Design of an ultra-wideband (UWB) bandpass filter using defected ground structure with improved out-of-band performances.
As the unlicensed use of ultra-wideband (UWB: 3.1-10.6 GHz) frequency spectrum for indoor and handheld wireless communications is released in 2002 (L. Zhu, S. Sun, and W. Menzel, 2005), a tremendous interest has been recently arousing in the exploration of a variety of UWB bandpass filters (BPFs) with a 110% fractional frequency bandwidth (S. Sun and L. Zhu, 2006). The first UWB BPF is a dual-stop band filter and it is formed by cascading several microstrip ring resonators with loaded open stubs .Later on, such a wideband filter with the specified passband is constructed by directly cascading a single low pass filter with a single high pass filter on microstrip line and suspended strip line ,cascading microstrip-to-coplanar waveguide (CPW) broadside-coupling sections together and non-periodically interrupting several short-circuited stubs with a uniform microstrip line in (G.M.Yang, R.Jin, and J.Geng, 2006). In parallel, the concept of a multiple-mode resonator (MMR) with stepped-impedance configuration is originated in to make up an UWB filter using its first three resonant modes together with two distributed parallel-coupled lines. In (G. M. Yang, R. Jin, J. Geng and X. Huang, 2007), a tapered coupled line topology is presented to allocate its transmission zero to the fourth resonant frequency, thus somehow raising the upper-end of the concerned upper-stop band from 13.8 to 15.9 GHz.
Microstrip transmission lines with an electromagnetic bandgap (EBG) structure exhibit stopband and slow-wave characteristics, which can be used as stop band or low-pass filters. Recently, many EBG structures have been developed for microwave circuits, which mostly have periods as photonic crystals (PCs). However, EBG structures have the disadvantage of many design parameters and difficulties in finding its equivalent circuits. Defected ground structure (DGS) which has etched defected in the ground plane, can also provide bandgap characteristics, making a slow-wave structure. Moreover, the equivalent circuit and parameters can be extracted with a one-step Butterworth low-pass prototype. However, the stopband bandwidth of photonic bandgap (PBG) and DGS are enhanced by using periodic structures, corresponding to sizes and transmission losses in passband. Moreover, the high attenuation rates are also obtained with cells in series .As reported in, wideband performance of filters was generated by using three cells in series. However, their cell configuration was composed of a traditional microstrip low-pass filter and their proposed EBG cell, resulted in larger size and loss. (G.M. Yang, R. Jin, J. Geng and X. Huang, 2007) have designed the triple EBG structures for a band stop filter, but there was a spurious response and passband ripple in their performances. In addition, more cell-sections were needed for a sharp rejection. In (S. Sun and L. Zhu, 2006), the elliptic-function low-pass filters using SIR hairpin resonators provide a wide-band stop band and a sharp cutoff frequency response, but they're designed as a compositing configuration, corresponding to larger size and are difficult to use. An SIR microstrip filter with tapped-line excitation at the input and output is developed to further extend the upper rejection band. By properly allocating the two transmission zeros, the first and/or second spurious resonances in this filter are effectively cancelled. In this letter, we propose an A type novel multimode resonator defected ground structure (CSDGS) Band pass filter. The proposed filter shows a sharper cutoff frequency response by using only one unit cell of CSDGS configuration. Furthermore, additional attenuation poles are added to suppress the high-order harmonics. An ultra-wide stop band bandwidth can be also obtained by SIR effect, due to different aperture widths in CSDGS configuration.
Uwb filter design:
MMR structure is originally used to constitute UWB filter in. That UWB filter consisted of stubs-loaded MMR at the center section and two identical coupled-lines located at the left and right section. Later on, some modified and new kinds of MMR were proposed, three open-ended stubs were introduced at the center of a stepped-impedance resonator to allocate the resonator modes more closely with each other. Also, a modified EBG-embedded MMR for UWB BPF with improved upper-stopband performance has been explored in (D. Ahn,2001). Nevertheless, these MMR based UWB filters are still limited by the existence of periodic, narrow passband in the upper-stopband. To circumvent this problem, a new topology of MMR is utilized to replace the traditional MMR. The MMR consists of a half-wavelength Low-impedance line section in the center and two identical high-impedance line sections at the two sides with respect to the UWB central frequency, i.e., 6.85 GHz. This MMR based UWB filter has a large horizontal circuit size and low selectivity. To solve these problems, a modified MMR with a inverted U-shape impedance line instead of the uniform half-wavelength low-impedance line in the center of the MMR is presented, as shown in Fig. 1(a). The inter digital external coupled-lines are represented by two transmission lines at the two sides and a J-inverter susceptance with a via in the middle. The simulated -magnitude responses and the group delay of the MMR circuit is shown in Fig. 2 and its equivalent transmission line network is shown in Fig 3.The three resonant modes are used to make up the desired UWB passband (3.1-10.6 GHz). As the coupling strength increases, the -magnitude curve in the UWB band gradually rises up to the desired band.
