在平面直角坐标系\(xOy\)中,曲线\(C_{1}\)过点\(P(a,1)\),其参数方程为\(\begin{cases} x=a+ \sqrt{2}t \\ y=1+ \sqrt{2}t \end{cases}(t\)为参数,\(a∈R).\)以\(O\)为极点,\(x\)轴非负半轴为极轴,建立极坐标系,曲线\(C_{2}\)的极坐标方程为\(ρ\cos ^{2}θ+4\cos θ-ρ=0\).
\((1)\)求曲线\(C\)\({\,\!}_{1}\)
的普通方程和曲线\(C\)\({\,\!}_{2}\)
的直角坐标方程; \((2)\)已知曲线\(C\)\({\,\!}_{1}\)与曲线\(C\)\({\,\!}_{2}\)交于\(A\),\(B\)两点,且\(|PA|=2|PB|\),求实数\(a\)的值.