A new microstrip bandpass filter using composite right/left-handed (CRLH) mushroom structure with interdigital capacitors and defected ground structure (DGS) is proposed. The proposed filter uses CRLH mushroom structure working at its first negative resonance mode to create the passband and DGS to increase rejection outside the passband. Simulation and measurement results are in good agreement, and low in-band insertion loss and great out-band rejection have been achieved. It is demonstrated that the combination of CRLH mushroom structure with interdigital capacitors and DGS has succeeded in achieving excellent performance. This new filter can be applied in transmitting and receiving antennas.
In the year 1967, the Russian physicist V. Veselago had speculated a new metamaterial. He called this material “left-handed material” because it could allow the propagation of electromagnetic waves with the electric field, the magnetic field, and the phase constant vectors building a left-handed triad, compared with conventional materials where this triad is known to be right-handed [
CRLH TLs have also been used in the filter applications. However, most reported filters employ the zeroth-order or the positive resonance modes. The negative modes, especially first negative resonance mode, are seldom discussed to design filters [
In this paper, a new microstrip bandpass filter using CRLH mushroom structure with interdigital capacitors and DGS is proposed. First, the CRLH mushroom structure with interdigital capacitors has been adopted to achieve high quality factor using its first negative resonance mode. Next, a new DGS with asymmetrical split rings is utilized to create transmission zeros and increase better rejection level outside the passband. It can be seen from the full-wave simulation and measurement results that by combining these two different structures excellent performance of this proposed filter has been achieved.
The proposed mushroom structure with interdigital capacitors is shown in Figures
Top view (a) and 3D view (b) of the triangle CRLH mushroom structure.
The equivalent circuit of one single mushroom structure.
Based on the Bloch-Floquet theorem, the propagation constant and the normalized impedance of the CRLH TL unit cell can be expressed as [
The dispersion diagram is shown in Figure
Dispersion curve of the mushroom structure.
As shown in Figure
Top view of the split-ring DGS.
The equivalent circuit of the DGS.
To design the proposed filter, first, the resonance frequencies of the mushroom structure with interdigital capacitors and DGS are calculated using the formulae above based on the design specifications. The next step is tuning and optimization due to the interinfluence of the two different structures. In our design, the calculation and optimization are done mostly using Matlab and EM simulation software. After the optimization, the design process is finished.
The topology of the proposed filter is shown in Figure
The topology of the proposed filter.
The photograph of the fabricated filter.
Simulation and measurement result.
The measurement is done using Rohde and Schwarz’s vector network analyzer. The center frequency of the passband frequency is 5.1 GHz with the insertion loss of 1.42 dB. This passband is produced by the first negative resonance of the CRLH mushroom structure. At the frequencies 4.3 GHz, 5.9 GHz, and 7.3 GHz, the DGS works to reject input signal from the feed line to enter the resonators, and, thus, transmission zeros have been created for better rejection. The filter is fabricated using the substrate Rogers 5880 with relative dielectric constant of 2.2, loss tangent
Geometric parameters of the proposed filter (in mm).
Parameter | Value | Parameter | Value | Parameter | Value | Parameter | Value |
---|---|---|---|---|---|---|---|
|
2.4 |
|
0.6 |
|
0.1 |
|
1.8 |
|
0.6 |
|
0.8 |
|
5.4 |
|
0.4 |
|
3.4 |
|
4.7 |
|
4.7 |
|
0.2 |
|
0.1 |
|
0.5 |
|
0.6 |
|
0.6 |
|
0.8 |
|
0.4 |
|
6.2 |
|
1.0 |
|
0.9 |
|
0.9 |
|
0.3 |
|
0.4 |
|
0.8 |
|
3.8 |
|
1.5 |
|
1.2 |
|
0.7 |
|
4.2 |
|
2.2 |
|
1.4 |
|
1.2 |
|
7.5 |
|
0.5 |
As shown in Figure
The simulated and measured dispersion curves.
In this paper, a new microstrip bandpass filter using CRLH mushroom structure with interdigital capacitors and DGS is proposed. The proposed filter uses CRLH mushroom structure working at its first negative resonance mode to create the passband and DGS to increase rejection outside the passband. Simulation and measurement results are in good agreement and low in-band insertion loss and great out-band rejection have been achieved. In real application, it is easy to redesign the filter according to new specifications. The filter is fabricated without complex fabrication process. It is demonstrated that the combination of CRLH mushroom structure with interdigital capacitors and DGS has succeeded in achieving excellent performance. This new filter can be applied in transmitting and receiving antennas.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work is supported by the National Natural Science Foundation of China (Grant no. 61201004) and the Fundamental Research Funds for the Central Universities (ZYGX2011J011).