Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Reexamination Certificate
1999-05-18
2001-02-20
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
C333S126000, C333S135000
Reexamination Certificate
active
06191670
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of European Patent Application No. 98460013.0, which was filed on May 18, 1998.
FIELD OF THE INVENTION
The present invention relates generally to the field of duplexers, and more particularly to duplexers for microwave signals.
BACKGROUND OF THE INVENTION
Duplexers are usually devices found at the end of a system in items of radio equipment, i.e. antennas. They are designed to separate the signals transmitted from the signals received by the antenna. A duplexer conventionally includes two passband filters, one responsible for filtering the transmitted signals and the other responsible for filtering the received signals.
Conventionally, a passband filter for microwave signals includes a tunnel having a succession of compartments communicating with one another through a longitudinal passage, the dimensions and number of compartments being a function of the size and the center frequency of the passband of the filter. A duplexer for microwave signals therefore generally has two tunnels of this type that are respectively connected by one end to the transmission part and to the reception part of the radio equipment and that open jointly into the other end on the antenna side.
These passband filters are designed to meet the following conditions:
high resistance under temperature throughout the range;
low loss in transmission and high return loss in the passband; and
high rejection in the near band.
With respect to the rejection of the highest frequencies, especially for the elimination of the harmonics of the filtered signal, the equipment is generally provided with a low pass filter interposed between the duplexer and the antenna.
To meet the first condition, existing duplexers are generally made of a material that is highly stable under temperature, for example invar which is an alloy of iron and nickel with a coefficient of thermal expansion that is practically zero. However, this type of material proves to be very costly and very difficult to machine. Thus, the method generally used to manufacture duplexers is to make tunnels out of invar plates and solder transversal partition walls thereto so as to obtain compartments in these tunnels.
These duplexers are then methodically provided with a system of settings by screws to obtain the desired signal filtering and transmission characteristics. Tapped holes are made in the upper wall of the tunnels to receive setting screws. In general, one setting screw is provided per compartment with another screw being provided in the partition walls of each compartment in the longitudinal passage. The setting operation then includes adjusting the part of the screw that projects into the compartment or into the longitudinal passage. This operation proves to be very complicated and very lengthy.
Consequently, the present invention seeks to overcome the prior art drawbacks by proposing a duplexer that does not require a system of settings by screws for the usual frequencies.
SUMMARY OF THE INVENTION
The present invention solves the above problems by providing a duplexer for microwave signals having two passband filters designed to process incoming signals and outgoing signals, respectively, and to process these signals simultaneously. The filters include two tunnels that open jointly at one end by a common part into a first hole and open independently at the other end into a second hole and a third hole. Each of these tunnels has a longitudinal passage and compartments demarcated by transversal partition walls. The compartments, longitudinal passages and common parts are hollowed out in the upper plane face of a monolithic block. The tunnels are closed at the top from the first hole up to the second and third holes by a lid that adheres uniformly to the plane surface. The functional characteristics of the two filters are determined by dimensional parameters within the tunnels. These parameters include the thickness of each wall, the longitudinal and transversal dimensions of each compartment and the width of each longitudinal passage. In order that the compartments, the longitudinal passages and the common part of the duplexer may be hollowed out with precision in the monolithic block, the block and the lid are preferably made of aluminum. Aluminum is indeed easier to machine than invar. Since this material is less stable under temperature than invar, it is enough to provide for a slightly wider passband to compensate for the drifts in temperature of the material and increase the slope on the flanks of the passband of the filters to obtain the desired near band rejection. The joining surface of the lid is covered with a uniform layer of a brazing alloy to obtain uniform adhesion on all the surfaces in contact with the monolithic block and with the lid after soldering. The surfaces within the tunnels of the monolithic block are preferably subjected to a surface treatment to ensure efficient transmission of the signals in the tunnels. For example, the surface treatment may include adding a surface layer of silver. In a preferred embodiment, the common part through which the tunnels open into the first hole has a Y-shape and the external sides of its arms are concave.
REFERENCES:
patent: 4890078 (1989-12-01), Radcliffe
patent: 5023624 (1991-06-01), Heckaman et al.
patent: 6031710 (2000-02-01), Wolf et al.
patent: 2346868 (1977-10-01), None
patent: 2 346 868 (1977-10-01), None
patent: 63308401 (1988-12-01), None
“Linear Phase Microwave Bandpass Filters”, by G. Pfitzenmaier, Proceedings of the European Microwave Conference, Brussel, 4-7, Sep., 1973, vol. 2 Conf. 3, Sep. 4, 1973, p. B.2.01 XP-002073863.
Nguyen Patricia T.
Pascal Robert
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