International Journal of Advances in Electrical and Electronics Engineering

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156

ISSN: 2319-1112

Designing a Microstrip Bandpass Filter with Defected Ground Structure (DGS) RAGANI TAOUFIK 1, FAIZE AHMED 2, ENNASAR MOHAMED ALI 3, MOMAHED.AGHOUTANE 1, NAIMA.AMAR.TOUHAMI 1 1 Electronics, Instrumentation and microwave Laboratory, University Abdelmalek Essaadi, Tetouan,Morocco 2 AL Jazari, Ensias Laboratory, University Mohammed V - Souissi 3 Systems of Telecommunications Laboratory, University Abdelmalek Essaadi, Tetouan,Morocco

ABSTRACT- In this paper, a bandpass filter is proposed with dumbbell shaped defected ground structure in ground plane of a 50Ω Microstrip line and a closed loop resonator in the conducting strip. This arrangement provides better coupling in pass band. Using DGS structure, forward transmission loss (S21) is -2 dB and return loss (S11) is -15 dB at the centre frequency 4 GHz with bandwidth of 200 MHz A conventional parallel coupled line bandpass filter has also been implemented with same design goals for the comparison. The proposed bandpass filter with DGS is quite promising with 25% size reduction. Keywords: bandpass filter,coupled line; cst 2011,DGS

I.

INTRODUCTION

A microwave filter is a two-port network used to control the frequency response at a certain point in a microwave system by providing transmission at frequencies within the pass band of the filter and attenuation in the stop band [1-3]. To meet the demands of modern wireless communications, many efforts have been made in recent years to build up a variety of compact bandpass filters having deep and sharp rejection outside the passband by the generation of transmission zeros and attenuation poles [4]. A new technique for the design of ultra-wide band band pass filters with harmonic suppression in pass-band is DGS. Different shapes of DGS structures, such as rectangular, square , circular , dumbbell, spiral, L-shaped, concentric ring, Ushaped and V-shaped, hairpin DGS, hexagonal DGS, cross shaped DGS and combined structures have appeared in the DGS is used to attain the sharp attenuation and wide pass band. All the simulation is carried out in Full EM wave Simulator CST microwave Studio 2011 [5]. The design goals and parameters have been shown in the Table 1. Table 1: Design Goals of the Filter Ordre of the Filtre Frequency

3 4 GHz


, FR4

4.3

Height of the Substrate

1.56 mm

Thickness of the conducting

0.035 mm

Loss tangent

0.025

Fractional Bandwidth

5% at 4 GHz

Bandwidth

200MHz

ISSN: 2319-1112 /V3N3:156-161 ©IJAEEE

157 Designing a Microstrip Bandpass Filter with Defected Ground Structure (DGS) (DGS II.

PARALLEL COUPLED LINES BANDPASS FILTER

Figure.1 .1 gives the circuit implementation of the filter by means of concentrated components like inductors (L) and capacitors (C), for the even and odd filter degree (n).

Figure 1: Realization of filter using LC components.

For i=1 to n

$2" % 1&   2 !"#$ & 2#

  1

Where n is the order of the filter and the i = 0, 1, 2, 3……….. g   1.0

(1) (2)

(3)

The component values can be calculated with the following rules II.

DESIGNING BANDPASS FILTER

Figure 2 shows the filter structure observed in this work. This filter type is known as parallel-coupled parallel filter. The strips are arranged parallel close to each other, so that they are coupled with certain coupling factors. We use the following equations for designing the parallel-coupled filter [6].  ,

     2 

 ;

  2   For j = 1 to n

,

     2 

(4)

(5)

(6)

FBW is the relative bandwidth as explained before, J; is the characteristic admittance of J inverter and Y is the characteristic admittance of the connecting transmission line.

ISSN: 2319-1112 /V3N3:156-161 ©IJAEEE

IJAEEE , Volume 3, Number 3 RAGANI TAOUFIK et al.

With the data of characteristic admittance of the inverter, we can calculate the characteristic impedances of even-mode even and odd-mode of the parallel-coupled coupled Microstrip transmission line, as follows [6]. Figure 2: Parallel Bandpass Filter

for j = 0 to n

;

; 6 1 $/01 &,  2 3 41 5 2 352 3 7   

and

(7)

;

; 6 1 $/0 &,  2 3 41 % 2 352 3 7   

for j = 0 to n

(8)

From these values, width, length and spacing of the parallel coupled line are calculated calculated and are shown in Table-2, Table Table 2 : Specifications Of Parallel coupled Microstrip Lines

n

*+

,- .+

,89 (Ω)

,88 $Ω)

W(mm)

L(mm)

S(mm)

