Well-established procedures are consolidated to determine the associated measurement uncertainty for a given antenna and measurements scenario [1-2]. Similar criteria for establishing uncertainties in numerical modelling of the same antenna are still to be established. In this paper, we investigate the achievable agreement between antenna measurement and simulation when external error sources are minimized. The test object, is a reflector fed by a wideband dual ridge horn (SR40-A and SH4000). The highly stable reference antenna has been selected to minimize uncertainty related to finite manufacturing and material parameter accuracy. Two frequencies, 10.7GHz and 18GHz have been selected for detailed investigation

Calvano, F.

Foged, Lars Jacob

Jorgensen, E.

Saporetti, M. A.

Sierra Castañer, Manuel

Tallini, D.

Voigt, Peter

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid

Measurement and Simulation of Reflector Antenna 
L.J.Foged , M.A. Saporetti , M. Sierra-Castanner , E. Jorgensen , T. Voigt , F. Calvano , D. Tallini 
Abstract— Well-established procedures are consolidated to 
determine the associated measurement uncertainty for a given 
antenna and measurements scenario [1-2]. Similar criteria for 
establishing uncertainties in numerical modelling of the same 
antenna are still to be established. In this paper, we investigate 
the achievable agreement between antenna measurement and 
simulation when external error sources are minimized. The test 
object, is a reflector fed by a wideband dual ridge horn (SR40-A 
and SH4000). The highly stable reference antenna has been 
selected to minimize uncertainty related to finite manufacturing 
and material parameter accuracy. Two frequencies, 10.7GHz 
and 18GHz have been selected for detailed investigation. 
The antenna has been measured in two reference spherical 
near-field measurement facilities as a preparatory activity for a 
Facility Comparison Campaign on this antenna in the frame of a 
EurAAP/WG5 activity. A full CAD model, in step compatible 
format, has been provided and the antenna has been simulated 
using different numerical methods from different software 
vendors [4-7]. Each participant was responsible for generating a 
suitable mesh and the numerical stability of their solution. 
Index Terms—antenna, measurement, simulation, numerical 
methods. 
I. TEST OBJECT 
The SR40-A and SH4000 antenna is shown in Fig. 1. The 
SR40-A is an offset parabolic reflector, precision machined 
from a single block of aluminum. The circular interface with 
precision holes allows the user to center the antenna with very 
high accuracy. The alignment accuracy is determined to within 
±0.01°. The SH4000 wide band Dual Ridge Horn is a highly 
stable reference antenna. The antenna is precision fitted to the 
mounting bracket of the reflector. 
This antenna is selected as test object in a comprehensive 
measurement facility comparison activity as a EurAAP 
Working Group 5, activity. 
II. MEASUREMENT CAMPAIGN 
Comparative measurements based on high accuracy 
reference antennas and involving different antenna 
measurement systems are important instruments in the 
evaluation, benchmarking and calibration of the measurement 
facilities. Regular inter comparisons are also an important 
instrument for traceability and quality maintenance. These 
activities promote and document the measurement confidence 
level among the participants and are an important prerequisite 
for official or unofficial certification of the facilities. 
Different European facility comparison campaigns, have 
been completed during the last years in the framework of 
different European Activities: Antenna Measurement Activity 
of the Antenna Centre of Excellence-VT UE Frame Program; 
COST ASSIST, IC0603 and COST-VISTA, IC1102. 
Activities related to facility comparisons are now included 
in the Antenna Measurement, Working Group 5 Activity of 
EurAAP, where a specific on-going task for Antenna 
Measurement Intercomparison has been approved. 
Fig. 1. Reflector SR 40-A fed by SH4000 Dual Ridge Horn: Antenna during 
