FSS PPT Final Show (2)

© Soumya Saha 1

Project on a Frequency Selective Surface with

Multi Frequency Operation1 Soumya Saha, 2 Supriyo Das,3 Sangita Sarkar,4 P.P. Sarkar

1,2,3,4 D.E.T.S, University Of Kalyani, Kalyani, India

© Soumya Saha 2

Introduction• Frequency Selective Surfaces (abbreviated as FSS) is any planar

surface designed as a ‘filter’ for microwave frequency waves. • These are formed by a two dimensional array of metallic patches

printed on a dielectric substrate.• The response of FSS to incident radiation varies with frequency. • They have found wide use in various applications such as screening a

radar transmitter or receiver from hostile emissions and providing a reflective surface for beam focussing in a reflector antenna system.

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FSS Characteristics• Typically narrow band• Periodic, typically In 2-D• Element type: dielectric r metallic/circuit• Depends upon element shape, size• Depends upon element spacing and orientation

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Evolution of FSS

• Once exposed to the electromagnetic radiation, a FSS acts like a spatial filter: some frequency bands are transmitted and some are reflected• Early 1960s, FSS structures have been the subject of intensive study

for Military Application.• Marconi and Franklin are believed, to be the early pioneers in this

area for their contribution of a parabolic reflectors.

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Evolution of FSS(Cont.)• Nippon designed shied film for windows that can shield the desired

frequency i.e. 2.45 GHz for WLAN or 1.9 GHz for PHS (Personal Hand phone Systems).

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FSS General Mechanism

• FSS is based on Resonance.• EM-wave illuminates an array of metallic elements, thus exciting

electric current on the elements.• The amplitude of the generated current depends on the strength of

the coupling of energy between the wave and the elements.• The coupling reaches its highest level at resonant frequency, when

the length of elements is a λ / 2.• Hence elements are shaped so that they are resonant near the

frequency of operation.

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FSS General Mechanism (Cont.)

• Current which acts as an EM source which gives a scattered field.• Each phase front has its on-delay. These scattered radiation add up

which makes transmission of that signal.• Scattered field + incident field which results total field in the space

surrounding the FSS. By controlling the scattered field, we can able to design required filter response.• Distribution of the current on the elements determines the frequency

behaviour of the FSS.

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Resonance Characteristics of FSSDepends upon:• On the way the surface is exposed to the electromagnetic wave.• Incidence angle of the wave.• Effective aperture size of the FSS• Diffraction gratings.• Periodicity of cells.• Substrate that supporting the FSS element• Inter element Spacing.• Arrangement of Elements.

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FSS Design Types• Patch-Type : Capacitive Response, acts as a Band Stop Filter• Mesh-Type : Array of slots is Inductive, acts as a Band Pass Filter

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Software Used• ANSOFT Designer® : is a microwave engineering CAD suite that allows

for circuit and full wave Simulation.

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Simulation Setup MethodsThe methods used to setup the simulation are outlined. In particular, the following steps were followed:• Planar EM Design Setup which includes • Layout Technology Selection• Layer Design & Type Selection

• Model Setup• Excitation Setup• Analysis Setup• Plotting Results

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Design Approach of FSSThe FSS structure consists of two dimensional arrays of patches. The arrays of metallic patches are aligned on top of a dielectric substrate. The substrate is basically glass-PTFE. Its dielectric constant is 2.4 and thickness is 1.6 mm in conventional FSS structure.

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• Reference Patch

Dimension of each patch is (20 x 20) mm. Periodicity is taken 24 mm along both X and Y direction for constructing array of patches.

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Observations• After Simulation, with ANSOFT Designer® the resonant frequency is

obtained at 11.2 GHz (the deeper one is considered) and the value of percentage bandwidth is 14.06.

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Observations (Cont.)• According to the transmission characteristics, this model is not

appropriate in the range between 11.8 GHz & 12.2 GHz, as the curve does not show considerable behaviour and gets highly congested in the tolerance level. • The design is further modified for improvements.

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• Modification 1In the 1st step of modification, the square reference patch is converted to H-shaped patch. Within this transformed patch, a circular shaped slot is cut.

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Observations• Further after Simulation, with ANSOFT Designer® the resonant

frequency is obtained at 5.67 GHz (1st one) and 6.86 GHz (2nd one), which shows reduction in resonant frequency (and multiple resonant frequencies indicate multi frequency operation).Compactness has been achieved as the resonant frequency shifts towards left side, i.e. which means size reduction. Also the value of percentage bandwidth obtained are 29.10 (1st one) and 11.7 (2nd one).

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Observations (Cont.)

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• Modification 2• In the 2nd step of modification, FSS patch is further modified by adding

metallic patches to the H-shaped patch as shown.

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frequency is obtained at 5.53 GHz (1st one) and 9.37 GHz (2nd one), which shows reduction in 1st resonant frequency (and multiple resonant frequencies indicate multi frequency operation).Compactness has been achieved as the resonant frequency shifts towards left side, i.e. which means size reduction. Also the value of percentage bandwidth obtained are 31.25 (1st one) and 20.91 (2nd one). Bandwidth utilization has been increased in this design segment.

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• Modification 3In the 3rd step of modification, within this transformed patch, a hexagonal shaped slot is cut.

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frequency is obtained at 3.83 GHz (1st one), 6.12 GHz (2nd one) and 9.20 (3rd one). So far, this is the best design as 3 different resonant frequency is obtained. Also compactness has been achieved as the resonant frequency shifts towards left side, i.e. which means size reduction. Further, the value of percentage bandwidth obtained are 23.45 (1st one), 3.96 (2nd one) and 10 (3rd one). • Being a simple design and having design similarities with the

Modification 1, this can be easily deduced from it.

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Why -10 Db Line ?Because at this level the reflected power is minimum and is equal to the 0.1 of that of the incident power. In theory -3 dB point is widely used where half of the maximum value was taken, but for practical accuracy, we refer to the logarithmic axis and the -10 dB line on the logarithmic scale.

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Conclusion• It has been seen that as the reference patch is modified step by step,

resonant frequency decreases in each step of modification. So it can be said, in each modification step, size reduction is achieved. In step 3 resonant frequency is shifted left most as compared to all other modified designs and reference patch. So the best size reduction is achieved in this step. • Considering number of resonant frequencies obtained in the modified

designs, it can be said that in step 3, three numbers of resonant frequencies are obtained. Frequency separation between resonant frequencies is quite good. In step 3 regarding resonant frequency and number of resonant frequency the best result is obtained. This proposed FSS can be used both as compact one and can be used in multiple resonant frequency operation.

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AcknowledgementOur sincere gratitude to Prof. Partha Pratim Sarkar, Project Head & H.O.D, Department of Engineering & Technological Studies, University of Kalyani, for providing us an opportunity to do our project work on “Frequency Selective Surface with Multi Frequency Operation” as a part of the Final Year B. Tech Curriculum. We, as a team sincerely thank you for your guidance and encouragement in carrying out this project work.

& Special thanks to our M. Tech senior Ms. Diptargha Baul for her support and guidance throughout the project.

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Thank You. Signing Off.Credits:

SOUMYA SAHASUPRIYO DASSANGITA SARKAR

Documents

FSS PPT Final Show (2)