There are two powerful options in the Antenna Theme i.e. Logo and Header Image. Here is the difference between them,
Logo: Logo will allow you to set your “Logo” (Whether big or small) via `Appearance > Customize > Theme Options > Logo`. So, please set your image (i am viewing in the screenshot bearing Updates typography and beautiful logo). Antenna will adjust the Logo according to dimensions and will be responsive.
Header Image: Header image will be displayed as a background of your logo. It will help you to beautiful the header background.
Antenna Demo has only Logo and No Header Image. If i will upload header image, than it will take the white space of logo.