How to do validation in $ionicPopup?

I'm trying to use $ionicPopup to handle login/registration on my app. I'm opening it from a service, so I created a new scope and attached it to the ionicPopup. It looks smth like this:

$ionicPopup.show
  template: '''
    <form name="loginForm" novalidate>
      ...
    </form>
  ''',
  scope: $scope,
  buttons: [
    { 
      text: 'Cancel',
    },
    {
      text: '<b>Save</b>',
      type: 'button-positive',
      onTap: ( e ) ->

        form = $scope.loginForm #why is it undefined?
    } 
  ]

So I named the form as loginForm, and I want to access it inside the onTap function to handle validation. But the loginForm does not exists on the $scope, like it would in a normal form validation inside a controller. So do you have any idea how I should handle the validation here?

Thanks!