Böyle birşey olması lazım denemedim

<html>
<head>
<script>
function gonder() {
window.location = "http://www.siteadresi.com/test?a=" + document.getElementById('a').value + "&c="+document.getElementById('c').value + "+ekyazi";
}
</script>
</head>

<body>
<form action="" method="get" >
<input type="hidden" name="a" value="b" id="a">
<input type="text" name="c" value="Arama " onfocus="this.value=''" id="c" />
<button type="button" onclick="gonder();">Ara</button>
</form>

</body>
</html>
tekrar dene