Hi folks. Below is a pic of an LNB that is used to receive signals for a satellite TV dish.

1) In a hypothetical scenario where this LNB is receiving a 5GHz, can someone please tell me how we decide on the dimensions of the wave guide?
2) How do we decide the slope of the wave guide?

Thanks 4 the replies!

 

Thanks 4 the replies!

Hello there I have only 1 reply .
I read it myself, it will give you tools to solve you're very good question.
https://www.allaboutcircuits.com/textbook/alternating-current/chpt-14/waveguides/

 

The waveguide is just the tubular part of input to the LNB, the conical part is the feed horn. The feed horn is an impedance matching device. The dish has a focal length just light a mirror and the end of the waveguide is placed at that focal point. Without the feed horn there would be a large mismatch between the dish and the waveguide.

The feed horn is akin to a horn antenna which is commonly used without a dish, directly, at microwave frequencies. The design of a horn antenna is an exercise in trading off gain which can be gotten with a larger aperture and length which increases radically as you increase aperture because the larger the opening the longer the slope must be for a match.

This article might help a bit. The topic is very complex and involves a lot of math. Generally specialized design software is used for feed horns as complex as what you see on DSB dish arrangements. It wouldn’t be practical to calculate by hand.

 

Hello,

There is a whole series of books on microwave design on the internet archive:
https://archive.org/details/microwaveandrfdesignvolume1radiosystemsthirdedition
https://archive.org/details/microwaveandrfdesignvolume2transmissionlinesthirdedition
https://archive.org/details/microwaveandrfdesignvolume3networksthirdedition
https://archive.org/details/microwaveandrfdesignvolume4modulesthirdedition
https://archive.org/details/microwaveandrfdesignvolume5amplifiersandoscillatorsthirdedition

Bertus