One of the most established vacuum electronic high power source- VED sources of radiation(at higher orders of power and frequency) [11],[12] is the backward wave oscillator (BWO) .A BWO is a VED that is used to generate microwaves up to very high frequency range and high power while keeping the device very compact . By adjusting the beam voltage, in [21], it is shown that , it tunes fully and rapidly over a very wide band ( around 50 percent) of frequencies. Its frequency is relatively independent of load impedance and it can be designed to be exceptionally stable in frequency. BWO are such VEDS whose size is of an inch also exist. So, compactness and its capability to be operational at broadband frequency sets it high on list of energy sources when one talks about microwave generation, especially high power accompanied at high frequency with compactness. This paper gives a detailed study on various stages that BWO has witnessed in high power microwave generation, from the time it evolved.
