Frequency-tuning characteristics of waveguide-mounted transferred-electron oscillators

It has been observed that there is an upper frequency limit to the mechanical tuning range of waveguide-mounted oscillators. This limit has been identified as being due to a transverse resonance of coaxial type along the diode mounting post. Reduction in waveguide height is shown to raise the transverse-resonance frequency to a limit determined by the encapsulation and diode parameters.     

Wide-Band Varactor-tuned Coaxial Oscillators

An experimental investigation into the effects of package and circuit reactances on wide-band varactor-tuned oscillators is described. The results are used to design an X-band Gunn coaxial oscillator with a tuning range in excess of 3 GHz. It is shown that the stray reactance, junction capacitance, and bond-wire inductance affect the varactor tuning characteristics. The characteristics are conveniently displayed by the reflection phase variation with tuning voltage and frequency. A general theory for wide-band varactor-tuned oscillators is presented which is related to the impedance characteristics. These results are used to design three coaxial varactor-tuned oscillators. The first two oscillators are series arrangements while the third oscillator is a parallel arrangement. A simple circuit technique is used to improve the tuning range of each arrangement. This technique is shown to increase the coupling to the varactor diode and decrease the oscillator Q by reactance compensation.     

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.     

Integrated Tunable Cavity Gunn Oscillator for 60-GHz Operation in Image Line Waveguide

The design, construction, and experimental test results of a mechanically tunable Gunn oscillator using a recessed diode metal coaxial cavity coupled to an image line waveguide is described. The oscillator frequency was changed by about 10-percent by varying the bias post length into the coaxial structure. The oscillator is designed so that both the Gunn diode and resonant cavity can be quickly replaced to provide extended frequency coverage and efficiency. This Gunn diode oscillator has provided up to 15-mW CW power at 60 GHz with 10-percent tuning range.     

Nonlinear behavior of the BARITT diode microwave oscillator

Nonlinear behavior of the free-running BARITT diode oscillator has been observed. Discontinuous changes in oscillation frequency and output power occur as the bias current changes. These non-linearities have been investigated in coaxial and waveguide oscillators and are caused by device and circuit interactions.     

Stability Analysis of a Second Harmonic Coaxial-Waveguide Gyrotron Backward-Wave Oscillator

This study analyzes the stability of a Ka-band second harmonic gyrotron backward-wave oscillator (gyro-BWO) with a coaxial interaction waveguide. All of the possible competing modes in the frequency tuning range are considered. To suppress various competing modes, the downstream part of the coaxial interaction waveguide is loaded with distributed losses. Although the competing modes have different kinds of transverse field distributions, simulation results show that the losses of the outer cylinder and those of the inner cylinder serve as complementary means of suppressing the competing modes. The losses can stabilize the competing modes while having minor effects on the start-oscillation current of the operating mode. Detailed investigations were performed involving the dependence of the start-oscillation currents on the parameters of the lossy inner cylinder and the lossy outer cylinder, including the resistivity and the length of the lossy section. Moreover, under stable operating conditions, the performances of the second harmonic coaxial gyro-BWO with different sets of circuit parameters are predicted and compared.     

Theoretical and Experimental Driving-Point Impedance Results of Resonance Circuits in a Gunn Waveguide Oscillator

The frequency tuning range of waveguide oscillator and its stability depend sensitively on the dimension of the resonance cap. Therefore the driving-point impedances with the various dimensions of the resonance cap are calculated by using HFSS(High Frequency Simulation System). In this paper the comparisons between theoretical results of the driving-point impedances as a function of frequency and that of experimental results are described. The oscillation frequency range could be predicted by using the theoretical evaluation methods which are proposed. It shows that resonance cap size and disc height have an effect on the frequency tuning characteristics of Gunn oscillator.     

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.     

Circuit considerations in the design of wide-band tunable transferred-electron oscillators

A theoretical and experimental investigation into a particular type of tunable microwave circuit commonly used for LSA operation of GaAs layers is reported. It is shown that certain effects which often impose severe limitations on the performance of wide-band transferred-electron oscillators (TEO's) such as frequency saturation, fixed frequency operation, resonance switching, deterioration of efficiency, and high FM noise may, in many instances, be attributed directly to the interaction of the equivalent circuit of the encapsulated device and the microwave circuit. The theoretical result are used to deduce design criteria for a J-band (11 to 19 GHz) waveguide circuit in order to optimize the performance of the oscillator with respect to tunning range, efficiency, and FM noise performance. In particular the results of the investigation indicats that, for continuous tuning combined with low FM noise over the tuning range, the parallel resonant frequency associated with the encapsulated device should be less than the minimum operating frequency, and that, by suitable design of the oscillator, frequency deviation due to fluctuation in the magnitude of the device capacitance can, in principle, be reduced to zero over a narrow bandwidth.     

