FR2505557A1 - RECTANGULAR GUITAR PASS FILTER HAVING HIGH FREQUENCY SELECTIVITY - Google Patents

Abstract

RECTANGULAR GUIDE BAND-PASS FILTER, PRESENTING HIGH FREQUENCY SELECTIVITY. THE FILTER CONTAINS A WAVE GUIDE 1 INSIDE WHICH T, T, T, T, T RODS DELIMINE BAND-PASS CAVITIES 2-5. BAND-CUT CAVITIES 6-9 EXTERIOR TO THE GUIDE ARE COUPLED TO THE BAND-PASS CAVITIES THROUGH IRIS 60, 70, 80, 90 HOLES IN THE WALL OF THE GUIDE. APPLICATION TO THE FIELD OF HYPERFREQUENCES.

Description

l

  RECTANGULAR GUITAR PASS FILTER,

  WITH HIGH FREQUENCY SELECTIVITY

  The present invention relates to band pass filters in a guide

  rectangular, having a high frequency selectivity.

  To obtain good frequency selectivity with a filter, it is known to make this filter so that its filter function has transmission zeros. To obtain a filtering function having transmission zeros it is known to employ either so-called elliptic filters using two-mode cavities, or cascade combinations of bandpass filters and notch filters. But the so-called elliptic filters using dual-mode cavities have narrow bandwidths; bandpass and notch filter combinations have the disadvantage of constituting

  bulky mechanical assemblies.

  The present invention aims to avoid the disadvantages of art

  previous without increasing the cost price of the filter.

  This is achieved by mixing with elements with a

  bandpass function, elements with a notch function.

  FIG. 1 is a cross-sectional view of a filter according to the invention. This figure shows a rectangular waveguide 1 with its two connecting flanges 10, 11. The interior of this guide is divided into four cavities 2, 3 , 4, 5, using rods such as T 1, T 2, T 3, T 4, T 5; these rods are arranged in pairs so as to delimit cavities of a length slightly less than g o At is the wavelength 2 g

  guided in the guide corresponding to an average frequency of

  8.1 GHz Screws with lock nuts 12, 13, 14, 15, 16 are associated with the rods to allow adjustment of the coupling between them.

  cavities, and the coupling between cavities 2 and 5 and the filter accesses from

  very screws with locking nuts, 20, 30, 40, 50, are respectively associated with the cavities 2, 3, 4, 5 into which they penetrate a length

  adjustment so as to constitute a means of adjustment of these cavities.

  The filter as just described so far constitutes a filter

  conventional bandpass with four bandpass cavities; following the description

  FIG. 1 will show how it is possible to associate with these four cavities four other cavities 6, 7, 8, 9 each having a role of

notch cavity.

  FIG. 1 shows that each of the cavities 2, 3, 4, 5 is pierced with an iris 60, 70, 80, 90 located on the long side of the waveguide opposite to that traversed by the adjusting screws. 20, 30, 40, 50 and in front of these adjustment screws These irises constitute a coupling element respectively between the cavities 2, 3, 4, 5, and four notch cavities 6, 7, 8, 9 constituted by sections of waveguides with the same section as the waveguide 1 arranged perpendicular to the long side of the waveguide 1, having their short sides lying in the same plane as the short sides of the waveguide 1 and whose height is substantially less than 2 g These sections of waveguides are welded at one end to the waveguide 1 and are closed at their other end by a metal plate that a screw, 61, 71, 81, 91, associated with a locking nut, passes through to ensure the

adjusting these cavities.

  From an electrical point of view, these cavities 6, 7, 8, 9 can be considered as being in series with the band-pass cavities 2, 3, 4, 5; they therefore add their notch function to the bandpass function of the cavities of the guide 1, so that the filter according to FIG. 1 is equivalent to a

  bandpass filter associated in series with a notch filter.

  Figure 2 is a top view of the filter according to the invention; in this figure the band-cut cavity 9 has been shown in section according to a

XX plane shown in Figure 1.

  FIG. 2 shows, in comparison with FIG. 1, that the cavities

  bandpass of the filter are made by means of pairs of rods T 1 -T'i, T 2-

  T'2, T 3-T'3, T-T'4 IT 5-T'5 perpendicular to the long side of the guide Figure 2 also shows that each pair of rods and the screw for the adjustment of the interchangeable coupling (12 to 16) are arranged in the same transverse plane of the guide 1 ends of the guide towards the center the rods have their diameter which increases while the spacing between the two rods of the same pair decreases In Figure 2 also appears that the irises such as, for coupling between a notch cavity, such as 9, and a

  band-pass cavity, have an oblong shape whose major axis is not

  tee is perpendicular to the edges of the guide 1.

