Comparison of time and frequency domain antenna measurements

Abstract

Summary form only given. Currently High-Power Microwave (HPM) systems make use of antennas to radiate the generated microwave pulse. Typically, HPM sources generate a single or dominant frequency with a pulse duration of several hundred microwave cycles. Typically, these antenna systems are calibrated or verified with a frequency domain technique using a Continuous Wave (CW) signal. The radiating system vacuum window or radome may be designed for the dominant frequency of the HPM source. However, the antenna/radome system may not properly accommodate the finite frequency bandwidth due to the finite pulse length or frequency variation. These finite microwave packet size issues can now be accommodated both computationally and experimentally. We will be presenting data comparing frequency domain and time domain simulations, along with experiments. The frequency domain simulations are done with the High Frequency Structure Simulator (HFSS), while the time domain simulations will be done with a Finite-Difference-Time-Domain (FDTD) code such as ICEPIC or VOLMAX. The experiments will compare the standard frequency domain measurements done with a Vector Network Analyzer, while the time domain measurements will be done with packets generated with a CW oscillator and an Arbitrary Waveform Generator (AWG). An example antenna/radome system is our existing Vlasov Antenna and fiberglass belljars. We will also be making use of a TEM to TM/sub 01/ launcher, which has a measured return loss of -20 dB over the frequency range of 1.1 to 1.6 GHz.