Millimeter-wave time-domain spectrum analysis system with unambiguous RF spectrum reconstruction

In this work a measurement system for detection of time-dependent effects in broad-band spectra of high-power millimeter-wave sources is demonstrated. The key feature is an unambiguous reconstruction of the RF spectrum from the intermediate frequency range at which the final spectral domain measurements are performed. This is done by evaluating the upper and lower mixer sidebands of two parallel heterodyne receiver channels simultaneously, resulting in a comparatively high instantaneous measurement bandwidth of 7 GHz and a sufficiently high dynamic range of more than 50 dB. Sample measurements obtained during experiments using a 140 GHz megawatt-class gyrotron demonstrate the unique capabilities of the system for detecting highly transient and broad-band effects in the tube's output spectrum.