диафрагмированные волноводные фильтры / e31d2806-cb9d-4df9-a616-be6744fe3c4b

Abstract-In this paper, a W-band bandpass filter using novel processing method based on LTCC technology is presented. The filter is a transfiguration of E-plane metal insert filter. It is composed of a special designed dielectric waveguide and printed iris which both utilized LTCC technology using a novel processing method. A five-order W-band bandpass filter is developed and verified by full-wave simulation. Simulation results show a good electric performance.

I.INTRODUCTION

E-plane metal insert technology is a conventional costeffective implementation of direct-coupled cavity filters. It has been widely employed in millimeter-wave applications for their ease of manufacturing and good electric performance [1]- [2]. However, despite their favorable characteristics, classical E-plane filter are of heavy weight and large size [3]. For overcoming the drawbacks of these filters, E-plane filters based on substrate integrated waveguide (SIW) are proposed [4]-[5]. This type waveguides has the advantages of high Q- factor, low cost, low insertion loss, and suitable for the realization of high performance band-pass filters. The vertical metal walls of substrate integrated waveguide (SIW) and metal fins of the waveguide resonators are realized by closely spaced metallic via-holes. And the coupling strengths are dependent on the size of the coupling via-holes. However, limited by processing precision, the metal fins are difficult to realize by via-holes in high frequency application such as W-band. Also for wideband filter design, as all the resonators are strongly coupled, especially the input and output coupling becomes very tight, the radius of the coupling via-holes become too small to physically realize [6].

In this paper, a W-band bandpass filter using novel processing method based on LTCC technology is developed. To overcome the machining precision limit, we use the substrate thickness as a dielectric waveguide broadside, so the printing surface parallels to the electric field direction. As a result, substrate printed strips can be placed in a dielectric loaded waveguide instead of coupling via-holes. The proposed filter is developed using multilayer LTCC technology, and the dielectric waveguide is realized by vertical metal walls. To confirm this method, a five-order bandpass filter is simulated

and excellent performances are obtained.

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978-1-4799-4 4- /14/$31.00 ©2014 IEEE

substrate integrated waveguide

coupling via-holes

a

b

(a)

printed strips

b

metallized wall

a a is the thickness of the LTCC substrate

(b)

Fig 1. (a) Structure of classical SIW E-plane filter. (b) The proposed structure of the E-plane filter.

II.PROPOSED PROCESSING METHOD AND FILTER DESIGN

A. Novel Processing Method

The structure of classical SIW E-plane filters is shown in Fig. 1(a). It consists of a substrate integrated waveguide (SIW) and some coupling via-holes planed in E-plane. The coupling strengths can be controlled by adjusting the radius of the coupling via-holes.

The SIW is realized by two lines of closely spaced metallic via-holes. Generally, the thickness of the substrate is used as the height of the SIW. The operating mechanism of the SIW is similar to that of a conventional waveguide, except that only TEm0 modes exit. Therefore, cut-off frequency of the SIW modes are calculated as follows [7]:

Where a and b are the width and height of the waveguide, ɛ is the relative permittivity of the substrate. It should be mentioned that only TEm0 modes exit.

From (1) we can know that the cut-off frequency of the SIW only depends on the width of the SIW. The dominant mode is TE10 when a is longer than b. So, if the thickness of the substrate is larger than the cut width, the cut-off frequency will be controlled by the thickness of the substrate and the electric field direction will parallel to the printing surface as shown in Fig. 1(b). To confirm this method, a dielectric waveguide is designed using twelve layers LTCC substrate Ferro-A6m for the thickness of each layer is 0.094mm. By considering manufacturing limits of LTCC technology and the theory above, the cut width is designed to be 1mm. So, a is 1.128mm, b is 1mm and ɛ is 5.7. The simulation model and its electric field distribution are shown in Fig. 2. Fig. 3 shows the S- parameters of the waveguide.

in Fig. 4 and Fig. 5. The filter consists of five resonators which are filled with LTCC substrate. Six printed strips are placed in the middle of the twelve layers LTCC substrate. These substrate printed strips in the middle of the waveguide broadside divide the waveguide into some adjacent equivalent resonant cavities.

The filter is direct-coupled resonator filter and the coupling between resonators is determined by the widths of printed strips on the substrate.

top layers

printed strips

bottom layers

Fig 4. Proposed multilayer LTCC E-plane five-pole bandpass filter.

designed cut width (1mm)

12 layers LTCC substrate (1.128mm)

Fig 2. Proposed dielectric waveguide and the electric field distribution of dominate mode TE10 at 94GHz.

