Klystron and Gunn Diode Microwave Test Benches

This article describes both the Klystron and Gunn oscillator microwave test benches. We’ll explore the block diagrams and components that make up these systems, which are essential for microwave module testing in the lab.

Introduction:

Microwave test benches are precision systems, typically built with rectangular microwave waveguide components. They’re used to test and measure various microwave modules. Let’s take a look at Klystron and Gunn oscillator based test benches.

Klystron Microwave Test Bench

Figure 1: Klystron Microwave Test Bench

The Klystron microwave test bench, as shown in Figure 1, includes:

• Klystron power supply
• Klystron mount tube
• Isolator
• Variable attenuator
• Frequency meter
• Slotted line section
• VSWR meter
• Load

Here’s a breakdown of each component’s function:

• Klystron power supply: Powers the low-power Klystron tube (like a 2K25). It often includes AM and FM modulation capabilities, as well as external modulation signal inputs. Displays usually show beam voltage, beam current, and repeller voltage.
• Klystron mount tube: Houses the reflex Klystron. It uses velocity modulation to transform a continuous electron beam into microwave power.
• Isolator: Allows microwave signals to pass in only one direction, blocking any signals traveling in the opposite direction.
• Variable attenuator: Reduces the microwave signal strength. Users can adjust the amount of attenuation.
• Frequency meter: Measures the frequency of the microwave signal.
• Slotted line section: Covers the desired frequency range and has an accurate scale/indicator for measurement.
• VSWR meter: Measures the Voltage Standing Wave Ratio (VSWR) using a suitable detector and slotted line (or waveguide) section. This helps determine the impedance matching and overall performance of the system. Designed to avoid harmonics of the line frequency.
• Load: A microwave matched termination with a characteristic impedance (typically 50 or 75 ohms). It absorbs the microwave power, preventing reflections.

Gunn Microwave Test Bench

Figure 2: Gunn Oscillator Microwave Test Bench

The Gunn microwave test bench (Figure 2) consists of:

• Gunn Power Supply
• Gunn Oscillator
• Isolator
• PIN modulator
• Variable attenuator
• Detector Mount
• SWR meter

The setup is often used for PC-to-PC communication experiments. The following steps are typically followed:

1. Set up the components as shown in the diagram and install communication software on both PCs.
2. Connect the necessary interfacing cables from the PCs to the microwave test bench.
3. Turn on the PC switch located at the rear of the SWR meter.
4. Turn on the Gunn power supply, setting the voltage to 10V.
5. Select the appropriate COM ports and start the communication software.
6. Adjust the comparator and potentiometer to optimize the output signal.