measurement (Left); CAD file for simulation (Right). 
A. Test Plan and Participating Facilities 
The measured SR40-A and SH4000 antenna is part of a 
currently ongoing larger measurement facility comparison 
campaign within a EurAAP Working Group 5 activity. Two 
spherical Near Field ranges, Technical University of Madrid 
(UPM), Spain and SATIMO SG 64 (MVG), France, have 
contributed to the reference measurements reported here. The 
measurements data requested for the facility comparison 
campaign are reported in TABLE I. A full list of information 
required from each participating facility, for the post 
processing and the comparison of data, is reported in [3]. 
TABLE I 
Full 
3D 
Gain 
Measu 
rement 
. MEASUREMENT DATA, REFLECTOR S R 40-A FED BY 
SH4000 DUAL RIDGE HORN 
Frequency Range 
Phi 
Theta 
Ports (K type 
female connectors) 
10.7, 12.6, 14.5,18, 19, 20, 28, 29, 
30, 31 ,33, 38 GHz 
From 0° to 135°(45° step) 
From -180° to 180° (1° step) 
Measurement: vertical 
polarization 
B. Determination of Measured Reference Pattern 
The access to measured data from different facilities in 
good agreement between them, increase the confidence level 
of the measured data. 
In [3], different data processing procedures have been 
investigated to derive reference patterns with increased 
confidence level based on measurements in different facilities. 
The reference pattern can be calculated as the simple mean or 
weighted mean of each measured data point where the weights 
are proportional to the estimated uncertainty. The uncertainty 
associated with the mean is “improved” if the measurements 
can be considered truly independent. 
For this activity, considering the availability of three sets of 
measurements data from U P M and M V G facilities, the simple 
mean of the radiation pattern, using amplitude data only, has 
been used to define the reference pattern. 
I I I . SIMULATION CAMPAIGN 
Simulations have been performed at 10.7GHz and 18GHz, 
considering the nominal dimensions of the feed and reflector 
and ignoring finite manufacturing and material parameter 
accuracy. The electrical conductivity of aluminum was 
assumed to 3.56 107 S/m in the simulation of ohmic losses. 
The complete C A D file of the antenna was provided to each of 
the participants involved. Each participant was responsible for 
generating a suitable mesh and the numerical stability of their 
solution. The information collected from simulations is 
reported below: 
• Peak directivity at 10.7 and 18 GHz; 
• Directivity patterns in 4 cuts (Ludwig III[8] Co/Cx 0º, 
45º, 90º & 135º) -180º to 180º in 1º and 0.1º step; 
• Return loss; 
• Ohmic losses; 
• Description of numerical method (with illustration – 
Ex: currents on reflector, grid used etc). 
A. GRASP (TICRA) 
GRASP offers a variety of analysis methods suitable for 
electrically large scattering and radiation problems such as 
reflector antennas and satellite platforms. The method used 
here is a frequency domain higher-order Method of Moments 
surface integral equation solver using curved mesh elements up 
to 2λ by 2λ. The solution is accelerated by a recently 
introduced Multi-level Fast Multipole Method (MLFMM) 
developed particularly for higher-order discretizations [14]. 
The new HO-MLFMM solver has been further enhanced with 
the ability to work with non-connected meshes, which provides 
increased robustness in practical applications. For the present 
problem, the fine details of the feed was modelled with tiny 
patches (0.01 λ) whereas the reflector surface was modelled 
with large patches (2λ). The surface current was then expanded 
in polynomials between 1st and 9th order depending on the 
electrical size of each patch. The MLFMM solver includes an 
efficient preconditioner that enables fast convergence while 
being rather insensitive to the presence of small geometrical 
details or the use of high polynomial orders. For the present 18 
GHz example, a relative solution error of 0.001 was reached 
after 20 iterations. The currents induced on the antenna 
structure, as well as the mesh used in the computations, are 
