Dual-Band SRR Using CRLH TL-Based Elements

Ousama Abu Safia, Larbi Talbi

Electrical Engineering Department

University of Quebec in Outaouais Gatineau, Quebec, Canada

abuo01@uqo.ca, larbi.talbi@uqo.ca

Khelifa Hettak

Wireless Systems Branch

Communications Research Centre

Ottawa, Ontario, Canada

khelifa.hettak@crc.ca

Abstract—In this paper, a new dual-band split ring resonator

based on composite right-/left-handed transmission line-based

elements is proposed. The distributed elements within the resonator

are patterned in the centre strip of a folded coplanar waveguide

transmission line. The new elements which are deployed in a

prototype transmission line-based inclusion provide a dual-band

resonance behavior. The design procedure and theory behind the

new inclusion are introduced. Simulated results agree well with the theoretical results.

I. INTRODUCTION

Microstrip and coplanar waveguide (CPW) transmission lines are usually used to synthesize left-handed artificial lines. Left-handed wave propagation mediums can be obtained by loading conventional lines with proper split-ring resonators (SRR) [1], or using passive elements [2]. The resultant is a combination of a right-handed and a left-handed propagation bands. Hence, these lines are called composite right-/left-handed transmission lines (CRLH TLs).

In [2], Caloz shows that CRLH TLs have a dual-band behavior. Several structures using this property have been reported [2],[3]. Dual-band microwave devices based on these lines have lower losses and larger bandwidths compared to conventional structures.

This paper introduces a new dual-band SRR inclusion based on a geometrical modification of a prototype transmission line-based SRR inclusion [4]. The new structure utilizes the two main metamaterial design approaches: the resonance-type approach, and the CRLH TL approach. The new inclusion can be used as a dual-band bandstop filter.

The paper is organized as follows: Section II develops the idea of using CRLH TLs within distributed passive elements to have the dual-band property. Section III proposes the design procedure for the new inclusion. Section IV introduces a design example of the new inclusion, and shows its simulated results as well as a brief discussion about the results.

II. THEORITICAL BACKGROUND

In conventional SRR, the capacitive and inductive elements within the inclusion are functions of the inclusion's geometry [1]. These elements are generally treated as frequency independent elements, and hence, one resonant frequency is considered [1].

Recently, a new SRR inclusion based on frequency-dependent passive elements is proposed [4]. Because its passive elements are based on conventional transmission lines, periodic resonances at odd harmonics are obtained. The inclusion resonates at a frequency having a guided wavelength equals eight times its stubs' lengths, as well as higher-order odd harmonics. Therefore, the second resonance can be controlled if suitable CRLH TLs replace the conventional lines [2].

Fig. 1 shows the layout of a dual-band distributed capacitor. This capacitor is placed in the new SRR inclusion as shown in the next section. The capacitor has an open-ended CRLH TL that replaces the conventional open-ended line [4]. The new line is patterned in the centre strip of a CPW TL. It has a left-handed part consists of two distributed capacitors across the gaps in the centre strip separated by shunt-connected inductive lines. The right-handed part of the line consists of the conventional lines sections located at each extremity of the left-handed part. The widths of the capacitive gaps and the inductive lines are chosen such to reflect the line's lumped elements values.

Fig. 1. Layout of the CRLH CPW TL-based capacitor

III. DUAL-BAND RESONANCE

Fig. 2 shows the TL-based inclusion proposed in [4]. The capacitive element is implemented using a folded open-ended line patterned in the centre strip of a CPW. The inductive element is implemented using a similar short-ended line. The formula of the resonant frequency is developed in [4].

Fig. 2. Layout of the transmission line-based SRR [4].

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The modified geometry which allows dual-band resonance behavior is shown in Fig. 3. The capacitor shown in Fig. 1 is folded and placed in the inclusion. Moreover, a similar folded short-ended element is used for the inductive element. The design procedure for the new inclusion is summarized as follows.

1) The values of the two resonances are specified. Moreover,

the characteristic impedance of the right-handed part of the

CRLH TL within the inclusion, and the left-handed cells'

number should be determined [5].

