extended hemispherical lens
{{refimprove|date=June 2018}}
The extended hemispherical lens is a commonly used lens for millimeter-wave electromagnetic radiation. Such lenses are typically fabricated from dielectric materials such as Teflon or silicon. The geometry consists of a hemisphere of radius {{mvar|R}} on a cylinder of length {{mvar|L}}, with the same radius.
Scanning performance
When a feed element is placed a distance {{mvar|d}} off the central axis, then the main beam will be steered an angle {{mvar|γ}} off-axis. The relation between {{mvar|d}} and {{mvar|γ}} can be determined from geometrical optics:{{cite journal |last1=Frid |first1=Henrik |title=
Closed-Form Relation Between the Scan Angle and Feed Position for Extended Hemispherical Lenses Based on Ray Tracing |journal=IEEE Antennas and Wireless Propagation Letters |date=2016|volume=15 |page=1963 |doi=10.1109/LAWP.2016.2545858 |bibcode=2016IAWPL..15.1963F |s2cid=24384665 }}
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This relation is used when designing focal plane arrays to be used with the extended hemispherical lens.