DE2006864C3 - Bandpass filter in a square waveguide - Google Patents

Description

35

The invention relates to a band pass filter. in which in the wave formation direction at a distance from one another and arranged parallel to one another in the interior of the waveguide protruding in the longitudinal direction of the broad sides and transversely / u the narrow sides extending blind guide elements arranged sun .. each of several, in a straight line aiii :, arranged parallel, mutually offset bars arranged at right angles to the broad side are formed and together with the waveguide form a cavity resonator, as well as at least one that forms a capacitive element and is attached to a broad side in the middle between two Blindleitwerlelemente arranged, into the shaft interior protruding adjustable screw.

In a transceiver of a microwave communication system a traveling wave tube is used as a power amplifier on the transmitting side. Line traveling wave tube, however, has a non-linearity, consequently higher harmonics are inevitably generated in the gain stage. Such harmonic components are not only unnecessary for microwave transmission, they are undesirable for the entire system since it requires excessive energy to carry the load. Such unwanted components should therefore be removed. Usually one is used for this purpose Bandpass filter to the output signal of the wall-mounted wave tube amplifier coupled

From "Microwaves". August IWo. S. ^l ) 3 to ' ¹ T. is a bandpass filter of the one described above ;! Kind known. With this bandpass filter in a Reel corner waveguide, however, it is not possible to suppress the higher harmonic components alone. Rather, undesired higher harmonic components can pass through together with the basic components. To remove the higher harmonic components, a low-pass filter must therefore also be connected in series with the band-pass filter.

It is the object of the invention. a bandpass filter in a rectangular waveguide of the type described above Create a way to suppress unwanted higher harmonic components, so that no additional filter is required.

This task is achieved by a bandpass filter in a rectangular waveguide of the type described above solved, which is characterized according to the invention. that the axial distance between equal to the susceptance elements designed as rods in the direction of wave propagation ', the waveguide wavelength and that the axis of the closest to the respective narrow side of the waveguide Coming rod of the Blindieitwertelemente from this a distance. one third of the total distance (ti) between the inner surfaces of the opposite narrow sides.

In this way, the second harmonic component becomes the higher harmonic component suppress

The invention is based on the fact that the higher harmonic components essentially can be suppressed by suppressing the second harmonic component, since the components higher than the second are very weak and can be neglected. Since the second higher harmonics are concentrated in the area in which the transmission frequency types the microwaves are concentrated, köiinei. the / wide higher harmonics through Elimination of the components of the higher vibration types be suppressed.

In the I- i g. 1 through 10 of the drawings is the The subject of the invention is illustrated, for example, and explained in more detail below. It shows

I x 1 g. I schematically a common band-pass filter.

I 1 g 2 a waveform diagram. from which the Characteristic curves of the bandpass filter in FIG. 1 emerge.

F i g. 3 different oscillation types that are possible in a bandpass filter of the square wave type are.

E i g. 4 characteristics of the filter to explain the principle of the invention.

E i g. Fig. 5 schematically shows a bandpass filter according to the invention.

E i g. 6 shows the characteristic curve of the filter in FIG. 5 and

F i g. 7 to 10 schematically further embodiments according to the invention.

In Fig. 1, which schematically shows a perspective view of the conventional band-pass filter, there are reactive value elements 11 and 11 '. each of which consists of three rods arranged vertically / u the broad side of a rectangular wave conductor 10 for the Tf, "- type of propagation, with a spacing of half a Leiler wavelength /." (d li. Ai; 2) and form a cavity resonator 12. Several resonators 12 and 13 are in series with an area of / .H 4 .in'V'ird'iet. .leder de; Resonators 12 and \) hesit / t a. Ahsiimnis / screw m. 11 to .111 each

006

sonator 12 and 13 to achieve the coordinated state.

