JPH0430202B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a harmonic suppression filter, for example, a harmonic suppression filter for suppressing the harmonic output of a waveguide type oscillator or amplifier using a microwave semiconductor element. This relates to suppression filters.

[Technical background of the invention and its problems]

Waveguide-type microwave oscillators and amplifiers (hereinafter simply referred to as oscillators) that use microwave semiconductor elements such as Gunn diodes, impact diodes, or FETs may generate unnecessary waves at frequencies other than ₀ due to nonlinear operation, such as n ₀ (n=2,
3...n) harmonics are generated. When a waveguide is used as an output line of these oscillators, etc., an operating frequency higher than the cutoff frequency of the waveguide and its harmonic components are output.

For this reason, especially in oscillators used in communication systems, etc., a harmonic suppression filter is often inserted at the output end. These harmonic suppression filters include, firstly, a band-stop filter that blocks the propagation of only frequencies around harmonic frequencies such as 2 ₀ 3 ₀ ...n ₀ , and secondly, a low-pass filter that passes frequencies below the operating frequency band. , and thirdly, there are band-pass filters whose passband is the operating frequency band.

Among these, the second low-pass filter is most commonly used for suppressing harmonics in waveguide circuits, and representative examples thereof include corrugate filters and Watsuful iron filters.
However, these have the following problems: first, they have a complicated structure and large external dimensions; second, they have a relatively large insertion loss of 1 to 2 dB; and third, they are expensive.

Furthermore, among the third bandpass filters, 2 ₀ ,
A harmonic suppression filter equipped with a resonant window plate (hereinafter referred to as a resonant window filter) is effective for blocking high frequencies such as 3 ₀ ...n _0. This resonant window filter has an extremely simple structure. In addition, although the insertion loss in the operating frequency band is very small, the load Q of the resonator is low and there is a problem that sufficient attenuation against harmonics cannot be obtained.

Next, an example of the structure of a conventional resonant window filter will be explained with reference to FIG.

First, Figure A is a diagram showing the structure of a resonant window, in which the resonant window plate 3 has a resonant window 3a formed in a metal plate having dimensions of the width a and the height b of the waveguide. This resonant window 3a is usually rectangular as shown in the figure, and its resonant frequency is determined by the width w and height h. Further, the Q _L (load Q) of the resonator is determined from the size of the resonance window 3a, and is usually about Q _L 10. Figure b and c
The figures show the structures of single-stage and two-stage resonant window filters 1, each constructed by attaching a resonant window plate to a waveguide. Figure c shows one in which two resonant window plates 3 ₁ and 3 ₂ are provided between the input and output. In the case of the two-stage type with these two resonant window plates 3 ₁ and 3 ₂ , the interval l between the resonant window plates 3 ₁ and 3 ₂ is such that the passage characteristics in the operating frequency band are almost symmetrical with respect to the resonance frequency ₀ . The length is chosen such that it has a so-called maximally flat shape characteristic.

That is, if the spatial wavelength at the resonance frequency ₀ is λ ₀ and the wavelength in the waveguide is λg, then the optimum value of l is 1=1/2 (λg ₀ /4+λ ₀ /4) to _{λg 0} /4). This method is described in the literature lnt.J.Electronics 1966,
Vol21, No.5, PP401−424 “Waveguide
Resonantiris Filters with very Wide
Passband and stopbands”.

FIG. 2 is an example of actually measured characteristics of a conventional resonant window filter, and shows the frequency characteristics of attenuation. That is, curve 11 is for the one-stage filter shown in FIG. 1b, where Q _L =2.5 (where Q _L is the load Q of the resonator), and the attenuation in the ₂₀ band is about 15 dB. Curve 12 is the two-stage filter shown in Figure 1c, and l is the optimum value (in the operating frequency band) described above.
Maximally flat characteristics). In other words, it has good filter characteristics near ₀ , but when 2 ₀
In the band of , it becomes almost a pass characteristic. In this way, the conventional resonant window filter cannot obtain sufficient attenuation in the ₂₀ band with a one-stage configuration, and with a two-stage configuration, it cannot provide sufficient attenuation in the ₂₀ band.
There was a problem in that the vicinity became a passband and sufficient performance as a harmonic suppression filter could not be obtained.

