corresponding to a measurement range of 11.0–15.0 GHz. The
measurement accuracy achieved here is comparable to that of
the previous works [4]–[6], which is acceptable for applications
where a rough but instantaneous microwave frequency estimation
is required. We believe that the noise generated in the PD
is the major source of measurement error. The influence of the
wavelength stability on the system performance is also studied.
It is estimated that a wavelength drift of 0.1 nm would lead to an
additional measurement error of about 5 MHz for the first case
of the experiment.