Characterization of Radar Absorber Based on Square Patch Textured Surface

Levy Olivia1,2, Adit Kurniawan2, Sugihartono2, Achmad Munir2

1Faculty of Electro and Communication, Institut Teknologi Telkom Bandung, West Java, 40257, Indonesia

2School of Electrical Engineering and Informatics, Institut Teknologi Bandung Bandung, West Java, 40132, Indonesia

Email: levy@students.itb.ac.id

Abstract — A square patch can operate whereby at the resonance frequency of resistively textured surface. The surface behaves like a perfect magnetic conductor; therefore the electric field would be in tangential to the surface. The developed patch that consists of square shape of metallic copper with length of 22mm and gap between patches of 2.0mm is placed on a single-sided 3.2mm thick grounded FR4 Epoxy dielectric substrate. Relative permittivity and tan

of the dielectric substrate are 4.04 and 0.02, respectively, whilst the thickness of metallic copper top patch as well as the ground plane is 0.035mm. The losses of dielectric substrate and copper conductive are also taken into account. Surface-mounted-resistive elements are incorporated midway connecting between the adjacent patches to reduce the amount of backscatter from the surface. The reflection coefficient of absorber with resistive elements of 440 where upon the incident electromagnetic energy should be absorbed is up to 34dB.

Index Terms — Perfect magnetic conductor, radar absorber, resistive element, square patch, textured surface.

I. INTRODUCTION

During the last few years, there has been increase research interest in electromagnetic metamaterials and their applications in microwave frequency. These metamaterials include all kind of artificial materials which have the structure possess the characteristics which are not found in the nature. An example of the metamaterials is artificial magnetic conductor (AMC) which has a physical approximation of perfect magnetic conductor (PMC). However, the AMC has zero degree reflection properties only in a narrow frequency band. The AMC which can be performed in its simplest form consists of doubly periodic array of printed metallic patch on a grounded dielectric substrate. Several forms of AMC like high impedance surface (HIS) have been investigated with or without vias included with positive implications on manufacturing simplicity [1]-[3]. Recently, the advent of HIS has opened up new possibility applications in microwave region such as antennas, reflectors, radar cross section and absorbers.

A conventional approach to design radar absorber material is the Salisbury screen [4]. This screen is a resistive sheet that positioned on /4 from a conducting metal ground plane so that destructive phasing exist at the

front face of the resistive sheet resulting in cancellation of the reflected signal. The major expectation in the design absorbing material is to reduce its thickness. One of the effective methods is by use of texture surface technology comprised of a HIS as a PMC. The method can remove the need of HIS for /4 spacing between resistive sheet and a perfectly conducting metal ground plane; as a result the thickness of absorber can be reduced drastically. The AMC has recently been used as ultra thin radar absorber. This method has been theoretically investigated and practically implemented with different physical structures for microwave absorber application [5]-[9].

In this work the characterization of microwave thin radar absorber based on textured surface technology is numerically investigated. The construction of absorber is comprised of a doubly periodic hexagonal patch with surface-mounted-resistive elements incorporated onto the array of surface to control its surface impedance. To investigate the characteristic of the absorber, a square metallic copper patch as a unit cell that can operate whereby at the resonance frequency of resistively textured surface is numerically analyzed. The surface behaves like a PMC; therefore the electric field is in tangential to the surface, i.e. x-axis direction. The numerical investigation is carried out by using 3D simulation software. Hence, the proposed methodology for the analysis is based on unit cell to save computational resources.

II. BRIEF OVERVIEW OF UNIT CELL METHODOLOGY

The structure of radar absorber used here is based on the construction in [8] but with a doubly periodic square patch placed on the different size of substrate. To conserve computational effort, as illustrated in Fig. 1, a unit cell is modeled for the numerical investigation. The unit cell consists of square shape of metallic copper with length of 22mm and the gap between patches in y-axis direction of 2.0mm. The patch is then placed on a single-sided thick 3.2mm grounded FR4 Epoxy dielectric substrate that has relative permittivity and tan of 4.04 and 0.02, respectively. The thickness of metallic copper top patch as well as the ground plane of the substrate is 0.035mm.

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Here, dielectric substrate and copper conductive losses are also accounted for. To reduce the amount of backscatter from the surface, surface-mounted-resistive elements are incorporated midway connecting between the adjacent patches in y-axis direction. A normal incident wave of simple TE mode in y-axis direction is applied to illuminate the patch surface. Boundary conditions are applied with perfect electric conductor (PEC) or electrical walls perpendicular to- and perfect magnetic conductor (PMC) or magnetic walls parallel to the E-field. The selected boundary conditions, i.e. PEC and PMC, are used to make the image of square patch to be a doubly periodic array of infinite extent.

