ARL-TN-0716 ● NOV 2015

US Army Research Laboratory

Numerical Computation of the Radar Cross 

Section of a 120-mm Mortar

by Christopher S Kenyon and Traian Dogaru

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ARL-TN-0716 ● NOV 2015

US Army Research Laboratory

Numerical Computation of the Radar Cross 

Section of a 120-mm Mortar

by Christopher S Kenyon and Traian Dogaru

Sensors and Electron Devices Directorate, ARL

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November 2015

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Technical Note

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10/01/2014–10/01/2015

4. TITLE AND SUBTITLE

Numerical Computation of the Radar Cross Section of a 120-mm Mortar

5a. CONTRACT NUMBER

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5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Christopher S Kenyon and Traian Dogaru

5d. PROJECT NUMBER

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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

US Army Research Laboratory

ATTN: RDRL-SER-U

2800 Powder Mill Road

Adelphi, MD 20783-1138

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ARL-TN-0716

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

This report investigates the modeling of radar scattering from a 120-mm mortar target in 4 radar frequency bands, L, S, C, and 

X, in a continuation of a previous report on radar cross-section (RCS) modeling of rockets and an artillery round. RCS 

calculations are performed by 2 different methods, implemented by the FEKO and AFDTD electromagnetic simulation 

software packages, over all the possible aspect angles. The solutions obtained by the 2 methods are compared for accuracy 

validation. The RCS analysis includes prediction of the variation with frequency and the azimuth angle, as well as a 

comparison among the 4 frequency bands of interest. The results indicated RCS returns slightly lower than the previously 

reported targets but still fairly close. No band stood out with stronger returns. The target signatures calculated in this study are 

an important tool for the radar engineers in system performance evaluation.

15. SUBJECT TERMS

radar, cross-section, mortar, FDTD, computation

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19a. NAME OF RESPONSIBLE PERSON

Christopher S Kenyon

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Contents

List of Figures iv

List of Tables iv

1. Introduction 1

2. Description of the 120-mm Mortar Round 2

3. Comparison of FEKO and AFDTD RCS Predictions 3

4. Variation of RCS with Frequency 6

5. Variation of RCS with Azimuth Angle 10

6. Conclusions 13

7. References 14

Distribution List 15
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iv

List of Figures

Fig. 1 FEKO computer model of 120-mm mortar round .................................2

Fig. 2 RCS of the 120-mm mortar round vs. elevation angles, computed by 

AFDTD and FEKO software in 4 frequency bands: a) L-band, φ=0°; 

b) L-band, φ=8°; c) S-band, φ=0°; d) S-band, φ=8°; e) C-band, φ=0°; 

f) C-band, φ=8°; g) X-band, φ=0°; and h) X-band, φ=8° ......................5

Fig. 3 Mean, mid-band, and upper-lower limits of the 120-mm mortar 

computed by AFDTD over a 200-MHz bandwidth in all 4 bands: a) Lband, V-V; b) L-band, H-H; c) S-band, V-V; d) S-band, H-H; e) Cband, V-V; f) C-band, H-H; g) X-band, V-V; and h) X-band, H-H ........7

Fig. 4 Comparison of 120-mm mortar RCS at 2.4 and at 2.45 GHz for a) V-V 

polarization and b) H-H polarization .....................................................8

Fig. 5 Average RCS of the 120-mm mortar round computed by AFDTD in 

all 4 radar frequency bands for a) V-V polarization and b) H-H 

polarization ............................................................................................9

Fig. 6 Mean and upper-lower limit RCS of the 120-mm mortar round 

computed by AFDTD over a 18° azimuth angular range, in all 4 radar 

frequency bands: a) L-band, V-V; b) L-band, H-H; c) S-band, V-V; d) 

S-band, H-H; e) C-band, V-V; f) C-band, H-H; g) X-band, V-V; and 

h) X-band, H-H ....................................................................................11

Fig. 7 RCS of the 120-mm mortar round at 3 azimuth angles in all 4 radar 

frequency bands: a) L-band, V-V; b) L-band, H-H; c) S-band, V-V; d) 

S-band, H-H; e) C-band, V-V; f) C-band, H-H; g) X-band, V-V; and 

h) X-band, H-H ....................................................................................12

