Design and Synthesis of Two Tunable Bandpass Filters Based On Varactors and Defected Ground Structure

This paper presents two types of microstrip bandpass
filter (BPF) at microwave frequencies. The first one is a tunable BPF
using planar patch resonators based on a varactor diode. The filter is
formed by a triple mode circular patch resonator with two pairs of
slots, in which the varactor diodes are connected. Indeed, this filter is
initially centered at 2.4 GHz; the center frequency of the tunable
patch filter could be tuned up to 1.8 GHz simultaneously with the
bandwidth, reaching high tuning ranges. Lossless simulations were
compared to those considering the substrate dielectric, conductor
losses and the equivalent electrical circuit model of the tuning
element in order to assess their effects. Within these variations,
simulation results showed insertion loss better than 2 dB and return
loss better than 10 dB over the passband. The second structure is a
BPF for ultra-wideband (UWB) applications based on multiple-mode
resonator (MMR) and rectangular-shaped defected ground structure
(DGS). This filter, which is compact size of 25.2 x 3.8 mm2, provides
in the pass band an insertion loss of 0.57 dB and a return loss greater
than 12 dB. The proposed filters presents good performances and the
simulation results are in satisfactory agreement with the
experimentation ones reported elsewhere.

• M. Boulakroune
• M. Challal
• H. Louazene
• S. Fentiz

• Defected ground structure
• varactor diode
• microstrip bandpass filter
• multiple-mode resonator.

[1] J.-S. Hong, and M. J. Lancaster, “Microstrip Filters for RF/Microwave
Applications,” Wiley, New York, 2001
[2] J.-K.Xiao, S.-P. Li, and Y. Li, “Novel planar bandpass Filters using
single patch resonators with corner cuts,” Journal of Electromagnetic
Waves and Applications, Vol. 20, No. 11, 2006, pp.1481-1493.
[3] Zhao, L.-P., X. Zhai, B. Wu, T. Su, W. Xue, and C.-H. Liang, “Novel
design of dual-mode bandpass Filter using rectangle structure,” Progress
In Electromagnetics Research B, Vol. 3, 2008, pp. 131-141.
[4] I. C. Hunter and J. D. Rhodes, “Electronically tunable microwave
bandpass filters,” IEEE Trans. Microw. Theory Tech., vol. 30, no. 9,
September 1982, pp. 1354–1360.
[5] S. J. Park and G. Rebeiz , “Low-Loss Two-Pole Tunable Filters With
Three Different Predefined Bandwidth Characteristics,” IEEE
Transactions on Microwave Theory and Techniques, vol. 56, no. 5, May
2008, pp 1137-1148.
[6] Y. Liu, C.H. Liang and Y.J. Wang, “Ultra-wideband bandpass filter
using hybrid quasi-lumped elements and defected ground
structure,". Electronics Letters, vol.45, no. 17, Aug. 2009.
[7] L. Zhu, S. Sun, and W. Menzel, “Ultra-wideband (UWB) bandpass
filters using multiple-mode resonator, ” IEEE Microwave Wireless
ComponLett, vol. 15 pp. 796–798, May 2005.
[8] Q.Bu, J. Ding, Ch. Jiang Guo, "New Design of Ultra-wideband
Bandpass Filter Using Interdigitated Coupled Lines CRLH-TL
Structure", IEEE, vol. 12, no.6, pp.486 – 489, 2012.
[9] M. S. Razalli , A. Ismail, and M. Adzir Mahdi," Novel Compact “Via-
Less” Ultra-Wide Band Filter Utilizing Capacitive Microstrip Patch", ,
Electromagnetics Research, PIER, vol.91, pp. 213-227, 2009.
[10] B. Mohammadi, J. Nourinia, C. Ghobadi , and A. Valizade," Design of
Compact UWB Band Pass Filter Using Radial Stub Loaded Resonator
and Cross-Shaped Coupled Lines with Improved Out-of-Band
Performance and Sharp Roll-Off," IEEE, vol.13, no.3, pp.978-982, 2013.
[11] M. Challal, F. Labu, M. Dehmas and A. Azrar, “Comparative Study of
Three Shapes of DGS Pattern and Design of Compact Microstrip Low-
Pass and Band-Pass Filters,” Wseas Trans. on Circuits and Systems, vol.
10, issue 12, pp. 413- 422, December 2011.