  Dunlap-Kenkre result states that Dynamical Localization (DL) of a field
driven quantum particle in a discrete periodic lattice happens when the ratio
of the field magnitude to the field frequency (say, $\eta$) of the diagonal
sinusoidal drive is a root of the ordinary Bessel function of order 0. This has
been experimentally verified. A generalization of the Dunlap-Kenkre result is
presented here. We analytically show that if we have an off-diagonal driving
field (with modulation $\delta$) and diagonal driving field with different
frequencies (say $\omega_1$ and $\omega_2$ respectively) and a definite phase
relationship $\phi$ between them, one can obtain DL if (1) $\eta$ is a zero of
the Bessel function of order 0 and $\phi$ is an odd multiple of $\pi/2$ for
equal and $\frac{\omega_1}{\omega_2}= odd integer$ driving frequencies, (2)
$\eta$ is a zero of the Bessel function of order 0 and $\phi$ is an integer
multiple of $\pi$ including zero for $\frac{\omega_1}{\omega_2}= even integer
\equiv m$, and (3) $\phi = -\arcsin(\frac{J_0(\eta)}{\delta J_m(\eta)})$ and
$\eta$ is not a zero of the Bessel function of the even order $m$.
