A new kind of high power tunable microwave radiation source is studied theoretically and experimentally. Following the previous works presented by Dorranian et al. (2003, 2004) in this paper more details about the radiation is presented. The theory of the radiation is developed to calculate the radiation spatial distribution, and more discussion on radiation behavior and characteristics is done. In this radiation scheme, a part of large amplitude electrostatic plasma wake, generated by an intense laser pulse or a relativistic electron bunch, are converted to electromagnetic oscillations by applying a modest dc magnetic field perpendicular to the wake propagation direction. A direct one-dimensional (1D) analytic procedure for calculating the magnetized plasma wake equations is developed and the properties of the radiation are investigated theoretically. The effects of the ramp plasma-vacuum boundary in coupling the radiation from plasma to vacuum is noticed and solved by employing a gas jet flow to generate a sharp boundary. Wakefield is excited by TW-100 fs Ti:sapphire laser beam operating at 800 nm wavelength. The neutral density of gas jet flow is measured with a Mach-Zehnder interferometer. The frequency of the emitted radiation with the pulse width of 200 ps (detection limitation) is in the millimeter wave range. Radiation is polarized perpendicularly to the dc magnetic field lines and propagates in the forward direction and normal direction with respect to the laser pulse propagation direction, both perpendiculars to the direction of the applied magnetic field. Intensity of the radiation in different plasma densities and different magnetic field strengths has been observed.