  In this paper, we will study increasing stability in the inverse source
problem for the Helmholtz equation in the plane when the source term is assumed
to be compactly supported in a bounded domain $\Omega$ with sufficiently smooth
boundary. Using the Fourier transform in the frequency domain, bounds for the
Hankel functions and for scattering solutions in the complex plane, improving
bounds for the analytic continuation, and exact observability for wave equation
led us to our goals which are a sharp uniqueness and increasing stability
estimate with larger wave numbers interval.
