RF Spectrum of Thermal Noise and Frequency Stability of a Microwave Cavity-Oscillator

The spectral distribution of the themal noise within a microwave cavity equipped with an extemal feedback loop has been calculated and measured. An equivalent electrical model is established from which the noise spectral density can be calculated at any post in the system, The effect of the gain and phase of the loop on the spectral distribution is measured with a spectrum analyzer through a heterodyne technique and comparison with theoretical calculations shows good agreement. Also, the modified cavity Q and resonant frequency is measured for various loop parameters. An experimental setup allowing precise measurement of frequency stability and FM noise close to carrier of microwave oscillators is presented and discussed. preliminary measurements of the short-term frequency stability of the system when operated as a microwave cavity-oscillator show a predominant flicker frequency noise. The measured FM noise close to carrier is related to time-domain measurements of frequency stabitity and to RF spectrum of the cavity-oscillator.     

Comparison of Indirect Optical Injection-Locking Techniques of Multiple X-Band Oscillators

Experimental results of indirect optical injection-locking of two X-band FET oscillators are presented. An S-band master source is used to synchronize both oscillators simultaneously, with 18-MHz locking range using the fiber-optic link nonlinearity. The source of the optical link nonlinearity is traced to the laser diode by interferometric measurement. Both the laser diode and the FET oscillator nonlinearities can be exploited to achieve frequency multiplication of the master oscillator signal. The merits of these different methods are evaluated based on the locking range and the FM noise level of the injection-locked oscillator.     

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.     

Determination of Equivalent Circuit Parameters Describing Noise from a Gunn Oscillator

The AM and FM fluctuations in an oscillator output are originated from impedance fluctuation in low frequencies (baseband noise) and voltage or current fluctuation in the vicinity of the carrier frequency (RF noise). In this paper, from newly defined "complex correlation coefficient between AM and FM noises," contributions of baseband and RF noises to the AM and FM noises are determined. Examples of data for X-band Gunn oscillators show that both the AM and FM noises are mainly caused by the baseband noise in the vicinity of the carrier frequency (within 1-kHz band), whereas they are mainly due to the RF noise at frequencies further than 10 kHz from the carrier frequency.     

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.     

The use of saw oscillators to suppress fm noise in local oscillators for on-board satellite applications

SAW oscillators can provide fundamental frequency operation to above 1·5 GHz, with stability and FM noise performance approaching that offered by bulk crystal oscillator technology. Their high fundamental frequency, small size and rugged construction gives SAW technology a unique capability at UHF and microwave frequencies. The low FM thermal noise floor associated with fundamental frequency operation can be combined with the stability and low close-to-carrier noise of multiplied bulk crystal oscillators by locking a high frequency SAW oscillator to a bulk crystal reference. SAW oscillator stability is compatible with conventional phase-locked-loop techniques and also with injection lock stabilization, and their own low close-to-carrier FM noise ensures that such locked sources exhibit minimum phase noise. Furthermore, locked oscillator phase noise is not significantly degraded when extreme operating conditions, such as those experienced in space applications, demand a reduced SAW device Q for reliable locking using either technique. Use of a PLL avoids any need for reference frequency multiplication, and provides additional design flexibility with respect to reference frequency selection and phase noise optimization. Injection locking offers design simplicity and uses fewer frequency control components, which can contribute additional noise in PLL sources.     

Linearity Improvement of Microwave FM Oscillators by Harmonic Tuning

A new linearizing method for microwave communication FM oscillators is presented. As a linearizing mechanism the frequency perturbation caused by tuned harmonic(s) is utilized. Analytical formulation of linearity requirements for the general case are given and explicit relations are delivered for the second harmonic-tuned FM oscillator. Linearity and noise loading results are shown, obtained with an experimental 250-mW X band Gunn diode FM oscillator and satisfying CCIR linearity and noise loading requirements for broad-band microwave radio links.     

