A spectrum analyzer is one of the basic measuring instruments for high-frequency signals and has a function to display a graph with frequency on the horizontal axis and power or voltage on the vertical axis. It is required to be able to correctly display the value of the vertical axis with linearity in accordance with the strength of the input signal. In general, a high-frequency variable attenuator with a known attenuation is used as a reference to evaluate this linearity. Actually, a variable attenuator is inserted between a signal generator and a spectrum analyzer. When the strength of the input signal to the spectrum analyzer is changed, the values between the attenuation and the displayed results are compared. However, this method has limitations in reducing the uncertainty of evaluation results because the correct value of the attenuation of the variable attenuator must be known previously and reflections at the input and output ports of the variable attenuator affect the evaluation results.

Therefore, this paper proposes a new method to evaluate the linearity of spectrum analyzers depending on the linearity of high-frequency power meters. This method does not require the correct attenuation value of the variable attenuator and can evaluate linearity without being affected by reflections at the input and output ports. This paper demonstrates that this method can evaluate linearity more accurately than conventional methods at a frequency of 10 GHz.

Recently, research and development of radio equipment using millimeter wave and terahertz bands has been conducted to realize ultra high-speed and large-capacity communications required for Beyond 5G/6G. In these frequency bands, the signals emitted from transmitters are generally converted to another frequency that can be measured by a spectrum analyzer using an external mixer, and then the signals are measured. The proposed method can evaluate the saturation level and linearity of the external mixer even if the attenuation of the variable attenuator in the millimeter wave and terahertz bands is not clear. The method proposed in this paper is expected to be used to promote research and development of wireless equipment in these frequency bands. For these reasons, this paper is highly evaluated as a paper worthy of the Paper Award of the IEICE.