Frequency Selective Surfaces

University of Kent

Faculty of Engineering and Digital Arts

Broadband and Mobile Communication Network

Master of Science Dissertation

by

Erdogan Kaygan

Supervisor’s name: Dr. John C. Batchelor

Examiner’s name: Dr. Robert Oven

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Table of Contents• Introduction

– Aim of the project

• Background Information– Frequency Selective Surface– Types of Frequency Selective Surface– Comparison Between FSS Elements

• Technical Approach and System Analysis

– Dimension of FSS Structure– Material Selection– Simulation Procedures– Fabrication Procedures– Measurement Setup

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• Experimental Results – Bandwidth Calculations– Simulation Results– Measured and Simulated Results– Comparison Between Measured and Simulated Results

• Conclusion and Recommendations for Future Works

• References

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Introduction• Frequency Selective Surfaces has gained many interests in recent years. It can be

essentially regarded as filters of electromagnetic radio waves which are consisting of periodic surface or array elements for band-pass and band-stop response respectively.

• The transmit band frequencies and reflect band frequencies are depended by the size of patch and unit cell.

• Application areas of Frequency Selective Surfaces are very wide and vary. For example; USA military facilities in Misawa Air Base Cryptology Operation Centre as shown in figure 1 [1].

• The project is to integrate these surfaces both finite and infinite size array into building to control the radio performance at mobile and wireless frequencies.

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Introduction (Continue)

Figure 1. Misawa Air Base Cryptology Operation Centre in Japan (It used for transparent to radar or radio waves to eliminate undesired

frequency components) [1]

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Aim of the Project

• The aim of the project is to assess the filtering performance of FSS at different angles of incidence which resonate frequencies between 2 GHz and 5 GHz. FSS responses are often a function of incident angle and it is therefore important to characterize them well for a range of multipath arrival angles.

• The second aim is to prove that 1x1 and 2x2 infinite FSS elements are perform the same performance.

• The third aim is to decrease transmission value for finite FSS design. • These works will be carried out on both finite and infinite FSS and will

form part of a wider project which is gaining much interest from government agencies and industrial architects.

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Background Information

• Frequency selective surfaces are array of periodic elements which are performing as a filter.

• FSS can be classified into two main groups as finite and infinite FSS. In infinite FSS, the array elements which are not fixed size are placed periodically into the substrates, however finite FSS use open space boundary and the elements are fixed size.

• FSS Investigations are started in 1950s. The most significant issue is how to make an appropriate model.

• In 1981, E. A. Parker and S. M. A. Hamdy introduced new elements for frequency selective surface design. They use simple array of ring elements on square PEC and also on a triangular PEC for reflector antennas to compare experimental transmission results with a modal computations [2].

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• As seen in figure 2 the simulation results and measurement results are almost same.

Figure 2: Simulated and Measurement Results for Ring Elements (0 : , 30 :, 45 :) [2]

45 :

30 :

0 :

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Comparison Between FSS Elements

• A widely cited letter by T.K. Wu, described the determination of the FSS elements. According to Wu’s measurements, square loop and ring loop FSS structures are the best choice for the building applications as illustrates in table 1.

Table 1 : Comparison Between the Performances of the Common FSS Elements [3]

Note: From 1 to 4 sensitivity is increasing

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Technical Approach and System Analysis

Figure 3 : FSS Design Work Flow

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Dimension of FSS Structure

Outer radius (R): 20 mmInner radius (r): 16 mmRing width: 4mm Patch ring thickness: 0.02 mmSubstrate thickness: 0.05 mm Substrate: 50 mm x 50 mm.

Outer radius (R): 20 mmInner radius (r): 16 mmRing width: 4mm Patch ring thickness: 0.02 mmSubstrate thickness: 0.05 mm Substrate: 100 mm x 100 mm.

Outer radius (R): 20 mmInner radius (r): 16 mmRing width: 4mm Patch ring thickness: 0.02 mmSubstrate thickness: 0.05 mm Substrate: 100 mm x 100 mm.PEC: 185 mm x 185 mm Length of PEC: 85 mm

Figure 4: Dimension of 1x1 Infinite FSS

Figure 5: Dimension of 2x2 Infinite and Finite FSS

Figure 6: Dimension of 1x1 Finite FSS With Metal Screen

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Material Selection

• Ring Material: Copper(Annealed )– High thermal and electrical conductivity

• Metal Screen Material: PEC( Perfect Electric Conductor)– PEC materials do not produce any losses

• Substrate Material: Polyimide – Flexible, light weight, and thermal control materials

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Simulation Setup

• CST Microwave Studio used to simulate the performance of FSS design. It provides excellent interface, simulation performance, and super visual feedback at all stages of the simulation process

Figure 7 : CST Microwave Studio

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Fabrication Procedures

• Print FSS design on translucent paper• Cut Mylar and Photoresist materials for lamination• Laminate FSS structures• Exposure the laminated FSS structures • Using Developer Tank, resolve non exposed part of photo resist materials• Put developed FSS structure in Etching Tank to remove unwanted coppers from the

design

Figure 8: Fabricated a)infinite FSS, b) Finite FSS c) Finite with PEC FSS

a b c

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Measurement Setup• Simply signals sending from transmitter antenna to receiver antenna, then the FSS

structure performance are followed by network analyser.

