In this paper, a new kind of terahertz oscillator is presented using plasma wave excitation in a resonant tunnel diode (RTD) gated high electron mobility transistor (HEMT). The plasma wave arising from the RTD-gated HEMT is equivalent to active transmission lines and induces negative differential conductance (NDC) of the oscillator. The proposed RTD-gated HEMT oscillator is more compact and has higher oscillation frequency than the transmission line loaded traditional RTD oscillator duo to plasma wave effect. This paper analyses and calculates the oscillation conditions, the relationships between device structures, oscillation frequency and the output power of the oscillator. The presented work may provide a new concept for fabricating terahertz oscillator.

This study describes the design of a resonant tunneling diode (RTD) oscillator (RTD oscillator) with a RTD-gated-graphene-2DEF (two dimensional electron fluid) and demonstrates the functioning of this RTD oscillator through a transmission line simulation model. Impedance of the RTD oscillator changes periodically when physical dimension of the device is of considerable fraction of the electrical wavelength. As long as impedance matching is achieved, the oscillation frequency is not limited by the size of the device. An RTD oscillator with a graphene film and negative differential resistance (NDR) will produce power amplification. The positive electrode of the DC power supply is modified and designed as an antenna. So, the reflected power can also be radiated to increase RTD oscillator output power. The output analysis shows that through the optimization of the antenna structure, it is possible to increase the RTD oscillator output to 22 mW at 1.9 THz and 20 mW at 6.1 THz respectively. Furthermore, the RTD oscillator has the potential to oscillate at 50 THz with a matching antenna.

No abstract

The position-sensitivity security communication scheme with orbital angular momentum (OAM) directional modulation (DM) beam pattern generated by the uniform circular frequency diverse array (FDA) is proposed. The transmitter employs FDA antennas to generate dual-mode range-dependent OAM beam and the direction information of OAM beam is modulated into the signal. The designed signal with random frequency offset excites the element of the uniform circular FDA to generate orthogonal OAM signals in the desired position. In the undesired position, the intensity pattern and the phase front of the radio beam vary randomly with the digital sequence transmission, which can make eavesdropping difficult. Since the modulation waveform has position-dependent, the signal can be purposely distorted in undesired positions to provide transmission security for the legitimate user. The composite dual-mode OAM signal makes it more difficult for eavesdroppers to demodulate correct messages. The receiver with a single antenna employs the phase compensation and helical phase factor to restore the correct digital signal in the desired position. Numerical results show that the space position-sensitivity OAM-DM technology based on FDA offers a security transmission scheme.

No abstract