1/f frequency noise of 2-GHZ high-Q thin-film sapphire resonators

We present experimental results on intrinsic 1/f frequency modulation (FM) noise in high-overtone thin-film sapphire resonators that operate at 2 GHz. The resonators exhibit several high-Q resonant modes approximately 100 kHz apart, which repeat every 13 MHz. A loaded Q of approximately 20000 was estimated from the phase response. The results show that the FM noise of the resonators varied between S_y (10 Hz)=-202 dB relative (rel) to 1/Hz and -210 dB rel to 1/Hz. The equivalent phase modulation (PM) noise of an oscillator using these resonators (assuming a noiseless amplifier) would range from L(10 Hz)=-39 to -47 dBc/Hz     

Short-Term Frequency Stability of the Rb87 Maser

Measurements of the short-term stability of the Rb87 maser are reported here. The measurements were made as a function of the maser power output and of the receiver cutoff frequency. The experimental data are compared to theoretical results obtained from an approximate theory. In this theory the transfer function of the maser for thermal noise is derived, and the spectral density of the phase fluctuations is calculated. An analytical expression for the "Allan variance" is also given. A comparison of the stability of the Rb87 maser with existing frequency standards shows its superiority for averaging times less than 1 s. We obtain ?f/f ? 1.3 × 10-3 ?-1. A stability of 5 × 10-12 for ? ?1000 s is also reported.     

On the flicker noise of ferrite circulators for ultra-stable oscillators

The flicker noise of the ferrite circulator is a critical element in ultra-stable microwave oscillators, in which the signal reflected from the input of the reference cavity is exploited to stabilize the frequency. This paper explains why the circulator noise must be measured in isolation mode, proposes a measurement scheme, and provides experimental results. The observed flicker spans from -162 to -170 dB[rad2]/Hz at 1 Hz off the 9.2 GHz carrier, and at +19 dBm of input power. In the same conditions, the instrument limit is below -180 dB[rad2]/Hz. Experiments also give information on the mechanical stability of the microwave assembly, which is in the range of 10(-11) m. The measurement method can be used as the phase detector of a corrected oscillator; and, in the field of solid-state physics, it can be used for the measurement of random fluctuations in magnetic materials.     

High-Q thermoelectric-stabilized sapphire microwave resonators forlow-noise applications

Two low-noise high-Q sapphire-loaded cavity (SLC) resonators, with unloaded Q values of 2×10⁵ and very low densities of spurious modes, have been constructed. They were designed to operate at 0°C with a center frequency of 10.000000 GHz. The cavity was cooled with a thermoelectric (TE) Peltier element, and in practice achieved the required center frequency near 1°C. The resonator has a measured frequency-temperature coefficient of -0.7 MHz/K, and a Q factor which is measured to be proportional to T^-2.5. An upper limit to the SLC residual phase noise of ℒ (100) Hz=-147 dBc/Hz, ℒ (1 kHz)=-155 dBc/Hz, and ℒ (10) kHz=-160 dBc/Hz has been measured. Also, we have created a free-running loop oscillator based on one of the SLC resonators, and measured a phase noise of ℒ(f)~-10-30log [f] dBc/Hz between f=10 /Hz and 25 kHz, using the other as a discriminator     

Noise properties of microwave signals synthesized with femtosecond lasers

We discuss various aspects of high resolution measurements of phase fluctuations at microwave frequencies. This includes methods to achieve thermal noise limited sensitivity, along with the improved immunity to oscillator amplitude noise. A few prototype measurement systems were developed to measure phase fluctuations of microwave signals extracted from the optical pulse trains generated by femtosecond lasers. This enabled first reliable measurements of the excess phase noise associated with optical-to-microwave frequency division. The spectral density of the excess phase noise was found to be -140 dBc/Hz at 100 Hz offset from the 10 GHz carrier which was almost 40 dB better than that of a high quality microwave synthesizer.     

Electronic subtracter for trace-gas detection with InGaAsP diode lasers

An electronic noise-cancellation scheme has been developed and tested for second-harmonic (2f) detection with short-external-cavity and distributed-feedback InGaAsP diode lasers and wavelength modulation. The 2f background signal and noise from, e.g., optical feedback, optical fringes, and power-supply pickup are effectively reduced by subtraction of a measure of the signal-beam photocurrent from a measure of the reference-beam photocurrent. The dynamic range required for the lock-in amplifier is also reduced because the signal owing to modulation of the laser output at the first harmonic is canceled. Reduction of the 2f background and dynamic range are important for atmospheric-pressure detection where a large wavelength modulation is necessary. The detector noise was minimized by the use of zero-biased detectors in the subtraction circuit. A beam-noise level (defined as 2× the rms value) equivalent to a line-center absorption of 1.6 × 10(-6) was achieved with an equivalent-noise bandwidth of 1.25 Hz for 2f detection at 10 kHz. The electronic circuit is easy to construct and low cost.     