shown in Fig.2. 
Fig. 2. GRASP currents induced on the antenna and mesh grid @18GHz. 
Reflector SR 40-and SH4000 fed (Left), Close-up of the feed (Right). 
B. HFSS (ANSYS) 
The currents induced on the structure for the present 
problem at 10.7GHz and 18GHz are shown in Fig. 3. 
Fig. 3. HFSS simulated surface current density Js@10.7GHz (Left) and 
18GHz (Right) Reflector SR 40-A with SH4000 Dual Ridge Horn. 
The hybrid FEBI [9] is a powerful new enhancement to 
the FEM [13] solver available in HFSS. This new technique 
gives the design engineer the advantages of an FEM 
simulation with the efficiency and accuracy of an IE solution 
for open boundary problems. This procedure is accurate for 
conformal, concave and/or separate air volumes, allowing 
users to reduce the size of the FEM solution region resulting 
in a significant reduction in the solution time and the amount 
of memory required to solve the problem. 
C. FEKO 
FEKO is a comprehensive electromagnetic software suite 
(now part of Altair’s HyperWorks CAE simulation software 
platform), which includes many frequency and time domain 
solvers to solve a wide set of problems, involving complex 
materials and electrically large objects. FEKO has two sets of 
methods (full-wave methods and asymptotic methods), which 
are also hybridized to take profit from the advantages of both. 
The method used for this problem is FEKO’s MLFMM, which 
was included in FEKO in 2004. Alternatively, and to cross-
validate the results, one could also use for this problem domain 
decomposition: first using MLFMM for the feeder and 
afterwards use such results as source while modelling the 
reflector with Physical Optics (PO). The currents induced on 
the antenna structure and the mesh grid used @ 18GHz are 
shown in Fig. 4. 
Fig. 4. FEKO currents induced on the antenna structure and applied mesh 
@18GHz on the Reflector SR 40-A with SH4000 Dual Ridge Horn. 
Currents (Left); Close-up of the feed (Right). 
D. CST STUDIO SUITE (CST ) 
CST offers several numerical simulation methods which 
are very efficient for reflector design. Given the frequencies 
and the electrical size of the reflector (24 λ x 28 λ @ 18 GHz) , 
all the provided results have been obtained in a single 
simulation run using the Time Domain Solver based on the 
Finite Integration Technique (FIT). Perfect Boundary 
Approximation (PBA) is used for the spatial discretization of 
the structure. The simulated structure and the electromagnetic 
fields are mapped to a hexahedral mesh. PBA allows a very 
good approximation of even curved surfaces within the cubic 
mesh cells. The obtained E-field for the present 
problem@10.7GHz and 18GHz is shown in Fig. 5. 
The results can be cross-checked using a hybrid approach 
in which an equivalent NF source from measurements or 
generated by a time domain simulation of the horn antenna can 
be used as an excitation source. The simulation of the reflector 
can be performed by the Integral Equation solver based on 
MLFMM or the Asymptotic Solver based on the Shooting and 
Bouncing Ray (SBR) method. Farfield results, generated using 
this approach, agree very closely with the full time domain 
simulation pattern. 
Fig. 5. CST Simulated E-field @10.7GHz (Left) and @18GHz (Right). 
Reflector SR 40-A with SH4000 Dual Ridge Horn. 
I V . COMPARISON RESULTS 
The simulations, based on different numerical methods are 
generally in very good agreement when compared to each 
other. The agreement between simulation and measurements is 
also considered excellent when considering uncertainties due 
to measurement and manufacturing. In the following, 
comparisons including the peak directivity, patterns, equivalent 
error level and losses are reported. 
A. Peak directivity comparison 
The peak directivity values are reported for measurements 
and simulations in T A B L E I I . The table confirms the very 
good agreement between measurements and simulations. 
T A B L E II . MEASURED AND SIMULATED PEAK DIRECTIVITY 
Peak Directivity [dBi] 
Frequency 
10.7 GHz 
18 GHz 
Meas 
30.99 
35.30 
CST 
30.96 
35.69 
