Input impedance characterization of the QSC ultra wide band feed

We have fabricated a prototype of the ultra wide band QSC feed with a 10:1 frequency bandwidth. We have characterized the input impedance of the QSC feed using a differential S-parameter approach. We have used a non-linear model fit in the frequency domain for de-embedding the coaxial fixture that connects to the antenna terminals. The non linear model included the parameterization of a family of loads as a series R-L in parallel with a capacitance. The characteristic ultra-wide band response of the QSC feed is already evident from the start, trough the antenna coaxial fixture, even prior to the de-embedding process.