I tried to recreate the crochet square pattern for this vintage afghan. Hmm, looks like I made the beginning chain ring too big. I started with chain 8, but chain 5 would probably work better.
Anyway, I'm sharing my pattern below.
Ch 8 (or better 5), join with sl st in ring.
Round 1: ch 2, dc2-tog in ring (counts as 1st cluster), ch 5, *dc3-tog, ch 2, dc3-tog, ch 5* three times, dc3-tog, ch 2, join with sl st to 1st cluster.
Round 2: sl st in next ch-3 space, ch 2, dc2-tog (counts as 1st cluster), ch 3, dc3-tog in same ch-3 space, *ch 2, 3 dc in next ch-2 space, ch 2, (dc3-tog, ch 3, dc3-tog) all in next ch-3 space (corner)* three times, ch 2, 3 dc in next ch-2 space, ch 2, join with sl st to 1st cluster.
Round 3: sl st in next ch-3 space, ch 2, dc2-tog, ch 3, dc3-tog in same ch-3 space, *ch 2, 2 dc in next ch-2 space, dc in next 3 dc, 2 dc in next ch-2 space, ch 2, (dc3-tog, ch 3, dc3-tog) all in next ch-3 space (corner)* three times, ch 2, 2 dc in next ch-2 space, dc in next 3 dc, 2 dc in next ch-2 space, ch 2, join with sl st to 1st cluster.
Round 4: sl st in next ch-3 space, ch 2, dc2-tog, ch 3, dc3-tog in same ch-3 space, *ch 2, 2 dc in next ch-2 space, dc in next each dc across, 2 dc in next ch-2 space, ch 2, (dc3-tog, ch 3, dc3-tog) all in next ch-3 space (corner)* three times, ch 2, 2 dc in next ch-2 space, dc in each dc across, 2 dc in next ch-2 space, ch 2, join with sl st to 1st cluster.
Round 5: same as Round 4, but you will have more dc across.
You can actually add more rounds if you wish. Simply continue crocheting as Round 4, but in each round you'll have more and more dc across.