MICROSTRIP UWB BANDPASS FILTER WITH DUAL NOTCH FREQUENCIES

MICROSTRIP UWB BANDPASSFILTER WITH DUAL NOTCH

FREQUENCIES

V.Reji1, R.Kavitha Sudha2

Assistant Professor, ECE Department,SRM University

[email protected]@rmp.srmuniv.ac.in

July 24, 2018

AbstractIn this paper, a miniaturized version of Ultra Wide Band

(UWB) BandPass Filter with dual notch frequencies is pre-sented. The Ultra Wide Band Pass Filter is formed by thecombination of a Low Pass Filter(LPF) and a High Pass Fil-ter(HPF) with chebyshev approximation. The Wide Passband specifications are achieved by Microstrip filter Design.The first method of dual frequency notches are at 5.75 GHzand 8.05 GHz obtained by embedding two open circuit stubson the main Microstrip Line. The equivalent circuit of theproposed filter is also presented in the paper. The filter de-sign is tested and simulated using the Integrated ElectronicSimulation (IE3D) software and the output graphs are alsopresented.

Keywords: Low pass, High Pass, Band pass, Notch,microstrip

1 Introduction

With the announcement of the unlicensed band (3.1 GHz 10.6GHz) by the Federal Communication Commission (FCC) there has

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been enormous research taking place to utilize this frequency band.This is due to the numerous applications that utilize this frequencyband such as surveillance systems, medical imaging system, pulsecommunication, ground penetration radar, etc.

But this unlicensed band of frequencies interferers with two li-censed frequencies namely 5.75 GHz and 8.05GHz which is used inWireless LAN and Satellite Communication respectively. Thus weneed a UWB BandPass Filter which has the ability of accepted theunlicensed band and rejecting the licensed frequencies so that it donot interfere with the applications of unlicensed band. UWB ellip-tical bandpass filter with dual band reported[1]-[3] and notch bandcreated at 2.4GHz and 5.2GHz by square patch resonators simu-lated by Z.C. Hao and J-S Hong et al..Y type filter, compact[4]-[11]ultra-wideband filter Quad notch bands to extract the interferenceof WLAN and WiMAX with good frequency response[2] and smallsize in 2011.Wideband ring resonator BPF with notch band dis-cussed by Kim[13] et.al. Many UWB BPF has been reported witha single notched band with better rejection performance by embed-ding /4 line on the main transmission line. In this paper we haveused the Chebyshev Filter design for both LPF and HPF.

In this paper we have used the Chebyshev Filter design for bothLPF and HPF. Chebyshev filters have the property that they mini-mize the error between the idealized and the actual filter character-istic over the range of the filter, but with ripples in the passband.Cheybyshev filter is a better option than the Butterworth Filter be-cause it gives steeper attenuation in the stop band and thus moreinclined towards the ideal characteristics[5]. Then as the waveg-uide form of LPF and HPF cannot be realised since waveguidesare basically high-pass lines and thus we form the Microstrip con-figuration. The proposed UWB filter is realised using substrate ofdielectric constant 2.2 and substrate height 0.787 mm. The rest ofthe paper contains the design procedure of the filter followed by theresults and discussions.

2 Filter Design

The Ultra Wide Band(UWB) Bandpass Filter is designed for thefrequency of 3 GHz to 11 GHz. To remove the two specified fre-

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quencies such as 5.75 GHz and 8.05GHz we use two individual opencircuit stubs. These are the two notches used for removing the twofrequencies to perturb WLAN and satellite signal interference.

The filter design chosen is the Microstrip Filter design. The[8]UWB filter is formed by the combination of the both the LPF andHPF with different cut off frequencies. Filter designs beyond 500MHz are difficult to realize with discrete components because thewavelength becomes comparable with the physical filter element di-mensions, resulting in various losses. Thus, to arrive at practicalfilters, the lumped components are converted into distributed ele-ment realizations[6]. In the rest of this section the detailed designprocess of each of the individuals sections is described.

