Circuit assembly for temperature-dependent cathode current tracking in traveling-wave tubes

A circuit assembly for temperature-dependent cathode current tracking in traveling-wave tubes having control electrodes and cathodes with a predetermined cathode current, in combination with a power supply, includes a temperature-dependent network thermally coupled to a given point of the traveling-wave tube for measuring the actual temperature of the tube, and an electronic control circuit in the power supply connected to the temperature-dependent network for keeping the predetermined cathode current substantially constant by varying the voltage at the control electrode of the tube.

The invention relates to a circuit assembly for temperature-dependent 
cathode current tracking in traveling-wave tubes and to a traveling-wave 
tube amplifier. 
When applying a constant control voltage, the cathode current and 
accordingly the gain of a traveling-wave tube is not constant in the event 
of temperature changes. The reason for this is the temperature-dependent 
change of the grid-cathode spacing in the tube. 
It is accordingly an object of the invention to provide a circuit for 
temperature-dependent cathode current tracking of the control voltage in 
traveling-wave tubes, which overcomes the hereinaforementioned 
disadvantages of the heretofore-known devices of this general type, in 
order to obtain a relatively constant cathode current as a function of the 
heating-up of the tube. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, a circuit assembly for 
temperature-dependent cathode current tracking in traveling-wave tubes 
having control electrodes and cathodes with a predetermined cathode 
current, in combination with a power supply, comprising a 
temperature-dependent network thermally coupled to a given or suitable 
point of the traveling-wave tube for measuring the actual temperature of 
the tube, i.e. the circuit assembly is coupled to the tube, and an 
electronic control circuit in the power supply connected to the 
temperature-dependent network for keeping the predetermined cathode 
current substantially constant by varying the voltage at the control 
electrode of the tube. 
Differently stated, there is provided a traveling-wave tube amplifier, 
comprising a traveling-wave tube having a control electrode and a cathode 
with a predetermined cathode current, a power supply, a 
temperature-dependent network thermally coupled to a given point of the 
traveling-wave tube for measuring the actual temperature of the tube, and 
an electronic control circuit in the power supply connected to the 
temperature-dependent network for keeping the predetermined cathode 
current substantially constant by varying the voltage at the control 
electrode of the tube. 
In accordance with another feature of the invention, the 
temperature-dependent network is thermally coupled in vicinity of and 
sufficiently close to the control electrode determining the cathode 
current. 
The circuit assembly or amplifier according to the invention has the 
advantage of providing an integrated circuit which is disposed at a 
suitable point of the tube and is formed of a temperature-dependent 
network which measures the actual tube temperature and prefereably tracks 
the G-2-voltage through a control input in the power supply with an 
electrically conducting connection in such a manner that a cathode current 
which is constant over a wide temperature range flows in the device and 
the output power remains accordingly constant. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
circuit assembly for temperature-dependent cathode current tracking in 
traveling-wave tubes, it is nevertheless not intended to be limited to the 
details shown, since various modifications and structural changes may be 
made therein without departing from the spirit of the invention and within 
the scope and range of equivalents of the claims.

Referring now to the figures of the drawing in detail and first 
particularly to FIG. 1 thereof, there is seen a basic circuit structure of 
a traveling-wave tube amplifier with temperature compensation. The 
amplifier is formed of a power supply N, a traveling-wave tube W and a 
temperature-dependent network T which measures the actual temperature of 
the tube. An electronic control circuit is provided in the power supply N, 
in order to keep the cathode current in the traveling-wave tube W nearly 
constant by varying the voltage at a control electrode, for instance a 
control electrode grid G. In this embodiment, the traveling-wave tube W is 
essentially formed of a cathode K, the control electrode grid G, a helix H 
and collectors C1 and C2. The power supply N is essentially formed of 
collector voltage sources NC 1 and NC 2, a helix voltage source NH, a grid 
voltage source NG and a temperature tracker NT. HF inputs and outputs of 
the traveling-wave tube W are indicated by arrows designated with 
reference symbols HF-EIN and HF-AUS, respectively. 
In FIG. 2, a circuit as actually built is shown. The circuit is 
substantially formed of a high-voltage resistance divider X, Y and Z, in 
which the basic adjustment of the cathode current is accomplished by the 
resistor Y. The temperature-dependent network T is shunted across the 
resistor Z in such a manner that the shunt current through the resistors 
X, Y and Z changes with the change of the resistance in the 
temperature-dependent network G, and an accompanying voltage change 
relative to the cathode K takes place at the resistor X. The voltage at 
the resistor X influences the cathode current through the control input G 
of the traveling-wave tube W. Corresponding to FIG. 1, the grid voltage 
source is provided with reference symbol NG and the delay line which is 
constructed in this embodiment as a helix, is provided with reference 
symbol H. 
The foregoing is a description corresponding in substance to German 
application No. P 33 11 674.1, filed Mar. 30, 1983, the International 
priority of which is being claimed for the instant application, and which 
is hereby made part of this application. Any material discrepancies 
between the foregoing specification and tne aforementioned corresponding 
German application are to be resolved in favor of the latter.