Measurement circuit, measurement instrument, and vector network analyzer

A measurement circuit, comprising

• a clock input configured to receive a reference clock signal;
• a frequency converter circuit that includes at least one radio-frequency (RF) interface being configured to receive at least one RF signal, and
• a first signal generator circuit that includes first clock generator circuit connected with the clock input, wherein the first clock generator circuit is configured to generate a first clock signal having an adaptable frequency based on the reference clock signal, the first signal generator circuit further including a first direct digital synthesizer (DDS) circuit, wherein the first DDS circuit is connected with the first clock generator circuit, wherein the first DDS circuit is configured to generate a local oscillator (LO) signal based on the first clock signal and based on an adaptable frequency tuning word (FTW) of the first DDS circuit,
• wherein the frequency converter circuit further comprises an LO input being configured to receive the LO signal,
• wherein the frequency converter circuit is configured to convert the at least one RF signal into at least one intermediate frequency (IF) signal based on the LO signal, and
• wherein the adaptable frequency of the first clock signal and the adaptable FTW of the first DDS circuit are configured such that the IF signal is free of spurs emitted by the first DDS circuit at least in a predetermined frequency band.