2) In order to have the dual-band resonance behavior, the

electrical lenght of the open-ended and short-ended CRLH TLs

should equal 450 at the first resonance and 1350 at the second

resonance [4]. These two values satisfy the resonance condition

in the inclusion [4]. Using the formulaus in [5] the values of the

reactive elements, CL , LL, and the electrical length of the right-

handed part of the CRLH lines can be determined.

3) The capacitance of the gap in the left-handed section is

adjusted by optimizing its width in order to get the closest

response to the equivalent LE capacitor's response. Moreover,

the width of the shunt-connected inductive line is chosen so that

its response matches its equivalent LE inductor's response.

4) The open-ended and short-ended lines are folded and

enclosed in a square-shape layout. Then, inclusion is loaded into

a suitable host transmission line.

IV. DESIGN, SIMULATION, AND RESULTS

In this section a design example of a dual-band SRR that resonates at 4 GHz, and 4.5 GHz is introduced. Fig. 3 shows the layout of the new inclusion loaded into a CPW TL. The inclusion is simulated on RT/Duroid 6010 substrate with a dielectric constant of 10.2 and a thickness of 0.635 mm.

The left-handed parts in the CRLH TLs consist of one symmetrical cell. The folded CPW TL used to build the inclusion has a characteristic impedance of 73.9 Ohms and an effective permittivity equals 5.54. Following the aforementioned design procedure, CL and LL equal 0.11 pF and 0.76 nH, respectively.

Fig. 3. Layout of the proposed inclusion loaded into a host CPW TL (a) Bottom

view. (b) Top view. (all dimentions in mm)

Fig. 4 shows the simulated response of the inclusion, and Table I shows its performance parametric.

Fig. 4. Simulated response of the dual-band SRR loaded into a CPW TL.

TABLE I. PERFORMANCE OF THE PROPOSED INCLUSION

Parameter First resonance Second resonance

Resonant frequency 4.08 GHz 4.44 GHz

Return loss 1.31 dB 0.98 dB

Insertion loss 17.5 dB 19.74 dB

Q-factor 227.11 246.78

The inclusion has two resonance at 4.08 GHz and 4.44 GHz.

A small shift at each resonance is noticed compared to the

theoretical designed values. This shift can be explained as a

result of the undesirable TL discontinuities within the inclusion.

The insertion losses, return losses, and Q-factors at each

resonance demonstrate the high performance of the inclusion.

V. CONCLUSION

This paper introduces a new design of a dual-band SRR using CRLH TL-based elements. The location of the two resonance frequencies is controlled by choosing the appropriate passive elements within the LH part, and the electrical length of the right-handed part of each of the CRLH TL-based elements. A design example which follows a proposed design procedure is introduced. The inclusion has a high performance response at each resonance.

REFERENCES

[1] R. Marqués, F. Martín, and M. Sorolla, Metamaterials With Negative Parameters: Theory, Design and Microwave Applications. New York:

Wiley, 2008.

[2] I-Hsiang Lin, M. DeVincentis, C. Caloz,and T. Itoh, “Arbitrary dual-band

components using composite right/left-handed transmission lines,” IEEE Transactions on Microwave Theory and Techniques, vol.52, no.4, pp.

1142- 1149, April 2004.

[3] Xian Qi Lin, Ruo Peng Liu, Xin Mi Yang, Ji Xin Chen, Xiao-Xing Yin; Qiang Cheng, and Cui, Tie-Jun, “Arbitrarily dual-band components using

simplified structures of conventional CRLH TLs,” IEEE Transactions on Microwave Theory and Techniques, vol.54, no.7, pp.2902,2909, July 2006.

[4] O. Abu Safia, L. Talbi, and K. Hettak, “A new type of transmission line-

based metamaterial resonator and its implementation in original applications,” IEEE Transactions on Magnetics, vol.49, no.3, pp. 968,973,

March 2013.

[5] C. Caloz and T. Itoh, Electromagnetic metamaterials: Transmission line theory and microwave applications, Wiley-IEEE Press, Hoboken, New

Jersey 2005.

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