Comparison and Analysis of Two Microwave Equivalent-Circuit Models for Resonant Tunneling Diode

The distinction between two microwave equivalent-circuit models,quasi Esaki tunneling model (QETM) and quantum well injection transit model (QWITM),for the resonant tunneling diode (RTD) is discussed in details,and two groups of circuit parameters are extracted from experiment data by the least square fit method.Both theory analysis and the comparison of fit results demonstrate that QWITM is much more precise than QETM.In addition,the rationality of QWITM circuit's parameters confirms it too.On this basis,the resistive frequency is calculated,whose influence factors and improvement method are simply discussed as well.

Analysis and design of the taper in metal-grating periodic slow-wave structures for rectangular Cerenkov masers

The hybrid-mode dispersion equation of the metal-grating periodic slow-wave structure for a rectangular Cerenkov maser is derived by using the Borgnis function and field-matching methods.An equivalent-circuit model for the taper of the groove depth that matches the smooth waveguide to the metal-grating structure is proposed.By using the equivalentcircuit method,as well as the Ansoft high frequency structure simulator（HFSS） code,an appropriate electromagnetic mode for beam-wave interaction is selected and the equivalent-circuit analysis on the taper is given.The calculated results show that a cumulative reflection coefficient of 0.025 for the beam-wave interaction structure at a working frequency of 78.1 GHz can be reached by designing the exponential taper with a TE z10 rectangular waveguide mode as the input and the desired TE x10 mode as the output.It is worth pointing out that by using the equivalent-circuit method,the complex field-matching problems from the traditional field-theory method for taper design can be avoided,so the taper analysis process is markedly simplified.

Quenched-Domain Mode of Photo-Activated Charge Domain in Semi-Insulating GaAs Devices

The quenched domain mode of the photo-activated charge domain （PACD） in semi-insulating （SI） GaAs photoconductive semiconductor switches （PCSSs） is observed. We find that the quenched domain is induced by the instantaneous electric field across the PCSS being lower than the sustaining electric field of the domain during the transit of the domain. The extinction of the domain before reaching the anode can lead to a current oscillation frequency larger than the transit- time frequency when the bias electric field is lower than the threshold electric field of the nonlinear PCSS. According to the operation circuit and the physical properties of a high-field domain,an equivalent circuit of the quenched domain is presented. The equivalent circuit parameters including capacitance, resonant frequency, and inductance are calculated and measured. Our calculations agree well with the experimental results. This research provides theoretical and experimental criteria for heightening the oscillation frequency and efficiency of PACD devices.