Analytic Model for Varactor-Tuned Waveguide Gunn Oscillators (Short Papers)

An analytic model for electronic tuning of an X-band waveguide transferred-electron oscillator is presented. The oscillator is electronically tunable by a varactor, and mechanically tunable by movement of a short circuit. The model is used to predict oscillation frequency, maximum electronic tuning range, and electronic tuning versus varactor bias voltage. Two different methods, the "zero reactance theory" and the Slater perturbation theory, are used to calculate the electronic tuning. The results of these calculations are compared to experimental results for two different oscillator configurations.     

Q Degradation in Varactor-Tuned Oscillators (Short Papers)

A general analysis of varactor-tuned negative-resistance oscillators is presented to show the varactor loading effect on the oscillator Q. The external Q of the varactor loaded circuit normalized with respect to the unperturbed external Q is plotted as a function of the tuning range for several values of the varactor Q and the capacitance ratio.     

High-Frequency Gunn Oscillators (Short Papers)

Recent work to achieve high output power of fundamental mode Gunn-effect oscillators at frequencies ranging from 25 to 71 GHz is described. Ambient powers of 370 mW at 6.7-percent efficiency at 25 GHz, 260 mW at 4.5-percent efficiency at 38 GHz 150 mW at 4-percent efficiency at 54 GHz, and 30 mW at 1-percent efficiency at 71 GHz were obtained from single-diode structures. Combining two diodes in a push-pull circuit yielded 400 mW at 3.5-percent efficiency at 32 GHz and 260 mW at 4.0-percent efficiency at 42 GHz. This represents some of the highest powers and efficiencies reported to date from millimeter-wave Gunn-effect oscillators.     

The Ridged-Waveguide-Cavity Gunn Oscillator for Wide-Band Tuning (Short Papers)

A method of construction of the Gunn oscillator for wideband frequency tuning has been developed using the ridged-waveguide cavity. The ridged waveguide can be designed to provide the dominant mode with a wide bandwidth, and also to provide the higher order cutoff modes whose resonance is a limiting factor of the tuning range for oscillators of conventional design with reduced stored energies to permit wide-band tuning. A prototype oscillator having a packaged X-band diode demonstrated an 8-18-GHz tuning range.     

Absolute Load Detection with Microwave Gunn Oscillators (Short Papers)

The change in the dc I-V properties of Gunn-flange microwave oscillators with a change in microwave load are shown to provide a method of measuring the physical properties of dielectric samples that only requires the measurement of dc voltages and currents. A phenomenological equivalent-circuit model has been developed that predicts a dependence of detection sensitivity on bias resistance that agrees closely with experiment and that explains the restrictions on such a bias resistor's maximum allowed value. Properties of a prototype system capable of measuring sample size with 8-percent accuracy are presented.     

Wide-Bandwidth Millimeter-Wave Gunn Amplifer in Reduced-Height Waveguide (Short Papers)

A Ka-band millimeter-wave Gunn-amplifier structure with 15-GHz gain1/2-bandwidth product has been fabricated in reduced-height waveguide. Measurements were taken of the terminal admittance of the diode and its mount and used in the computer optimization of impedance matching transformer sections.     

Broad-Band Varactor-Tuned Impatt-Diode Oscillator (Short Papers)

A varactor-tuned IMPATT-diode oscillator with a continuous and monotonic tuning bandwidth of 27 percent and a potential tuning range in excess of 40 percent is described. The results of a computer program which optimizes the tuning bandwidth of the equivalent circuit of the voltage-controlled oscillator (VCO) are presented. The VCO consists of two varactors located symmetrically on each side of an IMPATT diode all mounted in a ridged waveguide with two matched outputs into 50-Omega coaxial. Experimental results on bandwidth, power output, frequency linearity, and FM noise are presented.     

An Analytical Comparison of Two Simple High-Q Gunn Oscillators (Short Papers)

This note compares and analyzes two commonly used simple waveguide Gunn oscillators in terms of their loaded Q-factors. Suitable design criteria are established for both, and two oscillators which were tested conformed well to these. It is concluded that although the more mechanically complex oscillator, which is in common use, has a greater flexibility, the simpler oscillator is adequate for most applications.     

Cavity Stabilized X-Band Gunn Oscillator

The design and resultant experimental investigation of a pulling mechanism for a highly stable X-band Gunn oscillator, stabilized by a high Q TE/sub 011/-mode reflection cavity, are described. The oscillator shows a temperature coefficient of less than -7 x 10/sup -7/ / /spl deg/C,a low FM noise of 8 Hz per 1-kHz BW at 100 kHz from the carrier, and a wide-band mechanical-tuning capability of several hundred megahertz. In addition, experimental results concerning the hysteresis phenomena of oscillating frequencies, power, FM-noise versus cavity-pulling frequencies, and bias voltages are described.     

