MICROWAVE RESONATOR

TITLE

Design of resonator with split ring resonator and defected ground

structure with sharp transition band

AJEET KUMAR

TABLE OF CONTENTS

S no. TOPIC Page no.

1. Abstract 4

2. Introduction 5

3. Split ring resonators 6

4. Design Model Specifications 7

5. Design steps in HFSS 8

6. Simulated s-parameter output Graph 9

7. Coupled split Ring Resonator Structure 13

8. Advantage of SRR structure 17

9. Conclusion 19

10. References 20

ABSTRACTWe present a systematic simulated study of individual and coupled

split ring resonators (SRRs) of rectangular ring with one and two gaps. The behavior of the magnetic field, the magnetic resonance frequency and the currents in the SRRs from a single SRR to strongly interacting SRR pairs in different orientations. The coupling of SRRs along the E direction (y) results to shift of the magnetic resonance frequency to lower or higher values, depending on the capacitive or inductive nature of the coupling. The strong SRR coupling along propagation direction (x) results in splitting of the single SRR resonance into two distinct resonances associated with field and current distributions. For the design and simulation, HFSS 3D simulation tool is used. On comparison it is observed that the SRR filter provides improved performance over the conventional type filter designed using insertion loss or stepped impedance methods. Our aim is to design a deep sharp cutoff and compact low-pass filter.

INTRODUCTION

In modern wireless communication, compact size and high performance filters are required to reduce the cost and enhance system performances.

The defected ground structure (DGS) for microstrip lines or coplanar waveguide (CPW) such as various photonic band gap (PBG) structures have become interesting areas of research due to their extensive applicability and use in microwave circuits.

DGS, i.e. etching off a defected pattern from the backside metallic Ground-plane has periodic structures provide rejection of certain frequency band, like band gap effects.

The resonant elements allow larger attenuation in the stopband and higher harmonic suppressions to be obtained with less number of periodic structures as compared to the conventional DGS. Also, by using the proposed equivalent SRR model, a compact LPF has been optimally designed with very high attenuation at the cut-off frequency.

SPLIT RING RESONATORS

Design Model

Individual SRRs• Single gap• Two gaps• Four gaps

Design in HFSS

Graph for 0.2mm gap in Square SRR

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00Freq [GHz]

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

Y1

OneGapSRRDGSXY Plot 1 ANSOFT

Single gap Plot

-56dB at 4.2GHz

Curve Info

dB(S(1,1))Setup1 : Sw eep

dB(S(2,1))Setup1 : Sw eep

Graph for 1.2 times scaled dimension of each objects in the design

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

Y1

OneGapSRRwith1.2timesscaleXY Plot 1 ANSOFT

At 3.5GHz -16dB, w hich is no so much signif icant

Curve Info

dB(S(2,1))Setup1 : Sw eep

dB(S(1,1))Setup1 : Sw eep

Graph for 0.4mm gap in the Square SRR

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-35.00

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

Y1

OneGapSRRWith.4mmgapXY Plot 1 ANSOFT

Curve Info

dB(S(1,1))Setup1 : Sw eep

dB(S(2,1))Setup1 : Sw eep

It gives very sharp transition band as well as the stopbandattenuation (deep) is -31dB which is acceptable for practical purposes.

1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00Freq [GHz]

-45.00

-40.00

-35.00

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

Y1

HFSSDesign1XY Plot 1 ANSOFT

m1

m2 m3

At 4.1GHz the attenuation is -11.682dB

Curve Info

dB(S(P1,P1))Setup1 : Sw eep

dB(S(P2,P1))Setup1 : Sw eep

Name X Y

m1 4.1000 -11.6820

m2 3.9000 -2.4307

m3 4.6000 -2.4335

Graph with one gap SRR coupling for the given orientiation

COUPLED SPIT RING RESONATOR STRUCTURES

Coupling of the SRRs along the E direction results to shift of the magnetic

resonance frequency to lower or higher values, depending on the

capacitive or inductive nature of the coupling respectively.

Capacitive or inductive coupling is determined by the relative orientation of

the interacting SRRs. If orientation is associated with strong magnetic field

(and negligible electric field) in the area between the SRRs, it indicates

strong inductive coupling while if orientation is associated with strong

electric field (and negligible magnetic field), it indicates strong capacitive

coupling.

Different orientations and coupling of SRRs

Different orientations and coupling of SRRs

with four gaps

Note: Our aim is to simulate all the orientations and coupling off SRRs in HFSS

and to observe the resultant resonant frequency

ADVANTAGES OF DGS(SRR) STRUCTURE

It is simple to implement and analyze

Practical results are in agreement with simulation

It offers a wide range of frequency, since by changing orientation, number

of gaps or the gap width, we can decrease or increase the resonant

frequency or possibly the filter response as per the requirement.

Design is robust and is based on easy principle of inductive and capacitive

coupling

CONCLUSION

From the above design and simulated results, we come to conclusion that any type of filters can be designed just by varying the orientation of coupling of SRRs or by varying the gap width of SRR or by increasing the number of gaps in the SRR.The observed results are as follows:

Specification Cut-off frequency Stop-Band Attenuation

Gap 0.2mm 4.1 GHz -58 dB

Gap 0.4mm 5.0 GHz -37 dB

Designed parameters scaled to 1.2 times

3.5 GHz -16 dB

Coupling with Gap 0.2mm, d=1mm

4.1 GHz -11.68 dB

We also see that the transition band is much more sharp and the stop-band attenuation is also very high. The practical implementation of these filters are also easy and the give results approximate to the simulated result.

REFERENCES

[1] Microwave Engineering by David M Pozar, 3rd edition

[2] Multi-gap individual and coupled split-ring resonating structures by R.

S. Penciu, K. Aydin, M. Kafesaki,Th. Koschny, E. Ozbay, E. N. Economou,

C. M. Soukoulis

[3] Effects of a Lumped Element on DGS with Islands by Jonguk Kim, Jong-Sik Lim, Kwangsoo Kim, and Dal Ahn