The most common and most likely answer to this crossword clue is the 6 letter word SQUAWK
I've seen this crossword clue in The Times
S
Q
U
A
W
K
Buddy explains!
The straight part
We know that "Radar signal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case radar signal = squawk.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SQUAWK mean?
SQUAWK noun- A shrill noise, especially made by a voice or bird; a yell, scream, or call.
- A four-digit transponder code used by aircraft for identification or transmission of emergency signals.
- An issue or complaint related to aircraft maintenance.
- The American night heron.
- A warning message indicating a possible error.
- To make a squawking noise; to yell, scream, or call out shrilly.
- To speak out; to protest.
- To report an infraction; to rat on or tattle; to disclose a secret.
- To produce a warning message, indicating a possible error.
- To set or transmit a four-digit transponder code. (Normally followed by the specific code in question.)
- To back out in a mean way.