A communication device includes a first FSS (Frequency Selective Surface) element, a second FSS element, a feeding radiation element, a first electron gun, and a first electron collector. The second FFS element is adjacent to the first FSS element. The feeding radiation element generates an electromagnetic signal. The electromagnetic signal is propagated by using the first FSS element and the second FSS element. The first electron gun transmits a first electron beam. The first electron collector receives the first electron beam. An antenna structure is formed by the first FSS element, the second FSS element, and the feeding radiation element. A coupling effect is induced between the first electron beam and the electromagnetic signal, such that the radiation energy of the electromagnetic signal is enhanced.

A compact transmitting antenna includes a vacuum tube, a charged particle beam gun, a beam timing controller, and a beam speed controller. The charged particle beam gun is positioned for producing a beam of finite length of electrons or ions within the vacuum tube that moves within the vacuum tube at a controlled speed to generate an electromagnetic wave. The beam timing controller is arranged to control at least an on time and an off time of the beam. The beam speed controller is arranged to control speed of the beam within the vacuum tube. A frequency modulator is provided by the compact transmitting antenna, arranged to modulate the beam for carrying voice or data signals to transmit information from the compact transmitting antenna.

A compact transmitting antenna includes a vacuum tube, a charged particle beam gun, a beam timing controller, and a beam speed controller. The charged particle beam gun is positioned for producing a beam of finite length of electrons or ions within the vacuum tube that moves within the vacuum tube at a controlled speed to generate an electromagnetic wave. The beam timing controller is arranged to control at least an on time and an off time of the beam. The beam speed controller is arranged to control speed of the beam within the vacuum tube. A frequency modulator is provided by the compact transmitting antenna, arranged to modulate the beam for carrying voice or data signals to transmit information from the compact transmitting antenna.