Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Patent
1982-08-05
1984-09-18
Nussbaum, Marvin L.
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
333223, 333225, 333235, H01P 1202, H01P 1205, H01P 704
Patent
active
044726953
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a band pass filter tunable to a predetermined number of discrete frequencies spread over a broad frequency band, comprising at least one resonant coaxial cavity defined by an external conductor and an internal conductor.
Prior art contains numerous examples of band pass filters made from at least one resonant cavity constituted by a coaxial line comprising an internal conductor and an external conductor and terminating by a short circuit, with input or output coupling devices associated with the cavity.
Generally, the pass band of such a filter is very narrow and the devices for tuning to a given frequency of said band are comprised by mechanical adjustment devices.
Also manufactured have been ultra high frequency band pass filters constituted by a single coaxial line divided into several adjacent resonant cavities separated by coupling units such as pistons, with a tuning device being provided for each resonator and a coupling adjustment device being associated with each coupling unit between two successive resonant cavities.
Such a type of filter may also comprise a standard element capable of being adapted to slightly different frequencies in a frequency band, this by means of manual adjustment of the position of the pistons constituting coupling units for example, or by acting on other parameters of the system's geometry.
Also known are ultra high frequency filters with adjustable tuning rods comprising wave guide segments divided into several adjacent resonators by curtains of conducting rods and including a mechanical tuning device for each resonator such as an adjustable-position dielectric pin and a coupling adjustment device for each curtain of rods, such as a metallic screw.
With such a filter, it is possible to adjust the characteristics of a standard element from the outside by manually activating the mechanical adjustment parts, thereby adapting the pass band to a predetermined channel within a frequency range. It is not possible during operation, however, to modify the characteristics of the filter so as to pass instantaneously from one discrete frequency to another discrete frequency defined within a broad band of frequencies of one or two octaves.
The present invention aims specifically at making it possible to produce a band pass filter, basically constituted by a coaxial cavity, whose practically instantaneous tuning is possible for a certain number of discrete frequencies spread over a broad frequency band.
According to the invention, a coaxial band pass filter is thus essentially characterized in that at least one of the internal and external conductors of the coaxial cavity is divided into sections separated by breaks constituted by annular slits whose thickness is very slight in comparison with the wave length corresponding to the average frequency of the pass band and in that each section comprises at least one reactive tuning element and at least one commuting element located in the vicinity of the break in the corresponding section so as selectively to short-circuit the said break or to insert the reactive tuning element for the corresponding section in response to electronic actuating devices.
Each reactive tuning element is constituted by a portion of coaxial line wich is open or short-circuited in a section of internal conductor or external conductor.
The revolution cavities formed in sections of internal conductor or external conductor so as to achieve an open or short-circuited coaxial line have transversal dimensions which are very much larger than the thickness of one break but small in comparison to the wave length corresponding to the average frequency of the pass band.
Thus, in accordance with the present invention, thanks to a coaxial resonant cavity with predetermined geometric characteristics, it is possible to achieve, without manually actuating mechanical adjustment elements, an almost instantaneous tuning of the cavity to a discrete tuning frequency selected from among a large number of predetermined frequencies spread over a broad fre
REFERENCES:
patent: 3444485 (1969-05-01), Okean
patent: 3569874 (1971-03-01), Kuroda
patent: 3927347 (1975-12-01), Farney
patent: 4004257 (1977-01-01), Geissler
patent: 4066988 (1978-01-01), Karp
Beauquet Gilles
Devarhubli Vasudeo
Dubost Gerard
Nicolas Michel
Nussbaum Marvin L.
Societe SNECMA
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