Establishing Baseline Electromagnetic Quiet Zones for Pre Scan Testing
Establishing a verified pre-scan quiet zone baseline isolates host emissions from ambient noise, preventing costly formal accredited chamber retests.
Log Periodic Array
Meaning
A directional, multi-element antenna designed to operate over a wide frequency band provides uniform performance across the ultra-high frequency spectrum. The log periodic array is commonly used for immunity and emissions testing due to its broad frequency coverage and directional gain. This design combines the benefits of multiple narrow-band dipoles into a single mechanical structure.
Geometrical Scaling
The lengths and spacings of the dipole elements increase logarithmically from the front to the back of the antenna. Geometrical scaling ensures that as the operating frequency changes, the active region of the antenna shifts smoothly along its length. The shorter elements at the tip handle the higher frequencies, while the longer elements at the rear handle the lower frequencies.
This configuration maintains a constant beamwidth and gain across the entire operating spectrum, which is essential for uniform field generation.
Impedance Stability
Antenna impedance must remain matched to the fifty-ohm transmission line to prevent signal reflection. Impedance stability is achieved by feedline arrangements that alternate the phase of each successive element along the boom. This construction cancels reactive components and keeps the standing wave ratio low across multiple octaves.
Polarization Orientation
Physical orientation of the antenna must match the polarization of the electromagnetic wave being measured. Polarization orientation adjustments require a motorized positioner to switch between horizontal and vertical axes during testing.