Microstrip Wideband Band Stop Filter with IDC Loaded Open Loop Resonator

IJSTE - International Journal of Science Technology & Engineering | Volume 3 | Issue 04 | October 2016 ISSN (online): 2349-784X

Microstrip Wideband Band Stop Filter with IDC Loaded Open Loop Resonator Jitendra Kumar Department of Electronics & Communication Engineering Madan Mohan Malaviya university of Technology Gorakhpur, India

R. K. Chauhan Department of Electronics & Communication Engineering Madan Mohan Malaviya university of Technology Gorakhpur, India

Abstract Microstrip wideband band stop filter with inter-digital capacitor (IDC) loaded open loop resonator for ultra-wideband applications. The wideband characteristic of the proposed band stop open loop resonator is enhanced due to electrical coupling gap replaced by IDC. One additional stub is added at the corner of structure to increase the skirt selectivity. The properties of the designed filter have a small size, wideband rejection and better selectivity for the 50Ω input and output ports. The proposed band stop filter covers the size of 0.25λ_g×0.25λ_g.the proposed filter is designed using commerciality available simulation tool HFSS. Keywords: Band stop filter, Folded resonator, Inter-digital capacitor ________________________________________________________________________________________________________ I.

INTRODUCTION

Band stop filter are recently used in wireless communication system. It has many features such as good resolution for ranging, compact size and high selectivity. In this paper a new compact size band stop filter with IDC open loop resonator is design which has frequency bandwidth from 3.4 GHz to 6.6 GHz. This has many useful applications for medical imaging system and vehicular radar systems. Micro strip wideband band stop filter with open stubs for tunable bandwidth can be performed by setting the position of L-shaped stubs [1]. An additional open stub is used for improving the performance but also arises size problem [2]. A ripple level was introduced to enhance the rejection level by applying cross coupling across the stop band [3]. By increasing transmission zero the performance of band stop filter was improved by using extra open circuit quarter wavelength resonator because of this a large bandwidth was achieved but the size was large [4]. A 5th-order and 5th no. of zeros quasi-elliptic band stop filter is proposed in [5]. Uniplanar band stop filter has been proposed using two bended open-end stubs and a bended connecting line between these stubs [6].Another effective approach for improving the stop band performance by using load of shunt stubs at the input and output terminal [7]. Transmission zero can be obtained by the interference signal between two transmission paths [8].

In this letter a wideband band stop filter is achieved by inter-digital capacitor loaded (IDC) with open loop resonator and the performance of band stop filter is much improved. This filter has compact size and ease to fabricate. Many design technique have been use to minimize the size of micro strip filter [9-11]. But these filters are bulky in size and increase the complexity.

Therefore wide band reject filter have been designed to reduce the complexity and size. An EM simulation is performed using HFSS simulator based on EM theory of transmission lines.

II. FILTER STRUCTURE The proposed band stop filter is folded into C shape structure. Its length is less than the wavelength at center frequency 5.5 GHz. For improving the performance, coupling gap is replaced by interdigital capacitor (IDC) for the sharp rejection at both end, an additional stub is added at the corner of structure to create the transmission zero of both side of stop band and also increases the selectivity of band stop filter. The proposed band stop filter is used by electrically coupled open stubs with IDC load. Fig.1 shows the band stop filter using IDC loaded open loop resonator are λg /4, where λg is the guided wavelength of the micro strip line at the mid frequency.

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Microstrip Wideband Band Stop Filter with IDC Loaded Open Loop Resonator (IJSTE/ Volume 3 / Issue 04 / 032)

Fig.1 Configuration of the compact wideband band reject filter

Band stop filter is design on substrate of thickness (h)= 0.615mm and Rogers RT/ duroid 6006 with relative permittivity 6.15 and 50Ω line are terminated at both end of filter. HFSS simulation for is used for extracting the coupling coefficient to 50 ohm micro strip feed.

Study of the structure is done by breaking into two parts one is even mode and second is odd mode excitation. The proposed band stop resonator is used by electrically coupled open stubs with loaded by inter-digital capacitor.

(a) (b) (c) Fig. 2: (a) Design resonator with open stubs unit. (b) even-mode excitation (c) odd-mode excitation

Proposed band stop filter is based on the electromagnetic (EM) field theory and the Input impedances of the even mode and odd mode of the transmission line is as follows.

ZOe1 ∗ ZOe2 ZOe1 + ZOe2 ZO ∗ ZOo2 = o1 Z0o1 + ZOo2

Zoe = ZOo Where, Zoe1 = −jZo Cot(βl1 ), Zoe2 = −jZo Cot(βl2 ) ZOo1 = −jZ0 tan(βl1 ), ZOo2 = Zo

ZL Cos (βl1 ) + jZo Sin (βl2 ) Zo Cos (βl1 ) + jZL Sin (βl2 ) 1 ZL = jω(2c)

III. SIMULATION DESIGN The length of L1 is 6.5mm and L2 is 6.5mm with center frequency of 5.5 GHz. Width of the BSF is 0.93mm and the gap between inter-digital capacitor is 0.1mm and length of IDC IS 0.8mm. The input port is terminated at the 50Ω line as well as output port.

The center frequency lies at 5.5 GHz, and the overall bandwidth is 3.20 GHz below the 3 (dB). Fig.3 is shown the simulation result of the wideband BSF which has insertion loss (S21) is -16 dB and return loss (S11) is -0.05 dB. The overall physical size is 0.25λg×0.25λg .

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Microstrip Wideband Band Stop Filter with IDC Loaded Open Loop Resonator (IJSTE/ Volume 3 / Issue 04 / 032)

Fig. 3: frequency responses of the proposed wideband band reject filter Table – 1 COMPARISON WITH MANY WIDEBAND BANDSTOP FILTER Ref.

đ?‘“0 (đ??şđ??ťđ?‘§)

Order

No. of zeros

FBW %

Attenua-tion (dB)

[1] [3] [5] [7] [8] This work

6.1 4 1.5 1 2 5.5

1 5 5 7 1

2 3 5 5 4 2

47 113 140 100 64

33.9 23 20 20 20 17

Size đ?œ†đ?‘”2 0.101 0.181 0.040 0.056 0.109 0.062

IV. CONCLUSION A compact microstip wideband band stop filter with IDC loaded open loop resonator is designed. The proposed band stop filter has wide bandwidth of stop band, good insertion loss (S21) -16 dB and good return loss (S11) -0.05 dB. Proposed Filter has also very small in size as compare to other previously reported band stop filters that are given in Table 1 and designed resonator increases the sharp selectivity without increase the patch size.

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