RU2517397C1 - Higher frequencies waveguide filter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: filter represents a section of a rectangular waveguide with flanges and diaphragms of the preset height in-built into both narrow walls of the waveguide and one wide wall of the waveguide; in a cut nonradiating slot on the opposite wide side of the waveguide there is an in-built diaphragm with setting depth reconfigurable mechanically, which is intended for frequency change in the filter section.

EFFECT: provision of coarse measurement of powerful microwave radiation frequency in SHF devices and suppression of out-of-band and parasitic oscillations.

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Description

The invention relates to microwave electronics and can be used in waveguide paths of high power for rough measurement of the frequency of high-power microwave radiation, as well as to suppress out-of-band and spurious oscillations. When developing filters for coarse measuring the frequency of high-power microwave radiation, special attention is paid to ensuring high electric strength, minimal loss in the passband, significant suppression of the parasitic microwave signal outside the passband (more than 50 dB), and a large slope of the filter characteristics from suppression to pass mode. Using this type of filter, it is possible to measure the frequency of high-power microwave devices of a gigawatt power level - relativistic BWTs and TWTs, magnetrons, vircators, etc. Most often, filters based on a rectangular waveguide with conical matching junctions are used for these purposes.

The known design of the waveguide high-pass filter (HPF), based on a rectangular waveguide with conical matching junctions (see transmission lines of centimeter waves. Translation from English. Edited by Remez. Publishing House Soviet Radio. M .: 1951. S. 251.-251-251). In a waveguide below a certain critical frequency, the wave decays exponentially along the direction of propagation, the limiting frequency is called the critical frequency of the waveguide and depends on the geometry of the waveguide and on the type of wave. A filter in which a similar phenomenon takes place is called a waveguide filter at a critical frequency, and for this type of filter, the critical frequency and the cutoff frequency of the filter are the same. The filter has several disadvantages, such as: the complexity of manufacturing, the lack of tuning of the cutoff frequency.

As the closest analogue, a waveguide high-pass filter at a critical frequency was selected, as described in JP 8204404 (A), 1996-08-09, WAVEGUIDE HIGH-PASS FILTER. In this filter, the supercritical waveguide is matched with the input and output waveguides using diaphragms built into the entire width of the narrow walls of the waveguide with a stepwise change in the height of the diaphragm. The disadvantages of this filter include the following: it is complex and expensive to manufacture; there is no tuning of the cutoff frequency, as in the analog described above.

The problem to which this invention is directed is the development of a waveguide high-pass filter having a tunable cut-off frequency that is simple and relatively cheap to manufacture.

The technical result is achieved by the fact that the proposed high-pass waveguide filter, like the prototype filter, is a segment of a rectangular waveguide with flanges and diaphragms embedded in narrow waveguide walls over the entire width of the waveguide wall and ensures coordination with the input and output waveguides.

New in the proposed tunable high-frequency waveguide filter is that the diaphragms in the narrow walls of the waveguide have a constant specified height, from the side of one of the wide walls of the waveguide a diaphragm of a given height is also built in, from the side of the wide waveguide wall opposite to it, a mechanically tunable the depth of immersion of the diaphragm, and to improve matching in the passband of the filter, the end ends of the diaphragms are beveled at an angle.

The invention is illustrated by the following drawings.

Figure 1-3 presents a tunable waveguide high-pass filter: Figure 1 - three-dimensional image; Figure 2 is a cross section in a vertical plane; Figure 3 is a cross section in the horizontal plane.

The waveguide high-pass filter consists of a segment of a rectangular waveguide 1 with flanges, two diaphragms 2 and one diaphragm 3. The diaphragms 2 and 3 are soldered into the waveguide 1 and have a constant height. In addition, in the wall of the waveguide 1 opposite from the diaphragm 3, a diaphragm 4 mechanically tuned along the immersion depth is built into the cut-out non-radiating slit, which changes the cutoff frequency of the high-frequency waveguide filter. The slot through which the diaphragm 4 is inserted is cut along the wide wall of the waveguide 1 and is non-radiating. To improve alignment, the end ends of the diaphragms 2, 3 and 4 are beveled at an angle.