Frequency (GHz)

Fig 3. Simulated S-Parameters of the dielectric waveguide.

It can be seen that the electric field direction parallels to the printing surface from Fig. 2. This is consistent with our original expectations and this waveguide is suitable for E-plane filter designing.

B. Filter Design

A five-order bandpass filter using above method is designed and simulated. The configuration of the E-plane filter is shown

Fig 5. Layout of the printed strips.

The normalized inverter values for an equal-ripple bandpass filter are [8]:

Where gi’s are the element values of Chebyshev low-pass prototype filter, FBW is the bandwidth, and n is the order of the filter. On the other hand, Ki,i+1 can extracted from simulation result and in this structure Ki,i+1 is determined by Si. With a full-wave EM simulator, the relation curve of Ki,i+1 and the width of the strip can be obtained.

TABLE I

DESIGN PARAMETERS OF THE FILTER

The central frequency of the designed filter is 94GHz and 3dB bandwidth about 3GHz. A commercial full-wave 3-D

FEM simulator (Ansoft HFSS) is used to analyze and optimize the filter after the initial design. The optimized main parameters are listed in Table I.

III. FILTER RESULTS

Based on the above analysis, an optimized multilayer LTCC five-pole E-plane bandpass filter is designed using the substrate of Ferro-A6m with relative dielectric 5.7, thickness of each layer 0.094 mm. All the layout dimensions are optimized in the HFSS full-wave simulator. The simulation results are shown in Fig. 6.

Fig 6. Simulation results of the proposed filter.

Fig. 6 shows that the proposed filter has a center frequency of 94GHz with a 3dB bandwidth about 3.2% (3GHz). The return loss is better than 15dB over the passband and for the whole stop band performance, the rejection level is better than 40 dB from 78 to 91.3GHz and 97.8 to 110GHz.

IV. CONCLUSION

This paper proposed a W-band 5-pole E-plane bandpass filter using novel processing method based on multilayer LTCC technology. Different from traditional E-plane filter utilizing LTCC technology, we make use of the thickness of the LTCC substrate as the broad side of a dielectric waveguide. By this way, the electric field direction will parallel with the printing surface and metal inserts can be realized by printed strips. The simulation results of the filter show a good electric performance and this processing method could be used to design other microwave components.

ACKNOWLEDGMENT

This work was supported by Fundamental Research Funds for the Central Universities (ZYGX2012J022).

REFERENCES

[1]Shih, Y. C, and T. Itoh, “E-plane filters with finite-thickness septa,” IEEE Trans. Microw. Theory Tech., vol. 31, no. 12, pp. 1009–1013, Dec. 1983.

[2]Vahldieck, R, J. Bornemannn, F. Arndt, and D. Grauerholz, “Optimized waveguide E-plane metal insert filters for millimeter wave applications,”

IEEE Trans. Microw. Theory Tech., vol. 31, no. 1, pp. 65–69, Jan. 1983.

[3]Z. Wang, X. Zeng, B. Yan, R. Xu, and W. Lin, “A millimeter-wave e- plane band-pass filter using multilayer low temperature co-fired ceramic (LTCC) technology,” J. of Electromagn. Waves and Appl., vol. 24, pp. 71–79, 2010.

[4]Zhang, X. C, Z. Y. Yu, and J. Xu, “Novel band-pass substrate integrated waveguide (SIW) filter based on complementary split ring resonators

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[5]Stephens, D, P. R. Young, and I. D. Robertson, “Millimeter-wave substrate integrated waveguides and filters in photoimageable thick-film technology,” IEEE Trans. Microw. Theory Tech., vol. 53, no. 12, pp. 3832–3838, Dec. 2005.

[6]Zhengbin Xu, Cheng Qian, Jian Guo, Wenbin Dou, “A novel coupling structure for broad-band fin-line filter design,” Asia-Pacific Microw. Conf., pp. 2033-2036, 2009.

[7]Deslandes, D. and K. Wu, “Integrated microstrip and rectangular waveguide in planar form,” IEEE Microw. Wireless Compon. Lett., vol. 11, no. 2, pp. 68–70, Feb. 2001.

[8]Matthaei, G, L. Yong, and E. M. T. Jones, Microwave Filter, Impedancematching Networks, and Coupling Structures, Artech House, Boston, MA, 1980.