Broadband Waveguide to Coax Adapter for Measurement of Harmonic Distortion of Power Amplifier

This paper describes the design of broadband transition adapters from the R32 waveguide to the coaxial line. These adapters measure the harmonic distortion of the signal on a power amplifier designed for a radar transmitter in the S band at frequencies from 2.7 GHz to 2.9 GHz. The transition makes it possible to measure the level of harmonic components up to the third harmonic, i.e. up to an output frequency of 9 GHz off-line. The adapter is designed for an input power of 32 kW
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on the first harmonic. Behind the amplifier, a power ferrite insulator is inserted in the radar. When measuring harmonics, the insulator facilitates a high-quality impedance termination of the output of the power amplifier. This guarantees the reliable function of this device. The paper describes two solutions of these transitions: on the one hand a transition based on fin-line lines with small reflections in the baseband, and on the other hand a waveguide stepped transition with low reflections in the higher harmonic bands.