Abstract
Abstract. A compact (0.16 g × 0.08 g ) and wide stop-band lowpass filter design using open complementary split ring resonator (OCSRR) and defected ground structure (DGS) is presented in this paper. Low pass filter is con-structed using two cascaded stages of OCSRR. Since the rejection bandwidth of the OCSRR is narrow, tapered dumbbell shaped DGS section is placed under the OCSRR to enhance the bandwidth. The cutoff frequency (f c ) of the proposed lowpass filter is 1.09 GHz. The rejection band-width of the filter covers the entire ultra wideband spec-trum. Hence the spurious passband suppression is achieved up to 10 f c . The designed filter has been fabri-cated and validated by experimental results. Keywords Lowpass filter, defected ground structure (DGS), open complementary split ring resonator (OCSRR) 1. Introduction On the motive of conventional filter design methods such as stepped impedance and open stub suffering from poor skirt characteristics and spurious passband, re-searchers have paid great attention over the past few years in designing a compact and sharp cutoff lowpass filters with spurious free wide stopband. Lowpass filter using different defected ground structures (DGS), photonic bandgap (PBG) structures and electromagnetic bandgap structures have been proposed in various literatures [1–9]. Sharp cutoff and low insertion loss lowpass filter using a complementary split ring resonator (CSRR) is reported in [3]. Cascaded stages of CSRR with open stub configura-tion, exhibiting sharp cutoff lowpass response are pre-sented in [4]. Planar photonic bandgap (PBG) structures involving compact microstrip resonating cell (CMCR) are utilized to design a lowpass filter with wide stopband [5]. Recently, a lowpass filter with very sharp transition band using OCSRR is demonstrated in [6]. In this paper, a new technique is proposed to reduce the size of the lowpass filter and to obtain the wide spurious free stopband. The lowpass filter is designed using open complementary split ring resonator and a tapered dumbbell shaped DGS is placed under the OCSRRs to extend the stopband. The proposed lowpass filter is smaller and outperforming the existing filters in terms of insertion loss level, roll off rate and rejection bandwidth. Figure 1 shows the schematic of OCSRR printed on the microstrip line. This structure is first proposed in [6] for designing a sharp cutoff lowpass filter with compact size. OCSRR is a negative image of the open split ring resonator. To study the frequency response characteristics of the OCSRR, this structure is designed on Rogers 5880 substrate with a dielectric constant of 2.2 and a substrate thickness of 0.381 mm and simulated using an Ansys full wave simulator.
Highlights
On the motive of conventional filter design methods such as stepped impedance and open stub suffering from poor skirt characteristics and spurious passband, researchers have paid great attention over the past few years in designing a compact and sharp cutoff lowpass filters with spurious free wide stopband
Lowpass filter using different defected ground structures (DGS), photonic bandgap (PBG) structures and electromagnetic bandgap structures have been proposed in various literatures [1,2,3,4,5,6,7,8,9]
Since the open complementary split ring resonator (OCSRR) is printed on the microstrip itself, it will change the line inductance and capacitance resulting in a slow wave effect
Summary
On the motive of conventional filter design methods such as stepped impedance and open stub suffering from poor skirt characteristics and spurious passband, researchers have paid great attention over the past few years in designing a compact and sharp cutoff lowpass filters with spurious free wide stopband. Sharp cutoff and low insertion loss lowpass filter using a complementary split ring resonator (CSRR) is reported in [3]. Planar photonic bandgap (PBG) structures involving compact microstrip resonating cell (CMCR) are utilized to design a lowpass filter with wide stopband [5]. A transmission zero is observed at the resonance frequency f0 = 2.46 GHz. Since the OCSRR is printed on the microstrip itself, it will change the line inductance and capacitance resulting in a slow wave effect. It is observed that the SWF of the microstrip line loaded with OCSRR is increased by 73 % compared to the microstrip line without OCSRR. The increase in SWF validates the size reduction capability of the OCSRR for microwave applications
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