List of Tables

Table 1 Mean RCS of the 120-mm mortar round compared with the mean RCS 

of 3 targets considered in the previous study,3 computed over all 

possible aspect angles and a 200-MHz bandwidth within each of the 4 

frequency bands.....................................................................................9
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1. Introduction

The US Army is interested in the radar detection and tracking of artillery rounds 

grouped under the generic category of rockets, artillery, and mortar (RAM). One 

important step in the radar system design consists of analyzing the radar cross 

section (RCS) of the targets of interest. The electromagnetic (EM) modeling team 

at the US Army Research Laboratory (ARL) has developed capabilities for 

modeling the radar signature of a wide variety of targets, using multiple numerical 

EM simulation methods. In this report, we apply 2 of these EM software packages, 

AFDTD1 and FEKO2, to the RCS calculation of a 120-mm mortar round in a 

continuation of the work reported in a previous ARL technical report.3 The reader 

is referred to this previous report for extended details about this current work.

The computer model of the mortar round was created from pictures and drawings 

available on public websites and does not contain all the small details of the mortar 

such as the propellant mounts. The analysis does contain all features relevant to our 

phenomenological study. 

As stated in the preceding ARL technical report the goals are the following:

• Evaluate the RCS of the mortar round in the L, S, C, and X radar bands and 

compare their magnitudes across the bands. In all cases, the RCS is 

computed with respect to the aspect angle, with the target placed in a 

standard (upright) orientation.

• Assess the accuracy of the simulations by AFDTD and FEKO for this target, 

in the frequency bands of interest. 

• Quantify the variation of the target RCS for small frequency deviations 

within the radar bands already mentioned. This analysis is useful for a radar 

system that uses frequency agility.

• Study the variation of the target RCS with the azimuth angle for targets that 

cannot be described as rotationally symmetric. This is the case of the mortar.

Both of the RCS calculation techniques, used by AFDTD and FEKO here, are 

advanced exact computational EM solvers as opposed to approximate solvers often 

used in the past. The validated AFDTD software was developed in-house at ARL 

and uses the finite-difference time-domain algorithm. We used a surface integral 

solver, Method of Moments, in the commercial FEKO software to assess the 

accuracy of the AFDTD results. 

This report is broken into 5 more sections. In Section 2 we describe the mortar 

target. Section 3 compares the AFDTD and FEKO results. Section 4 shows the 
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variations of RCS among the 4 frequency bands of interest as well as variations of 

RCS within the bands. Section 5 looks at RCS variation with azimuth angle and 

Section 6 presents conclusions. 

2. Description of the 120-mm Mortar Round

A computer model of our chosen 120-mm mortar round is shown in Fig. 1. The 

120 mm is a common mortar bore diameter and there are many types of ammunition 

rounds for it from different countries and manufacturers. We have given the fins a 

thickness of 4 mm. Judging by surveying web images of mortar rounds, the one we 

have chosen is fairly typical, but the designs can vary in length and somewhat in 

shape. The body can have a fairly rounded shape or a more tubular shape. The nose 

can be longer and the fins are probably the most variable part. The fin number can 

be fewer than 10, but 10, as our mortar round has, is fairly common. The fin shapes 

can vary significantly, too. While the fin shape and dimensions may have an impact 

on the radar signature, we expect the mortar length and diameter to largely 

determine the target RCS. 

Fig. 1 FEKO computer model of 120-mm mortar round

We have modeled the mortar as a perfect electric conductor (PEC) and oriented it 

vertically with tip up aligned with its axis on the Z-axis. In this way, using the 

spherical polar coordinate convention, the radar incidence angle is measured by the 

polar angle, θ, from the Z-axis. Azimuth variations were computed with the 

incidence varying in the φ direction about the Z-axis measured from the X-axis. 
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The polar incidence angle, θ, was varied 0° to 90°. Since the 10 fins were 36° apart 

we computed all θ incidences with φ varied from 0°, along a fin, to 18°, between 

the fins. By this means, with both vertical and horizontal polarization, we covered 

the possible combination of incident angles for the mortar geometry, excepting 

incidence from its rear hemisphere. 

The triangle mesh surface model of the mortar shown in Fig. 1 was created in the 

CADFEKO frontend of FEKO from web drawings.

4 FEKO computed the RCS 

using this surface mesh. The triangle meshes for the model were then exported as 

STL files and imported into the ARL software, AFDTDGRID,

5 to create a 

volumetric grid of small cubic cells for use with the AFDTD computations. 

