I have this banner on my website that shows retargeting ads.I wonder if I can track which ad is getting how many clicks without adding UTM parameters.
If you're able to capture something to identify the Ad with - you can record it as a custom event within Google Analytics.
Make sure the GA container has been created (pageview sent in your header) and then call this code:
ad_name is whatever variable you've captured to ID the ad (depends on provider)
ga('send', 'event', 'Ad Clicks', ad_name);