A NOVEL MULTI-FOLD HAIRPIN LINE MICROSTRIP BANDPASS

Shivhare et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945
Research Paper
A NOVEL MULTI-FOLD HAIRPIN LINE MICROSTRIP
BANDPASS FILTER AT 1260 MHz FOR WIRELESS
COMMUNICATIONS
Jagdish Shivhare1, S B Jain 2
Address for Correspondence
1
Department of Electrical, Electronics and Communication Engineering, ITM University, Sector-23A,
Gurgaon-122 017, India
2
.Department of Electronics and Communication, Indira Gandhi Institute of Technology, Indraprashth
University Campus, Delhi, India
ABSTRACTThis paper presents the design, simulation/optimization and measured results of a 4-resonator multi-folded hairpin line
microstrip bandpass filter at 1260 MHz with great reduction in size compared to the conventional hairpin line structure. In
the proposed filter the cross couplings have been realized between adjacent and non-adjacent resonators.
KEYWORDS Multi-fold filter, miniaturized hairpin line, insertion loss, bandwidth, coupling coefficients, 4-pole resonator,
ADS software.
I INTRODUCTION
The hairpin line resonators are composed of a
transmission line and a lumped element capacitor and
is represented by parallel-coupled lines instead of the
lumped capacitor, shown in fig. 1a, 1b, 1c and 1d. To
reduce the size of hairpin resonators, the arms of the
resonator are reactively loaded with parallel coupled
lines. Filters using these miniaturized resonators are
50-60 percent smaller in size than filters that use
conventional hairpin resonators. Design calculations
of a 4-resonator double-folded filter has been done in
the following steps: 1-Finding the element values of
LPF prototype by using the approximate synthesis
method and the relations between the band pass
design parameters and the low pass elements, 2calculatiosn for the resonator parameters, 3calculations of the coupling parameters between the
resonators. The values of coefficient of coupling
between resonators can be calculated against the
distances between the resonators. The design
technique uses an approximation polynomial and a
low filter prototype. The loaded Q factor and the
mixed coupling coefficients between the different
resonators can be calculated by using empirical
equations [1][2].
In the proposed filter the multi-folded resonators are
cross coupled. Such a filter can be realized using
filter with cross coupling between adjacent resonators
[1][2][3]
II DESIGN PROCEDURE
To reduce the size of hairpin resonators, the arms of
the resonator are folded to reduce the size compare to
the conventional hairpin resonators [4-6]. Design
calculations of a 4 section multi-folded filter can be
done in the following steps:
a. Specify the centre frequency, passband ripple
and the bandwidth of the bandpass filter.
b. Design of a single half-wavelength resonator.
c. Calculate the fractional bandwidth FBW.
d. Calculate the external quality factor.
e. Calculate the desired coupling coefficients.
f. Determine the gaps between the resonators.
g. Optimize the filter cicuit for the desired
response.
Int J Adv Engg Tech/Vol. V/Issue I/Jan.-March.,2014/05-06
h. In this work we have used A substrate of
dielectric constant 9.8, thickness of 1.27 mm
and tangent loss of 0.003
III.
DESIGN
SPECIFICATIONS
AND
DIMENSIONS
1. Center Frequency
: 1260 GHz
2. Insertion Loss
: < 3dB
3. 3dB Bandwidth
: ± 18 MHz w.r.t.c.f
4. Stopband bandwidth
: ± 36 MHz w.r.t.c.f
5. Lower side attenuation
: 30 dBc at 1224 MHz
6. Upper side attenuation
: 30 dBc at 1296 MHz
7. Intput impedance
: 50 Ohms
8. Output impedance
: 50 Ohms
Fig.2. A resonator of multi-fold hairpin line microstrip
bandpass filter.
here, L1 : 9.23 mm, L2 : 6.09 mm, L3 : 4.51 mm
W1: 1.39 mm W2 : 0.58 mm , G1: 0.55 mm
G2 : 0.47 mm G3 : 0.49 mm, G4: 0.93 mm
D12 = D34 : 1.54 mm, D23 = D23 : 1.55 mm
Fig.3 Arrangement of 4-resonators in the multi-fold
filter
Shivhare et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945
IV SIMULATED RESPONSE BY USING ADS
AGILENT-MAKE SOFTWARE
Fig.4 Simulated and measured results of the filter
1. Center Frequency
: 1260 MHz
2. Insrtion Loss
: < 3d B
3. 3dB Bandwidth
: ± 20 MHz w.r.t.c.f
4. Stopband bandwidth
: ± 40 MHz w.r.t.c.f
5. Lower side attenuation : > 30 dBc at 1220 MHz
6. Upper side attenuation : > 30 dBc at 1300 MHz
Measured results of the Filter:
1. Center Frequency
: 1260 MHz
2.Insertion loss
: < 3 dB
3. 3dB Bandwidth
: ± 19 MHz w.r.t.c.f
4. Stopband bandwidth
: ± 41 MHz w.r.t.c.f
5. Lower side attenuation : > 30 dBc at 1219 MHz
6. Upper side attenuation : > 30 dBc at 1301 MHz
V FABRICATION OF FILTERS
The filter circuit is fabricated on RT-Duroid dielectric
substrate having εr: 9.8 and thickness 1.27 mm.
Standard fabrication process have been adopted [7-9].
The simulated results are very close to the measured
results[6][10]
VI CONCLUSION
This paper describes a 4-pole multi-fold hairpin line
bandpass filter design technique. The limitations of
the design results in terms of inaccuracy of coupling
between the adjacent and cross coupled multi-fold
hairpin line resonators. The measured results are very
close to the designed and simulated/optimized results.
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Int J Adv Engg Tech/Vol. V/Issue I/Jan.-March.,2014/05-06

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