For this model we used FEKO’s “standard” meshing on a PC for each frequency so 

that the FEKO mesh triangles averaged λ/12 on a side, where λ is the radar radiation 

wavelength. The AFDTD grid cell size was set at 1 mm to minimize any effects 

from stair stepping over the surface of the model. The previous report had 

confirmed that a 1-mm AFDTD grid size gave better results than a 2-mm grid.

3 The 

AFDTD computation was done on ARL’s Excalibur high-performance computing 

(HPC) 6 system using 32 cores for each incidence angle. With both the FEKO and 

AFDTD, computations produced both vertical-vertical (V-V) and horizontalhorizontal (H-H) polarized RCS that we analyze in this study. We focused on 

results for 4 specific frequencies, 1.3, 2.4, 5.6, and 9.5 GHz, to characterize the 

L-, S-, C-, and X-bands, respectively. Additionally, in some of the analysis we 

included frequencies ±100 MHz, at 50-MHz intervals about these frequencies, to 

cover the possibility of frequency hopping radar.

3. Comparison of FEKO and AFDTD RCS Predictions

In this section, we show the computed AFDTD and FEKO RCS results for the 

120-mm mortar. Figure 2 shows both the RCS at both V-V and H-H polarizations 

for the L, S, C, and X frequency bands versus incidence angle θ for the 2 azimuth 

angles, 0° and 8°. The latter angle was chosen as a sample of a radar return for a 

geometry not symmetrical about the incidence plane for our model with fins 

separated by 36° in azimuth. 

The results shown in Fig. 2 show a high level of agreement between the AFDTD 

and FEKO results, consistent with the earlier report3 that included a 107-mm rocket 

with fins had shown. Again, over most of the ranges agreement held to within 2 dB 

with a few nulls being some exceptions. Since the 3-dimensional (3D) cubic 

geometry of AFDTD and the triangular surface geometry for the FEKO model are 

slightly different representations of the mortar round, one would not necessarily 

expect nulls, whose position and depth would be highly sensitive to geometry and 
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therefore slightly different, to be exactly the same in the results. Mismatch in the 

higher frequency results shown in the C- and X-bands would again be more likely 

to occur as both methods lose some accuracy at those higher frequencies. 

The RCS for this round shows little tendency to increase as the incidence angle 

goes from nose-on to broadside incidence, unlike the simulations for the artillery 

round and 107-mm rocket showed. This is likely due to the very limited cylindrical 

character of the mortar round body. Viewed from the side, it is bowed out in the 

middle and has only a short prolonged surface parallel to its axis in contrast to the 

earlier 155-mm artillery round and 107-mm rocket. For near broadside incidence, 

a V-V polarized radar beam would not have a long tube to excite in phase. The 

variable circumference length that an H-H polarized radar would excite would 

possibly induce returns not in phase, so that their received sum, or equivalently the 

H-H polarized RCS, would be diminished.

The VV radar return is 10 dB or more higher than the H-H return between 10° and 

30° incidence from the nose. Possibly, this could be due to a surface wave being 

generated on parts of its surface along its length.

7 Notice that the first RCS peak 

gets closer to 0° as the frequency increases, which is consistent with surface wave 

behavior. As we noted in the earlier report,

3 we saw evidence of a surface wave 

return in the simulated time signature of the radar return for the 107-mm rocket and 

expect the same phenomenon to occur with the mortar round.
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(a) (b)

(c) (d)

(e) (f)

(g) (h)

Fig. 2 RCS of the 120-mm mortar round vs. elevation angles, computed by AFDTD and 

FEKO software in 4 frequency bands: a) L-band, φ=0°; b) L-band, φ=8°; c) S-band, φ=0°; 

d) S-band, φ=8°; e) C-band, φ=0°; f) C-band, φ=8°; g) X-band, φ=0°; and h) X-band, φ=8°

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

AFDTD VV

FEKO VV

AFDTD HH

FEKO HH

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

AFDTD VV

FEKO VV

AFDTD HH

FEKO HH

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

AFDTD VV

FEKO VV

AFDTD HH

FEKO HH

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

AFDTD VV

FEKO VV

AFDTD HH

FEKO HH

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

AFDTD VV

FEKO VV

AFDTD HH

FEKO HH

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

AFDTD VV

FEKO VV

AFDTD HH

FEKO HH

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

AFDTD VV

FEKO VV

AFDTD HH

FEKO HH

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

AFDTD VV

FEKO VV

AFDTD HH

FEKO HH
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4. Variation of RCS with Frequency

