Effects of Radar Absorbing Material (RAM) on the 

Radiated Power of Monopoles with Finite Ground Plane 

by Christos E. Maragoudakis and Vernon Kopsa 

ARL-TN-0340 January 2009 

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Army Research Laboratory 

White Sands Missile Range, NM 88002-5513 

ARL-TN-0340 January 2009 

Effects of Radar Absorbing Material (RAM) on the 

Radiated Power of Monopoles with Finite Ground Plane 

Christos E. Maragoudakis and Vernon Kopsa 

Survivability/Lethality Analysis Directorate, ARL 

Approved for public release; distribution unlimited. 
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1. REPORT DATE (DD-MM-YYYY)

January 2009 

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1 – 30 June 2008 

5a. CONTRACT NUMBER 

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4. TITLE AND SUBTITLE 

Effects of Radar Absorbing Material (RAM) on the Radiated Power of Monopoles with 

Finite Ground Plane 

5c. PROGRAM ELEMENT NUMBER 

5d. PROJECT NUMBER 

5e. TASK NUMBER 

6. AUTHOR(S) 

Christos E. Maragoudakis and Vernon Kopsa 

5f. WORK UNIT NUMBER 

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

U.S. Army Research Laboratory 

Information and Electronic Protection Division 

Survivability/Lethality Analysis Directorate (ATTN: AMSRD-ARL-SL-EM) 

White Sands Missile Range, NM 88002-5513 

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ARL-TN-0340 

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13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

The effects of Radar Absorbing Material (RAM) on the radiation pattern of a monopole over finite ground plane are presented. The 

transmitted power of the monopole antenna was measured while varying the separation distances between the ground plane and the RAM. 

The findings of the measurements are presented in graphical form. 

15. SUBJECT TERMS

Antenna, Radiation, RAM, Effects 

16. SECURITY CLASSIFICATION OF:

19a. NAME OF RESPONSIBLE PERSON

Christos E. Maragoudakis 

a. REPORT 

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b. ABSTRACT 

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c. THIS PAGE 

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575-678-3145 

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iii 

Contents 

1. Introduction 1

2. Test Set-up and Procedure 1

3. Results 2

4. Conclusions 3

5. Recommendations 3 

Distribution List 5 
iv 

INTENTIONALLY LEFT BLANK. 
1 

1. Introduction 

During testing performed in anechoic chambers, antennas are placed near the chamber walls 

which are covered with radar absorbing material (RAM). Furthermore, the antennas could be 

placed near or on RAM structures. Normally “rules of thumb” are used to determine the 

minimum distance at which the radiators must be placed from the walls. Unfortunately, these 

rules do not provide any information on the effects on the radiated power when the radiators are 

placed at a distance shorter than the optimum distance. In this technical note the results of an 

investigation that was performed to determine the effects of RAM on power radiated by a 

monopole antenna over finite ground plane placed on a RAM block are presented. 

2. Test Set-up and Procedure 

The monopole with the finite ground plane for which radiation was to be measured was placed at 

a distance 2 above the block of RAM at the center of the chamber. A 20-decibel (dB) standard 

gain horn antenna mounted on mast at the end of the chamber was used as a receiver. The 

receiving antenna was rotated to maximize the received power. When the separation distance 

was 2, the received power was used as a reference for the experiment. The separation distance 

between the ground plane and the RAM was then reduced and the received power was recorded 

and normalized. The test set-up used for the investigation is shown in figure 1. 
2 

Figure 1. Test set-up. 

3. Results 

The effects of the RAM on the radiated power were determined by measuring the radiated power 

and varying the distance between the ground plane and the RAM. The power levels were then 

normalized to power received when the separation distance between the ground plane and the 

RAM was 2. The attenuation as a function of the separation distance between the ground 

plane and the RAM is shown in figure 2. 
3 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0.00 0.25 0.50

Distance between ground plane and RAM ()

Attenuation (dB)

Figure 2. Effects of RAM on radiated power. 

As seen from the graph, the radiated power is mostly affected when the ground plane is placed 

on the RAM. When the distance between the ground plane and the RAM is about /16, the 

attenuation is about –3 dB and it decreases as the distance between the RAM and the ground 

plane increases. When the distance between the RAM and the ground plane is /2, the effects of 

the RAM are negligible. 

4. Conclusions 

The distance between the ground plane and the RAM greatly affects the radiated power from a 

monopole over finite ground when it is placed on RAM. To minimize the effects of the RAM 

the ground plane must be placed at least /2 above the RAM. 

5. Recommendations 

It is recommended that the effects of RAM on the radiated power of other antennas be 

determined when the antennas are placed at distances less than 2 from the RAM. 
4 

INTENTIONALLY LEFT BLANK. 
5 

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