[Purpose of the invention]

The present invention has been made in view of the conventional problems described above, and by appropriately setting the spacing between the resonant window plates, the present invention can effectively suppress harmonic components such as the second harmonic and third harmonic bands. The purpose is to provide a wave suppression filter.

[Summary of the invention]

That is, the harmonic suppression filter of the present invention is a harmonic suppression filter in which a plurality of resonant window plates are arranged in a waveguide, and when 1/4 of the wavelength in the waveguide at the operating center frequency is l ₀ . is characterized in that the interval l between the plurality of resonance windows satisfies 0.2≦l/l ₀ ≦0.8 or 1.1≦l/l _{0 ≦} 1.6, for example, a conductor using a microwave semiconductor element. This is a harmonic suppression filter that can effectively suppress the harmonic output of wave tube shaped oscillators and amplifiers.

[Embodiments of the invention]

Next, one embodiment of the harmonic suppression filter of the present invention will be described with reference to FIGS. 3 and 4.

That is, the harmonic suppression filter 31 consists of two resonant window plates 33 ₁ and 33 ₂ attached to the waveguide 32 with a distance l between them.
The configuration of a stepped filter is shown. And this interval l is 1/ of the wavelength λg ₀ in the waveguide 32 at the operating center frequency.
4 as l ₀ , in order to suppress the second harmonic band 2 ₀ , 0.2≦l/l ₀ ≦0.8, or 1.1≦l/l ₀ ≦1.6.
and the second harmonic band 2 ₀ and the third harmonic band
3 To suppress ₀ , 0.2≦l/l ₀ ≦0.5 or 0.6
It is characterized by selecting ≦l/l ₀ ≦0.8 or 1.15≦l/l ₀ ≦1.6.

FIG. 4 is an experimental example of this embodiment, and shows the frequency characteristics of the amount of transmission attenuation of the two-stage resonant window filter.
That is, curve 41 has l/l ₀ =0.525, curve 42 has l/l 0 =0.525, and curve 42 has l/l 0 =0.525.
This is the case where l ₀ = 1.4. In this case, the Q _L of the single resonant window plate is Q _L 2.5, which is the same as in the conventional example shown in FIG. As can be seen from the curve in Figure 4, l/l ₀ = 0.525 and l/l ₀ = 1.4.
It has a low-loss pass characteristic near ₀ , and the attenuation is 25 dB or more in the ₂₀ band, indicating that harmonics in this band are suppressed well.

FIG. 5 is a diagram showing the calculation results of the characteristics of the two-stage resonant window filter of the embodiment described above. Tazushi Q _L
= 3.0.

That is, curves 51 and 52 are the attenuation at 2 ₀ and 3 ₀ , respectively, calculated with respect to the change in l/l ₀ , and the shaded area 53 indicates the attenuation at 0.2 dB or less in the operating frequency ₀ band. It shows the change in the difference between the upper limit frequency curve 53a and the lower limit frequency curve 53b. In other words, the normally required fractional bandwidth of 5% (/ ₀ = 1 ± 0.025) or more has been obtained for any l/l ₀ , and from curves 51 and 52, the effective attenuation amount (25 dB) in the ₂₀ band In order to obtain l/l ₀ , use the range A _2-1 or A _2-2 in the figure, 2 ₀ ,
In order to obtain effective attenuation in the ₃₀ band, A _3-1 ,
You can choose between A _3-2 and A _3-3 . In addition, A (0.9
≦l/l ₀ ≦1.0) is a conventional suppression filter,
It can be seen that the pass area is around _2.0 . Also, even when l/l ₀ ≧1.8, the characteristic curves 51 and 52 repeat similar attenuation characteristics, but 1</ ₀ < 2, 2</
₀ <3 Multiple passbands occur in the band, which is not practical.

