<form name="myForm" ng-submit="submitForm()" ng-controller="ExampleController">
   <input type="radio" ng-model="color" value="red" ng-required="!color">  Red <br/>
   <input type="radio" ng-model="color" value="green" ng-required="!color"> Green <br/>
   <input type="radio" ng-model="color" value="blue" ng-required="!color"> Blue <br/>
   <tt>color = {{color | json}}</tt><br/>
   <button
   data-ng-disabled="myForm.$invalid"
   type="submit">Submit</button>
  </form>