High-frequency measurements calibration standards

All the physical quantities are measured with respect to a reference, which is called a standard for example, a meter for length, gram for mass, etc. Similarly, the device calibration at high frequency is done by measuring various known physical devices called standards. The frequency response of these devices is known. In most of the calibration techniques, commonly used standards are the short circuit, open circuit, load, and a thru line. Together, these standards calibrate the RF path between the measurement device and the DUT. But no standard is ideal and has losses as the EM energy travels only in a part of the device owing to skin effect. So we have correction factors which, in turn, make up for tiie nonideal behavior of the calibration standards. It is very important to note that the correction factors, commonly known as calibration co cients are only valid for a combination of test system... 

The simplest and most accurate way to calibrate a TCSPC system is to use the pulse period of a high repetition rate laser as a time standard. The pulse period of Ti Sapphire lasers is between 78 and 90 MHz and accurately known. Diode lasers are usually controlled by a quartz oscillator and have an absolute frequency accuracy of the order of several tens of ppm. The signal is recorded in the reversed start-stop mode with a frequency divider in the reference path. The recorded waveform covers several laser periods, and the time between the pulses can be measured and compared with the known pulse period. 

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