The radiation patterns of antennas and arrays are traditionally measured in anechoic chambers. The size of the chamber, its architecture and the quality of the surrounding absorbers all affect the chamber's frequency range of operation and the accuracy of the measured results. For example, in order to characterize an HF antenna operating at 40MHz, you need a very large and deep anechoic chamber several meters long. Anechoic chamber facilities are very expensive, require a large space and are hard to operate and maintain. Compact ranges are smaller replacements for full-sized chambers.
Near-field scanning systems are by far the most compact alternatives for antenna pattern measurement. Yet, conventional near-field scanning systems have substantial downsides. These systems involve metallic radiators that act as receivers for picking up the near field of the antenna under test (AUT). Such metallic pick-up pickup antennas cannot get close to the AUT since they would perturb its near fields. They also limit the operational bandwidth of the system, and their accuracy degrades significantly at lower frequency bands. Sophisticated error correction and compensation algorithms are often used in conjunction with these systems to de-embed and minimize various errors due to their specific architectures and configurations.
{{#ev:youtube|https://www.youtube.com/watch?v=l5KjauYge5o|500|right|<b>VIDEO</b>: Mapping the near-fields of a 64-element X-band patch antenna array with a corporate feed network.|frame}}
[[NeoScan]]'s non-invasive electro-optic probes have made it possible to directly measure and map the aperture-level fields of a radiating antenna. When dealing with radiating systems, mapping the near fields can have two different purposes. For the purpose of far-field radiation pattern estimation, you don't want to get too close to the surface of the antenna to avoid picking up all the reactive fields and evanescent modes. If you do so, you will need a rather high spatial resolution to capture the field variations with very precise details. On the other hand, for the purpose of diagnostic near-field mapping, you do need a very high spatial resolution and you want to maintain the field probe as close as possible to the surface of the antenna under test. [[NeoScan]] does both jobs for you and meets both sets of requirements with one system and the same probes.
For instance, you can examine the inter-element coupling effects in passive and active phased arrays. The figure below shows a 64-element fixed-beam X-band patch antenna array with an elaborate micostrip corporate feed network operating at 10.65GHz. The array was designed with a uniform amplitude distribution, i.e., it should supply equal powers to all the 64 patch radiators. As the video shows, the low-resolution near-field maps at a higher height above the array surface provide a good estimate of the far-field radiation patterns, but they do not reveal much about the field distribution of the individual radiating elements. To accomplish the latter, you have to bring the probe down much closer to the radiating aperture. From the figures below, you can easily see that a large portion of the supplied RF power is trapped in the feeding transmission lines, and some patch elements receive much lower power levels than the others.
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In short, with [[NeoScan]], you get a compact portable self-contained system that characterizes your antenna system from the very near fields to the very far fields without requiring considerable real estate.
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For instance, you can examine the inter-element coupling effects in passive and active phased arrays.
[[NeoScan]] is particularly useful for phase characterization and calibration large antenna arrays.