GaAs W-band IMPATT diodes for very low-noise oscillators

W-band single-drift flat-profile IMPATT diodes were fabricated from GaAs MBE material and tested in a full-height waveguide resonant cavity with resonant cap. A quasi-optical parabolic Fabry-Perot resonator was used to determine the FM noise of the GaAs IMPATT oscillator. With a minimum noise measure of 20 dB at power levels around 20 mW, IMPATT diode oscillators can compete well with oscillators using Gunn devices. The (N/C)/sub FM/=-82 dBc measured at 100 kHz frequency off-carrier and at Q/sub EX/=95 is comparable to the value obtained from Gunn devices. The maximum available output power of 270 mW, however, markedly exceeds that of Gunn oscillators.<>     

A theory of noise in GaAs FET microwave oscillators and its experimental verification

A theory has been developed which provides an entirely analytical approach to the calculation of AM and FM noise in free-running GaAs FET microwave oscillators. The theory is based on the model that low-frequency device noise is mixed with the carrier signal via the nonlinearity of the FET and upconverted to microwave frequencies. Because of the analytical nature of the theory, all the important device and circuit parameters on which the noise generation depends are explicitly given. Two GaAs FET oscillators have been fabricated and used to investigate the FM noise. The theory predicts well both the spectral dependence and the absolute magnitude of the FM noise in both oscillators. The noise performance of the oscillators differs by 19 dB. The theory indicates that no single factor is responsible for this, and moreover that attention should be given to the optimization of many device and circuit features in the design of a low noise FET oscillator.     

Optically controlled oscillators for millimeter-wave phased-arrayantennas

An approach for the design of optically synchronized millimeter-wave local oscillators based on a subharmonically injection-locked phase-lock-loop technique is introduced. The experimental results support the desired goal of frequency and phase coherency, phase shift control of millimeter-wave oscillators, and self-oscillating mixing to downconvert a millimeter-wave RF signal. Experimental results and theoretical analysis show the advantages of the proposed approach: large locking range of two subharmonically locked oscillators, lower FM noise degradation, and smaller phase error caused by frequency detuning     

Sources of residual frequency modulation in X-band two-cavity klystron oscillators

The sources of FM noise modulation in two-cavity klystron oscillators have been studied in detail. The theoretical effects upon FM of RF beam current noise and the bunching parameter are shown to be in agreement with experimental observations. The importance of other FM noise sources is discussed.     

Experimental Evaluation of Noise Parameters in Gunn and Avalanche Oscillators

Equations are presented that express noise-to-carrier ratio and rms frequency deviation of a negative-resistance oscillator with a multiple-resonant circuit in terms of effective available noise power densities of both 1/f and white-noise sources, an effective saturation factor, and an appropriate Q/sub L/ of the oscillator. Experimental evaluation of the noise parameters in Gunn and avalanche oscillators by use of these equations is described. AM and FM noise measurements have been made on X-band Gunn oscillators and Si and GaAs avalanche oscillators for frequency off carriers extending from 1 kHz to 10 MHz. Both 1/f and white noise have been observed in these oscillators. The validity of the above equations has been verified for Gunn oscillators from the dependence of the noise spectra on Q/sub L/. For Gunn oscillators and Si and GaAs avalanche oscillators, the effective noise-temperature ratio for white noise, N/kT/sub 0/, has been found to be 23~29, 41~51, and 38~44 dB, and the effective saturation factor to be 2~2.9, 0.5~2.4, and 2, respectively. An increase of N/kT/sub 0/ with the RF voltage across the diode has been observed in Si avalanche oscillators. Parameters for 1/f noise have also been evaluated approximately.     

Noise in Synchronized Oscillators

Noise in synchronized oscillators is analyzed using a simple oscillator model. It is shown that the FM noise can be considerably improved by synchronization while the AM noise degrades slightly. It is also shown how the noise spectrum becomes unsymmetrical with respect to the synchronizing freqnency when it differs from the free-running frequency.     