In this part of our analysis, we look at the RCS variation with frequency for our 

chosen mortar round target. Specifically, we examine the variation the RCS within 

a 200-MHz band about the central frequency of our chosen bands. We computed 

RCS between 1.2 and 1.4 GHz for the L-band, between 2.3 and 2.5 GHz for the Sband, between 5.5 and 5.7 GHz for the C-band, and between 9.4 and 9.6 GHz for 

the X-band. Within these bands, we computed RCS at 50-MHz intervals. 

The purpose of this particular effort was to cover a radar designed to operate at 

slightly different frequencies within a band at another time, in a manner termed 

“frequency hopping.” With these simulations, we can see how much the RCS could 

vary within a given band. 

Figure 3 shows graphs of the variation of RCS within each band as error bar plots. 

The green bars show the maximum and minimum RCS over each 200-MHz band 

for each incidence angle. The blue line shows the mean RCS for the band, while 

the red line shows the RCS for the center frequency of the band as in Fig. 2. Just as 

in the case for the 155-mm artillery round and the 107-mm rocket, the RCS 

variation within a frequency band is smaller at higher baseline RCS values, 

especially when approaching –10 dBsm. Again, this is consistent with the fact the 

RCS is represented as logarithms or ratios of the strength. 

Also, the variation is larger where the baseline is varying more with the incidence 

angle. Where the baseline RCS changes more rapidly with changes in incidence 

angle, the different frequencies within a band will respond at incident angles 

somewhat offset from where the baseline did. For a slightly higher frequency, the 

RCS pattern will respond much as though the target cross section presented to them 

were slightly larger. This procedure may also reveal somewhat different nulls in the 

RCS curves, which are sampled in a discrete manner in both polar angle or 

frequency. 

At incidence angles near nose-on, the effective size of the target is increasing more 

rapidly than when the incidence approaches broadside. If the RCS is changing

rapidly with incidence angle along parts of the graph, then small frequency 

variations will cause an effective broadening in the characterization of the RCS 

over those angles. For example, in Fig. 4, we compare the RCS at

2.40 and 2.45 MHz (within the S-band). It is apparent in this figure that the shift in 

the RCS peaks and nulls corresponding to frequency increases is equivalent to 

increasing the target size while keeping the frequency constant. When considering 

bands with multiple, closely spaced frequencies, this phenomenon is a source of 

effective broadening of the RCS response.
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(a) (b)

(c) (d)

(e) (f)

(g) (h)

Fig. 3 Mean, mid-band, and upper-lower limits of the 120-mm mortar computed by AFDTD 

over a 200-MHz bandwidth in all 4 bands: a) L-band, V-V; b) L-band, H-H; c) S-band, V-V; 

d) S-band, H-H; e) C-band, V-V; f) C-band, H-H; g) X-band, V-V; and h) X-band, H-H

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

Mid-band

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

Mid-band

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

Mid-band

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

Mid-band

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

Mid-band

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

Mid-band

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

Mid-band

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

Mid-band
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 (a) (b)

Fig. 4 Comparison of 120-mm mortar RCS at 2.4 and at 2.45 GHz for a) V-V polarization 

and b) H-H polarization

In Fig. 5 we compare the RCS versus incidence angle for all 4 frequency bands 

averaging over the 5 frequencies in each 200-MHz band and over 10 azimuth angles 

from 0° to 18° (from along a fin to the middle between fins). The curves in the 

graphs tend to follow each other within a 10-dB band, with the exception of the Lband RCS, which runs about 10 dB higher roughly between 20° and 40° incidence. 

