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.     

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.     

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.     

Intrinsic FM noise of Gunn oscillators

It has been experimentally shown that the product of the mean frequency deviation of FM noise and the external quality factor varies inversely proportional to the power output of Gunn oscillators. This behavior of FM noise of Gunn oscillators with power output is in very good agreement with theoretical predictions of large-signal diffusion noise in GaAs devices. At optimum power output, the calculated and experimentally determined noise measure ranges between 17 and 22 dB.     

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.     

Frequency-temperature relationships of X-band Gunn oscillators

Considerable differences have been encountered in the frequency-ambient temperature relation of c.w. X-band Gunn oscillators with silver-tin or n⁺ cathode contacts. The former devices usually have a large frequency variation (200 MHz from −70°C to +70°C is common in a half-wavelength coaxial cavity). The n⁺ devices appear to have two modes of operation, one of which is at least an order of magnitude more stable than typical silver-tin devices. Several simple models are advanced to semi-quantitatively account for the temperature effects and their differences.     

AM noise of millimeter-wave Gunn oscillators

AM noise of a waveguide cavity Gunn oscillator operating around 33.0 GHz has been measured for frequency off carrier extending from 10 kHz to 1.5 MHz. The measurements indicate that AM noise, (N/C) AM, DSB is typically -165 dB/Hz, at frequencies sufficiently away from the carrier where contribution due to 1/f noise becomes small.     

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.     

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.     

Stability criterion for Gunn oscillators with heavy surface loading

The conditions for domain suppression in a Gunn diode with finite longitudinal and transverse dimensions are derived by studying the eigenfrequencies of the general wave solution of the system. For long samples a critical nd product holds, as well as an ?d product for the lowest-order oscillation frequency.     

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.     

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.