Fig. 1 Square patch unit cell with resistive elements (in mm)

III. CHARACTERIZATION AND DISCUSSION

One of the important things in the design of radar absorber is the amount of the energy that can be absorbed. The characterization method to get coefficient reflection of radar absorber which consists of square patches with resistive elements is illustrated in Fig. 2 using parallel plate waveguide (PPW) simulator. It is clearly shown from the figure that to obtain more absorbed energy, the textured surfaces impedance should match with the free space impedance as close as possible. In this characterization, the resistive-elements incorporated into a textured surface of square patches is designated to gain the impedance of textured surfaces gets closer to the impedance of free space without changing the resonant frequency. To obtain the impedance matching of textured surface, the value of resistive-elements interconnects the square patch unit cell is set to be 440Ω as it shows the optimum performance result of absorption rate.

Figure 3 shows the characterization results using PPW simulator to analyze the characteristic of anisotropic thin radar absorber consists of resistive-elements incorporated into square patches at normal incidence. The resistive-element of 440Ω are connected midway between the adjacent patches along y-axis direction of textured surface

and a y-directed linearly polarized E-field applied at normal incidence. The incident wave is launched from a waveguide transducer of WG10 type which operates in the frequency range of dominant mode from 2.6GHz to 3.95GHz, whilst the PPW simulator has taper length of 100mm, plate length of 400mm, plate width of 200mm, and plate separation of 90mm.

Fig. 2 Characterization method of radar absorber consists of square patches incorporated with resistive elements (unit in mm)

2 2.2 2.4 2.6 2.8 3[×109]

-30

-20

-10

0

absorber with resistor without resistor

Frequency (Hz)

Ref

lect

ion

Coe

ffici

ent (

dB)

Fig. 3 The characterization results of radar absorber using PPW simulator

From the result, it is shown that the square patch

absorber type with resistive elements produces better

y

x

x

400

100

200

90

WG10 E

z

y x

FR4 Epoxy dielectric substrate

3.2 square patch

ground plane

22

20

1

resistive element

resistive element

2012 IEEE International Symposium on Radio-Frequency Integration Technology (RFIT) 211

return loss at 3.0GHz than the square patches absorber without resistive element which is almost around 8dB. It can be figured out that the additional eternal resistive element of 440Ω can increase the absorption of incident electromagnetic energy up to 34dB.

IV. CONCLUSION

It has been demonstrated that the appropriate value of resistive element of 440Ω interconnecting a textured surface of radar absorber consists of square patches improves significantly the return loss up to 8dB. This energy absorption yields better reflections coefficients than the similar structure without resistive element. A characterization method to get the reflection coefficient of radar absorber has also been provided by using a PPW simulator. More realistic investigation in the characterization of a manufactured radar absorber based on square patch textured surface is still in progress where more reliable properties of radar absorber will be demonstrated later.

ACKNOWLEDGEMENT

This work was supported by the Ministry of Research and Technology, the Republic of Indonesia, under the Grant of Incentive Research Program 2012, Contract No. 1.26/SEK/IRS/PPK/I/2012.

REFERENCES

[1] R.L. Fante and M.T. McCormack, “Reflection properties of the Salisbury screen,” IEEE Trans. Antennas Propagat., vol. 36, pp. 1443-1454, Oct. 1988.

[2] Y. Zhang, J.Von Hagen and W. Wiesbeck, “Patch array as artificial magnetic conductors for antenna gain improvement,” Microw. Opt. Technol. Lett., vol. 35, pp. 172–175, 2002.

[3] Y. Zhang, J. Von Hagen, M. Younis, C. Fischer and W Wiesbeck, “Planar artificial magnetic conductors and patch antennas,” IEEE Trans. Antennas and Propagat., vol. 51, no. 10, pp. 2704-2712, Oct. 2003.

[4] G. Goussetis, A.P. Feresidis, and J.C. Vardaxoglou, “Tailoring the AMC and EBG characteristics of periodic metallic arrays printed on grounded dielectric substrate,” IEEE Trans. Antennas Propagat., vol. 54, no. 1, pp 82-89, Jan. 2006.

[5] V. Fusco and S. Simms, “Textured surface slot antenna with reduced radar cross-section,” Electron. Lett., vol. 43, no. 8, pp. 438-440, Apr. 2007.

[6] V. Fusco, A. Munir and M. Euler, “Planar two-bit phase encoded transpolarising reflector using textured surface technology,” in 3rd European Conference on Antennas and Propagation (EuCAP), Berlin, Germany, Mar. 2009.

[7] A. Munir and V. Fusco, “Characterization of microwave anisotropic thin radar absorber using artificial magnetic ground plane,” in Asia-Pacific Microwave Conference (APMC), Hongkong, China, Dec. 2008.

[8] A. Munir and V. Fusco, “Effect of surface resistor loading on high impedance surface radar absorber return loss and bandwidth,” Microwave and Optical Tech. Lett., vol. 51, no.7, pp. 1773-1775, Jul. 2009.

[9] L. Olivia, F. Kurniasih and A. Munir, “Characterization of microwave thin radar absorber composed of hexagonal patch array,” in 28th Progress In Electromagnetics Research Symposium (PIERS), Cambridge, USA, Jul. 2010.

212 2012 IEEE International Symposium on Radio-Frequency Integration Technology (RFIT)