Responsive Doubles
After partner doubles and the RHO raises LHO's suit, a responsive double would show:
over a major raise 4-4 in the minors
over a minor raise 4-4 in the majors
Examples:
Opp Part Opp You
1H double 2H Double = shows 4-4 in the minors
2S = shows 4+ spades
3C/3D = shows 4+ suit
1C double 2C double = shows 4-4 in the majors
2D = shows 4+ diamonds
2H/2S = shows 4+ suit
Some also play responsive doubles over 1NT by RHO.
1H double 1NT double = 4-4 in the minors
Also, some play responsive doubles when partner overcalls and RHO raises LHO, except this shows the other two suits.
1H 1S 2H double = 4-4 in diamonds and clubs
or
1D 1S 1NT double = 4-4 in hearts and clubs