The invention relates to manufacturing an inner conductor of a resonator.
Resonator structures of a high frequency area, a radio frequency area in particular, are used e.g. in base stations of mobile telephone networks. Filters may utilize resonator structures e.g. as adapting and filtering circuits in transmitter and receiver units of the base stations.
A resonator structure comprises an inner conductor of the resonator attached to an attachment surface, which in practice most often is an end, such as a bottom or a cover, of a housing structure serving as an outer conductor of the resonator structure. The inner conductor is thus short-circuited to the attachment surface, i.e. in practice to the outer conductor. A short-circuited end of the inner conductor, at which the inner conductor is thus short-circuited to the outer conductor, is also called an inductive end owing to the fact that signal coupling at the short-circuited end is mainly carried out inductively.
At a second end of the inner conductor, the inner conductor is galvanically separated from the outer conductor, so this end is the xe2x80x9cfreexe2x80x9d end of the inner conductor. The free end of the inner conductor is also called a capacitive end of the inner conductor owing to the fact that signal coupling at this end is mainly carried out capacitively. The outer conductor and the inner conductor located within a section defined by the outer conductor together form a resonance circuit. In practice, the resonator structures often comprise a plurality of circuits, i.e. the resonator structure comprises several pairs comprising an inner conductor and an outer conductor, i.e. each section formed by the outer conductor comprises a separate inner conductor. The resonance circuits of a multi-circuit resonator structure together form a desired frequency response for the resonator structure.
Normally in a coaxial resonator, the inner conductor of the resonator is a straight wire or a pin attached only to the bottom of the resonator. Such a resonator is long and thus takes a lot of space. The resonator pin is quite easy to manufacture. The problem then is, however, how to adjust the coupling of the resonator since it is difficult to attach such a controlling element to the resonator pin that would enable the resonator to be easily coupled to e.g. an adjacent resonator. Furthermore, the capacitive coupling provided by the wire-like inner conductor is poor.
In order to decrease the space required by the resonator, for instance a helix coil is used as the inner conductor, in which helix coil the same operational length fits into a shorter space since the resonator in the helix resonator is formed as a coil. The helix coil is, however, difficult to manufacture. A further drawback is that it is extremely difficult to attach to the helix coil a coupling wire or other such projection necessary when the coupling between two resonance circuits is to be adjusted. A further problem with the helix resonators is the difficulty to support them and carry out the temperature compensation. An inner conductor implemented by utilizing a helix coil cannot provide a high-quality capacitive coupling.
A known solution for controlling the resonance frequency of a resonator circuit is a solution wherein an adjuster bolt located in the cover of a filter serves as the frequency controlling element, and the distance of the adjuster bolt with respect to the free end of the resonator located in a section under the cover is adjusted by turning the bolt. The solution is not the best possible one since it requires additional structures on the outer surface of the housing. A further problem is that the adjuster bolt requires that the cover of the filter should be thick or the cover should at least comprise a thicker section to enable threads to be provided on the cover for the adjuster bolt, or, alternatively, to enable a nut-like part with threads attached to the cover to be used. The cover has to be thick particularly because it also needs to be rigid in order to prevent the distance of the frequency controlling element in the cover with respect to the resonator from changing after the controlling procedure and from further causing the capacitance, and thus the resonance frequency, to change in an undesired manner.
An object of the invention is thus to provide a method of manufacturing an inner conductor of a resonator, and an inner conductor so as to enable the above-mentioned problems to be alleviated. This is achieved by a method disclosed in the introduction, characterized by manufacturing at least part of the inner conductor from a uniform, electrically conductive material blank by utilizing a deep-drawing method wherein the blank is struck or pressed with a tip of an impact device, whereby during each stroke or pressing, the tip draws more and more blank material in the direction of the stroke.
The invention further relates to an inner conductor of a resonator comprising a first end and a second end, which is free.
The inner conductor of the invention is characterized in that at least part of the inner conductor is deep-drawn from a uniform, electrically conductive blank.
Preferred embodiments of the invention are disclosed in the dependent claims.
The idea underlying the invention is that the inner conductor is manufactured by utilizing a deep-drawing method.
Several advantages are achieved by the method and inner conductor of the invention. The deep-drawing method enables the inner conductor and a flange located at the free end thereof to be manufactured virtually simultaneously. In addition, a potential projection or a site for the same can be manufactured in connection with manufacturing the inner conductor. The drawing method is a quick and low-cost way to manufacture inner conductors. The drawing method enables flanges and projections for the inner conductors to be manufactured that are all integrated in the same uniform material piece. Therefore, the inner conductor is mechanically strong.
Since the inner conductor is deep-drawn, the surface of the inner conductor is extremely smooth, which enables the inner conductor to be readily coated e.g. with silver. Thanks to the smoothness of the surface, the surface area to be coated is smaller than it would be if the surface was uneven. It thus takes less coating material to coat an even surface than an uneven one.
An inner conductor manufactured by utilizing the deep drawing method has a small surface resistance, so the electric loss of the resonator remains small and the Q factor of the resonator can be retained good.
A further advantage of the deep drawing method is that the inner conductor can be manufactured e.g. from a copper blank, in which case the resulting inner conductor does not necessarily have to be coated. The inner conductor manufactured of copper is attached by a specific sleeve, which means that the inner conductor made of copper does not have to be mechanized for the screw threads in a fixing screw.
Since it is possible to attach the inner conductor by a sleeve, the thickness of the walls of the inner conductor can be retained small, which gives a lightweight inner conductor. The advantage provided by the inner conductor being light is that it is highly tolerant e.g. of vibration. Consequently, external vibration does not easily cause the inner conductor to move or become detached. The structure and attachment of the inner conductor thus enable intermodulation noise to be reduced.