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1000-Watt
Impedance Matching Networks Manual and Automatic Coaxial
Power Systems Ltd manufacture two styles of impedance matching network to link
the load to the RF generator. The purpose of the network is to adjust the input
impedance of the load to 50 Ohms so that maximum power is transferred from the
generator, whose output impedance is 50 Ohms, to the load. The network must be
installed as close a possible to the load. The best possible position, in a
plasma application for example, would be to mount the network directly on the
vacuum chamber with a direct connection to the electrode or magnetron. Coaxial
Power Systems Ltd. manufacture two types of network - Manual and Automatic Manual Matching Network The
manual matching network consists of two adjustable vacuum capacitors and a fixed
inductor, which are usually arranged as an ”L” network. (The arrangement can
be simply converted to a “Pi” network if required). Cranked knobs with built
in turns counters are used to adjust the capacitors for minimum reflected power
as displayed on the generator reflected power meter. When the reflected power is
zero, the system is “tuned” and all of the power output of the generator is
being fed to the load.
Automatic Matching Network The
automatic matching network is similar to the manual version except that
servomotors drive the capacitors. At
the input of the network, a phase and magnitude detector determines the position
of the capacitors. This information is transferred to the separate controller.
The controller then drives the servomotors to the positions, which give zero, or
minimum reflected power. The
controller is ½ rack, 4U high and is usually fitted in the same enclosure as
the generator.
Alternatively
the controller may be fitted inside a generator with the readouts and controls
on the generator front panel. The
position of each variable capacitor is shown on a 31/2 digit LED meter.
Automatic or Manual mode is switch selectable - in manual mode the servomotors
are controlled by spring loaded switches. The
start position of the capacitors can be individually adjusted. When RF power is
detected, the capacitors automatically adjust for minimum reflected power. When
the RF is turned off, the motors drive the capacitors back to heir original
position. The start positions are adjusted using potentiometers accessible via
the controller front panel Option:
Model DCP-1 : Dark Space Bias Voltage Measurement and Control A
probe, installed inside the network, measures the d.c voltage (0 to 1999V)
developed across the dark space in plasma applications such as sputtering and
reactive ion etching. The voltage is converted to a 0 to 5V signal which can be
fed back to the generator control system. The voltage
is displayed on the loading capacitor position meter. Includes all
necessary cables to link to any generator in the low power range manufactured by
Coaxial Power Systems Ltd. Note:
This option not available on manual networks (07.06.2007) |
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