Table 1 condenses the comparison even further by taking the average over all the 

incidence angles and compares the average RCS in each band for the mortar round 

with the 155-mm artillery round and the 2 versions of the 107-mm rocket. Although 

most of the mortar’s RCS values shown in the table are within 3 or 4 dB of the other 

targets, they are mostly somewhat lower, which is consistent with its smaller size 

and more curved surfaces.
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(a)

(b)

Fig. 5 Average RCS of the 120-mm mortar round computed by AFDTD in all 4 radar 

frequency bands for a) V-V polarization and b) H-H polarization

Table 1 Mean RCS of the 120-mm mortar round compared with the mean RCS of 3 targets 

considered in the previous study,

3 computed over all possible aspect angles and a 200-MHz 

bandwidth within each of the 4 frequency bands

Target 155-mm Round

107-mm 

Rocket(no fins)

107-mm 

Rocket(with fins)

120-mm Mortar 

Round

Polarization V-V H-H V-V H-H V-V H-H V-V H-H

L-band –10.91 –11.71 –11.04 –14.27 –10.20 –12.37 –10.91 –14.39

S-band –12.36 –13.28 –12.66 –13.57 –10.60 –11.76 –13.44 –16.85

C-band –12.18 –12.64 –13.06 –13.60 –10.10 –10.20 –13.75 –15.99

X-band –12.11 –12.64 –13.76 –14.62 –9.89 –8.42 –13.96 –15.99

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

L-band

S-band

C-band

X-band

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

L-band

S-band

C-band

X-band
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5. Variation of RCS with Azimuth Angle

In this part of the study, we examine the effect of variation in azimuth angle for the 

120-mm mortar round. This round has 10 fins, each separated by 36° in azimuth 

from its neighbors. With this geometry, we can fully capture the effect of 

differences in the azimuth by computing RCS over any 18° azimuth span. We 

computed RCS for the middle value of each frequency band over the usual range 

of θ from 0° to 90°, while choosing azimuth, or φ, to vary from 0° to 18° in 2° 

intervals, where 0° was aligned with a fin. The graphs in Fig. 6 show the mean RCS 

over the azimuth range as well as the maximum and minimum RCS over the φ 

range for each θ angle, depicted by the error bars.

What is interesting here is the lack of variation from the mean RCS in the L-band 

and S-band cases, but with a strong presence of the variations in the C- and X-band 

cases, at least beyond 30° from nose-on. The variations that occur in the C- and Xband are strong even at higher RCS magnitudes. The 0° to 30° incidence in θ is not 

expected to show much azimuthal variance since it is at, or near, nose-on. However, 

for L- and S-band, both the high density of fins and their smaller size relative to 

these wavelengths have eliminated variations that otherwise do appear in the Cand X-bands. The fins are about 56 mm high and 40 mm long (from the main body),

and their tips are separated by only 33 mm. This compares with the S-band 

wavelength of 125 mm and the C-band wavelength of 54 mm. In the case of Sband, the fins are less than 1⁄2 wavelength and the fins appear not to have been 

completely resolved. Consequently, there is no difference in response when the 

azimuthal aspect changes. This lack of resolution is even more evident for the Lband. However, for C- and X-band, the fins are close to or larger than a wavelength, 

and so differences do appear with different azimuthal incidences when the polar 

angle θ is larger than 30°. The graph in Fig. 7 also illustrates this issue, by halving 

the θ angular sampling interval to 0.25° and looking at 3 separate azimuthal 

incidence angles, 0°, 8°, and 18°. The curves are virtually unseparated until the 

radar frequency reaches into the C- and X-bands. 

This lack of resolution of the separate fins for the mortar round is in contrast to the 

107-mm rocket with 4 fins, where the variance of the RCS curve over various 

azimuth aspects is fairly large over most of the θ angular incidence and all 4 

frequency bands. In the case of the finned 107-mm rocket, the fins are roughly twice 

as large and larger than or comparable to the radar wavelengths. The lower fin 

density also means the geometrical or optical broadside cross section will clearly 

change with azimuth angle. Also, in the 107-mm finned rocket, the wider fin 

spacing may allow more effective corner-type scattering at broadside.
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(a) (b)

(c) (d)

(e) (f)

(g) (h)

Fig. 6 Mean and upper-lower limit RCS of the 120-mm mortar round computed by 

AFDTD over a 18° azimuth angular range, in all 4 radar frequency bands: a) L-band, V-V; 

b) L-band, H-H; c) S-band, V-V; d) S-band, H-H; e) C-band, V-V; f) C-band, H-H;

g) X-band, V-V; and h) X-band, H-H

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

Min:Max

Mean
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12

(a) (b)

(c) (d)

(e) (f)

(g) (h)

