диафрагмированные волноводные фильтры / 43355a3f-6aaf-4f6b-849d-c84e55c31b91

Abstract— This paper presents the results of the designing Ka-band band-pass filter with HTS E-plane insert in the cross waveguide. Mainly electromagnetic features of the proposed filter are presented. The approach to the design of the filter is used based on the results of the characteristics analysis of two coupled resonators in a chain of multiple coupled resonators formed by E-plane insert in the cross waveguide.

Keywords—HTS; band-pass filter; cross waveguide; E-plane insert; insert loss

I. INTRODUCTION

The performance of modern receivers of both satellite microwave links and radio telescopes depends greatly on the performance of the band-pass filter (BPF) with low insertion loss. In very low-noise systems the filter is installed at lownoise amplifier (LNA) input and jointly cooled to cryogenic temperatures. The BPF insertion loss increases the receiving system noise temperature. The mentioned noise addition depends on operating temperature and level of the LNA insertion loss. The introduction of HTS elements in the filter resonators increases the unloaded Q, therefore, should reduce insertion loss. The idea of the application of HTS materials in the waveguide E-plane BPF was expressed earlier [1], where the authors proposed to cover the waveguide internal walls with the bulk HTS material or to replace the normal metal E- plane insert by the insert of HTS material. This idea was advanced in [2] while creating two-pole X-band filter with HTS E-insert. However, the promising directions of developing HTS E-plane filtersremained unclear so far.

In [3] the results of the design and testing of seven-pole BPF Ka-band with bilateral HTS insert in the E-plane rectangular waveguide were presented. Study of the possibility of reducing the insertion loss in the E-plane filters with HTS inserts compared with losses in the filters with normal metal inserts was a purpose of the work. The authors of [3] made two conclusions, namely, 1) application of HTS materials in creating BPF is expedient only for narrow-band filters and 2) to ensure good electrical and thermal contact, they need to tightly clamp the insert between the half housing parts; however this leads to mechanical stresses in the brittle single crystal substrate with HTS film, which is insert, under cooling

and as a result to frequent cracking of inserts. Therefore, it is necessary to find new solutions to the problem marked.

The idea of using the cross-shaped waveguide with HTS insert in the E-plane of the waveguide is the basis of the technical solution protected by a patent [4]. The reference [5] is the first work, where the results of the design and testing of Ka-band filter of a new type are given completely. A given paper presents results, underlining mainly electromagnetic features of the proposed filter, and the algorithm for design of new filter in a case when analytical solution of the electrodynamic problem is absent.

II.DESIGN OF NEW FILTER

A.Objectives and the task

Objectives of the work are as follows:

to design BPF with HTS insert in the cross waveguide and to test experimentally the feasibility of the ideas underlying the patent [4];

to design BPF with normal metal insert in a rectangular waveguide for comparative study of characteristics of two filters experimentally.

BPF with HTS insert in the cross waveguide and BPF with normal metal insert in the rectangular waveguide must have approximately equal bandwidths.

The general structure of the filter is shown in Fig. 1.

Fig.1. Band-pass filter with HTS E-plane insert in a cross waveguide. 1, 5 – cross waveguide; 2, 3 - HTS insert (2 – MgO, 3 - YBaCuO);4 – resonator; 6 – waveguide body of the filter

The simulation of MW currents in band-pass filters with HTS E-plane insert in a rectangular waveguide (Fig. 2a) and a cross waveguide (Fig. 2b) shows a significant difference in the distribution of currents in the waveguides of two types. It is evident that current density in a place of fixing HTS E-plane

insert is much smaller in the cross waveguide.S ,A1,A2, 1, 2,Qn1,Qn2, fn1, fn2

a)

b)

Fig.2. Distribution of MW currents in band-pass filters with HTS E-plane insert. HTS insert in a rectangular waveguide (a) and a cross waveguide (b).

In this work, the task is set for the purpose of carrying out the electrodynamic analysis of the proposed device and developing an algorithm of its design. We designed a 5-pole filter of the bandwidth BW≈140 МHz and a center frequency 30.5 GHz

Fig.3. The results of the design of 5-step BPF with normal metal insert in a rectangular waveguide of 7.2 х 3.4 mm2

The results of the design of 5-pole BPF with normal metal insert in a rectangular waveguide of 7.2 х 3.4 mm2 are presented in Fig.3. Here simulation for perfect conducting (PEC) insert was carried out using System of electromagnetic simulation (MWD II) developed at Institute for Radiophysics and Electronics of NASU. After the program product “CST Microwave Studio” was used for calculation taking into account final conductivity of E-plane insert (see Fig. 3). Comparison of the synthesis and testing results demonstrates a good correspondence.

The width (w = 1.71 mm) and depth (h = 1.0 mm) of the groove, in which the insert is fixed in a cross waveguide, are chosen on minimum losses in 2-pole BPF.