3 Low pass Filter Design

A Chebyshevs LPF is designed for the cut off frequency of 11GHz.The ripple in the Chebyshev response is considered 0.5 dB. Bythe Chebyshev LPF design the order of the filter is obtained as 5thus indication the existence of 5 components in the filter. TheChebyshev filter design is chosen to get steeper attenuation in thestop band and equal ripples in stop and pass band. A Pi () typeLPF is considered with 3 capacitors and 2 inductors. The basicformula for lumped element LPF for Chebyshevs filter is:

(1)

To calculate the value of each component of the filter, two im-portant transformations, namely, Impedance and Frequency Trans-formations is used. Further, these low frequency components areconverted to distributed elements for the Microstrip design. Theconversion into distributed elements involves:

(2)

(3)

(4)

The LPF design is shown in the fig. 1

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Figure 1. Dimensions of LPF

The design is implemented based on the two conditions, W/h¡=1and W/h¿=1 and based on that the eff and impedance value iscalculated. These values help in calculating the individual striplengths. The individual capacitive and inductive lengths are cal-culated to get the overall size of the filter. Thus the overall sizeof LPF filter turns out to be 25.347 mm or 2.5347 cm. The Mi-crostrip design helps in achieving the miniaturized version of thefilter. Thus the above mentioned LPF is designed for the cut offfrequency of 11 GHz and with and overall size of 2.5347 cm.

4 High pass Filter Design

To restrict the frequencies below 3 GHz, a High Pass Filter (HPF)is designed with cut off frequency of 3 GHz using Chebyshev design.The filter is designed for 0.2 dB ripple. The Chebyshev HPF de-sign leads to the order of filter as 5 indicating 5 filter components.APi (π) type HPF is considered with 2 capacitors and 3 inductors.The conversion of the lumped elements into distributed elements inHPF is done using namely two transformations: Richards Trans-formation and Kurodas Identities.

(5)

To accomplish this conversion Richards Transformation allowsopen- and short-circuit transmission line segments to emulate theinductive and capacitive behavior of the discrete components. Now

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the series inductance implemented by a short-circuit transmissionline segment is more complicated to realize than a shunt stub line.Thus Kurodas Identity converts the series stub lines to the shuntstubs. The transformed filter after the Richards and Kurodas Iden-tity is shown below in fig. 2.

Figure 2. Kurodas Transformation

Now the elements obtained above are de-normalized and equiv-alent microstrips are obtained[7]. De-normalizing involves scalingthe unit element to the 50Ω input and output impedances and com-puting the length of the lines. Using λ0/8 = vp/(8fc ), the lengthis found out to be l =λ0/8 = 7.5 mm where fc = 3GHz. The finaldesign of the HPF is shown below in fig. 3. Thus the overall lengthof the HFP comes out to be 33.65 mm or 3.3365 cm. Now with theUWB filter design we have achieved selecting frequencies from 3 11GHz. Now the stubs are designed to remove the two frequencies5.75 GHz and 8.05 GHz. The length of the stubs is chosen to beλ0/8 to suit our miniaturized model. The length of the stubs forboth frequencies is 3.91mm and 2.795mm.

Figure 3. Dimensions of HPF

5 Stub Design

The filter not only accepts wide range of frequencies but also re-jects two frequencies of 5.75GHz and 8.05GHz. For this purposetwo open circuited stubs are formed in the HPF. Forming of short

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circuited stub is not possible in HPF because it is all conductingportion and thus open circuit stub is an option. The two stubsformed are the folded stubs and the lengths of both the stubs donot exceed 0/4.When the width of the stub is increased the fre-quency will be shifted little bit as shown in fig11.