Figure 9: Measurement Setup

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Experimental Results

Bandwidth Calculation:

To calculate bandwidth, maximum frequency and minimum frequencies at a point such as -10 dB need to know. Maximum and minimum frequency can be easily find out as shown in figure 13. Then Bandwidth value is calculated as shown in equation 1.

  BW (Bandwidth) = (Maximum Frequency) – (Minimum Frequency) (1)

Figure 10: Fmin and Fmax for Bandwidth Calculation

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Simulation Results

Figure 11: 1x1 and 2x2 Infinite FSS Transmission Signals

Both 1x1 and 2x2 infinite FSS transmission signals are shown in figure. It proves both FSS design perform the same performance at 3.241 GHz

Simulation Results for Infinite FSSat Different Angles

Figure 12: Simulation Results for Infinite FSS TM 0°, 30°, and 60°

3.232 GHz, 3.201 GHz, 2.945 GHz

Figure 13: Simulation Results for Infinite FSS TE 0°, 30°, and 60°

3.241 GHz, 3.132 GHz, 2.9808 GHz 18

Simulation Results for Finite FSSat Different Angles

Figure 14: Simulation Results for Finite FSS TM 0°, 30°, and 60°

3.169 GHz, 3.105 GHz, 3.025 GHz

Figure 15: Simulation Results for Finite FSS TE 0°, 30°, and 60°3.268 GHz, 3.196 GHz, 3.142 GHz 19

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Simulation Results for Finite with PEC FSS at Different Angles

Figure 16: Simulation Results for Finite with PEC FSS TE 0°, 30°,and 60°

3.34 GHz, 3.223 GHz, 3.106 GHz

Figure 17: Simulation Results for Finite with PEC FSS TM 0°, 30°,and 60°

3.322 GHz, 3.241 GHz, 3.088 GHz

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Measured and Simulation Results for Infinite FSS

Figure 18: Measured and Simulated Results for Infinite FSS TE 0°

Figure 19: Measured and Simulated Results for Infinite FSS TE 30°

Figure 20: Measured and Simulated Results for Infinite FSS TE 60°

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Measured and Simulation Results for Finite FSS

Figure 24: Measured and Simulated Results for Finite FSS TE 0°

Figure 25: Measured and Simulated Results for Finite FSS TE 30°

Figure 26: Measured and Simulated Results for Finite FSS TE 60°

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Measured and Simulation Results for Finite with PEC FSS

Figure 33: Measured and Simulated Results for Finite with PEC FSS TE 0°

Figure 34: Measured and Simulated Results for Finite with PEC FSS TE 30°

Figure 35: Measured and Simulated Results for Finite with PEC FSS TE 60°

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Comparison Between Infinite, Finite and Finite with PEC

FSS Design

InfiniteFSS

FiniteFSS

Finite FSS+PEC

Angle ( )𝜃 Frequency (GHz)

Bandwidth (GHz)

Frequency (GHz)

Bandwidth (GHz)

Frequency (GHz)

Bandwidth (GHz)

Simulated

0° 3.241 0.594 3.268 0.598 3.34 0.60230° 3.132 0.360 3.196 0.476 3.223 0.57560° 2.9808 0.226 3.106 0.421 3.142 0.539

Measured

0° 3.256 0.592 3.259 0.211 3.313 0.60130° 3.11 0.320 3.169 0.191 3.178 0.56860° 2.9626 0.224 3.005 0.176 3.025 0.526

Table 2: Simulated and Measured Results for TE polarization

Table 3: Simulated and Measured Results Differences

InfiniteFSS

FiniteFSS

Finite FSS+PEC

Angle ( )𝜃 % age % age % age

Measured and

Simulated

0° 0.46 0.275 0.808330° 0.7016 0.8448 1.39660° 0.6105 3.251 3.7239

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Conclusion and Recommendations for Future Work

• TE mode shows greater dependence on variation of the scan angle in theta ( ) than the TM mode does. 𝜃

• 1x1 and 2x2 Infinite FSS show the same performance.

• PEC components increased the resonant frequency and also reduce the transmission signals.

• The expected resonance frequencies are achieved (2-5 GHz).

• Measured and simulated results are similar.

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Future Work

• Rings elements can be applied to high power microwave applications as Aviation sector does [4].

• Minimizing the circle dimension, high resonance frequencies will be obtain.

• The sensitivity of elements can be reduce further.• That design can be used for 3D circular ring application

which is already proved in [5].• Measured Finite FSS Bandwidth size can be increase.

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References

[1]. F. Bayatpur, "Metamaterial-Inspired Frequency-Selective Surfaces," University of Michigan, pp.1-4, 2009.

[2]. E. Parker and S. Hamdy, "Rings as elements for frequency selective surfaces," Electronics letters, vol. 17, pp. 612-614, 1981.

[3]. T. K. Wu, "Frequency-selective surface and grid array," Wiley, New York, 1995.

[4]. S. Pugh, "Investigating the Use of Frequency Selective Surfaces in High Power Microwave Applications," Air Force Institute of Technology, DTIC Document 2010. 

[5]. S. N. Azemi, K. Ghorbani, and W. S. T. Rowe, "3D Frequency Selective Surfaces," Progress In Electromagnetics Research C, vol. 29, pp. 191-203, 2012.

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Thank You for Listening