Time-domain measurements of the frequency-dependent delay of broadband antennas

We present a new time-domain technique for direct measurement of the frequency-dependent delay of broadband antenna structures. By utilizing a series of fixed-bandwidth, variable center frequency waveforms synthesized in a photonics-based electromagnetic pulse shaper, we perform high time resolution (similar to 54 ps over similar to 10 ns) measurements of several broadband antenna structures. Our results show excellent agreement with the delay extracted via time-domain impulse response measurements, however, compared to conventional impulse response measurements, our method ensures a higher signal-to-noise ratio because it relies on several relatively narrowband measurements as opposed to a single broadband measurement. In addition, the delay uncertainty in our technique (similar to 54 ps) is significantly below that of impulse response measurements (similar to 300 ps) where numerical differentiation of noisy data leads to substantial errors. Our technique is well suited as a diagnostic tool for future variable-frequency fixed-bandwidth systems.