Extending Usable Low Frequency Range of an Anechoic Chamber for Antenna Calibrations Using Time Domain Deconvolution Filter

摘要

It is usually impractical to calibrate antennas in an anechoic chamber down to the VHF frequency range, because absorbers do not perform adequately at these frequencies. Time domain gating can be used to the extent that the antenna ring-down time is short enough, and the reflections are far enough away, so that a gate can be applied without cutting into the antenna intrinsic response. Although it could be possible to apply time domain gating at a closer distance in many chambers, it is typically not feasible to do so in the far field where the path lengths of the reflected signals are too close to that of the direct signal. In this study, we investigate calibrating broadband biconical antennas from 75 MHz to 2 GHz in a chamber designed for above 1 GHz measurements (in which the absorbers have severely degraded performances in the VHF frequency range, and chamber walls are too close to be gated out directly) using time domain deconvolution filter before a gate is applied. After applying the deconvolution filter acquired from a 3 m measurement in the same chamber, we successfully obtained the free space response for a far field distance (e.g., 8 or 9 m) for biconical antennas operating from 75 MHz to 2 GHz.