Wave transmission lines and networks – Coupling networks – Wave filters including long line elements
Patent
1993-03-01
1995-09-05
Ham, Seungsook
Wave transmission lines and networks
Coupling networks
Wave filters including long line elements
333235, H01P 1203
Patent
active
054482100
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to the field of microwave bandstop filters.
It finds general application in the processing of microwave signals and more particularly in the microwave receiving stages for which it may be necessary to filter unstable noise signals of generally unknown frequency to be able to analyze and identify useful signals with a good signal-to-noise ratio.
Tunable microwave bandstop filter devices are already known.
For example, in French patent No. 88 03187 published under the number 2 628 571, the THOMSON company proposed a tunable microwave bandstop filter device which comprises: coupled to the main transmission line and arranged parallel to and remotely from the latter, and a tunable LC resonant circuit.
A signal applied to one of the ends of the transmission line is filtered and the centre frequency of the filtering device thus obtained can be varied by controlling the voltage applied to the tunable LC resonant circuit.
In patent No. 88 03187, the segment of the stripline has an open-circuit first end and a second end connected to ground potential via the tunable LC resonant circuit containing in particular a varactor diode.
Such an arrangement has the following drawbacks.
Firstly, the connection from the second end of the stripline segment to the ground potential via the resonant circuit is made by means of a plated-through hole which, at microwave frequencies, gives rise to residual inductance of a typical value of 0.2 to 0.3 nanohenrys. Now the consequence of this is to limit the application of the filter device to the high-frequency range (typically above 12 GHz). Furthermore, the losses associated with this plated-through hole reduce the overall performance of the filter and in particular the Q-factor of the resonant circuit.
Next, to ensure proper filter operation the access from the plated-through hole to the earth plane must be easy and rapid. But this excludes so-called suspended substrate technology and stripline type technology has to be used exclusively.
Finally, the filter cell supplying the varactor diode in the above-mentioned patent is very difficult to produce for operations in a very wide usable band and/or with a very high tuning speed.
SUMMARY OF THE INVENTION
One of the aims of the invention is to remedy these drawbacks.
To this end, the invention proposes a new arrangement which enables the coupling of the tunable LC resonant circuit to be modified.
According to a principal feature of the invention the tunable LC resonant circuit is placed between one of the ends of the coupled line segment and the main microwave transmission line.
This arrangement according to the invention, which is derived from the fixed-frequency arrangement referred to by the expert as "SPURLINE", exhibits the following advantages: usable band and the tuning frequency; of using suspended substrate technology.
According to a preferred way of carrying out the invention, the tunable LC resonant circuit contains an inductor placed in series with a variable capacitance, the other end of the coupled line segment being open-circuit.
In this case the variable capacitance is advantageously comprised of a varactor diode, one of whose electrodes is connected to one end of the coupled line segment and whose other electrode is, on the one hand, connected to one of the terminals of the inductor and, on the other hand, to a control circuit.
According to another preferred way of carrying out the invention, the tunable LC resonant circuit contains an inductor placed in parallel with a variable capacitance, the other end of the coupled line segment being connected to ground.
However, this last arrangement has the drawback of requiring a microwave plated-through hole.
In conventional filter arrangements the varactor diode is controlled by a control circuit comprising a voltage source decoupled from radio frequencies by a self-inductance or by a diplexer.
The applicant is faced with the problem of controlling the varactor diode in a simpler way and at low cost, at the same time improvin
REFERENCES:
patent: 4004257 (1977-01-01), Geissler
patent: 4467296 (1984-08-01), Cohen et al.
patent: 4468644 (1984-08-01), Teague et al.
patent: 4835499 (1989-05-01), Pickett
patent: 5065119 (1991-11-01), Jachowski
patent: 5150085 (1992-09-01), Hales
Mehrdad Mehdizadeh et al., "High Speed Varactor Tuned Notch Filter," 1985 IEEE MTT-S Digest, pp. 531-534.
J. L. Lacombe, "Switchable Band-Stop Filter for M.I.C.," 14th European Microwave Conference, Conference Proceedings, Sep. 10-13, 1984, pp. 376-381.
W. J. Getsinger, "Circuit Duals on Planar Transmission Media," 1983 IEEE MTT-S Digest, pp. 154-156.
I. C. Hunter et al., "Electronically Tunable Microwave Bandstop Filters," IEEE Transactions on Microwave Theory and Techniques, vol. MTT-30, No. 9, Sep. 1982, pp. 1361-1367.
Dassault Electronique
Ham Seungsook
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