This bandpass filter has the damping frequency characteristic. as shown in FIG. 2 is shown. In the drawing it is shown that the cutoff frequency (c ₂ o for the ΤΙ -. ,,, - type is given by

If the length / cavity resonates, then

The resonance frequency / at the cavity length is given by equations (1) and (2)

where α denotes the width of the broadside and c denotes the speed of light. It can also be seen from the curve that the bandpass filter is selective only in the region. in which the frequency / is less than fc ₂₀ In the range above / c ₂₀ , the properties become indeterminate, since the occurrence of possible higher oscillation types disrupts the function of the filter. In general, the second harmonic 2 / \ _m , which is twice as large as the frequency / "" of the pass band of the band pass filter, is higher than Ic ₂₀ and is included in the range in which a disturbance is caused.

The F 1 g. 3i | a) to 3 (0 show field intensity disturbances (in absolute values) of the TE ₁₀₁ basic type and its higher types TE _201. TE _102. TE, «,. TE ₂₀₂ and TE _{103 of} a bandpass filter, which is composed of susceptance values 21 and 21 ' each of which comprises e.g. and the longitudinal axis lies in the Z-axis. The intensity distribution of the electric field of the TE ₁ , "- circular type has a single sinusoidal stool in the XYF plane and the YZ plane (which extends between the inductance columns 21 and 21 ') Fig. 3 (b) shows a field intensity distribution of the higher type TE ₂₀₁ . which has a sinusoidal double hump in the .YYI hene and a single stool in the YZ level (which extends between the inductance bars 21 and 2Γ). Fi g. 3 (c) shows a similar distribution of the higher type TE ₁₀₂ . which has a single sinusoidal stool in the .YY plane and a double hump in the YZ plane (which extends between the inductance bars 21 and 2Γ). In the same way, FIGS. d). 3 (c) and 3 (f) intensity distributions of higher types TE ,,,,. TE ₂₀ , and TE ₁ ,,,. In general, the reference symbols »mc and» π ·· of the expression TE ₁₁₁₁₁ “denote the number of stools of the intensity distribution of the electric field observed in the YY and YZ planes

It is assumed that the internal width measured in the Y-direction of the rectangular waveguide 20 is α and that the axial length of the waveguide section or cavity defined by the rows of rods 21 and 21 'is measured in Direction of Z-Acr.se. / is the waveguide wavelength / g of the electromagnetic wave, which see 111 propagates along the waveguide as 1 ,,,,,,, - Iyp, is then auv.iedri.ickI

The equations (3) are normalized by using the cutoff frequency / o (= -r) and the cutoff wavelength Äf (= 2a), then equation (3) changes

25th

/1

nc

From equation (4 / follow! Then

/.c

¹ VCfJ-

30 da / _ /
2Y1 ~ Äf '

F i g. 4 shows characteristics, the results of the calculation , ms are equation (5). In Fig. 4 represents the

.Abscissa (the resonance frequency for the TE _lm , "- type, normalized by the cut-off frequency / ', (- ., J for the ΤΕ ,,,, - Gruiullyp) and the ordinate represents _{; (} .

Cavity, normalized by the e Äf (= 2d) of the TE ₁₀₁ -Gundlyps)

(the length / des
Cutoff wavelength
i!; tr. The parameters for these characteristics are the numbers m and / i. The characteristic curve 31 shows the relationship between the resonance frequency / for the basic type TE ₁ ,,, and the cavity length /. normalized by the cutoff frequencies / and the cutoff wavelength for type TE ₁₀ , itself.

Cutoff wavelength for the
The characteristic curve 32 shows the relationship / between the resonance frequency / of a higher type TE ,,,, and the cavity length / normalized by the quantities / frequcn / / ',. and the size / corrugation length / c of the basic type TE _10,. In the same way / the characteristics 3 to 7 the relationship between the resonance frequency f for the higher types TE ,,,,. TE ₃₀₁ . TE ₂₀₂ . TE ₁₀ , and TF ₃₀₂ and the cavity length c. normalized by the cutoff frequency / ', and the Grenzwcllenlängc Äf for the basic type TE ₁₀₁ .

