Efficiency levels of microwave generation up to 10 % have been achieved in a vhcator driven by pinched electron beam. This vircator is composed of a graphite cathode, at 0,l-mm Ta wire-mesh anode and a virtual cathode at the image side of the real cathode. Our high-voltage set-up ensures pulses of 120-kV voltage and of 12-kA current. The duratiion of the voltage pulse is 20 ns. The TM 01 mode with an output power of 150 MW has been generated at the X-band. The power increases with the cathode diameter, the anode mesh transparency enhancing. We are going to use the above mentioned vircator in multielement antenna arrays. Microwave generators on virtual cathodes, called vircators, are most commonly used as sources of microwave radiation powerful pulses. The advantages of vircators are as follows: constsuction simplicity, Row demands to beam quality, s ac i en t ;bandwidth of the generated radiation. However, operating ;generators, well-known from literature [1,2], are far from being perfect: the transfomation efficiency of high voltage pulsed power, applied to vircator upstream region, in microwave radiation power doesn‘t exceed 5 YO. The above-mentioned efficiency of the vircator described .in this work exceeds 10 %. The absence of electron beam magnetic insulation as well as considerable excess of beam current, injected into the vircator tube with reference {to relative ultimate current (about 10-12 times) are the main wircator peculiarities. In spite of the fact that vircators of this type are insufficiently investigated, they display the ability to ensure necessary conditions for high electron beam pinching [3,4].