Improve the ability to receive weak signals, in addition to increasing the antenna aperture, but also need to improve the sensitivity of the receiving system to achieve. Since the manufacturing cost of a large-diameter antenna is very high and subject to certain restrictions, it is particularly important to develop receiver sensitivity in a receiving system.
The receiver sensitivity depends on the noise figure of the preamplifier. Generally, the noise figure of the amplifier at 20K (-253°C) ambient temperature is only about one-tenth of the normal temperature, which can greatly improve the receiver's sensitivity index. However, in order to maintain a low temperature operating environment, a vacuum dewar is used to encapsulate the cryogenic amplifier. A waveguide vacuum window must be introduced between the feed output and the cryogenic amplifier. The magnetic brake vacuum window is a key component in the refrigeration receiver dewar assembly.
At present, domestic and foreign refrigeration receivers have been widely used in deep space detection systems and radio astronomy systems. For the first time, a cat cable low loss waveguide vacuum window was developed in China. The waveguide vacuum window not only has low loss to the input microwave signal, but also has the ability to vacuum seal, heat insulation, and pressure.
Because the microwave loss of the waveguide vacuum window is directly superimposed on the noise of the low noise amplifier, its insertion loss and standing wave performance are the key indicators that directly affect the receiver sensitivity. At the time of initial measurement, it may be considered to design two dedicated waveguides for coaxial conversion. Before testing, it is necessary to repeatedly calibrate the insertion loss and return loss of the coaxial conversion of the two waveguides. This method is difficult to measure accurately. Generally, the vacuum window is installed in the Dewar module. After the low-temperature amplifier is connected, the noise value of the window is calculated by using the noise difference between the amplifier with and without the window to calculate the actual loss. .
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