Optical waveguides – Accessories – Attenuator
Reexamination Certificate
2000-03-27
2001-05-29
Bovernick, Rodney (Department: 2874)
Optical waveguides
Accessories
Attenuator
C385S134000, C385S147000
Reexamination Certificate
active
06240237
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a variable attenuator device for a rectangular waveguide.
2. Description of the Related Art
Known attenuators are in general produced using PIN diodes arranged on a printed-circuit substrate in a &pgr; or T arrangement, and connected by microstrip lines. The diodes are used as controlled resistors to absorb the microwave variably, with good performance in terms of the reproducibility of the various attenuation values which can be selected in this way, since the resistor properties of PIN diodes are fairly stable. However, the microwave propagating in the guide must undergo a guide/line transition upstream of the attenuator and a line/guide transition downstream of it (relative to the propagation direction of waves in the guide), and this transition may give rise to matching problems. Above all, an attenuator device of this type exhibits insertion losses, that is to say residual attenuation of the microwave even when the attenuator is at its minimum setting, due to its very presence. These insertion losses are due to the intrinsic characteristics of PIN diodes and may be as much as two to three decibels (dB). Such losses are unacceptable in certain practical applications, in particular at the output of a microwave transmission system.
It is also known to introduce a plate into the waveguide through a longitudinal slot parallel to the propagation direction of the microwave.
If the plate is made of a resistive material which absorbs the energy propagated in the guide, this energy will be reduced downstream of the plate relative to the propagation direction: this produces an attenuator.
The amplitude of the attenuation depends in each case on the size of the plate and the extent to which it forms an obstacle to the propagation of the wave in the guide. It is thus possible to produce a variable attenuator by modifying the depth to which the plate is inserted into the guide, or the distance separating it from the symmetry axis of the guide parallel to the propagation direction (where the amplitude of the field is greatest).
However, the attenuator is thus dependent on a large number of uncontrolled factors. The result of this, in particular, is that the attenuation is not a linear function of the position or insertion of the plate. For this reason, the positional slaving of this plate will have its gain vary as a function of the setpoint value. In certain cases, there is a risk of the slaving being slack, and in other cases there is a risk of it oscillating.
SUMMARY OF THE INVENTION
The object of the present invention is to over-come these drawbacks of the prior art, by providing a variable attenuator device which is moreover simple and reliable.
Specifically, the present invention provides an attenuator device for a rectangular waveguide, of the type comprising a plunger element of substantially plane shape which can be inserted into the guide through a longitudinal slot along the propagation axis formed in a first face of the guide, in which the plunger element is rotated about an eccentric axis orthogonal to the propagation axis by drive means, so that the height to which the plunger element is inserted into the guide is a function of the angular position of the said element.
In particular, the invention concerns an attenuator of the above type, in which the plunger element is made of ALKAR 80, a trademark registered by UOP Inc. This material is a semi-conductor which has good attenuation perforce and good thermal stability for the power of the waves to be propagated in the application in question, which is of the order of 100 milliwatts (mW).
The eccentric drive of the plunger makes it possible to convert its rotation about the axis into a movement by which it is inserted into the guide. According to one advantage of the invention, the height to which the plunger is inserted is a direct function of its angular position. Moreover, it is known to produce angular position slaving which is simple, precise, does not vary according to working conditions nor is degraded over time.
According to another advantageous characteristic, the shape of the contour of the plunger intended to penetrate into the guide is designed in such a way that both the intrinsic response of the device (i.e. the attenuation value expressed in decibels, or gain of the attenuator) is linear and its frequency response is constant in the frequency band for which it is designed.
REFERENCES:
patent: 2619538 (1952-11-01), Grant
patent: 3209288 (1965-09-01), Bashore et al.
patent: 3443216 (1969-05-01), Tsuchiya et al.
patent: 57-194604 (1982-11-01), None
International Search Report, dated Nov. 2, 1998.
Preliminary Search Report, dated Jul. 4, 1997.
Bovernick Rodney
Kim Ellen E.
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