A low-cost 2.4GHz frequency measurement system for microsecond time domain pulses based on Six-Port technology

This paper presents a fast responding frequency measurement system based on Six-Port technology being able to determine precisely the frequency of very short time domain pulses of one microsecond and even less in the 2.4 GHz ISM band. By using a delay line the frequency measurement can be reduced to a phase measurement that can be quickly evaluated by the Six-Port network implemented with lumped components. The delay line, currently realized by a SMA cable, is extremely sensitive to temperature variations even in the range of 0.1K due to changes of the effective relative permittivity of the inner insulator. Thus, a temperature compensation method based on reference measurements is proposed and final measurements show that this system can reach a calibrated and temperature compensated error of only a few parts per million (ppm).