B.The synthesis method of the resonator geometry on the known coefficient of mutual coupling and external Q- factor

At the beginning, by using the low-frequency prototype one can obtain the extern quality factor QEX= 230.7 and the coefficients of mutual coupling K1,2= K4,5=0.0033, K2,3= K3,4=0.0032 between the neighboring resonators, where 1, …, 5 are numbers of the resonators. After an approach to the filter, in which the characteristics of two coupled resonators are determined, is used (Fig.4).

a)

b)

Fig.4. Longitudinal section of two-pole filter with E-insertion in the cross waveguide (a) and equivalent circuit of the filter with two resonators (b)

In this approach the amplitudefrequency characteristic of reflection is written in a form

S ,A1,A2, 1, 2,Qn1,Qn2, fn1, fn2

which is a vector of parameters indicated in the curly brackets, and n,i ( f fni )/ fni ), i 1,2

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The normalized impedance expressed in terms of (f) for the circuit (Fig.4)

allows one to calculate the accurate mutual coupling coefficient between resonators κ2=κ1κ2 and external Q-factor QEX in terms of parameters a0, a1, c0 and c1.

In turn, the obtained data allows one to find dimensions of the windows in the E-plane insert and distance between them.

C.Geometry optimization of BPF using “CST Microwave Studio”

As a result of the above procedure we obtain geometric dimensions of the HTS insert (Fig.5), which were optimized (Table 1) for the purpose to obtained the simulated performance shown in Fig.6.

III. DISCUSSION.COMPARISON OF TWO TYPES OF WAVEGUIDE

BAND-PASS FILTERS

Simulation shows the reduced insertion loss about 1dB in BPF with HTS insert in cross waveguide compared with the insertion loss of the cooled BPF with copper metal insert in the rectangular waveguide.

The presence of technological gaps between the HTS insert and the filter body (housing) is not appreciably affected the increase in insertion loss. In this case we can wait that the insert loss in BPF with HTS E-plane insert in cross waveguide can be less or not higher compared with the insertion loss of the filter with HTS insert in the rectangular waveguide. Hence the problem of cracking of brittle dielectric inserts can be solved by means of using the cross waveguide with HTS E- plane insert for making band-pass filter. It is expedient to produce such filters in mm-wave range up to frequencies at which a notable advantage of HTS compared to normal metals is achieved.

However, production of the proposed filter can meet the technological problem of achieving the implementation of geometry accuracy of E-insert resonant windows and the distance between them.

Fig.6. Simulated performance of 5-pole filter with HTS E-plane insert of optimized dimensions in the cross waveguide

TABLE 1. The optimized dimensions of HTS E-plane insert

b)

Fig.7. Simulated S11 of 5-pole filter with HTS E-plane insert in cross waveguide at 1 m variation of the windows length, Var5If is the optimized |case (a) and distance between windows (b).

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To answer this question an analysis of the impact of small variations in the length of the window and the distance between windows on the frequency response of the filter was carried out. The simulation shows that 1 m variation of the windows length makes worse |S11| substantially (Fig. 7a). However even 10 m variation of the distance between the windows does not change |S11| notably. Thus, the need to improve manufacturing precision concerning the resonator lengths in HTS insert to ± 0.2 μm is shown for the Ka band BPF.

IV. CONCLUSION

The idea of using the cross-shaped waveguide with HTS insert in the E-plane of the waveguide is considered. Hence the problem of cracking of brittle dielectric inserts with HTS film can be solved. The synthesis method of the resonator geometry on the known coefficient of mutual coupling and external Q-factor is proposed and developed. The lowfrequency prototype approach remains as the first stage of the filter synthesis.

The insert loss in BPF with HTS E-plane insert in cross waveguide can be less or not higher compared with the insertion loss of the filter with HTS insert in the rectangular waveguide. The authors underline that producing the proposed filter demands improved manufacturing technology.

ACKNOWLEDGMENT

The work is performed within the framework of Agreement between IOP CAS (Beijing), China, and IRE NASU (Kharkiv), Ukraine, concerning the establishment of scientific and technical cooperation.

REFERENCES

[1]R.R. Mansour, A. Zybura, “Superconducting Millimeter-Wave E-Plane Filters”, IEEE Trans. Microwave Theory Tech., vol.39, pp. 1588-1492, September 1991.

[2]L. Han, Y. Chen, Y. Wang, Q. Cheng, S. Yang and P. Wu, “Design and Performance of Waveguide E-Plane HTSC Insert Filters”, 1992 IEEE IMS-Digest, IF2 1-4, pp. 912-916.

[3]V.N.Skresanov, A.A.Barannik, N.T.Cherpak, Y.He, V.V.Glamazdin, V.A. Zolotaryov, A.I.Shubny, L. Sun, J.Wang, Y.Wu, “Experience in developing Ka-band waveguide filter with HTS E-plane insert”, MSMW, p.661-663, 2013.

[4]V.N. Skresanov, A.A. Barannik, V.V. Glamazdin, V.A. Zolotaryov, M.P. Natarov N.T. Cherpak, A.I. Shubny, Yusheng He, Liang Sun, Jia Wang, Xu Wang, Yun Wu, “Band-Pass Filter”, Favorable decision for Patent № 1065/ЗА/15, Ukraine, 19th May 2015.

[5]Y.-S.He, V.S.Skresanov, A.A.Barannik, L.Sun, N.T.Cherpak, M.P.Natarov, V.A.Zolotaryov, Jia Wang, Xu Wang, Yun Wu, “Novel Design of Band-Pass Waveguide Filter with HTS Е - Plane Insert”, ASC 2016 (unpublished).

[6]V.N. Skresanov, V.V. Glamazdin, N.T. Cherpak, “The Novel Approach to Coupled Mode Parameters Recovery from Microwave Resonator Amplitude Frequency Response”, Proceedings of the 41st European Microwave Conference (EuMC 2011), 10-13 October 2011, Manchester, UK, p. 726-729, 2011.

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