The principle of operation of the proposed waveguide high-pass filter can be explained using the theory of waveguides. The diaphragms 2, 3 and 4 change the cross section of a rectangular waveguide so that it becomes P or H-shaped (see L.A. Weinstein. Electromagnetic waves. 2nd ed., Revised and additional - M: Radio and communication , 1988.440 s. - p. 154-155). The critical frequency of such a waveguide is determined not only by the transverse size of the waveguide A, (the gap between the diaphragms 2), but also by the gap Δ ₂ between the diaphragm 3 and the opposite wall of the waveguide. If there is a diaphragm 4, Δ ₂ is the gap between the diaphragms 3 and 4. By changing the gap Δ ₂ by mechanically moving the diaphragm 4, the critical frequency of the H-shaped waveguide can be tuned, which in our case is the cutoff frequency of the high-pass waveguide filter. Then the transmission coefficient of the signal T (f) through the waveguide high-pass filter depending on the signal frequency f [Hz] can be represented as follows

T (f) [dB] = 20 lge ^{-k (f) L} ,

- мнимая часть продольного волнового числа П- или Н-образного волновода с критической частотой f_кр [Гц], c [м/с] - скорость света в вакууме,Where $$\mathrm{to}\left(f\right)=\mathrm{Im}\lfloor 2\pi /c\sqrt{f^2-f_{\mathrm{to}\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="00000004.png"\; state="\{\{state\}\}">R</figure-callout>}}^2}\rfloor$$

- the imaginary part of the longitudinal wave number of a U- or H-shaped waveguide with a critical frequency f _cr [Hz], c [m / s] is the speed of light in vacuum,

L [m] is the waveguide length.

The change in the cutoff frequency of the high-pass waveguide filter can also be explained as follows. Diaphragms 2 from the side of the narrow side walls are analogous to inductances, diaphragms 3 and 4 from the side of the wide walls of the waveguide are analogous to the series capacitance. The larger the gap Δ ₁ between the diaphragms 2, the greater the inductance and the lower the cut-off frequency of the high-pass waveguide filter. On the other hand, the larger the capacitive gap Δ ₂ between the diaphragms 3 and 4, the lower the capacitance and the higher the cutoff frequency of the high-frequency waveguide filter.

By selecting the lengths of the side diaphragms 2, 3, and 4, as well as the values of the bevel of their end ends, it is possible to minimize losses (<2 dB) in the working frequency band of the high-frequency waveguide filter above the cutoff frequency, and also achieve relatively large suppression (> 50 dB) outside it bandwidth.

The main matching of the high-pass waveguide filter with the input and output waveguides is carried out directly due to its configuration. Due to the fact that the end ends of the diaphragms 2, 3 and 4 are beveled at an angle, additional matching occurs in the filter passband.

A prototype waveguide high-pass filter was implemented in the 3-cm wavelength range. Variation in the immersion depth of the diaphragm 4 within the range of 0-3.5 mm made it possible to reconstruct the cutoff frequency of the high-pass filter in the range from 0 to 20% of its value, without significantly affecting the loss in its working band (<2 dB). When using the standard micrometer screw in the diaphragm 4 movement mechanism, the accuracy of setting the cutoff frequency is no worse than 10 MHz.

The dielectric strength of the filter is determined mainly by the capacitive gap Δ ₂ . The waveguide high-pass filter was tested for electrical strength in the 3-centimeter wavelength range. With a capacitance gap of Δ ₂ = 6 mm between the diaphragm 3 and the opposite wall of waveguide 1, the pulse power level at which the high-frequency waveguide filter showed operation without breakdowns was ~ 150 kW with a radiation pulse duration of 1.5 μs.

Thus, the proposed waveguide high-pass filter provides tuning according to the cutoff frequency, is not difficult to manufacture, has good electrical strength, satisfies the conditions of minimal loss in the passband and significant suppression of spurious microwave signal outside the passband.

A set of such tunable high-frequency waveguide filters with different cut-off frequencies makes it possible to roughly measure the frequency of microwave radiation. The presence of tuning of the cutoff frequency of the filter allows you to minimize the number of filters required to cover the required frequency range. For example, to cover the frequency range of 8-12 GHz, it is sufficient to use the two proposed tunable high-pass waveguide filters, each of which provides a smooth tuning of the cutoff frequency with an accuracy of no worse than 10 MHz. For comparison, to cover the same frequency range, it is necessary to use nine non-tunable prototype filters with cutoff frequencies different by 500 MHz.

The waveguide high-pass filter is intended for use in the decimeter and centimeter wavelength ranges. Using special technology for the manufacture of diaphragms and seats for them in the waveguide (for example, by EDM) allows us to produce filters of the proposed design for use in the millimeter wavelength range.

Claims (1)

The high-frequency waveguide filter, which is a segment of a rectangular waveguide with flanges and with diaphragms embedded in the narrow walls of the waveguide over the entire width of the waveguide wall, ensures matching with the input and output waveguides, characterized in that the diaphragms in the narrow walls of the waveguide have a constant specified height, with on one side of one of the wide walls of the waveguide, a diaphragm of a predetermined height is also integrated; on the side of the opposite wide wall of the waveguide, it is mechanically integrated into the slotted non-radiating slot erestraivaemaya aperture immersion depth, and to improve matching in the passband of the filter end face are chamfered at an angle of diaphragms.

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