  FIG. 3 is an end view, on the side of the flange 10, of the filter already shown in FIGS. 1 and 2. Through the opening of the guide 1 there appear the adjustment screws 12 and 20 as well as the rods T 1 and T '1 and the rods T 2, T'2, T 3, T'3 partially hidden In this figure also appear the notch cavity 6 and the screw with locking nut, 61, allowing the adjustment of this cavity As shown 3, the flange 10 is a square flange pierced, in the vicinity of its four corners, of threaded holes, 101 to 104, intended to allow the mechanical connection of the

  filter to the other elements of the assemblies for which it is intended.

  The filter which has just been described with reference to FIGS. 1 to 3 is a filter intended to operate with a central frequency of 8.1 GHz; this filter has a flattened bandwidth of 300 M Hz and losses at 8.1 G Hz of

  0.25 d B The main mechanical dimensions of this filter are the following:

  total length of the filter 140 mm internal width of the long sides of the guide and the long sides of the notch cavities: 28.5 mm internal width of the short sides of the guide and the short sides of the notch cavities: 12.5 mm interval separating the adjusting screws of the band-pass cavities 20,, 40, 50: 28 mm

  inner height of the notch cavity: 20 mm.

  FIG. 4 is a graph showing, by two curves A and B, the frequency responses of the filter according to FIGS. 1 to 3 (curve A) and of this same filter without the band-cut qualities 6 to 9 and without the iris of coupling, 70, 80, 90 (curve B) that is to say a conventional band-pass filter. Comparison of the curves A and B of FIG. 4 shows that the response of the filter according to FIGS. 1 to 3 is much more selective in frequency than that of the corresponding conventional bandpass filter: drop from 0 to -47 dB over about 120 M Hz while the same fall is about

270 M Hz with the conventional filter.

  FIG. 4 also shows the reflection losses due to the filter, as a function of frequency (curve C). This curve shows that in the portion of the flat of the response curve of the filter according to FIGS. by reflection are at the maximum of the order

  of 25 d B, which corresponds to a stationary wave ratio (ROS) of 1.1.

  It should be noted that the notch cavity 6 and 8 were tuned to 7.9 GHz while the notch cavity 7 and 9 were tuned to 8.3 GHz, which explains why the front flank of the rear flank of curve A has much steeper slopes than the corresponding flanks of curve B. For some applications it may be interesting to have a steep slope (as in curve A) and the another side with a steeper slope (as in curve B); in the case of the described filter and, for example, having only the sloping front flank

  steep, all that is needed is to tune the four notch filters to 7.9 GHz.

  In general, when Pune at least slopes of the frequency response of a cavity bandpass filter, conventional will have to be made steeper, one or more notch cavities will be coupled respectively to one or more cavities passes -band of the classic filter; the choice of the number of notch cavities and their tuning frequency depends on the shape of the flanks to be obtained, it being understood that the frequency

  agree will be one of the frequencies relating to the flanks to get.

  The invention is not limited to the example described. It is thus, for example, that the band-pass cavities may be of the iris or flap separation type and that the number of notch cavities may be less than the number. bandpass cavities of the filter, some of these latter cavities not being associated with a notch cavity Similarly, the notch cavities may be arranged differently with respect to the guide of the band-pass cavities, for example always perpendicular to one of the long sides of this guide but with the long sides of their cross-section making an angle different from 90 with the transverse edges of the guide; experience has shown that it is also possible to arrange the notch cavities perpendicularly to the narrow sides of the bandpass cavity guide. The number and location of the notch cavities are parameters which make it possible to intervene on the form of the answer

  in frequency of the filter according to the invention.

Claims (2)

  1 band-pass filter in rectangular guide, with high frequency selectivity, comprising a rectangular guide (1) inside which shunt susceptances (T 1, T'1 T 4, T'4) delimit N (n upper integer at 0) main cavities (2-5), characterized in that it comprises m (m integer greater than 0 and less than or equal to n) notch cavities (6-9) respectively coupled to m of the N cavities main bandpass filter according to claim 1, characterized in that   the notch cavities (6-9) formed by rectangular guide sections   lair, closed at both ends by a metal plate, the metal plate of their first end being one of the walls of the guide (1) inside which are delimited the N main cavities and being pierced with an iris (60, 70 , 8090) 1 3 band-pass filter according to claim 2, characterized in that the sections have the same cross section as the guide (1) within which are delimited the N main cavities, and have their short sides respectively located in the same plans that the little sides of the guide mentioned last.   4 bandpass filter according to one of the claims   previous, characterized in that k of the band-stop cavities have their tuning frequency included in the frequencies of the leading edge of the frequency response of the filter and p of the m notch cavities have their tuning frequency included in the frequencies of the trailing edge of the filter's frequency response (with k and p positive or null integers and k + p = m).