How to implement AdMob Adaptive Banner Ad?
When you integrate Adaptive Banner Ad in your Android app, keep the following key points in mind:

Make sure that your banner ad view background is opaque
You don’t need to place regular banner code in the XML file. It uses a frame layout instead of a regular banner ad view
The Banner ad sizes are designed to work best when using the full available width
The SDK can able to fetch the optimized size of the ad
The anchored banner height is never larger than 15% of the device’s height and never smaller than 50 dp.