Microwave interferometry: application to precision measurements and noise reduction techniques

A concept of interferometric measurements has been applied to the development of ultra-sensitive microwave noise measurement systems. These systems are capable of reaching a noise performance limited only by the thermal fluctuations in their lossy components. The noise floor of a real time microwave measurement system has been measured to be equal to -193 dBc/Hz at Fourier frequencies above 1 kHz. This performance is 40 dB better than that of conventional systems and has allowed the first experimental evidence of the intrinsic phase fluctuations in microwave isolators and circulators. Microwave frequency discriminators with interferometric signal processing have proved to be extremely effective for measuring and cancelling the phase noise in oscillators. This technique has allowed the design of X-band microwave oscillators with a phase noise spectral density of order -150 dBc/Hz at 1 kHz Fourier frequency, without the use of cryogenics. Another possible application of the interferometric noise measurements systems include “flicker noise-free” microwave amplifiers and advanced two oscillator noise measurement systems     

Measurement and analysis of a microwave oscillator stabilized by a sapphire dielectric ring resonator for ultra-low noise

Phase-noise measurements are presented for a microwave oscillator whose frequency is stabilized by a whispering gallery mode sapphire ring resonator with Q of 2x10(5). The nature of the mode, which involves little metallic conduction, allows nearly full use of the very low dielectric loss in sapphire. Several mode families have been identified with good agreement with calculated frequency predictions. Waveguide coupling parameters have been characterized for the principal (lowest frequency) mode family, for n=5 to n =10 full waves around the perimeter. For a 5-cm wheel resonator in a 7.6-cm container, Q-values of above 10(5) were found at room temperature for all of the modes in this sequence. Coupling Q-values for the same modes ranged from 10(4) (n =5) to 10(5) (n=10) for a WR112 waveguide port at the center of the cylinder wall of the containing can. Phase noise measurements for a transistor oscillator locked to the n=10 (7.84-GHz) mode showed a 1/f(3) dependence for low offset frequencies, and a value of L(f)=-55 dB/Hz at an offset of 10 Hz from the carrier. The oscillator shows phase noise below the previously reported for any X-band source.     

Short-Term Frequency Stability of Relaxation Crystal Oscillators

Due to the need for stable frequency rectangular wave signals, various relaxation quartz crystal oscillators were designed. Therefore it is of interest to have data on their short-term frequency stability. The generally accepted definitions of measures for short-term frequency stability and measurement procedures are reviewed in this paper. Measurement results for the short-term frequency stability of quartz crystal multivibrators in time and frequency domains show a high spectral purity of the multivibrator output signal. The single-sideband-to-carrier phase noise has values lower than -90 and -120 dB on the offset frequencies of 1 and 10 Hz, respectively. The white phase noise is about -160 dB. The power law spectral density model of fractional frequency fluctuations for the quartz multivibrators is established and a discussion on the noise sources is given.     

The state of the art of flicker frequency noise in BAW and SAW quartz resonators

Experimental results of the last 15 years are reviewed. Noise properties of crystal filters and oscillators are reported, along with practical measurements. It is shown that the additional phase fluctuations are compensated by frequency fluctuations and vice versa. With the assistance of these theoretical results the flicker and white frequency noise coefficients, h(-1) and h(0), respectively, are plotted versus unloaded Q and carrier frequency f(0) for the measured and published crystal oscillator noise characteristics. The dependence of h(-1) approximately 10(-12.75) Q(2) (u) is verified.     

