Filter by brand

Hi, I was hoping someone could help. I am trying to filter products by brand and am using the below code

<?php 

perch_shop_products([
    'filter' => 'shop_brand',
    'match' => 'eq',
    'value' => perch_get('b'),
]);?>

I also want to be able to filter by brand when in a sub-category. So an example url would be products.php?cat=products/clothing/disposable?b=adidas. Could some one help please? Thanks!