FEKO 
31.11 
35.56 
GRASP 
31.09 
35.59 
HFSS 
31.04 
35.53 
B. Pattern comparison 
The co-polar and cross-polar components at four patterns 
cuts, phi=0°, 45°, 90° and 135° @ 10.7GHz and 18GHz are 
compared with measurements in Fig. 6 to Fig. 13. MEAS is the 
measured reference as the mean of three measurements 
performed at UPM and MVG. The simulated results are from 
GRASP, FEKO, CST and HFSS. 
The agreement between simulation and measurements in 
the plots is good especially considering that simulation results 
have been plotted with 0.1° angular step, while the step for 
measurements is 1°. 
The agreement can also be evaluated as a single value. The 
pattern correlation or equivalent noise level [3] is reported in 
the following paragraph. 
s 
i 
° 
I 
_ . _ • = ! • = • — . _ _ _ 
A A / \ 
I J 
AA 
Al I 1 
A/^ 
/\ A A / \ i 
\M>M*W\IM 
ft ytt 1Í 
1 
11IV li * \ i 
rill I víl ^ \ / ^ ^ f 
Theta H 
Fig. 6. Reflector SR 40-A with SH4000: measured and simulated 
(FEKO, CST, GRASP, HFSS) directivity pattern @10.7GHz, phi=0°. 
Fig. 10. Reflector SR 40-A with SH4000: measured and simulated 
(FEKO, CST, GRASP, HFSS) directivity pattern @18GHz, phi=0°. 
Fig. 7. Reflector SR 40-A with SH4000: measured and simulated 
(FEKO, CST, GRASP, HFSS) directivity pattern @10.7GHz, phi=45°. 
Fig. 11. Reflector SR 40-A with SH4000: measured and simulated 
(FEKO, CST, GRASP, HFSS) directivity pattern @18GHz, phi=45°. 
SR40 + SH4000 Polar V / Directivity pattern @ phi=90° / 10700 MHz 
3 
1 
1 
7 u ' 
r 
N 
, 
: 
r> 
J'~\ 
/ 
,„ 
>, 
. '.; 
H V 
,. 
1 /;'\ / ,'X' !,r\'i )Ú'V^)¡\ ; ;*/}/"\ 1 
Theta (") 
Fig. 8. Reflector SR 40-A with SH4000: measured and simulated 
(FEKO, CST, GRASP, HFSS) directivity pattern @10.7GHz, phi=90°. 
Fig. 12. Reflector SR 40-A with SH4000: measured and simulated 
(FEKO, CST, GRASP, HFSS) directivity pattern @18GHz, phi=90°. 
Fig. 9. Reflector SR 40-A with SH4000: measured and simulated 
(FEKO, CST, GRASP, HFSS) directivity pattern @10.7GHz, phi=135°. 
Fig. 13. Reflector SR 40-A with SH4000: measured and simulated 
(FEKO, CST, GRASP, HFSS) directivity pattern @18GHz, phi=135°. 
C. Pattern Correlation / Equivalent Noise Level 
The visible pattern agreement is confirmed by computing 
the pattern correlation or equivalent noise level [3]. Correlation 
of simulation and measurement has been computed in a ±20° 
conical angle for both polarizations as reported in TABLE III. 
Correlation values of ~40dB are similar to what has been 
achieved in recent measurement comparisons [3]. 
T A B L E III. EQUIVALENT NOISE LEVEL@10.7 AND 18 G H Z 
Equivalent Noise Level wrt Measurements [dB] @10.7 GHz 
Phi 
0° 
90° 
CST 
CO 
-42.52 
-44.08 
CX 
-48.20 
-43.24 
FEKO 
CO 
-42.07 
-42.41 
CX 
-48.09 
-43.86 
GRASP 
CO 
-43.57 
-43.91 
CX 
-48.86 
-43.22 
HFSS 
CO 
-44.05 
-44.73 
CX 
-48.47 
-43.38 
Equivalent Noise Level wrt Measurements [dB]@18 GHz 
Phi 
0° 
90° 
CST 
CO 
-41.61 
-39.18 
CX 
-42.70 
-42.33 
FEKO 
CO 
-41.74 
-40.57 
CX 
-44.94 
-42.36 
GRASP 
CO 
-41.47 
-40.21 
CX 
-44.84 
-42.22 
HFSS 
CO 
-43.12 
-40.56 
CX 
-44.40 
-42.29 
D. Dissipation Loss Comparison 
The measured and simulated dissipation losses are reported 
in TABLE IV. Measured losses are obtained as the difference 
between the IEEE Gain and the Directivity, therefore the 
accuracy is related to the gain accuracy of the measurement 
facilities. 
All simulations give similar dissipation estimates. It seems 
that simulations slightly underestimate the losses. A plausible 
explanation is connector losses, not included in the simulation 
scenarios and the uncertainty of the aluminum electrical 
conductivity considered in the simulations. The vendor sheet 
value has been used in the simulation with no experimental 
verification. 
T A B L E IV . DISSIPATION LOSS 
Dissipation Loss [dB] 
Frequency 
10.7 GHz 
18 GHz 
Meas 
-0.27 
-0.34 
CST 
-0.11 
-0.14 
FEKO 
-0.09 
-0.11 
GRASP 
-0.08 
-0.11 
HFSS 
-0.07 
-0.34 
E. Matching / Return Loss Comparison 
The measured and simulated return loss values are reported 
in TABLE V. There are visible differences between 
