диафрагмированные волноводные фильтры / 01a2c79f-34e0-4c11-8170-2b7b53770864

Abstract—In this paper we discuss two types of band-pass filters at W-band, one is a parallel coupled microstrip band-pass filter and the other is an e-plane metal insert waveguide bandpass filter. The -20dB bandwidth of the parallel coupled microstrip filter is lager than 2.4GHz, while the -20dB bandwidth of the e-plane metal insert waveguide filter is lager than 1.8GHz. The simulation results are better than those in the literatures. Actual design methods are illustrated in this paper, which could play an important role in the design of these two kinds of filters at W-band quickly and efficiently.

Keywords—band-pass filter; coupled lines; microstrip filter; E- plane metal insert waveguide filter

I.INTRODUCTION

The filters are one of the primary and necessary components in the RF front end of microwave and wireless communication systems. There are many kinds of filters, such as end coupled filters, parallel coupled microstrip filters, hairpin-line filters[1], e-plane metal insert waveguide filters[2], and so on.

Due to the advantages of planar structure, simple design, implementation and a wide bandwidth range, the parallelcoupled microstrip band-pass filter is widely used in the last few decades. Many researches have be done on this, but almost on low frequencies[3][4].

Waveguide filters making use of conventional inductive elements such as rods, transverse rods, and transverse diaphragms has many disadvantages such as high cost, and hard to put into mass production due to their complicated structure. In 1974, a new structure was proposed by Konishi, which could solve these problems to a certain extent. That was the predecessor of the waveguide e-plane filter. Waveguide e- plane filters with metal inserts in it requiring no supporting dielectrics, which were originally proposed as low-cost massproducible circuits for microwave frequencies[5]. Then, it was put used into millimeter-wave applications[6]. Millimeter-wave E-plane integrated low insertion loss filters’ high-Q potential is fully utilized. The E-plane circuit is developed on a metal sheet by photo-etching, pressing, or stamping.

In this paper, we discuss two types of band-pass filters at W-band. One is a parallel-coupled microstrip filter, the other is an e-plane metal insert waveguide filter. The -20dB bandwidth is lager than 2.4GHz of the parallel coupled microstrip filter,

while the -20dB bandwidth of the e-plane metal insert waveguide filter is lager than 1.8GHz.

II.DESIGN OF THE PARALLEL COUPLED MICROSTRIP

FILLTER

A. Basic Theory

Figture1 illustrate a general structure of parallel-coupled microstrip band-pass filters which use half-wavelength line resonators which are positioned to each other along half of their length[1]. This structure is particularly good for constructing filters having a wider bandwidth, because the parallel arrangement gives effective coupling for a given spacing between resonators. The design equations for the type of filter are given as follows[7]:

the relative bandwidth of a bandpass filter. J j, j 1 is the

characteristic admittance of J , while Y0 is the characteristic

admittance of the terminal lines. Next step is to calculate the even-mode and odd-mode characteristic impedances.

Then we can use the impedance to calculate the width of the microstrip through a software called linecale.

Fig. 1. General structure of parallel-coupled microstrip band-pass filter

B. Simulation

At first, we could obtain the normalized frequency according the equation of (6)

Consider a five-pole(n=5) Chebyshev prototype microstrip band-pass filter with a 0.1 dB ripple, the n=5 prototype parameters are

According to equation (1)(2)(3), we can come out with the Z0e and Z0o . Then with the help of the software of linecale, we can obtain initial values of the length, width.

The substrate of the filter is Al2O3 , the thick of which is

0.127mm.Relative permittivity is 9.8, while the permeability is 1. The center of the frequency is set to 93GHz. To be helpful for the integration of the system, the input and output ports are parallel. The model is shown in Fig2. During the design,

parameters of W1,2,3 , G1,2,3 and L1,2,3 can be calculated through the method described above.

(a)

L3

L2

L1

(b)

Fig. 2. The model and the key parameters of the parallel-coupled microstrip band-pass filter

C. Results

The S parameters of the proposed parallel-coupled microstrip band-pass filter in simulation is shown in Fig3. It is clear from the response that the filter has better insertion loss than -0.2dB and lower return loss of -32dB. The -10dB bandwidth is lager than 3.6GHz, while the -20dB bandwidth is lager than 2.4GHz. The results are better than that in [11].

