[en] Recently new schemes have been proposed for plasma based microwave sources that could lead to output power increases by orders of magnitude, as well as offer new possibilities such as broad band tuning and frequency chirping, ultra-short pulse generation, pulse design, etc. In the first scheme, the static field of an alternatively biased capacitor is directly converted into short pulses of turnable electromagnetic (em) radiation upon transmission through a relativistic; under dense ionization front. The structure presently under investigation consists of pin pairs (capacitors) inserted into an X-band waveguide through its narrow sidewall and separated by 1.134 cm. The generated frequency is in the X-band frequency range (8.4--12.4 GHz) when operated with plasma densities between 10¹¹ and 10¹² cm^-3. The output power is in the 100 W range with an applied voltage of 6 kV and is limited by high voltage (HV) breakdown inside the structure. Much higher output power levels are expected with the new, shorter pulse, HV pulser, since the output power is proportional to the square of the applied voltage. At larger plasma densities, generation of a higher order mode traveling in the backward direction is also observed. In the second scheme, a fraction of the large amplitude electrostatic (es) wave generated in a plasma beat wave acceleration (PBWA) experiment (up to 3 GeV/m) is converted into em radiation by applying a static magnetic field perpendicularly to the driving laser beam. The two-frequency CO₂ laser beam resonantly drives the es wave, and couples to the L branch of the XO mode of the magnetized plasma through Cherenkov radiation. The radiation is emitted predominantly in the forward direction (direction of the laser beam), and is at the plasma frequency (n_c ∼10¹⁶ cm^-3, f∼1 THz). With an applied magnetic field of 6 kG the output power is calculated to be in the megawatt range (for a sharp plasma/vacuum boundary). The parameters of the emitted radiation will also be used as a diagnostic for the plasma wave of a PBWA experiment, measuring its amplitude, phase, lifetime, etc. Design and experimental results are presented