A bandpass liller made from a rectangular waveguide

fto is generally designed to start with the value ^ works in the range between 1.4 and I .S. For example is in a WRI - 4 - VVellcnleilerlyp füi

1 λ πη, ι ι (■>->, nc

, -Value range between 2.X and 3.3 or wipe /

3.1 and 3.6 are suppressed muli around this goal to achieve, the resonance / curves should never be in this Area fall. In Fig. 4, the hatched area fulfills this condition. To be more precise it is

Area favorable in which the value. is in the range between 0.2 and 0.3. The reason for this is the following: If the values are in the range 0.3

and 0.6, the characteristic curves 33, 35 and 36 appear for the types IT-Ki _2, respectively. TH ₃₁₁₂ and TIi ₁₀ . This is not convenient for eliminating the higher types. In the same way, in the range above 0.6, the resonance frequency for the basic Kp TE ₁₀₁ becomes lower than the desired resonance frequency / "and is very difficult to increase. In the range below 0.2, the resonance frequency is unnecessarily high and also difficult to lower. Therefore, if the cavity length / is chosen so that it falls within this range, then the second harmonic component can be suppressed. However, this increases the

Value of . to a value ranging from 1.9 to 2.7.

as shown by the characteristic curve 31. To put it back in the range between 1.4 and 1.8, a capacitive element must be inserted into the cavity of FIG. 3 (a) in order to reduce the resonance frequency for the basic type TF. ,,,,. In this case, the resonance frequencies of the higher types must be TF. _2O i · TE ,,,,. TF ₃₀₁ . TL ₂₁₁₂ and

Tl κ ,, be designed so that not in the

Range between 2.4 and 3.6 can come as this range is the undesirable second higher Heard harmonics that might resonate with the higher types. The procedure to do this achieve is as follows:

As indicated by the characteristic curve 32 in FIG. 4, it is sufficient for the higher type TE ₂₁₁₁ to reduce its resonance frequency or to leave it unchanged. As in F i p. 3 (b). the point at which the field of type TE _{201 has} a minimum lies on the center line EE ' on the main plane of the rectangular waveguide 20. This means that the resonance frequency of type TE _{201 is} achieved by inserting a capacitive rod at a point with the exception of EE' can be reduced. In this case the cutoff frequency is ₇ / r20. normalized by the cutoff frequency / 0 for type TE ₁₀₁ ( . '"J equals 2. a value that is sufficiently above the frequency range for type TE _1n , which extends from 1.4 to 1.8. This means that for type TE ₂₀₁ the capacitive rod can be placed anywhere. Since the resonance frequencies for the higher types TE ,,,,. TE _401, TE ₃₀₂ with the exception of TE _{103 are also} sufficiently high, the suppression of the wide harmonics is not problematic types TE ₁₀₂ , TE ₃₀ , and TE _202. To prevent the resonance frequencies for the three types TE _102, TE ₃₀ , and TE _{202 from} becoming too low and a certain particular band as a result of the insertion of the capacitive rod reach into the cavity, this capacitive rod must be placed in such a place, where the field of each higher type TF ₁ ,,,, TF ₁₁₁₁

and TF _{202 has} a minimum. In order to also lower the resonance frequency of the fundamental TE ₁₀ , the capacitive rod must be arranged at such a point where the field of the basic type TE, _{0 (has} a maximum. For type TE ₁₀₂ , the capacitive rod should be on the center line AA ' of the cavity as shown in Fig. 3 (c) For the IFj ₀₁ type, the capacitive rods should be placed on the dividing lines β-β 'and CC on the main plane along the longitudinal axis, as in Fig 3 (d). For type TE ₂₀₂ the element is on the centerline AA 'of the cavity and also the centerline EE' on the principal plane of the rectangular waveguide as shown in Fig. 3 (e).

The locations common to these types are D and D '. where the center line AA 'of the cavity intersects with the triangular lines BB' and CC ", as shown in Fig. 3 (f). As described above, with the type TE ₂₀ , there is no problem. the second To suppress the TE ₂₀₁ type, it is necessary to make the bandpass filter symmetrical, since the field intensity distribution on one cable is opposite in phase to that on the other side, based on the center line EE ' on the main plane, and therefore a component of one phase should always be accompanied by a corresponding component of the opposite phase in a waveguide

