Given that the eccentricity of the ellipse $\frac { x ^ { 2 } } { a ^ { 2 } } + \frac { y ^ { 2 } } { b ^ { 2 } } = 1 ( a > b > 0 )$ is $\frac { 1 } { 2 }$, then
(A) $a ^ { 2 } = 2 b ^ { 2 }$
(B) $3 a ^ { 2 } = 4 b ^ { 2 }$
(C) $a = 2 b$
(D) $3 a = 4 b$