F (GHz)

Fig. 3. Simulation S-Parameters

III.DESIGN OF THE E-PLANE METAL INSERT WAVEGUIDE

FILTER

The E-plane filter show in Fig.4 has been analyzed in many literatures [8][9]. It is suitable for both broad-band and narrowband. Such a structure consists of metal strips inserted along

the E-plane of a rectangular waveguide. The metal planes function as impedance inventers while the hole between metal strips are half-wavelength resonators. The widths of the slot patterns on the metal sheet are equal to the height of the waveguide. Thus the structure is consisted of several resonators separated by some strips.

Fig. 4. Basic structure of E-plane metal insert waveguide filter

In this paper, we adopt a five-pole (n=5) E-plane metal insert waveguide filter. The parameter of W1,2,3 and L1,2,3 can be calculated according [10].

Commercial finite-element method (HFSS) is used for the numerical optimization of the pairs (W123 , L1,2,3 , L ) in order to

produce five resonators all at the same central frequency. The thickness of the metal is assumed 0.1mm for all resonators. The material of the metal is gold, while the waveguide is made of aluminum. After simulation, the transverse dimensions of all the parameters are given in the next table.

Fig.5 shows the S-parameter of this E-plane metal insert waveguide filter. From the response we can see that the filter has more stable performance than the parallel coupled microstrip filter. Its insertion loss is better than -0.1dB and return loss is better than -50dB. The -20dB bandwidth is lager than 1.8GHz.

F (GHz)

Fig. 5. Simulation S-Parameters

IV. CONCLUSION

Two W band low loss filters are presented, one is a parallel coupled microstrip band-pass filter and the other is an e-plane metal insert waveguide band-pass filter. Base on the analysis of the equation of the parallel coupled microstrip filter, the approach of the basic design is given. What’more, the specific parameters of the e-plane metal insert waveguide filter is also given. All the simulations and optimizations are achieved by Ansoft HFSS. Excellent simulation results are obtained.

REFERENCES

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[2]Arndt, F., Bornemann, J. E. N. S., Vahldieck, R. U. D. I. G. E. R., & Grauerholz, D. (1984). E-Plane Integrated Circuit Filters with Improved Stopband Attenuation (Short Papers). Microwave Theory and Techniques, IEEE Transactions on, 32(10), 1391-1394.

[3]Kuo, J. T., Chen, S. P., & Jiang, M. (2003). Parallel-coupled microstrip filters with over-coupled end stages for suppression of spurious responses. Microwave and Wireless Components Letters, IEEE, 13(10), 440-442.

[4]Cheng, C. M., & Yang, C. F. (2010). Develop quad-band (1.57/2.45/3.5/5.2 GHz) bandpass filters on the ceramic substrate. Microwave and Wireless Components Letters, IEEE, 20(5), 268-270.

[5]Konishi, Yoshihiro, and K. Uenakada. "The Design of a Bandpass Filter with Inductive Strip--Planar Circuit Mounted in Waveguide." Microwave Theory and Techniques, IEEE Transactions on 22.10 (1974): 869-873.

[6]Vahldieck R, Bornemann J, Arndt F, et al. Optimized waveguide E- plane metal insert filters for millimeter-wave applications [J]. Microwave Theory and Techniques, IEEE Transactions on, 1983, 31(1): 65-69.

[7]Jedamzik D, Menolascino R, Pizarroso M, et al. Evaluation of HTS subsystems for cellular basestations[J]. Applied Superconductivity, IEEE Transactions on, 1999, 9(2): 4022-4025.

[8]L.Q. Bui. D. Ball. T. ltoh. “Broadband millimeter-wave E-plane bandpass filters”. IEEE T-MTI’: Vol. MTT-32, ppl655I658.Dec. 1983

[9]Hunter, Ian. Theory and design of microwave filters. No. 48. Iet, 2001.

[10]Jin H, Liu F. Waveguide E-plane bandpass filters with Butterworth characteristics[C]//Microwave and Millimeter Wave Technology, 2002. Proceedings. ICMMT 2002. 2002 3rd International Conference on. IEEE, 2002: 1009-1012.

[11]Lindo, A. O., et al. "Parallel and end coupled microstrip band pass filters at W-band." Microwave Conference, 2009. APMC 2009. Asia Pacific. IEEE, 2009.