Why antenna have no return-loss can still receive signals

Dear all,
I'm new to this forum. I have an active AM/FM antenna
the antenna measured no return-loss, but it can work normally
It's gain is -60dBm(and above).
Could anyone please help me to explain this.
Thanks a lot !

In the AM and short wave broadcast bands the signal strengths are so large that what little gets through to the receiver is adequate. You can try an experiment by putting your finger on the hot terminal of the antenna connector and tuning around to see what you can receive.

You can do some paper analysis. Draw the receiver equivalent input impedance, the transmission line, the Thevenin equivalent of the antenna. Then transfer the receiver input impedance through the transmission line using a Smith chart or the algebra. You will then have a lumped element circuit with two impedances forming a voltage divider.