Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/20—Frequency-selective devices, e.g. filters
  • H01P1/201—Filters for transverse electromagnetic waves
  • H01P1/202—Coaxial filters

Definitions

• the invention relates to a microwave filter in coaxial structure comprising an outer conductive core and an inner conductive core extending in an axial direction inside the outer core and forming therewith a succession of concentric slots according to the direction.
• axial defining successive sections of coaxial line of low characteristic impedance and of coaxial line of high characteristic impedance.
• the book “Microwave Filters, Impedance-Matching Networks and Coupling Structures”, MgrawHill, 1962 presents such a microwave filter, in particular a low-pass filter, in which the conductive outer core is conventionally constituted by a metallic cylindrical tube and the conductive inner core is constituted by a metal rod carrying concentric metal discs spaced in the axial direction, the metal discs forming the succession of concentric slots.
• the cross-section of the inner core therefore varies in the axial direction so that each section of the large-diameter inner core (corresponding to a metal disc) defines a section of coaxial line of very low impedance and each section of the core inner diameter (corresponding to the interval between two consecutive discs) defines a section of coaxial line of high impedance.
• the dimensions of the sections are adjusted so as to carry out the transfer function of the filter.
• the production of such a microwave filter in coaxial structure is however complex and costly to produce in particular to maintain perfect coaxiality between the inner core and the outer core of the filter. Plastic or other dielectric spacers are generally used to maintain coaxiality, but this introduces dielectric losses.
• the invention proposes a microwave filter with a coaxial structure of simpler and less expensive construction suitable for volume production and at low cost.
• the invention relates to a microwave filter in coaxial structure constituted by a tube made of synthetic foam, the tube having a constant internal diameter and an entirely metallized external surface with, in the axial direction, a profile according to a periodic function. , or constant and by a bar of entirely metallized synthetic material foam, with a constant external profile or according to a periodic function, the largest diameter of the bar being substantially equal to the internal diameter of the tube so that the bar can sink into the tube while maintaining coaxiality between the tube and the bar.
• the foam used is preferably a polymetacrylate imide foam known for its electrical characteristics close to those of air, for its mechanical characteristics of rigidity and lightness and for its low cost price.
• a polymethacrylate imide foam sold under the name "ROHACELL HF”.
• the periodic function, or constant by pieces is a niche function, the niches can have different dimensions from one niche to another.
• the thickness of the tube is chosen to maintain electrical insulation between the metallized surface of the tube and the bar.
• a microwave filter can easily be associated with a monopole or dipole type antenna.
• the invention extends to a method of manufacturing a microwave filter as defined above according to which the periodic function is performed by thermoforming the foam tube or the foam bar.
• thermoforming the foam tube or the foam bar use will preferably be made of a hot pressing molding which is adapted to an objective of production in volume and at low cost.
• the metalization of the foam tube or of the foam bar is preferably a non-directive metallization by projection or with a brush.
• Figure 1 illustrates very schematically in exploded perspective a first embodiment of a microwave filter in coaxial structure according to the invention.
• FIG. 2 schematically illustrates in axial section a second embodiment of a microwave filter in coaxial structure according to the invention associated with a monopole type antenna.
• FIG. 3 schematically illustrates, in axial section, a filter according to the first embodiment associated with a dipole type antenna.
• a first example of a microwave filter in coaxial structure according to the invention is shown in FIG. 1 according to an exploded perspective view.
• outer conductive tube 1 and the inner conductive bar 2 of the filter are shown in FIG. 1 separated from one another for greater clarity, but it should be understood that the inner bar 2 extends in the axial direction A to l inside the outer tube 1.
• the internal bar 2 of the filter consists of a cylindrical bar of synthetic foam, the external surface of which follows in the axial direction, a periodic function. It preferably forms a succession of concentric slots 3A to 3D performing the transfer function of the filter, for example a transfer function of a low-pass filter by defining successive sections of coaxial line of low characteristic impedance and of line coaxial with high characteristic impedance.
• the conformation of the foam bar 2 is carried out by thermoforming, in particular according to a molding technique by hot pressing.
• the outer surface of the foam bar 2 is preferably metallized by projection or with a brush.
• the outer tube 1 of the filter consists of a cylindrical tube made of synthetic foam having a constant internal section, the inner diameter of the tube being very slightly greater than the largest outer diameter of the foam bar 2 to allow insertion of the bar into the tube.
• the cylindrical tube 1 has a fully metallized outer surface according to the metallization technique indicated above. The thickness of the tube 1 is chosen to provide electrical insulation between its metallized exterior surface and the bar.
• the synthetic foam used is preferably a polymetacrylate imide foam.
• the structure of the filter shown in FIG. 1 can be reinforced by two half-shells (not shown) surrounding the tube 1 which can be made of a plastic material or of synthetic foam material.
• the tube 1 and the bar 2 of foam could have a section other than circular, for example rectangular or square without departing from the scope of the invention.
• FIG. 2 shows another embodiment of a filter according to the invention.
• the outer tube 1 'of the filter consists of a cylindrical tube made of synthetic foam, the metallized outer surface of which is shaped to define the succession of slots 3A'-3B' in the axial direction A while the inner bar 2 'of the filter consists of a cylindrical conductive bar of constant section. Therefore, the outer surface of the tube has, in the axial direction, a profile according to a periodic or constant function in pieces such as a slot function.
• the conductive bar 2 ′ may consist of a solid or hollow metallic cylindrical tube.
• FIG. 1 'of the filter consists of a cylindrical tube made of synthetic foam, the metallized outer surface of which is shaped to define the succession of slots 3A'-3B' in the axial direction A while the inner bar 2 'of the filter consists of a cylindrical conductive bar of constant section. Therefore, the outer surface of the tube has, in the axial direction
• the microwave filter according to the invention is associated with a monopoly type antenna 4 constituted by an extension of the inner core 2 'of the filter.
• FIG. 3 shows a microwave filter according to the invention which is analogous to that shown in FIG. 1 with an outer tube constituted by a foam tube 1 "of constant section and an inner bar constituted by a foam bar 2" of section variable along the axial direction A.
• the filter is associated here with a dipole 5 type antenna.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Control Of Motors That Do Not Use Commutators (AREA)
• Details Of Aerials (AREA)

Applications Claiming Priority (3)

Publications (2)

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Family Applications (1)

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• 2003
  • 2003-01-03 FR FR0300048A patent/FR2849719A1/fr active Pending
  • 2003-12-22 JP JP2004567028A patent/JP4304159B2/ja not_active Expired - Fee Related
  • 2003-12-22 KR KR1020057012055A patent/KR20050088228A/ko not_active Withdrawn
  • 2003-12-22 EP EP03810010A patent/EP1579526B1/de not_active Expired - Lifetime
  • 2003-12-22 CN CN200380107503A patent/CN100583550C/zh not_active Expired - Fee Related
  • 2003-12-22 BR BR0317649-5A patent/BR0317649A/pt not_active IP Right Cessation
  • 2003-12-22 DE DE60326763T patent/DE60326763D1/de not_active Expired - Lifetime
  • 2003-12-22 WO PCT/FR2003/050200 patent/WO2004066429A2/fr not_active Ceased
  • 2003-12-22 AU AU2003302195A patent/AU2003302195A1/en not_active Abandoned
  • 2003-12-22 MX MXPA05007105A patent/MXPA05007105A/es unknown
  • 2003-12-22 US US10/540,147 patent/US7355495B2/en not_active Expired - Fee Related

Non-Patent Citations (1)

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