PROPOSED TRAVELLING WAVE TUNNETT AMPLIFIER AND OSCILLATOR FOR AIRBORNE RADARS

Two travelling wave TUNNETT diode structures are propoposed. The first one is a distributed TUNNETT which is proposed in order to overcome the inherent limitations on the power output of the discrete TUNNETT structure. ItAs shown that this structure can be used as resonant lengths of transmission line in order to tune out the diode depletion layer capacitance. Therefore, the distributed structure can have a much higher impedance, a larger area and a higher output power than the discrete one and will be much easier to match. It is found that a relatively high substrate resistivity gives better performance. It is also found that for a given substrate resistivity there is an optimum value of substrate thickness. Design graphs for the proposed device are presented. An output power of about 12 watts has been optained at a frequency of 30 GHz which is an important result. The second proposed structure is a multistream TUNNETT structure which is based on the space charge interactions of electron streaming layers. Each layer has a different average velocity due to a properly chosen concentration gradiant along the direction transverse to the motion of electrons. A numerical analysis is used to determine the gain of the proposed structure when it is used as a travelling wave amplifier. It is found that this gain decreases with increasing the diode thickness and slightly increases with the operating frequency in the frequency range considered. The proposed devices suffer no transit-time limitations sotheir bandwidth is much wider than that of a discrete TUNNETT. The possible applications of the proposed devices in airborne radars are indicated.