 1999.
[3] K. Kim and W. R. Scott, Jr., "Numerical Analysis of the Impulse-Radiating
Antenna", Sensor and Simulation Note 474, June 2003.
[4] D. V. Giri and Carl Baum, "Reflector IRA Design and Boresight Temporal
Waveforms", Sensor and Simulation Note 365, February 1994.
[5] L. H. Bowen, E. G. Farr, C. E. Baum, T. C. Tran, "Optimization of Impulse
Radiating Antennas", in Mokole et al (eds.), pp. 281-290 in Ultra-Wideband, ShortPulse Electromagnetics 6, New York, Plenum, 2003.
[6] L. H. Bowen, E. G. Farr, C. E. Baum, T. C. Tran and W. D. Prather, "Results of
Optimization Experiments on a Solid Reflector IRA", Sensor and Simulation Note
463, January 2002.
[7] E. Farr, "Experimental Validation of IRA Models", Sensor and Simulation Note
364, January 1994.
[8] E. Farr, "Analysis of the Impulse Radiating Antenna", Sensor and Simulation Note
329, July 1991.
[9] E. Farr, "IRA-2 Dimensions", Farr Research, Inc. document dated March 15, 2000.
[10] M. C. Taylor and T. K. Sarkar, "An Electromagnetic Analysis of the 46cm
Diameter Impulse Radiating Antenna (IRA)", Syracuse University CEM Lab Report
submitted to AFRL, October 1, 2004.
[11] B. M. Kolundzija, J. S. Ognjanovic and T. K. Sarkar, "VVIPL-D (for Windows
manual)", Artech House, Norwood, Mass. 2000 (http://wipl-d.com).
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