Wide-Band Phase Locking and Phase Shifting Using Feedback Control of Oscillators (Short Papers)

Two Yig-tuned Gunn oscillators/sup 1/ have been frequency locked over a 3-GHz range in X-band. Injected power into the locked oscillator was approximately 10 dB below its output power. Analog frequency-tracking circuitry was used together with phase-comparator feedback to achieve output phase which remained within /spl plus mn/10/spl deg/ over a 1.2 GHz bandwidth. Controlled phase shifting was obtained by applying dc voltages within the feedback loop.     

Influence of the Harmonics on the Power Generated by Waveguide-Tunable Gunn Oscillators (Short Papers)

It has been observed that in many cases the power generated by waveguide-tunable Gunn oscillators varies irregularly and rapidly with the tuning. These power variations, which are not to be confused with those deriving from mode switching, markedly depend on the components connected to the oscillator, and are present in spite of their good matching in the operating band. Theoretical evaluations and an experimental test have been performed which allows one to ascribe this phenomenon to the interaction between the fundamental and harmonic signals due to the diode nonlinearity. The understanding of this phenomenon allows one to design the oscillator in such a way as to reduce its effects.     

Impedance Characterization of a Two-Post Mounting Structure for Varactor-Tuned Gunn Oscillators

A lumped equivalent circuit is used to characterize a two-post waveguide mounting structure frequently utilized in varactor-tuned Gunn oscillators. Analytical expressions for the different elements are derived. Comparison with experimental results enabled us to refine the model by the introduction of correction factors which compensate for the simplifying assumptions of the theoretical model. This equivalent circuit would facilitate the optimization of the performance of this type of oscillator.     

Ridged Circular Waveguide (Short Papers)

Characteristics of wave propagation inside a ridged circular waveguide are studied. The waveguide is a hollow, conducting circular cylinder with a pair of semicircular conducting ridges diametrically attached to its inside wall. Results of a perturbation analysis suggest that in this device a lower attenuation and a wider bandwidth than those of a conventional circular waveguide can be achieved. Certain numerical results are graphically presented.     

An X-Band Four-Diode Power Combiner Using Gunn Diodes (Short Paper)

A four-diode X-band Gunn diode combiner is described, and the performance characteristics are presented for combining efficiency, tuning range, pushing fire, frequency drift, external Q, and FM noise.     

Some General Observations on the Tuning Characteristics of "Electromechanically" Tuned Gunn Oscillators (Short Papers)

The nature of mechanical and electronic (varactor) tuning characteristics of "electromechanically" tuned Gunn oscillators in waveguide and coaxial configurations has been investigated and their interactions studied. Some general conclusions about the family of electromechanically tuned Gunn oscillators have been drawn and their limitations pointed out. It is suggested that these limitations are imposed by a distributed circuit on a point source.     

Metallic Frame Beam Waveguide (Short Papers)

Experimental tests performed on metallic frame beam waveguides are described. Two types of metallic structures have been considered. The first one constituted by thin annular frames has the same attenuation value as that of an iris beam waveguide (infinite slit) of the same aperture, but presents guiding properties which are polarization sensitive. The second type of a more complex structure is essentially a dielectric frame beam waveguide in which the dielectric of suitable refraction index is simulated by metallic parallel plate waveguide sections.     

Q-dependence of Gunn Oscillator FM Noise (Short Papers)

Measurements of FM noise and the external quality factor Q/sub ex/ of X-band Gunn oscillators are reported which show that both unconverted and intrinsic FM noise vary inversely as Q/sub ex/, if bias voltage, RF power, and frequency are kept constant.     

RF Cavity Irradiation Dosimetry (Short Papers)

A right circular cylindrical cavity designed to resonate at 380 MHz was developed to irradiate a monkey head with little or no radio frequency exposure to other tissues. The system is used in studies of the behavioral effects of the absorption of radiant power. Dose-rate measurements were made with an electrically equivalent calorimetric load, consisting of a saline-filled plastic cylinder whose geometry and position in the cavity reproduced cavity and transmission line parameters measured with a test animal. Since integral dose rate P/sub m/ (total power absorbed) is proportional to the net power transmitted to the cavity P/sub t/ the constant of proportionality K/sub m/= P/sub m/ / P/sub t/ must account for the absorption of field energy by the tissue. K/sub m/ was determined by comparing the temperature rise produced in a fixed time period by the dissipation of dc power to the temperature rise produced by RF radiation in the same time period. It was found that, at an ambient temperature of 25/spl plusmn/2/spl deg/C and a relative humidity of 55 /spl plusmn/ 5 percent, K/sub m/ was 0.62.     

A Generalized Locking Equation for Oscillators (Short Papers)

Locking equations are derived which account for nonsinusoidal device waveforms. Locking bandwidth is related to Q values and device voltage amplitudes. Effective Q values are calculated for cavities having tuned and untuned harmonics.     

A Wide-Band Rotating Coupler for VHF Use (Short Papers)

A device which transmits wide-band signals in the VHF range across a rotating structure is described. It has potential application to rotating antenna systems and to telemetry systems between stationary and rotating elements. No electrical contact is necessary between the stationary and rotating terminals, and bandwidths on the order of 1000:1 are feasible. From the theoretical analysis given here, predicted device behavior agrees well with measurements on a prototype model.