- #1

GhostLoveScore

- 149

- 9

- TL;DR Summary
- Designing parabolic dish and feedhorn

I need to design a parabolic dish. Only requirement is that it's 3m in diameter. Everything else can change.

I may seem like a bit confused. That's because I have 50 tabs open about the topic.

First thing is I need to calculate dish gain. If I'm going to calculate it according to this equation

I need to know "k" or the efficiency of the parabolic reflector.

Some pages say I can just put 50-60% real world efficiency in the gain equation and use that. Some say efficiency is directly proportional to f/D ratio. That turned out to be wrong when I read a chapter from the book "Antenna theory" by Balanis. And besides, it makes no sense when f/D is above 1. If I understand correctly, efficiency does depend on f/D ratio, BUT only if we keep the same feedhorn. If we use optimal feedhorn design for that specific dish f/D ratio, then the aperture efficiency is about 70-80 % for any f/D ratio as seen here:

N is feed directivity. I think.

What I need is an advice. What are the correct steps, what parameters should I determine first before calculating the rest? Honestly, I have no clue if I'm doing anything correctly so I'm asking for your help.

Frequency is 1420MHz, and purpose is for listening to hydrogen line.

I'm going to stop here for now, to not overwhelm you with questions.

I may seem like a bit confused. That's because I have 50 tabs open about the topic.

First thing is I need to calculate dish gain. If I'm going to calculate it according to this equation

I need to know "k" or the efficiency of the parabolic reflector.

Some pages say I can just put 50-60% real world efficiency in the gain equation and use that. Some say efficiency is directly proportional to f/D ratio. That turned out to be wrong when I read a chapter from the book "Antenna theory" by Balanis. And besides, it makes no sense when f/D is above 1. If I understand correctly, efficiency does depend on f/D ratio, BUT only if we keep the same feedhorn. If we use optimal feedhorn design for that specific dish f/D ratio, then the aperture efficiency is about 70-80 % for any f/D ratio as seen here:

N is feed directivity. I think.

What I need is an advice. What are the correct steps, what parameters should I determine first before calculating the rest? Honestly, I have no clue if I'm doing anything correctly so I'm asking for your help.

Frequency is 1420MHz, and purpose is for listening to hydrogen line.

I'm going to stop here for now, to not overwhelm you with questions.

Last edited: