Near field diagnostics for HPM sources

Summary form only given, as follows. The ability to diagnose the radiated pulse from an HPM source is difficult because of the power densities, collecting areas, and data cables employed. One typically has to place diagnostics at large radii from the antenna phase center to keep the voltages induced on data cables at reasonable levels, typically c 1.5 kV breakdown threshold of 50 Ohm cable. To place the diagnostics closer required reducing the effective area of the probe to receiving microwave power. We will be discussing our use of S-band waveguide to coaxial type-N transitions to measure the radiated power from L-band HPM sources. First, we will discuss the calibration and simulation of these diagnostics. We will also show how these diagnostics have been used to measure the power radiated through Vlasov and conical antennas, and how the in-band harmonics are de-coupled from the below cutoff signals of interest. The results from these S-band probes have compared favorably with probes sampling the traveling waves in waveguides between the HPM source and the antennas.