Figure 4. Dimensions of stub

W1=0.6mm L1=12.78mmW2=0.2mm L2=3.8mmW3=0.1mm L3=1.33mmW4=0.1mm L4=2.7mm

6 Hardware Design

The filter is designed using the FR4 substrate with HPF fabricatedon the top portion while LPF is fabricated on the bottom side.Both the filters are joined using a metallic via and at the end theBNC connectors are used.Fig9 and 10 shows the top and bottomview of the filter

Figure 9. Top view of the designed filter(HPF)

Figure 10. Bottom view of desinged filter(LPF)

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7 Result and Discussion

Figure 7. Simulation result of LPF

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Figure 8. Simulation result of HPF

Figure 7 and 8 shows the low pass and high pass filter response.In both filter the return loss is very less .Figure 9 shows the band

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pass response without notch. It shows the return loss nearly -25dB.The output graphs are obtained by using the high frequency sim-ulation software. Electromagnetic simulation is an advanced tech-nology to yield high accuracy analysis and design of complicatedmicrowave and RF printed circuit, antennas, high-speed digital cir-cuits and other electronic components. The overall length of thefilter is 48.360mm and width is 9.350mm. The resulting area of thefilter is 4.52166∗102mm2. The prototype has a wide pass-band from3 to 11 GHz with insertion loss less than 0.5dB. The attenuationis greater than 20dB at the centre of each band pertaining to 5.75and 8.05GHz. The proposed filter also shows a wide upper stopband extending up to 25GHz with attenuation more than 20dB.The black and red colour line shows the S21 and S11 parameters ofNotch BPF when the W2 value will be increased to 0.1mm.

8 Conclusion

In this paper a miniaturized UWB Band Pass Filter is presented byforming two individual HPF and LPF with the filters realised withMicrostrip design. The dual notch property is achieved by intro-ducing two embedded open circuit stubs at 5.75GHz and 8.05GHz.Because of its compact size of just 4.52166 ∗ 102mm2 the filter canbe useful modern UWB communication technology.

References

[1] PankajSarkar , RowdaGhatak, Manimala Pal and D.R. Poddar”Compact UWB Bandpass Filter With Dual Notch Bands Us-ing Open Circuited Stubs”, IEEE. VOL.22,NO.9, September2012.

[2] Xan Luo, Jian Guo ma ”Compact Utra-ideband BPF withultra-narrow dual and Quad-Notched Bands” ”IEEE trans. Onmicrowave theory and tec.VO.59, No.6, june2011.

[3] S. Sun and L.Zhu,”Multimode resonator based band pass fil-ters, ”IEEE Microw. Mag., vol. 10, no.2, pp.88-98, Apr.

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[4] Z.C. Hao and J-S Hong,”Ultrawideband filter technologies,”IEEE microw. Mag., vol.11, no. 4, pp. 56-68, Jun. 2010.

[5] B.Yao, Y.Zho, Q.Cao and Y.Chen, ”Compact UWB band passfilter with improved upper stop band performance, ”IEEE Mi-cro. Wireless compon.lett., vol. 19, no. 1, pp. 27-29, Jan 2009.

[6] K.Song and Q.Xue,” Compact Ultra wide band bandpass fil-ters with multiple notches bands,”IEEE Micro. Wireless com-pon. Let., vol. 20, no. 8, pp. 447-449, Aug. 2010.

[7] R.Ghatak, P.Sarkar, R.K.Mishra, and D.R.Poddar,”A Com-pact UWB bandpass filter with embedded SIR as band notchstructure,” IEEEmicro. Wireless compon. Let., vol. 21 no. 5,pp. 261-263. May 2011.

[8] C.H.Kim and K.Chang,”Ultra Wideband ring resonator band-pass filter with a notch band,” IEEE Microw. Compon. Let.,vol. 21 no. 4 pp. 206-208, Apr. 2011

[9] http : //www1.sphere.ne.jp/i− lab/ilab/tool/ms line e.html

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Figure 10. Simulation result of BPF11


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Figure 11. Simulation result of BPF with notch

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MICROSTRIP UWB BANDPASS FILTER WITH DUAL NOTCH FREQUENCIES

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