How to focus 10.525 GHz micro waves of low power of 10mW

QUESTION
How we can make a pencil beam of microwaves generated from a microwave generator? The generator is not a magnetron but a microwave motion sensor.

Please give me some technical information about it.

REPLIES

IRstuff
Not practical; a 1-deg beam width would require a 78-in antenna.

SOURCE
https://www.eng-tips.com/viewthread.cfm?qid=403897
Above is a snippet.

@IRStuff, Nice and succinct! :)