Novel technique for improving the frequency stability of Gunn oscillators

The frequency stability of a Gunn oscillator employing waveguide below cutoff as a resonator is investigated over the temperature range 20?100°C. A novel technique is described for improving the frequency stability of the oscillator. Experimental results using the negative temperature coefficient of the permittivity of titania are presented in support of this method.     

Simple theory for improving the efficiency of Gunn oscillators

The letter considers improvements in efficiency to be expected from varying the area or donor-density profile of a Gunn device. A method is given to design a diode theoretically capable of efficiencies approaching 40% for the best-quality GaAs with a peak/valley ratio approaching 3.     

Angle modulation of frequency locked Gunn oscillators

It is shown experimentally and theoretically that frequency modulation through the bias circuit of free-running Gunn oscillators at low modulation frequencies can be converted to an equivalent phase modulation by frequency locking. Judicious choice of locking bandwidth causes the low-frequency phase-modulation coefficient to be of the same order of magnitude as that measured at high modulation frequencies. The phase-modulation coefficient at high frequencies is unaltered by frequency locking.     

Direct frequency demodulation with frequency-locked Gunn oscillators

The use of a frequency-locked Gunn oscillator as a frequency demodulator is described. A detection sensitivity of ?40 to ?30 dBm is obtainable with detected signals in the millivolt range.     

Frequency/temperature characteristics of Gunn devices

The variability and large magnitude of the frequency/temperature coefficient of Gunn oscillators has limited the application of these devices. The letter outlines a program of experiments and computer simulations aimed at achieving an understanding of the basic ?f/?T mechanism and thus producing a deep stable oscillator. Our simulations successfully predict observed trends in the ?f/?T behaviour of Gunn devices with both alloyed metal and n+ regrown contacts. The results of our study show that stable oscillators with a small loaded Q factor and near maximum power output are realisable.     

Upper frequency limit for Gunn oscillators imposed by carrier energy-relaxation time

The small-signal microwave conductivity of semiconductors in the presence of Large steady electric fields is highly frequency-dependent, owing to the finite energy-relaxation time of the heated carriers. Considering the Gunn oscillator, in view of these effects, it can be seen that an upper limit for oscillation frequency exists. Methods useful for calculation of this limit are proposed.     

Direct frequency modulation with CW Gunn and IMPATT oscillators

Demodulation of frequency-modulated signals has been carried out with frequency-locked CW Gunn and IMPATT oscillators. The process utilized the coupling between the bias current or voltage, respectively and the frequency deviation of the locked oscillator. A full characterization of this coupling is presented. An incremental model of the large-signal oscillator behavior is developed and shown to be in good agreement with the linear and nonlinear behavior of the demodulator.     

Thermal effects in the bias circuit frequency modulation of Gunn oscillators

Observations have been made of the relation between temperature and bias-induced frequency variations of CW X-band Gunn oscillators. The results indicate that a large part of the frequency modulation through the bias circuit at modulation frequencies below approximately 1 MHz can be caused by modulation of the device temperature. Other modulation processes also occur.     

Theoretical study of the effect of temperature on X band Gunn oscillators

The output power of X band gallium-arsenide oscillators has been calculated numerically as a function of temperature and bias voltage. Results are presented and compared with experimental data obtained previously. The existence of a hybrid of the domain and l.s.a. modes of operation is predicted.     

Frequency-modulation sensitivity of Gunn oscillators

It is shown that, when Gunn oscillators are frequency-modulated by means of a small a.c. component superimposed on the bias supply, the resulting microwave-frequency deviation and the impedance presented by the diode to the modulation supply are dependent on the modulation frequency. The magnitudes of the frequency-modulation sensitivity and diode terminal impedance have been measured for modulation frequencies in the range 100Hz?100kHz.     

Temperature compensation of Gunn oscillators

Two mechanically simple techniques are described for improving the temperature stability of Gunn oscillators. The ease of operation of relatively low-Q factor systems is maintained, making these particularly useful for pulsed oscillators.     

Temperature compensation of cavity-stabilised Gunn oscillators

A temperature-compensation method is described, which uses two compensators instead of one, to improve the frequency stability of cavity-stabilised Gunn oscillators. It is particuarly useful if very high frequency stability must be obtained.     

A simple circuit for FSK modulation of Gunn oscillators

A simple transmission cavity placed in the output transmission line of a CW Gunn oscillator can be adjusted to allow simple and cheap digital frequency modulation by bias modulation. Transition rates down to 10 ns have been demonstrated. A threshold switching voltage is required so that the circuit has noise immunity.     

Injection-locking of Gunn oscillators with feedback stabilization

A microwave phase stabilization feedback circuit used with injection-locking increases the locking range of a Gunn oscillator and reduces the voltage fluctuations in the bias circuit.     

Computer optimized design of pulsed Gunn oscillators

The usefulness of computer simulation in the empirical design of a simple Gunn diode oscillator was investigated with encouraging results. The optimum design of a 5-GHz oscillator is discussed in detail. The results do not support Copeland'sN/fscaling criterion. It is also shown that a doping profile favoring dipole space-charge formation is not necessarily at a disadvantage when compared with domain-suppressed design.     

Initial growth of domains in Gunn oscillators

An expression is given for the initial growth of domain voltage. A condition for domain growth is also derived.     

A circuit technique for broadbanding the electronic tuning range of Gunn oscillators

A circuit technique is described whereby the electronic tuning range obtained by varactor tuning solid-state oscillators, such as Gunn oscillators, can be improved. The principle of the technique has been demonstrated by doubling the tuning range obtained from a coaxial X-band Gunn oscillator using distributed circuit elements. An analytical expression for the improved tuning range is presented and predictions for the improvement in an existing microstrip X-band oscillator using chip devices given.     

High-speed phase and amplitude modulation of Gunn oscillators

Linear phase and amplitude modulation of X band Gunn oscillators up to 3 GHz modulating rates has been observed. The modulating signal was applied through the bias circuit, and typical sensitivities were 0.1 rad/V and 10% depth of modulation/volt, respectively. A simple theoretical explanation of the results is given.     

Monte Carlo comparison of heterojunction cathode Gunn oscillators

The authors have performed Monte Carlo simulations to investigate the physics of heterojunction cathode Gunn oscillators. They show that a simple heterojunction cathode does not improve the device performance because the Gunn domain matures too quickly. The inclusion of a thin n/sup +/ layer at the heterojunction allows the Gunn domain to grow throughout the length of the device. This yields improved performance as was recently experimentally observed.<>     

An investigation of multiple domain Gunn effect oscillators

The quenched multiple domain mode of oscillation is proposed in GaAs Gunn diodes. Operating conditions for this mode are explored by means of a computer simulation and a simplified linearized-lumped analysis that was developed to generate waveforms for quenched domain devices. Optimum efficiency is seen when a maximum number of "hybrid sized" domains are packed into a device which is operated at the transit frequency associated with the width of a domain. By reducing the voltage across a device, nonhybrid sized domains form and the device operates at less than peak efficiency. The investigation includes a discussion of device performance when nonidentical but comparably sized domains are present in the device. Experimentally, multiple domain devices have been fabricated using diodes with coplanar contacts. The experimental results tend to confirm the existence of multiple domains in the diodes as well as the results of our analysis.