In the above explanation, a suppression filter using two stages of resonant window plates has been explained, but if the amount of attenuation is insufficient, it can be attenuated by using more stages and setting the interval between each resonant window plate within the claimed range. Of course, the amount can be further increased.

Next, an application example of the harmonic suppression filter of the present invention will be explained with reference to FIG.

That is, the circulators 62 and 63 are connected to an oscillator (injection locking type or negative resistance type) 61 using a microwave oscillation element, and the circulator 62
As shown in the figure, a matching load 64 is connected to the circulator 63 to act as an isolator. 65 is the second embodiment of the present invention described above.
This is a staged resonant window type suppression filter, and is sandwiched between a circulator 63 and an output waveguide 66. The suppression filter 65 is composed of a resonant window plate 65a, a spacer waveguide 65b _, and a resonant _window plate _65c . Set it to be either A _3-1 , A _3-2 , or A _3-3 .

With this kind of circuit configuration, the normal oscillator etc. 61
Since the amount of ₂₀ and ₃₀ components generated is considered to be less than -20dB, the amount of harmonic suppression by the resonant window filter 65 is
If it is 20 dB or more, it is possible to easily obtain the harmonic leakage amount at the output end of -40 dBc or less, which is normally required.

〔Effect of the invention〕

As mentioned above, in a harmonic suppression filter consisting of a multi-stage resonant window plate, the interval l between the resonant window plates is
When l ₀ = λg ₀ /4, 0.2≦ for second harmonic suppression
l/l ₀ ≦0.8 or 1.1≦l/l ₀ ≦1.6, for second and third harmonic suppression 0.2≦l/l ₀ ≦0.5, or 0.6≦l/l ₀ =0.8, or 1.15≦ By setting l/l ₀ ≦1.6, the second harmonic band or the second harmonic,
It is possible to provide a small, low-cost harmonic suppression filter that can sufficiently suppress harmonic components in the third harmonic band, and has a practically sufficient passband with low loss in the operating frequency band. Its industrial value is extremely large.

[Brief explanation of drawings]

Figure 1 is a diagram showing a harmonic suppression filter using a conventional resonant window plate. Figure a is a plan view showing the structure of the resonant window plate, and figure b is a harmonic suppression filter using a single-stage resonant window plate. A simplified sectional view showing the filter, Figure c is 2
A simplified cross-sectional view showing a harmonic suppression filter using resonant window plates in stages, Fig. 2 is a curve diagram showing the attenuation characteristics of a conventional harmonic suppression filter, and Figs. 3 and 5 show the harmonic suppression filter of the present invention. FIG. 3 is a simplified sectional view, FIG. 4 is a curve diagram showing attenuation characteristics of this embodiment, and FIG. 5 is a characteristic diagram for explaining the characteristics of the present invention. The calculation curve diagram, FIG. 6, is a simplified explanatory diagram showing an application example of the harmonic suppression filter of the present invention. 1, 31, 65...resonant window filter, 3, 3 ₁ ,
3 ₂ , 33 ₁ , 33 ₂ , 65a, 65c...resonant window plate,
2, 32... Waveguide, 11, 12, 41, 42, 5
1, 52... Attenuation characteristic curve, 53... Pass ratio band,
61...Oscillator or amplifier, 62, 63...Circulator, 64...Matched load, 66...Output waveguide.

Claims (1)

[Claims] 1 In a harmonic suppression filter in which a plurality of resonant window plates are arranged in a waveguide, when 1/4 of the wavelength in the waveguide at the operating center frequency is l ₀ , the plurality of resonant window plates 1. A harmonic suppression filter characterized in that the gap l is set to satisfy 0.2≦l/l ₀ ≦0.8, or 1.1≦l/l ₀ ≦1.6.