Design of the UWB filter:
The geometry of the proposed UWB BPF using DGS is shown in Fig. 1 (a) is top view and (b) is bottom view. The proposed UWB BPF is composed of coupled double step impedance resonator and open loop defected ground structure as a BPF, and the conventional DGS part as a BPF. The coupled double step impedance resonator is simulated Microwave CST studio on the same side as the input/output-port microstrip lines, as shown in Fig. 1(a), while the slot line defected ground structure is located on the ground, as shown in Fig. 1(b). First, three different configurations including a coupled double step impedance resonator have been examined. Fig. 1 shows the geometry of the coupled double step impedance resonator and open loop defected ground structure. The dimensions are listed in Table 1.Fig 1 shows the simulated magnitude response of the insertion loss above -12dBfrom 4.5 to 12.6GHz and the group delay in 1.5 ns
Slot line DGS Characterization:
Due to introducing the notched structure, the common-mode suppression around the notched frequency became degraded. Hence, a slot-line DGS pattern is proposed to etch in the ground plane which exhibits bandgap characteristic and can improve the common-mode performance [H. L. Hu, X. D. Huang, 2006]. Fig. 3 shows the differential-mode and common-mode current and charge distribution of the slot-line DGS which is applied in the proposed differential filter. The common-mode signals can be cancelled out in the virtual short plane while the differential-mode bandgap could help generating higher notch attenuation. By optimized geometry design of the slot-line DGS, the effective suppression of common-mode noise at 2.45 GHz notched frequency is obtained as shown in Fig. 4. Common-mode noise is suppressed more than 30 dB below 2.5 GHz and the circuit size can be reduced about 10% due to the slow wave effect of the slot-line DGS
Proposed coupled MMR to improve the out of band performances:
A novel compact ultra-wideband band-pass filter with good transmission characteristic and group delay is presented by using a new kind of multiple-mode resonator (MMR), open stubs and DGS. The out of band performance has been improved by cascading the structure through coupling mechanism which in turn helps in size reduction. The dimension of this structure is 10.74 mm x 2.82 mm (not including the 50 Q microstrip), which is much less than conventional structure.
Received 3 September 2014
Received in revised form 30 October 2014
Accepted 4 November 2014
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(1) V. Mariselvam, (2) S. Raju, (3) S. Kanthamani, (4) V. Abhaikumar
(1) PhD Research Scholar, Department of Electronics and Communication Engineering, Thiagarajar College of Engineering, Madurai, India,
(2) Associate Professor, Department of Electronics and Communication Engineering, Thiagarajar College of Engineering, Madurai, India
(3) Associate Professor, Department of Electronics and Communication Engineering, Thiagarajar College of Engineering, Madurai, India
(4) Principal Thiagarajar College of engineering
Corresponding Author: V. Mariselvam PhD research scholar, Department of Electronics and Communication Engineering, Thiagarajar College of Engineering, Madurai-15 India
Table 1: Dimensions of the Proposed filter. Sl.no Parameters Dimensions Parameters Dimensions in mm in mm 1. L 2.97 W 0.28 2. L1 4.8 W1 0.75 3. L2 2.07 W2 0.96 4. h 1.5 w 0.5 5. h1 1.1 w1 0.29 6. h2 0.8 w2 0.2 7. g1 0.5 g2 0.5 8. gi 0.7 wi 0.2 9 gil 1.5 gi2 0.05
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|Author:||Mariselvam, V.; Raju, S.; Kanthamani, S.; Abhaikumar, V.|
|Publication:||Advances in Natural and Applied Sciences|
|Date:||Oct 15, 2014|
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