1

1

0.28

68

40

2.4

9.4

0.3

2

2

0.05

53

48

2.9

9.4

1.2

3

1

0.05

53

48

2.9

9.4

1.2

4

1

0.28

68

40

2.4

9.4

0.3

III. A.

SIMULATED S-PARAMETERS

Geometry on simulator

In this proposed design the height of the substrate is 1.56 1.5 mm and relative permittivity 4.3 and the conductor thickness 0.035 mm and loss tangent is 0.025, figure 3 shows the 3-dimensional dimensional view of proposed bandpass filter. Proposed design is simulated sim in CST microwave studio 2011 [5]. Figure 3: Geometry of MicrostripBandpass Filter

ISSN: 2319-1112 /V3N3:156-161 ©IJAEEE

159 Designing a Microstrip Bandpass Filter with Defected Ground Structure (DGS) (DGS

B.

Simulation Result

Fig.4 shows the simulation response of conventional parallel-coupled parallel coupled Microstrip line Bandpass filter with centre frequency 4 GHz.

Figure 4: Simulation S S-parameters parameters of parallel coupled line Bandpass filter at 4 GHz

IV.

DESIGN CONFIGURATION AND SIMULATED RESULTS Figure 5:. Geometry of proposed Bandpass filter

ISSN: 2319-1112 /V3N3:156-161 ©IJAEEE

IJAEEE , Volume 3, Number 3 RAGANI TAOUFIK et al.

In this proposed design the height of the substrate is 1.5 mm and relative permittivity 4.3 and the conductor thickness 0.035mm and loss tangent is 0.025; width of conducting strip is 4 mm and 16 mm. the proposed design topology is shown in Fig.4. The transmission smission line model is used to design bandpass filter for resonant frequency 4 GHz. The filter size 28mm×16mm=448mm2 is better compatible for the different applications. The creation of a dumbbell shaped DGS in the ground plane of the filter is used for thee size reduction of the bandpass filter for working at the frequency of 4 GHz. Figure 6: Proposed Bandpass Filter

(a)Top view

(b) Bottom View

(c) both View

The optimized dimensions for the band Bandpass filters are a=b=4 mm, g = 2 mm, and G= 0.3 mm The gap (G) in the conducting strip introduces the gap capacitance and due to this capacitance the Bandpass characteristics will appear. The simulated results are shown in the Fig.7, which shows the S21 -2dB att the center frequency. Hence the total bandwidth of the proposed filter is 200 MHzAll the simulations are carried out in CST Microwave Studio EM simulator 2011. Figure 7: Simulated S-parameters of proposed filter

V.

RESULTS AND DISCUSSIONS

Fig.7 and Fig.4 shows the simulated S--parameters parameters for conventional and proposed bandpass filter. Both the simulated results are shown at the center frequency with insertions loss below - 2 dB with. The proposed design meets all the specification with suppressed ssed harmonics as in case conventional type parallel coupled lines bandpass filter.

ISSN: 2319-1112 /V3N3:156-161 ©IJAEEE

161 Designing a Microstrip Bandpass Filter with Defected Ground Structure (DGS) VI.

CONCLUSION

From the simulations, it is very appreciated that the proposed filter with Dumbbell shaped DGS offers a size reduction 25% with reduced harmonics in the passband. It is clear that in conventional parallel coupled bandpass filter the filter size is 1780mm2 and in proposed design the filter size is 448mm2. REFERENCES [1] S. S. B. Bhabani Sankar Nayak, Atul Shah, "Study and Realization of Defected Ground Structures in the Perspective of Microstrip Filters and Optimization through ANN," Internation Journal of Advances in Engineering and Technology, vol. 2, pp. 323-330, January 2012. [2] V. M. Anerao, et al., "Parallel Coupled Microstrip Band Pass Filter," in Emerging Trends in Engineering and Technology (ICETET), pp. 1206-1209, 2009 2nd International Conference on, 2009. [3] S. Amari, et al., "Theory of Coupled Resonator Microwave Bandpass Filters of Arbitrary Bandwidth," Microwave Theory and Techniques, IEEE Transactions on, vol. 58, pp. 2188-2203, 2010. [4] A. B. A. Boutejdar, M. H. Awida, E. P. Burte, and A. Omar, "Design of new bandpass filter with sharp transition band using multilayertechnique and U-defected ground structure," IET Microwaves, Antennas & Propagation, vol. 4, pp. 1415-1420, 10th December 2010. [5] CST Microwave Studio 2011. [6] J.S. Hong, and M.J. Lancaster, Microstrip Filters for RF/Microwave Applications, Wiley, New York, 2001

ISSN: 2319-1112 /V3N3:156-161 ©IJAEEE