Ok, it is not so difficult to serve responsive ads with pictures/graphics. You only have to make the picture/graphic responsive with some code and save it with "do not alter html":
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
.responsive {
width: 100%;
max-width: 728px;
height: auto;
}
</style>
</head>
<body>
<a href="link" target="_blank" /a><img src="picture" alt="Sigma" class="responsive" width="728" height="90">
</body>
</html>