Cross Coupled Band-Pass Filter Using Dual Square Complementary Split Ring Resonator For Wireless Communication

Aviral Verma *   Manish Kumar **  
* PG Scholar, Department of Electronics and Communication Engineering, Madan Mohan Malaviya University of Technology, Gorakhpur (U.P.), India.
** Associate Professor, Department of Electronics and Communication Engineering, Madan Mohan Malaviya University of Technology, Gorakhpur (U.P), India.

Abstract

This paper proposes a wide pass-band filter using combination of transmission lines and square resonator structures arranged in symmetrical fashion, for numerous wide band applications. Dual-Square Complementary Split Ring Resonators with permittivity of 2.65 are identified to contribute for wider bandwidth of the filter. This novel approach enhances the coupling phenomenon and also reduces the insertion loss in the spectrum of passband. To demonstrate the advantages and practicality of this approach at the preferred band, the return and insertion losses of the filter were scrutinized. Band-pass filters play a considerable role in wireless sector. Frequency selection plays a central role in filtering. Signals have to be filtered at a specific center frequency with certain bandwidth during acquisitions. Cross dualparallel coupling at the arms provide better results in terms of frequency selectivity, rejection rates, fraction band width, and Q-factor along with low average insertion losses in comparison to other filtering techniques.

Keywords :

Introduction

Filter techniques are used for frequency selections and especially in regions which are prone to interference of data and information. Band-pass filter is able to perform selection of signals within a specified passband at particular center frequency while discarding unwanted frequencies (Alaydrus, 2010). Band-pass filters are used for transmission of signals and to eliminate undesired signals (Darwis and Permana, 2012).

Micro-strip filtering is a vital component of wireless communication systems (Gao et al., 2012; Kuo and Lai, 2012). Harmonic fluctuations in micro-strip filters unfortunately degrade the performance of the system (Lopetegi et al., 2001; Hong and Lancaster, 2004). Considering the basic mechanism of microwave, these band-pass filters have found varied applications in Radio Frequency (RF) /Microwave Circuits and contribute largely for the performance enhancement in communication systems. Band-pass filters are used in wireless applications like satellite and mobile communication.

Standard patch filters are preferably used by engineers as they provide simple designing, planar structure and easy fabrication. Researchers have proposed diverse prototypes for minimizing the size and improving the performance of filters. Hairpin resonator, step impedance resonator, ring resonator, defected ground structures are some designs to improve the band-width of filtering techniques (Srisathit et al., 2010). Ring resonators are used as they provide small size and sharp rejection rates (Chang, 1996; Hong and Lancaster, 2004).

Easy fabrication, wider bandwidth and planar frame can be attained using coupling designs (La and Han, 2016). Excellent coupling and enhanced band-width is proposed by Shaman (2012), which uses three coupled lines. Loading stubs are implemented along with line resonators (Shaman and Hong, 2007). Use of transmission elements and microstrips can constrict the rejection band (Nguyen, 1994). Each micro-strip line distributed at the edges is grounded, which provides transmission zeros at the passband. Multimode resonators amalgamated with micro-strip lines provide increased wide band (Zhu et al., 2005; Wong and Zhu, 2009). Spectral domain filter approach proposed by Schwindt and Nguyen (1994) provides a Fractional Bandwidth (FBW) of nearly 60%. Wide band-pass filter which uses three or more coupling have also been proposed (Deng et al., 2010; Sun and Zhu, 2006; Kuo et al., 2001; Chu et al., 2011; Wu et al., 2011; Chu and Tian, 2010). Quasi- Chebyshev technique to achieve a FBW of 50% using multiple mode resonators is shown in the works of Chiou et al., (2006). Metamaterials designed with Split Ring Resonators (SRR) are essential structures to depict Negative permittivity, whereas Complementary Split Ring Resonators (CSRR) are used as negative permittivity (Pendry et al., 1999). Resonator structures are used to increase the frequency selectivity and rejection rate of the filter (Bonache et al., 2007).

This paper aims to develop a wide passband filter using cross coupling of micro-strip lines with symmetrically aligned Dual Square Complementary Split Ring Resonators (DS-CSRR), to enhance the characteristics and frequency selection rates. Lower value of resonant frequency is obtained and also transmission zeros are present at the edges. Characteristic impedance of 50 ohm is designed for input/output feed lines. The proposed wide bandpass filter and the results obtained are discussed in further sections of this work.

1. Proposed Wide Band-Pass Filter Design

The proposed design conceptualizes improvement in previous filter designs and also, how its operability can be extended to acquire enhanced fractional bandwidth and lower value of Q-factor. A novel cross coupled structure with CSRR is shown in Figure 1. Benzocyclobutene (BCB) is used as substrate material. It has a permittivity of 2.65 and a thickness of 0.8 mm which is maintained throughout the design.

 

To match the characteristic impedance of 50 ohm, 2.14 mm width (w) of micro-strip line is used. Simulation is done using ANSOFT HFSS 13.0. Cross coupled arms which have Quad coupling features along with two symmetrically aligned CSRR are used in the design.

The dimensions of the structure and the vivid parameters used are listed in Table 1. Cross coupled micro-strips and SRR structures are used for attaining wider bandwidth.

Table1. Various Parameter Dimensions in the Design

2. Results and Discussion

The simulation carried on using software ANSOFT HFSS 13.0 and the spread of frequency for the proposed design of filter are shown in Figures 2 and 3. Figure 2 shows the return loss spectra of the design which is approaching 13 decibels whereas Figure 3 shows the results of insertion loss in close proximity of 0 decibel in the spread. The insertion loss of wide-band filter is below 30 decibels in the range of 0 to 2.7 GHz and below 12.8 decibels in the range of 6.7 to 8 GHz. Return loss in the stop-band spectrum is close to zero decibel. Fractional bandwidth is nearly 60% which states a low Q-factor.

Figure 2. Return Loss Result of Proposed Cross Coupled BPF using CSRR

Figure 3. Insertion Loss Result of Proposed Cross Coupled BPF using CSRR

High rejection rate and selectivity of -45.2 decibels at 2.7 GHz and -40.4 decibels at 6.7 GHz respectively are seen due to transmission zeros present on both sides of passband. Figures 4 and 5 determine the group delay characteristics of S11 and S21 transmission parameters respectively. A nearly constant group delay in close proximity of 0.3 ns (nanosecond) is shown in Figure 5 at the respective centre frequency of 4.97 GHz. Table 2 shows the comparison of various other designs of band-pass filter.

Figure 4. Group Delay Response at S11

Figure 5. Group Delay Response at S21

Table 2. Comparison with Various other Topologies

Conclusion

An improved band-pass filter at an operating frequency of 4.97 GHz is designed and presented in this work. Cross coupled lines and symmetrically aligned square shaped CSRR is used in the design. Cross micro-strips provide a firm coupling. Insertion loss, on an average, is low in the passband. Return loss is somewhat more than 13 decibels. Further, FBW is excellent resulting in very low Q-factor, which demonstrates a wider spectrum; compact size, planar configuration along with excellent frequency selectivity and keen rejection rate of passband are also attained.

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