диафрагмированные волноводные фильтры / 34be03ce-f876-4f89-9cbd-0ba20bac3e72

2017 Progress In Electromagnetics Research Symposium — Spring (PIERS), St Petersburg, Russia, 22–25 May

Full Wave Analysis and Design of Waveguide Diplexer with Ridged Sections and Diaphragms

M. B. Manuilov and K. V. Kobrin

Southern Federal University, Russian Federation

Abstract— A novel design of waveguide diplexer for microwave and millimeter wave applications is proposed. The diplexer is based on E-plane metal insert filters with ridge sections and longitudinal diaphragms in rectangular waveguide. The proposed design provides high slope selectivity of the filters, extended stop-band, increased attenuation within stop-band and reduced dimensions. Full wave CAD of filters and diplexers is based on mode matching technique, Galerkin method and generalized scattering matrix method. This approach ensures fast convergence and accuracy of the total hybrid solution. Compact K-band diplexer with high electrical characteristics is designed for operation within frequency bands 24.5–25 GHz and 25.5–26 GHz. The length of diplexer is reduced at a factor 1.5 in comparison with the known designs.

1. INTRODUCTION

The various waveguide filters and diplexers based on E-plane all-metal inserts are widely used in the many microwave and millimeter-wave communication systems [1–5]. These filters and diplexers have the low-cost, easy-to-manufacture and well reproducible design, low insertion loss and they can operate within frequency band from 10 GHz to 150 GHz.

The convenient design of the band-pass filters based on E-plane longitudinal inductive irises [1, 2] has the parasitic pass-band too close to operational pass-band. A number of filter designs has been proposed to overcome this disadvantage. One of these structures is a combined structure based on the ridged resonators and inductive irises on the common metal sheet [4, 6, 7]. This kind of filters has the improved slope of the frequency characteristic and its symmetry, extended upper stop-band, low insertion loss and more compact size in comparison with convenient design.

In view of these considerations a novel waveguide diplexer is presented below, which is based on the quasi-planar channel filters with the E-plane ridged sections and inductive irises.

2. DIPLEXER DESIGN

The proposed diplexer (Fig. 1) is implemented on the base of E-plane waveguide bifurcation, since it has more wide-band frequency response in comparison with, for example, H-plane waveguide T-junction [1]. The diplexer contains the matching stepped waveguide transition with the any number of sections. The channel waveguide filters are carried out using cut-o waveguide section with the reduced width of the waveguide wide wall (sections Lf in Fig. 1(b)).

The waveguide housing is decomposed in E-plane into two halves between which the metal sheet with the filters layout is inserted. The resonant elements of the filters are the double ridged waveguide sections coupled by cut-o waveguide sections. The longitudinal inductive irises are placed between the ridged sections. Such a design is low-cost and easy-to-manufacture, since it allows the precise fabrication of the both filters layout on the common metal sheet. Due to the inductive irises the coupling section lengths are reduced as well as the total length of the filters. The increased height of the cut-o waveguide provides the large gaps of double ridged sections, so the total insertion loss of diplexer is decreased.

3. ANALYSIS METHOD

Let us assume that the structure under consideration (Fig. 1) contains any number of the step discontinuities and the ridged sections in the filters. The e cient hybrid full wave method for analysis of this class of the waveguide problems is presented in this paper. The suggested solution is based on Galerkin method with taking into account the edge condition, mode matching method and generalized scattering matrix method.

The solution consists of the following steps: (i) decomposition of the complicated waveguide structure into the key building blocks (waveguide discontinuities); (ii) solution of the eigenvalue problems for the ridged waveguides (evaluation of the cut-o frequencies and modal spectrum of the ridged waveguide); (iii) solving of the key scattering problems for the basic discontinuities (building blocks) and calculation of their generalized scattering matrices; (iv) direct combining of

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2017 Progress In Electromagnetics Research Symposium — Spring (PIERS), St Petersburg, Russia, 22–25 May

(a)

(b)

Figure 1: Waveguide diplexer based on the quasi-planar filters with E-plane ridged sections and inductive irises: (a) 3D model, (b) E-plane section of structure.

the generalized S-matrices of discontinuities and calculation of the S-matrices of filters and waveguide bifurcation with the matching stepped waveguide transition; (v) calculation of the scattering matrix of the diplexer.

In the first step the diplexer is decomposed into the following building blocks for which the key scattering problems are solved: junction between the rectangular waveguide and ridged waveguide, junction between two rectangular waveguides, waveguide bifurcation. The modal expansions into the H- and E-waves are utilized by solving of the scattering problems.

Secondly, the eigenvalue problems for the H- and E-waves of the ridged waveguide are solved independently and the cut-o frequencies as well as eigenfunctions are evaluated [4]. The eigenvalue problems are reduced to the uniform integral equation for unknown electric field tangential component at the common boundary of the regular subregions. The integral equation is solved by Galerkin method with weighted Gegenbauer polynomials as basis functions taking into account the field asymptotic at the metal edges of the structure.

The determinant of the obtained homogeneous system of linear algebraic equations is assumed to be zero providing the corresponding transcendent equation for calculation of the spectrum of the ridged waveguide cut-o frequencies. The fast convergence and high accuracy of the suggested eigenvalue problem solution ensure the high numerical e ciency of the presented hybrid technique for rigorous analysis of diplexers.

In the next step the generalized scattering matrixes are computed for the key building blocks: junction between the rectangular waveguide and ridged waveguide, junction between two rectangular waveguides of the di erent cross section, waveguide bifurcation.