simulations and measurements. These can be explained from 
the difference in matching condition in the simulation scenario 
and actual antenna. Simulations have been performed 
considering a discrete excitation port of the SH4000 with 
definitions depending on the numerical tool. Measurements are 
referred to a 50 high precision connector. The availability, of 
the return loss, as a curve over the frequency band, instead of 
two discrete points would probably have been more 
meaningful for the comparison. 
T A B L E V . RETURN LOSS 
Return Loss [dB] 
Frequency 
10.7 GHz 
18 GHz 
Meas 
-12.87 
-17.27 
CST 
-13.95 
-14.34 
FEKO 
-9.41 
-15.04 
GRASP 
-12.30 
-16.70 
HFSS 
-12.60 
-14.00 
V . CONCLUSIONS 
The achievable agreement between antenna measurement 
and numerical simulation has been investigated. The 
experiment has been designed to minimize error sources not 
pertinent to simulation/measurement. 
The simulations, based on different numerical methods are 
generally in very good agreement when compared to each 
other. The agreement between simulation and measurements is 
deemed excellent, considering uncertainties due to simulation, 
measurement and manufacturing. The level of correlation 
between measurements and simulation achieved here are better 
than what has been found in recent facility comparisons 
campaigns. Very good agreement has been achieved for 
performance parameters such as peak directivity, pattern, and 
gain contributions such as dissipation loss and matching. 
REFERENCES 
[I] A N S I / I E E E Std 149-1979, “Standard Test Procedures for Antennas” 
[2] I E E E Std 1720 2012, “Recommended Practice for Near Field Antenna 
Measurements”. 
[3] L . J. Foged, M . Sierra Castañer, L . Scialacqua “Facility Comparison 
Campaigns within EurAAP”, 5th European conference on Antennas and 
propagation, EuCAP2011, Rome, April 2011. 
[4] www.cst.com, CST STUDIO SUITE™, CST AG, Germany 
[5] www.feko.info, Altair Engineering GmbH, Germany 
[6] www.ansys.com/Products/Simulation+Technology/Electronics/Signal+I 
ntegrity/ANSYS+HFSS, A N S Y S Inc. U S A 
[7] www.ticra.com, Denmark 
[8] A . C . Ludwig, “The Definition of CrossPolarization”, I E E E Trans. 
Antennas Propagation, vol. AP-21 no.1, pp. 116-119, Jan. 1973. 
[9] X . Yuan, “Three-dimensional Electromagnetic Scattering from 
Inhomogeneous Objects by the Hybrid Moment and Finite Element 
Method,” IEEETransactions on Microwave Theory and Techniques, 
Vol. 38, No. 8, August 1990, pp. 1053-1058. 
[10] W . C . Chew, J. M . Jin, E . Michielssen, and J. M . Song, Fast and 
Efficient Algorithms in Computational Electromagnetics, Artech House, 
Boston, M A , 2001. 
[II] Poggio, A . J. and Miller, E . K., "Integral Equation Solutions of Three-
Dimensional Scattering Problems." Computer Techniques for 
Electromagnetics, edited R . Mittra, Pergamon Press, New York, 1973 
[12] M . Sabbadini, G . Guida, M . Bandinelli,The Antenna Design Framework 
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[13] J. Jin, The Finite Element Method in Electromagnetics, Second Edition, 
John Wiley & Sons Inc., New York, N Y , 2002. 
[14] O . Borries, P . Meincke, E . Jørgensen, and P . C . Hansen, “Multilevel 
Fast Multipole Method for Higher-Order Discretizations,” I E E E 
Transactions on Antennas and Propagation, vol. 62, no. 9, pp. 4695– 
4705, Sep. 2014. 
[15] T . Weiland: " R F & Microwave Simulators - From Component to 
System Design" Proceedings of the European Microwave Week 
( E U M W 2003), München, Oktober 2003, Vol. 2, pp. 591 - 596. 
[16] B . Krietenstein, R . Schuhmann, P . Thoma, T . Weiland: "The Perfect 
Boundary Approximation Technique facing the big challenge of High 
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[17] D . Reinecke, P . Thoma, T . Weiland: "Treatment of thin, arbitrary 
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18 G z -17.27 -14.34 -15.04 -16.70 -14.00 


Measurement and simulation of reflector antenna

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Measurement and simulation of reflector antenna

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