A half mode substrate integrated waveguide-to-defected ground structure (HMSIW-DGS) cell and its embedded form are proposed to miniaturize a bandpass filter. Both cells can purchase wideband frequency response and low insertion loss, as well as simple and easy fabrication. By cascading two of them according to design requirement, an X-band bandpass filter is designed and measured to meet compact size, low insertion loss, good return loss, second harmonic suppression, and linear phase.
In the past decade, substrate integrated waveguide (SIW) has attracted plenty of attention and has been utilized in different microwave and millimeter wave components design due to its merits of higher quality factor, low cost, high power handling capability, and easy integration [
The defected ground structure (DGS), which is etched in the ground plane of planar circuit board, provides a promising approach to increase stopband reduction and reduce size of passive components [
As unique DGS shapes, the complementary split ring resonator (CSRR) [
In this paper, a novel HMSIW-DGS cell with a simple DGS shape and its embedded form, which can also be used as a cell, are proposed. By utilizing these two kinds of cells, a three-pole cascade bandpass filter is realized. According to its measured results, low insertion loss, good return loss, compact size, and suppressed second harmonic are achieved.
Proposed HMSIW-DGS cell and its embedded form are shown in Figures
Proposed HMSIW-DGS cell, its embedded form, and equivalent circuit. (a) Proposed cell, (b) embedded form, and (c) equivalent circuit.
To simplify the analysis, the bandpass transmission characteristic of proposed HMSIW-DGS cell can be seen as a combination of the inherent highpass characteristic provided by HMSIW and the bandgap function created by DGS. Whichever for SIW and HMSIW, as discussed in [
Comparison of cutoff frequencies and transmission characteristics of SIW and HMSIW. The geometrical parameters are
From (
As depicted in [
To make the transmission behavior and working principles of proposed HMSIW-DGS cell clearer, some investigations on different parameters are discussed in detail. All investigations are carried out under the same conditions of relative permittivity
Simulated results of proposed HMSIW-DGS cell with different “
“
Simulated results of proposed HMSIW-DGS cell with different “
Figure
Simulated results of proposed HMSIW-DGS cell with different “
For the embedded form of proposed HMSIW-DGS cell, when the lengths of DGS (“
Based on the two proposed HMSIW-DGS cells, a three-cell cascaded bandpass filter is designed. There are two essential elements for a cascaded filter design. One is the basic transmission characteristics of the unit cell; the other is the intercoupling between the adjunct cells. For proposed HMSIW-DGS cells, the strength of the intercoupling is mainly controlled by the space between two adjunct cells, as labeled as “
Simulated results of intercoupling between two HMSIW-DGS cells for varied “
Geometrical configuration and dimensions of proposed HMSIW-DGS filter.
The proposed filter, with photograph shown in Figure
Photograph of fabricated HMSIW-DGS filter.
Comparison between measured and simulated scattering parameters of proposed HMSW-DGS filter.
Comparison between measured and simulated group delay of proposed HMSW-DGS filter.
To inspect the performance of proposed filter clearer, some comparisons between proposed filter and previous SIW-DGS or HMSIW-DGS filters reported in the reference are summarized in Table
Comparison with filters presented in references.
Reference filter | Order | Topology | FBW* and |
Insertion loss (dB) | Return loss (dB) | Size |
2nd harmonic suppression (dBc) |
---|---|---|---|---|---|---|---|
[ |
3 | HMSIW-slot | 22% and 7.80 | 1.50 | >10 | 0.52 | >20 |
[ |
5 | HMSIW-slot | 40% and 8.79 | 1.20 | >10 | 0.37 | >28 |
[ |
3 | SIW-CSRR | 23% and 8.15 | 2.16 | 11.6 | 0.64 | |
[ |
3 | SIW-CSRR-DGS (bottom) | 30% and 9.40 | 1.00 | 16 | 1.02 | >20 |
This work | 3 | HMSIW-DGS | 29% and 8.80 | 0.91–1.14 | 30 | 0.40 | >35 |
An X-band three-cell cascaded bandpass filter based on the two proposed HMSIW-DGS cells is designed, fabricated, and measured. The measured results show good agreement with the simulated one. Compared with some reported filters using the same technology and operating at similar frequency, the proposed filter has better performance in low insertion loss, good return loss, compact size, and second harmonic suppression.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was supported in part by Excellent Ph.D. Candidate Academic Foundation of UESTC under Grant YBXSZC20130154, in part by the Fundamental Research Funds for the Central Universities under Grant ZYGX2013J006, and in part by the Scientific Research Foundation of UESTC under Grant Y02002010101063.