内容关联字段变量模块名称如何调用

使用开发者工具创建的模块内容关联字段，

<?php echo dr_fieldform('{"name":"关联文章","fieldname":"news_id","ismain":"1","fieldtype":"Related","setting":{"option":{"module":"news","title":"文章名称","limit":"1","pagesize":"","css":""},"validate":{"required":"0","pattern":"","errortips":"","check":"","filter":"","formattr":"","tips":""}},"ismember":"1"}', $product_id, 1, 1);?>

放在后台模板中，

但是关联的模块名称是变量的

{php $news_module = 'news';} //其它方式控制

如下这样无效，

:{"module":{$news_module},"title":"产品名称"

请问该如何实现呢