Are the brown bare spots showing up in the exact same places each year? If so, have you checked to see whether something is buried in the soil there which prevents the grass from rooting in.
If the brown spots appear more randomly, it's likely a disease problem. There are fungicides that can help prevent diseases on grass, but they may be expensive and more bother to apply than you wish.
As you replant the area this year, work the soil thoroughly, incorporating some organic matter to provide better rooting for the grass seed. The earlier in the season you seed the better. It also helps to use a patch kit with mulch to keep the area moist until the grass is well established.