AdMob banner not displayed Phonegap + JqueryMobile

I would like to use admob in my apps, but if i add a new campaign in a开发者_Python百科dMob administration (I selected smartphone web) and add generated code to my app banner, the ad is not shown.

I checked, that I have allowed prermission in AndroidManifest.xml and looks it O.K.

What is the problem?

In the XML i define a RelativeLayout with the id banner_admob then I start the banner from Java code.

RelativeLayout root = (RelativeLayout) findViewById(R.id.banner_admob);
AdView banner = new AdView(mActivity, AdSize.BANNER, "banner");
banner.loadAd(new AdRequest());
root.addView(banner);