This application claims the benefit under 35 U.S.C. § 119 of French application number 0303923, filed Mar. 31, 2003.
A floating microwave filter in a waveguide structure has been described in particular in patent document U.S. Pat. No. 4,990,870.
Conventional microwave filters in a waveguide structure use filtering elements that are in electrical and mechanical contact with the walls of the waveguide. In a technology known as “Finline” or a technology called “E plane”, resonant metal features are etched either in a thin dielectric substrate or directly in a metal foil. This etched substrate or foil is then attached in the E plane of a rectangular waveguide, which ensures perfect positioning of the substrate or foil in the waveguide and perfect electrical continuity between the metal walls of the waveguide and the metallized portions of the substrate or foil.
In a floating microwave filter in a waveguide structure, the filtering elements are not in electrical and mechanical contact with the walls of the waveguide.
The floating microwave filter in a waveguide structure known from the aforementioned document is assembled by inserting a printed circuit mounted on the back of a foam bar into a metal waveguide of rectangular cross section and in a plane parallel to the short side of the cross section of the waveguide, which simplifies the assembly technique compared to that of a conventional filter and reduces the production costs. Moreover, a floating microwave filter in a waveguide structure has, compared with a conventional filter, improved characteristics as regards insertion losses.
It is an object of the invention to improve a floating microwave filter in a waveguide structure in order to further lower the manufacturing costs.
According to the invention, a floating microwave filter in a waveguide structure, comprising filtering elements sandwiched between two foam half-bars that are placed inside a waveguide, is characterized in that the filtering elements are metal features etched in the surface of one of the two foam half-bars and in that the waveguide is an internally hollowed-out block of foam having a metallized outer surface.
This arrangement helps to lower the manufacturing costs of a floating microwave filter at the same time as improving the performance of the filter (low insertion losses and high selectivity).
Illustrative embodiments of a floating microwave filter according to the invention are described below and illustrated in the drawings.
The foam used is preferably a polymethacrylimide foam known for its electrical properties similar to those of air, for its mechanical properties of stiffness and lightness and for its low manufacturing cost. In particular, a polymethacrylimide foam sold under the name ROHACELL HF may be used.
The foam block 2 is preferably metallized nondirectionally, by spraying, or brushing on, a paint of the silver or derivative type exhibiting conductivity and mechanical bonding characteristics.
The foam block constituting the waveguide 2 has an internal axial cavity of cylindrical cross section. The cylindrical cavity may be produced by drilling or moulding. The cylindrical shape of the cavity has the advantage of ensuring that the filter array is correctly positioned with respect to the walls of the waveguide.
The floating filter 1 comprises filtering elements 3 inserted in an axial plane 4 of a cylindrical foam bar. More particularly, the cylindrical foam bar consists of two identical superposed half-bars 5, 6 and the filtering element 3 sandwiched between the two foam half-bars are features etched into the surface of one of the two foam half-bars, for example in the joint surface of the lower foam half-bar 6 in
The foam used for the foam bars is the same as that used for the foam waveguide 2. The features of the filter array are etched as indicated above in the case of metalization of the external surface of the foam waveguide.
The two superposed foam half-bars 5, 6 with the etched filtering elements 3 sandwiched between the two foam half-bars are inserted into the cylindrical cavity of the foam waveguide.
The process according to the invention can be applied to a foam waveguide having a cavity of elliptical, square, diamond or other cross section.
Number | Date | Country | Kind |
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03 03923 | Mar 2003 | FR | national |
Number | Name | Date | Kind |
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2783440 | Lovick, Jr. | Feb 1957 | A |
3914713 | Konishi et al. | Oct 1975 | A |
4521755 | Carlson et al. | Jun 1985 | A |
4897623 | Reindel | Jan 1990 | A |
4990870 | Reindel | Feb 1991 | A |
5818313 | Estes et al. | Oct 1998 | A |
Number | Date | Country |
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2829620 | Mar 2003 | FR |
Number | Date | Country | |
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20040201437 A1 | Oct 2004 | US |