Embodiments of the invention are further illustrated by FIG. 1 g. 5 and 6. In order to prevent the resonance frequency of the types other than TE _{201 from} falling in the range below the frequency twice as large as the resonance frequency of the fundamental wave c, the length / cavity of the rectangular waveguide becomes V, Ag in contrast to that corresponding length 1/2 Ag of the usual bandpass filter and adjustable capacitive elements (screws) 41 and 4Γ are installed at two points at which the three-U'ilungslinicn 42 and 42 'on the main plane of the rectangular waveguide 40 with the bisector 43 of the area / between the inductive rods 44 and 44 'so that one end protrudes into the interior of the cavity. As shown in FIGS. 3 (c). 3 (d) and 3 (e) and their description can be seen. the capacitive rods are arranged at the points. at which the field intensity has a minimum with respect to the higher types TE ₁₀₂ , TE ₃₀₁ and TE ₂₀₂ and essentially a maximum with respect to the basic type TF ₁₀₁ . By using the capacitive adjustable screws 41 and 41 ', a desired pass band can be obtained for the basic type TF ₁₀₁ , the resonance frequencies for the higher types being kept outside the pass band. The type TE ₂₀ I is also suppressed due to the symmetry of the filter

F i g. 6 shows the attenuation / frequency characteristics of the filter of FIG. 5 to suppress the second harmonic. As can be seen from the characteristic, this filter is able to suppress the higher types in the frequency range which is twice as high as the resonance frequencies of the basic type. In particular, this filter suppresses the higher types in the range where _{f is} from 2.8 to 3.6

/
reached, while the value for the Durchlaßbereichn

the fundamental wave from 1.4 to 1.8 r. I. Thus becomes the second harmonic wave component is eliminated.

The F i g. 7 to 9 show further embodiments. These are based on the fact that. As described above, the higher type "TTi ₂₀₁ " can be left out of consideration if the second harmonic is to be suppressed and therefore the structure of the band-pass filter need not be symmetrical.

F i g. 7 shows an embodiment. in which only one of the symmetrical elements of FIG. 5 is used.

F i g. 8 shows a further embodiment in which one of the adjustable capacitive elements (Screw) is attached to the opposite major surface of the waveguide.

F i g. 9 shows a further embodiment. at where two capacitive elements are placed in place of one near the point that is the capacitive one Elements of FIG. 7 corresponds. Similarly, the arrangements of FIGS. 5 and 8

by replacing the single capacitive element with several capacitive elements around the bodies like in Fig. 5 or 8 are arranged, can be modified.

F i g. 10 shows an arrangement in which the capacitive elements as in FIG. 7 also on the are arranged lower main plane of the waveguide. The same arrangement can be used in conjunction with the 1 i g. 5 and 7 can be carried out.

Single-stage bandpass filters have been described on the basis of the various exemplary embodiments. In general the bandpass filters for suppressing higher harmonics consist of several stages. Of course, the invention can also be applied to such multi-stage bandpass filters. the The invention is also based on a quarter-length coupling and direct coupling bandpass filters can be used to suppress higher harmonics.

The invention can also be used to suppress higher harmonics than the second harmonic will.

In addition 5 sheets of drawings

509 62E

ijgf -Jt. || i.'iJLJjMg ^ l ·, "* - ¹ SiSffi _ -

Claims (2)

Patent claims: 1. Bandpass filter in a rectangular waveguide, in which in the direction of wave propagation at a distance from each other and parallel to each other arranged into the interior of the waveguide, extending in the longitudinal direction of the broad sides and transversely to the narrow sides are arranged susceptance elements, each of several arranged in a straight line parallel rods offset from one another, arranged at right angles to the broad side, and together with the waveguide form a cavity resonator, as well as at least one adjustable slide, which forms a capacitive element, is fastened to a broad side and is located in the middle between two reactive conductance elements and protrudes into the interior . characterized in that the axial distance / between the rod-shaped susceptance elements (II, 11 '. 21, 21 '; 44, 44 ') in the direction of wave propagation is equal to', the waveguide waveguide, and that the axis of the respective narrow side of the waveguide on The next next rod of the susceptibility element has a distance of one third of the total distance (ti) between the inner surfaces of the opposite narrow sides. 2. Bandpass filter in a rectangular waveguide according to claim 1, characterized in that two screws acting as capacitive elements (41. 41 ') are provided.