диафрагмированные волноводные фильтры / 225babc1-d059-4821-8bdd-95a01b5c20f2

N. Mohottige, U. Jankovic and D. Budimir

Wireless Communications Research Group,

School of Electronics and Computer Science, University

of Westminster, London, W1W 6UW, UK

d.budimir@wmin.ac.uk

Abstract—This paper presents electromagnetic simulation of a varactor-tuned E-plane waveguide band-pass filter. Silicon varactor diodes which can operate through X band are placed between gaps in the centre fins of an E-plane extracted pole section to provide tuneability for the filter structures. The simulation of the filter was carried out by CST Microwave Studio with the diodes being modelled by its Spice model in CST Design Studio. Tuning range of 280 MHz is achieved.

I.INTRODUCTION

U. Jankovic

School of Electrical Engineering,

University of Belgrade

11120 Belgrade, Serbia

is represented by presenting the PEC pad to allow a bridge over the gap where as off stage can be represented by the absense of the PEC pad. A more accurate representation is to model the PIN diode in CST Design Studio using lumped elements or by importing Spice equivalent circuit of the diode. Fig. 2 shows the schematic diagram of the Silicon Varactor diode used. The ports used to connect the diodes to the filtering structure were first defined as descrete ports in the gaps during the filter design process.

E-plane waveguide filters are a sustainable solution for high performance, low cost and low loss filter applications [1]- [4]. Tuneable and reconfigurable waveguide filters have gained a noticeable attention in wireless and satellite communication systems over the past few years due to their capability of minimizing sizes of the front ends of multi functional systems as required for both satellite and terrestrial applications.

Tuneable waveguide filters have been previously proposed using magnetic tuning [5], and using embedded High-Q RF MEMS [6], [7]. The first has disadvantage of bulkiness and consumes considerable power, where as the later requires more complex customized MEMS design. High-Q GaAs varactor diodes can be used for tuneability but similarly at higher costs. MEMS on the other hand also provide good insertion loss and isolation characteristics; however unlike Silicon varactor diodes it is incapable of handling high power.

In this paper electromagnetic simulation of a third-order tuneable E-plane extracted pole waveguide filter using spice model of a Silicon Varactor diode is presented. The S- parameter responses show that the structure can achieve 280 MHz tuning range.

II.PROPOSED FILTER STRUCTURE

The proposed 3rd order tuneable E-plane extracted pole waveguide band-pass filter structure is shown in Fig. 1. The structure consists of three extracted pole sections inductively coupled via metallic septa. The septa and fins are etched on a metallo-dielectric substrate (Tacconic RF-35) with dielectric permitivity (εr) of 3.5 and metalisation thickness of 0.02 mm. The resonant frequency of a single extracted pole section can be controlled either though varying the length of the section or by changing the length of the fin. Therefore a small gap of 0.5 mm has been placed within each fin in order to realise different lengths. The behaviour of a diode placed between this gap can be represented in two ways. First representation in the simulation process is to simply model it as a PEC pad. On stage

Figure 1. Configuration of tuneable extracted pole waveguide band-pass filter.

Figure 2. Schematic diagram of the Silicon Varactor diodes used in simulation.

III.RESULTS

The 3rd-order E-plane extracted pole band-pass filter was designed and simulated in CST which utilizes a single metallodielectric insert within the conventional rectangular waveguide. The dimensions of the structure are presented in Table I. The properties of the diode are presented by its Spice file which has a zero bias junction capacitance of 0.838pF with a minimum to maximum capacitance ratio of 5, and its configuration is shown

in Fig. 2. The S-parameter responses of the tuneable filter are shown in Fig. 3 and Fig. 4, respectively. The reverse bias voltages applied to the diode was varied from 0 to 25 V.

As the reverse bias voltages are increased, junction capacitance of the diode decreases, thereby increasing the gap length, thus a shorter fin length is realised. The centre frequency of the filter was shifted from 9.405 GHz to 9.685 GHz which shows that the filter structure achieves a tuning range of around 280 MHz.

TABLE I

DIMENSIONS OF PROPOSED TUNEABLE EPS FILTER (MM).

Frequency (GHz)

Figure 3. Simulated |S11| of the proposed 3rd order varactor-tuned filter.

Frequency (GHz)

Figure 4. Simulated |S21| of the proposed 3rd order varactor-tuned filter.

IV. CONCLUSION

A 3rd order tuneable E-pane extracted pole waveguide filter have been designed and simulated. In a practical point of view, this structure can be realized through utilization of metallodielectric insert within standard air filled rectangular waveguide and small holes can be drilled on top of the waveguide housing to provide biasing for the Silicon diodes. The simulated filter structure shows that a tuneable range of 280 MHz has been achieved.

REFERENCES

[1]Vicente E. Boria and Benito Gimeno, “Waveguide Filters for Satellites” IEEE Microwave Magazine, Vol.8, Issue 5, pp.60-70, October 2007.

[2]I. C. Hunter, Laurent Billonet, Bernard Jarry, Pierre Guillon, “Microwave Filters—Applications and Technology” IEEE Trans. Microwave Theory Tech.,Vol.50, pp. 794-805, Mar. 2002.

[3]D. Budimir, "Generalized Filter Design by Computer Optimization", ISBN 0-89006-579-9, Atrtech House Books, 1998.

[4]Y. Konishi, and K. Uenakada, “The Design of a Bandpass Filter With Inductive Strip Planar Circuit Mounted in Waveguide,”

IEEE Trans. Microwave Theory Tech., vol. MTT-22, pp. 869873, Oct.1974.

[5]P. Bernardi, F. Valdoni, "Fundamentals of a new class of magnetically tunable waveguide filters," Magnetics, IEEE Transactions on , vol.2, no.3, pp. 264268, Sep 1966.

[6]Sang-June Park, I. Reines, C. Patel, G.M Rebeiz, "High-Q RFMEMS 4–6-GHz Tunable Evanescent-Mode Cavity Filter,"

Microwave Theory and Techniques, IEEE Transactions on , vol.58, no.2, pp.381-389, Feb. 2010.

[7]Winter Dong Yan, R.R Mansour, "Tunable Dielectric Resonator Bandpass Filter With Embedded MEMS Tuning Elements,"

Microwave Theory and Techniques, IEEE Transactions on , vol.55, no.1, pp.154-160, Jan. 2007.

[8]Microwave Studio, CST, 2012.