To evaluate the generalized scattering matrix of diplexer we start from the calculation of S- matrices of the filters and the matching stepped transition combined with the waveguide bifurcation. To this end the numerically e cient procedure is used for direct combining of generalized scattering matrices of two cascaded discontinuities [4]. The proposed procedure taking into account the symmetry of the S-matrices is used for any number of the cascaded discontinuities. In this way we obtain S-matrices of the filters and the common S-matrix of the stepped transition with the waveguide bifurcation. The final direct combining procedure for the diplexer S-matrix is carried out similarly to [3].

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2017 Progress In Electromagnetics Research Symposium — Spring (PIERS), St Petersburg, Russia, 22–25 May

4. RESULTS

The proposed hybrid method for full wave analysis of the waveguide diplexers shows high numerical e ciency, since the most appropriate and e cient solutions are utilized for each particular subproblem. In particular, Galerkin method with taking into account the edge condition has the dramatically fast convergence. It is normally to take only three or four basis functions to obtain the cut-o frequencies of ridged waveguide with the five correct digits. The comparison of the obtained numerical results with the known from literature theoretical and experimental data [6] as well as finite element method [9] shows a very good agreement which confirms the high accuracy of the proposed technique. The computation time of the suggested method is less than the computation time of the finite element method at a factor about an order [9].

The numerically optimized frequency responses of two filters and diplexer operating within K- band are presented in Figs. 2, 3. All dimensions of the diplexer are shown in Fig. 1 and in Table 1. As we can see in Fig. 2, the presented filters have the frequency characteristics with the symmetric slopes and the extended stop-band with high attenuation. These features of the filters are very important for the use in diplexers and multiplexers.

Figure 2: Frequency responses of the (a) filter 1 and (b) filter 2 (see dimensions in Table 1).

Figure 3: Frequency responses of the K-band diplexer (see dimensions in Table 1).

The diplexer consists of two five-resonator filters (Fig. 1) and it separates the receiving and transmitting channels operating in frequency bands 24.5–25 GHz and 25.5–26 GHz. It corresponds to 2% pass-band of the filters (Fig. 3). The reflection coe cient in the common port is better than 27 dB. The isolation of the diplexer channels is 46 dB. The length of diplexer is less than the length of convenient structure with E-plane longitudinal inductive irises at a factor about 1.5.

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2017 Progress In Electromagnetics Research Symposium — Spring (PIERS), St Petersburg, Russia, 22–25 May

Table 1: Dimensions of diplexer in Fig. 1 (in mm).

5. CONCLUSION

A novel compact waveguide diplexer design is proposed for microwave and millimeter-wave applications. The presented diplexer has a low-cost, easy-to-manufacture design and high electrical characteristics including low insertion loss. The suggested structure is carried out on the base of E-plane waveguide bifurcation and the filters with ridged resonators and longitudinal inductive irises. Both filters are implemented on the common metal sheet which is inserted in E-plane of the waveguides between of two halves of diplexer housing.

The e cient hybrid full wave method is proposed for electromagnetic analysis of a wide class of waveguide diplexers. This technique is based on Galerkin method with taking into account the edge condition, mode matching method and generalized scattering matrix method. The frequency characteristics of the optimized K-band diplexer are presented. The length of diplexer is more compact in comparison with the convenient diplexers based on E-plane inductive irises. The length of a novel diplexer is reduced in a factor about 1.5.

REFERENCES

1.Dittlo , J. and F. Arndt, “Rigorous field theory design of millimeter-wave E-plane integrated circuit multiplexers,” IEEE Trans. Microwave Theory and Tech., Vol. 37, No. 2, 340–350, 1989.

2.Morini, A., T. Rozzi, and D. Angelis, “A Novel matched diplexer configuration in E-plane technology,” IEEE MTT-S Intern. Microwave Symposium Digest, 1077–1080, 1993.

3.Manuilov, M. B. and G. P. Sinyavsky, “Wave scattering by multielement irregularities included into waveguide filters and multiplexers,” Journal of Communications Technology and Electronics, Vol. 46, No. 2, 127–133, 2001.

4.Sinyavsky, G. P., M. B. Manuilov, and K. V. Kobrin, “Quasi-planar waveguide filters with improved characteristics,” Uspekhi Sovremennoi Radioelectroniki, Vol. 4, 5–26, 2006 (in Russian).

5.Ofli, E., R. Vahldieck, and S. Amari, “Novel E-plane filters and diplexers with elliptic response for millimeter-wave applications,” IEEE Trans. Microwave Theory and Techn., Vol. 53, No. 3, 843–851, 2005.

6.Kirilenko, A., L. Rud, V. Tkachenko, and D. Kulic, “Evanescent-mode ridged waveguide bandpass filters with improved perfomance,” IEEE Trans. Microwave Theory and Tech., Vol. 50, No. 5, 1324–1328, 2002,

7.Manuilov, M. B., K. V. Kobrin, G. P. Sinyavsky, and O. S. Labunko, “Full wave hybrid technique for CAD of passive waveguide components with complex cross section,” PIERS Proceedings, 1459–1463, Moscow, Russia, August 18–21, 2009.

8.Bornemann, J. and F. Arndt, “Modal S-matrix design of optimum stepped ridged and finned waveguide transformers,” IEEE Trans. Microw. Theory and Tech., Vol. 35, No. 6, 561–567, 1987.

9.Ansys HFSS. On-line: http://www.ansys.com.

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