Oscillation Characteristics of Millimeter-Wave IMPATT Diodes Mounted in Low-Impedance Waveguide Mounts (Short Papers)

Experiments on dc-bias-current-tuned IMPATT diodes mounted in low-impedance waveguide mounts are described. Broad-band bias-current-tuned IMPATT oscillators were obtained which cover almost the full waveguide band; 20-, 24-, and 18-GHz tuning bandwidths were obtained with the R-500, R-620, and R-740 waveguide, respectively. From experiments it became evident that there are some suitable relations for broad-band bias tuning among the diode breakdown voltage, the oscillation frequency, and the waveguide dimension. The results are very useful for the design of the circuit and diode parameter for broad-band millimeterwave IMPATT sweep oscillators. The feasibility of applying bias-current-tuned IMPATT oscillators to a broad-band measuring instrument is expected.     

Broad-Band Cavity-Type Parametric Amplifier Design

This paper tells how maximum bandwidth can be obtained from a nondegenerate parametric amplifier which utilizes a circulator. Expressions are derived for the gain bandwidth product and maximum possible gain bandwidth product. It is then shown how the Q of the cavities used for the signal and idler circuits may be kept at a minimum without degrading the noise performance of the amplifier. It is shown that best performance results when the TEM mode is used in coax, or, if waveguide is used, when the operating frequency is far away from the waveguide cutoff frequency. The diode used should have as high a self-resonant frequency as possible and the line admittance should be approximately the diode susceptance. Using a diode with a self-resonant frequency at the idler frequency will be seen to give optimum performance. This paper also discusses double tuning the signal circuit to achieve broader bandwidths. In this case, the addition of the second tuned circuit will be seen to give much broader bandwidths than one would expect from conventional filter theory. Two sample amplifiers are considered and their bandwidths calculated. The effect of double tuning one of the amplifiers is then considered.     

Experimental investigation of millimeter wave Gunn oscillator circuits in circular waveguides

Millimeter wave Gunn oscillator circuits using circular waveguides for 33–50 GHz and 75–110 GHz frequency bands are described. These oscillators are simpler to construct at millimeter wavelengths compared to the conventional rectangular waveguide circuits. The effect of various circuit parameters on the oscillator frequency and output power has been experimentally studied. The CW power and mechanical tuning range obtained from the circular waveguide Gunn oscillators are found to be comparable and sometimes even better than those obtained with conventional rectangular waveguide circuits using the same Gunn device.     

Simulation Investigation of Millimeter Wave Varactor-tuned Transmission Cavity-stabilized Oscillator

A new circuit configuration for millimeter wave varactor-tuned transmission cavity-stabilized oscillator has been proposed in this paper. Compared to conventional varactor-tuned reflection cavity-stabilized oscillator, in this configuration, a high quality factor transmission cavity directly coupled to varactor diode is employed to improve the performances of the oscillator. The operation frequency of this oscillator can be tuned by varying the resonant frequency of the transmission cavity through changing bias voltage of the varactor diode. An equivalent circuit model for the oscillator has been presented in order to theoretically investigate the performance characteristics of the oscillator. On the basis of this model, electrical tuning characteristics have been studied. Mode jumping phenomena during electrical tuning process have been analyzed for obtaining stable operations of the oscillator. The analytical formulae of quality factor and efficiency have been derived in terms of relevant circuit parameters. Particular emphasis has been paid on several circuit parameters which have a substantial impact on circuit performance. Some design considerations have been pointed out according to the simulation results, which are useful to the design and fabrication of this type of oscillators.     

Punchthrough oscillator?new microwave solid-state source

The performances of silicon p-n-p punchthrough oscillators have been studied experimentally at X band in a coaxial cavity. A range of mechanical tuning of more than 3 GHz has been obtained. The oscillator performance at current densities up to about 200 A/cm has been related to the measured diode impedance. The wide-active-band, sensitive-electronic-tuning and low-noise properties of the punchthrough oscillator suggest promising applications as a microwave signal source, as a local oscillator, in f.m.-c.w. radar and in a.f.c.     

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.     

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.     

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.     

Investigations on optically controlled millimeter wave Gunn oscillators

There is a growing interest in optically controlled millimeter wave oscillators. In this paper, we have investigated the external-circuit impedances of an optically controlled millimeter wave subharmonic Gunn diode oscillator, which is illuminated by GaAs/GaAlAs laser beam. The variation of the external-circuit impedances looking outward from the Gunn diode with respect to the optical injection plasma density are calculated based on a field analysis method. The results give some useful conclusions for optically controlled millimeter wave Gunn diode oscillator design. Experimentally an optical tuning frequency shift of 7MHz is achieved at W-band.     

Effect of varactor Q-factor on tuning sensitivity of microwave oscillators, including reverse tuning

It is shown how the effect of resistive losses in a varactor diode can drastically affect the tuning characteristics of millimetre-wave oscillators and can even cause the oscillator to tune in the reverse direction.