диафрагмированные волноводные фильтры / fc724bf2-0912-41d3-95ec-2b7ba85c4fcf

Abstract- In this paper, a novel compact E-plane bandpass waveguide filter in Ka-band with high selectivity is proposed. An extra resonant cell is designed and integrated to the metal septa E­ plane bandpass filter to improve the performance. Two transmission zeros at both sides of the passband are obtained, which contribute to the high-skirt selectivity. The E-plane bandpass filter can achieve different performance by changing the size of the extra resonant cell.

I.INTRODUCTION

In lower frequency-band, coaxial or microstrip-based filters are widely adopted for their compact size, easy integration and low cost. But in higher frequency-band such as millimeter-wave band, the waveguide filters are preferred because of their high cavity quality (Q) value, low insertion loss, large rejection and high power capacity. The waveguide filters have many different configurations. For example, direct-coupled cavity filters is composed of waveguide cavities coupled through thick inductive irises [1-2]. In some of these configurations, tuning screws are preferred to make the filters adjustable [3], and more recently fractal-shaped irises have been proposed to further improve their performances [4]. Moreover, the dual-mode [5-7] or multi-mode [8] waveguide filters can implement nonadjacent couplings between resonators, which results in more complex filtering functions and complex filter structures and hard fabrications. These methods are able to provide improved performances such as high selectivity and low insertion losses, but they suffer from high costs and are hard to fabricate. The waveguideE-plane septum filter was introduced by Konishi in 1974 [9], and since then it has been developed as an effective way to design waveguide filters [10-12]. In this filter configuration, the impedance inverters are synthesized through the thin metal septa which inserted in theE-plane of waveguide. ThisE-plane bandpass filter configuration has the advantage of simple manufacturing processes and low cost, and suitable for massive production. The electrical responses of this kind of filters are dominated by the patterns of theE-plane metal septa, we need lots of these septa to increase the selectivity, which lead to uncontrollable sizes and insertion losses.

In this paper, we improve the selectivity to a new level, as two transmission zeros are added at both sides of the passband, by employing a resonant cell in between of thin metal septa. In addition, the introduction of the resonator allows us to get rid of large numbers of septa, and thus compact sizes are realized.

The theory to design the compactE-plane bandpass waveguide filter with high selectivity is presented in section II. Finally

some conclusions are presented in section III

II.DESIGN AND ANALYSIS

A.Characteristics ofE-plane waveguidefilters with only two metal septa inserted.

In this subsection, we first investigate the characteristics ofE­ plane waveguide filters with only two metal septa resulting in a half-wavelength resonator before the design and analysis of our proposed filter. The half-wavelength resonator is fabricated on the Rogers 5880 substrate (with thickness of 0.254 mm and relative permittivity &, = 2.2), which is inserted inE-plane of a

standard Ka-band waveguide (WR 28 with a=7.ll2mm and b=3.556mm), as shown in Fig. l. When fixed the width of the metal septa, its band-pass properties are controlled by the distance d between the two metal septa.

From the Fig.l, theE-plane bandpass filter with only one half­ wavelength resonator structured by two metal septa has slow attenuation in the stop-band. Affected by a negative length brought by the K-impedance inverters, the distance between the two metal septa is slightly less than 0.5 Ag [13-15]. And the

normalized K-impedance inverter value and negative electrical length can be approximately given by [14].

Fig. 1 E-plane waveguide filters with two metal septa (w,=O.3mm)