Microwave components

Details Microwave components Microwave components

2002-08-08

2004-10-26

Wilmer, Michael C. (Department: 2821)

Communications: radio wave antennas

Antennas

Wave guide type

C029S600000, C333S208000, C333S239000

Reexamination Certificate

active

06809696

ABSTRACT:

TECHNICAL FIELD
The present invention relates to microwave components with an at least partially enclosed cavity which are suitable for mass production and which satisfy high quality requirements. Examples of such microwave components are microwave filters, waveguides and horn antennas. The invention further relates to a method of manufacturing such components.
BACKGROUND
The manufacture of products of the above-mentioned kind has up to now been very complicated and expensive. Today the manufacture is primarily performed by working aluminium, inter alia by high-speed milling and subsequent surface finishing, such as silver-plating, coating, etc. As a result, it is time-consuming to manufacture each component and a great number of manual operations are necessary. Furthermore, it is difficult to obtain the desired dimensional tolerances and quality of the product by this manufacturing process. Thus, as a rule these products need considerable after-treatment.
To solve these problems, the filter casings have, for instance, been provided with trimming means, which allow trimming of the filters after final assembly. However, this makes the filters even more complicated and expensive to manufacture. Moreover, this makes it necessary to test and trim each filter separately by a specialist.
The manufacturing process also significantly limits the possibility of manufacturing certain component parts. High-speed milling allows milling of simple geometric designs only, which makes it necessary to manufacture complicated geometric designs in several pieces, which are subsequently assembled into one functional unit. However, such assembly of several subcomponents into a microwave component almost inevitably leads to a lower degree of dimensional accuracy in the final product, which results in an even greater need for trimming, for instance, of filters after assembly. To arrange trimming means on the filters is time-consuming and considerably increases the costs.
The use of trimming means, such as trimming screws, and the assembly of products from several including parts also constitute a risk of electric disorders, so called passive intermodulation (PIM). In some applications, this can be disastrous.
The making of the structural or supporting parts of aluminium also limits the thermal dimensional stability and the weight.
As an alternative, it has been proposed in JP 61 079 303 to manufacture waveguides on fusible cores. Around this core, silver and copper are plated, and a carbon fibre fabric is subsequently wound around the core until a thickness of about 2 mm. During the winding, the fabric is impregnated with epoxy resin, and the wound support structure is subsequently cured by supplying heat and pressure, after which the core is melted out. The resulting waveguide consists of a composite structure having continuous carbon fibres with an inner layer of copper and silver.
However, also this manufacturing method suffers from a number of drawbacks. The method is expensive and complicated and requires a great number of manual operations. Thus the method is not suitable for mass production, and the manufacturing time for each component is long and the costs are high.
In addition, the technique is not applicable to the manufacture of filter casings, since it is not possible to wind the carbon fibre fabric in the narrow, downwardly projecting, often circular cavities in the filter casings, or corrugations in horn antennas.
Furthermore, in the prior-art wound carbon fibre waveguide the copper layer cannot affect the rigidity and the thermal stability of the component. In this case, the higher e-module of the carbon fibre structure completely dominates the copper layer, and at temperature changes, which frequently occur in microwave components, this may cause micro-cracking problems in the metal layer. Other problems that may arise are reduced adherence of the composite to the metal and galvanic corrosion due to humidity entering the waveguide through the cracks. The presence of micro-cracks in microwave components, and especially microwave filters, immediately results in reduced electric properties.
It is also a problem with prior-art microwave components that the sensitive electric layer, which internally faces the cavity, often gets damaged either during the manufacturing process or during the use of the component due to different types of environmental influence. This is very serious, since it considerably changes and deteriorates the qualities of the component and usually makes it necessary to replace and discard the component.
Consequently, there is a need for microwave components which can be manufactured at a lower cost and in a more efficient manner, in particular on a large scale, and which also provide better products, have a greater resistance against environmental influence, improved dimensional accuracy, improved thermal dimensional stability, fewer including parts to be integrated and improved electric properties.
OBJECT OF THE INVENTION
Thus, the object of the present invention is to provide microwave components with cavities, which wholly or at least partly obviate the above-mentioned problems. The invention also provides a method of manufacturing such microwave components.
This object is achieved by means of a microwave component and a method according to the appended claims.
SUMMARY OF THE INVENTION
The invention relates to microwave components with an at least partially enclosed cavity, comprising an outer support structure and an electric layer, which is preferably made of silver and which is arranged on the inside of the support structure. The microwave components according to the invention are distinguished in that they further comprise a first inner protective layer of gold (D), said protective layer being arranged on the electric layer (C) and facing the cavity.
The protective layer is preferably a chemically precipitated gold layer. By arranging such a protective layer, the sensitive electric layer is protected against environmental influence and damage, at the same time as the electric function is not affected to any substantial degree. Unlike prior-art methods of protecting silver surfaces for electric use in microwave components, a gold layer arranged directly on the silver surface has the advantage that it can be made thin, yet completely tight, and it also provides a lasting protection against the environment. In contrast to galvanically applied gold, a chemically applied gold layer provides completely tight layers in the small thicknesses that are electrically acceptable in these connections.
The structure of the electric layer is of great importance. Silver offers by far the best electric properties compared with other conducting materials. The electric properties have a great influence on the performance of microwave components, The application of silver by pulse-plating additionally improves the evenness and tightness of the layer. Pulse-plated silver also permits satisfactory macro spreading, thus allowing plating in narrow spaces, which is not possible by conventional direct-current plating. This is crucial as the cavities almost exclusively have partial surfaces and edges that are located at different distances from the power source. The addition of a protecting chemically precipitated gold layer on the silver layer has surprisingly been found to offer many advantages. A chemically precipitated gold layer is considerably tighter than, for instance, galvanically precipitated gold layers. One advantage of chemically precipitated gold on pulse-plated silver is thus that the even and tight silver is protected by a gold layer which is very thin but still tight. The alternative of using a galvanically applied gold layer requires a considerably thicker layer to attain the same tightness, usually more than ten times thicker. Microwaves in a component penetrate into the metal layers and a great disadvantage of galvanically applied layers is that the thicker gold layer reduces the electric properties of the component due to the lower conductivity of the gold. In addit

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