Noise in IMPATT Diode Amplifiers and Oscillators

The results of experimental and theoretical investigations of the noise characteristics of lMPATT diode amplifiers and oscillators are presented. The oscillator noise is shown to consist of three different contributions: modulation noise, selectively amplified primary noise, and conversion noise. The influence of the active device nonlinearity and load circuit parameters is discussed in detail. The experimental results are in good agreement with the theoretical predictions. It is especially pointed out that the large correlation between AM and FM fluctuations, usually measured in IMPATT oscillators, indicates nonoptimum AM noise performance. Experimental techniques for achieving optimum AM noise performance are demonstrated (orthogonal noise tuning). By a simple extension of the model, the noise behavior of an injection phase-locked oscillator can be described. The calculated AM and FM noise power spectra for the synchronized oscillator are also shown to be in good agreement with experimental results. Finally the signal-to-noise ratio for current modulated IMPATT oscillators is investigated and optimization is demonstrated.     

Transferred electron (Gunn) amplifiers and oscillators for microwave applications

Transferred electron amplifiers and oscillators are now well established as important members of the family of active microwave solid-state devices. The combination of power output, gain-bandwidth product, and noise figure that has been achieved with stable linear transferred electron amplifiers cannot be matched by any other type of microwave solid-state amplifier. Transferred electron oscillators have produced the highest power output obtained so far from a single solid-state device at microwave frequencies, they can be electronically and mechanically tuned over larger frequency ranges than other types of solid-state oscillators, and well designed transferred electron oscillators have exceptionally low AM and FM noise. An introductory survey of the history and the current status of the theory, technology, and application of transferred electron devices is presented. The future outlook for these devices appears bright.     

Noise in IMPATT-diode oscillators at large-signal levels

A theory is formulated which describes the noise properties of IMPATT-diode oscillators operating at large-signal levels. This theory is based directly on the work of Convert [17] and Hines [18]. The theory takes into account the signal dependence of the noise generation process, and also the intermodulation effects occurring between the various frequency bands. The equations are conveniently arranged in matrix form; such a formulation provides physical insight and facilitates the obtaining of quantitative results in terms of measurable noise parameters. The AM, FM, and low-frequency noise of low-Q IMPATT-diode oscillators operating at high output power levels has been measured and compared with the values predicted by this theory. Si p⁺-n, Si n⁺-p, and n-GaAs S.B. IMPATT diodes have been used. Agreement between the measured and theoretically predicted values is good. Special experimental evidence for the signal dependence of the noise-generating mechanism is obtained by considering the ratio of the AM and FM noise. The Comparatively few measurements published on the correlation between AM, FM, and low-frequency noise have been compared with our theoretical results; as far as can be judged, the trends are similar. Finally, an experiment is described in which a Si n⁺-p diode was used in a high-Q Kurokawa circuit. The experimental value of the rms frequency deviation of 0.8 Hz in a 100-Hz bandwidth was found to be in reasonable agreement with the present theory, extended with an equivalent circuit describing the high-Q circuit.     

Wide-Band Varactor-Tuned X-Band Gunn Oscillators in Full-Height Waveguide Cavity (Short Papers)

Some results on X-band varactor-tuned Gunn oscillators in a full-height waveguide cavity are presented. It is shown that it is possible to obtain an electronic tuning range of over 1 GHz at X band with an appreciable output power level, which is also nearly constant with frequency. Results of FM noise measurements on one such oscillator are also reported.     

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.     

测控系统中振荡器短稳对测速精度的影响

本文采用时域分析方法得到了测速误差与测控系统中各振荡器短稳的关系式，分析与工程实践的结果说明，测速误差不仅与频标源的短稳有关，而且与系统中各相干本振的附加相位噪声有关，在工程研制中，必须合理地分配各振荡器的短稳指标并减小其短稳损失，才能获得高的测速精度。