Discussion
Why is the subreflector of a Cassegrain often made slightly larger than geometry requires?
Answer: A
A subreflector only a few wavelengths across diffracts appreciably at its rim, so it is oversized to capture the feed pattern properly, and the trade against increased blockage sets the optimum. This is why Cassegrain geometry works poorly on small dishes at low frequencies, where the subreflector would be an unacceptable fraction of the aperture. Mechanical margin, deliberate blockage and interchangeability are not the reason. Diffraction becomes a first order effect whenever a component is only a few wavelengths in size.
No comment is present. Be the first to comment.
Loading…
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development