Fig. 7 RCS of the 120-mm mortar round at 3 azimuth angles in all 4 radar frequency 

bands: a) L-band, V-V; b) L-band, H-H; c) S-band, V-V; d) S-band, H-H; e) C-band, 

V-V; f) C-band, H-H; g) X-band, V-V; and h) X-band, H-H

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

VV = 0 °

VV = 8 °

VV = 18 °

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

HH = 0 °

HH = 8 °

HH = 18 °

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

VV = 0 °

VV = 8 °

VV = 18 °

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

HH = 0 °

HH = 8 °

HH = 18 °

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

VV = 0 °

VV = 8 °

VV = 18 °

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

HH = 0 °

HH = 8 °

HH = 18 °

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

VV = 0 °

VV = 8 °

VV = 18 °

 (degrees)

0 10 20 30 40 50 60 70 80 90

RCS (dBsm) -60

-50

-40

-30

-20

-10

0

10

HH = 0 °

HH = 8 °

HH = 18 °
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13

6. Conclusions

We have extended our Numerical Computation of the Radar Cross Section of 

Rockets and Artillery Rounds report3 by modeling a fairly close representation of 

an actual 120-mm mortar. Again the AFDTD and FEKO results were in excellent 

agreement for the frequencies and incidence angles of our study, even though the 

modeling techniques of the 2 software were different. 

Also, we found that the RCS of the mortar round was not greatly different from that 

of the previous 3 models in the earlier report, namely, the artillery round and the 

two 107-mm rocket models when we considered ±100-MHz deviation from the 

central frequency of the L-, S-, C-, and X-bands. The RCS at broadside incidence 

was slightly lower for our mortar round and the overall RCS was slightly lower, 

consistent with a slightly smaller and more rounded target. We found significant 

variations in the RCS with azimuth aspect angle in the C- and X-bands. However,

these variations disappeared with the lower frequency, L- and S-bands. This 

suppression of the azimuthal RCS variation was consistent with the smaller fin size 

relative to wavelength as compared to the 107-mm rocket. The density of the fins 

in our 10-fin mortar round as compared to the 4-fin, 107-mm rocket also played a 

major role in the different effect of the azimuth angle on RCS between the 2 targets. 

This could suggest that the radar return for this mortar would be more predictable

at the lower frequencies than at the higher frequencies, especially since the azimuth 

incidence angle of the radar beam on a finned target would be uncertain.

Overall, however, no radar band return stood out as consistently stronger than the 

others. Higher frequencies might be more sensitive to details in the target, but for 

azimuthally non-symmetric targets, such as finned mortars and rockets, their spin 

could result in a higher variance of the radar signature. 
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14

7. References

1. Dogaru T. AFDTD user’s manual. Adelphi (MD): Army Research Laboratory 

(US); March 2010. Report No.: ARL-TR-5145.

2. FEKO electromagnetic simulation software website [accessed September, 

2015]. http://www.feko.info.

3. Kenyon C, Dogaru T. Numerical computation of the radar cross section of 

rockets and artillery rounds. Adelphi (MD): Army Research Laboratory (US); 

September 2015. Report No.: ARL-TR-7468.

4. Armaco. 120-mm Mortar Round VOF-843B [accessed August 27, 2015]. 

http://www.armaco.bg/en/product/mortar-bombs-c19/120mm-mortar-roundsp474.

5. Dogaru T. The AFDTDGRID mesh generation software user’s manual. 

Adelphi (MD): Army Research Laboratory (US); October 2010. Report No.: 

ARL-TR-5380.

6. The website for the ARL DSRC Excalibur HPC can be found at 

http://www.arl.hpc.mil/hardware/index.html#excalibur.

7. Knott EF, Shaeffer JF, Tuley MT. Radar cross section, Artech House, Inc. 

1993.
Approved for public release; distribution unlimited.

15

1 DEFENSE TECH INFO CTR

(PDF) DTIC OCA

2 US ARMY RSRCH LAB

(PDF) IMAL HRA MAIL & RECORDS MGMT

RDRL CIO LL TECHL LIB

1 GOVT PRNTG OFC

(PDF) A MALHOTRA

7 US ARMY RSRCH LAB

(PDF) RDRL SER U 

 A SULLIVAN 

 C KENYON

 C LE

 D LIAO

 T DOGARU 

RDRL SER M 

 A HEDDEN

 D WIKNER
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