Residual phase noise measurements of VHF, UHF, and microwavecomponents

The results of residual phase noise measurements on a number of VHF, UHF, and microwave amplifiers, both silicon (Si) bipolar junction transistor (BJT) and gallium arsenide (GaAs) field effect transistor (FET) based, electronic phase shifters, frequency dividers and multipliers, etc., which are commonly used in a wide variety of frequency source and synthesizer applications are presented. The measurement technique has also been used to evaluate feedback oscillator components, such as the loop and buffer amplifiers, which can play important roles in determining an oscillator's output phase noise spectrum (often in very subtle ways). While some information has previously been published related to component residual phase noise properties, it generally focused on the flicker noise levels of the devices under test, for carrier offset frequencies less than 10 kHz. The work reported herein makes use of an extremely low noise, 500 MHz surface acoustic wave resonator oscillator (SAWRO) test source for residual phase noise measurements, both close-to-and far-from-the-carrier. Using this SAWRO-based test source at 500 MHz, we have been able to achieve a measurement system phase noise floor of -184 dBc/Hz, or better, for carrier offset frequencies greater than 10 kHz, and a system flicker phase noise floor of -150 dBc/Hz, or better, at 1 Hz carrier offset. The paper discusses the results of detailed residual phase noise measurements performed on a number of components using this overall system configuration. Several interesting observations related to the residual phase noise properties of moderate to high power RF amplifiers, i.e., amplifiers with 1 dB gain compression points in the range of +20 to +33 dBm, are highlighted     

Secondary standard for PM and AM noise at 5, 10, and 100 MHz

A practical implementation of a portable secondary standard for phase modulation (PM) and amplitude modulation (AM) noise at 5, 10, and 100 MHz is described. The accuracy of the standard for both PM and AM noise is +0.14 dB, and the temperature coefficient is less than 0.02 dB/K. The noise floor S_φ (10 kHz) of the standard for PM noise measurements is less than -190 dBC relative to 1 rad²/Hz at 5, 10, and 100 MHz. The noise floor for AM measurements depends on the configuration. A calibrated level of PM and AM noise of approximately -130±0.2 dB relative to 1 rad² /Hz (for Fourier frequencies from approximately 1 Hz to 10% of the carrier frequency) is used to evaluate the accuracy versus Fourier frequency. Similar PM/AM noise standards are under test at 10 GHz. This new standard can also be used as an alternative to the normal method of calibrating the conversion sensitivity of the PM/AM detector for PM/AM measurements. Some types of time-domain measurement equipment can also be calibrated     

高Br纳米晶Fe73Cu1Nb2V1.5Si13.5B9合金的铁损行为(I)低频损耗行为

在f=10-3×103Hz和Bm=0.1-1.0T范围内,研究了高Br纳米晶Fe73Cu1Nb2V1.5Si13.5B9合金的每周总损耗和频率的关系.P/f对f的行为明显地呈现非线性.大约在200Hz以下的范围内,非线性特征特别明显.用损耗统计理论中的"磁体"的行为能相当好地描述这种非线性行为.在较低的频段内,活动的磁体数n和动态过剩场Hexc是线性相关的,而在较宽和较高频段内,n与Hexc的关系是非线性的.     

Absolute frequency stability of a diode-laser-pumped Nd:YAG laser stabilized to a high-finesse optical cavity

We report the frequency stabilization of a diode-laser-pumped monolithic ring Nd:YAG laser locked to a high-finesse optical cavity. With an independent cavity as a frequency discriminator, the absolute frequency noise was measured to be as low as 2 × 10(-2) Hz/Hz(1/2) at the Fourier frequency of approximately 3 kHz. We also measured the heterodyne beat note between two lasers locked to the independent cavities. The beat linewidth is narrower than 30 Hz and the minimum root Allan variance is approximately 6 × 10(-14).     

Investigation of Environmental Noise in Small Electrical Conductors

Large excess resistance noise has been observed in small conductors surrounded by air. The conductor resistance was found to have a well-defined average power spectral density over the observed frequency range from 10^-4 to 200 Hz and the dependence of the noise was measured as a function of bias current, temperature, temperature coefficient of resistance (TCR), spatial correlation, and state of the surrounding air. In this paper, three different mechanisms were identified that produce the noise. The room-temperature fluctuations were measured and found to have a spectral density nearly proportional to f^-2 over the observed six-order-of-magnitude frequency range. The lowest frequency noise around 10^-4 Hz could be predicted from the measured temperature fluctuations using the TCR. Above 10^-3 Hz and below 1 Hz, enclosing the wire in a box greatly reduces the noise, and placing the wire in a vacuum eliminates the predominant noise. This noise was directly related to the temperature of the conductor, somewhat proportional to the TCR, independent of bias current, and has a correlation length smaller than the specimen size. The highest frequency noise does not depend on the conductor temperature, TCR, or the presence of air. It had a very strong dependence on bias current and had a long spatial correlation. The mechanism that generates this noise is not understood     

An Improved 5 MHz Reference Oscillator for Time and Frequency Standard Applications

An improved 5 MHz reference oscillator for use in time and frequency standards has been developed. This oscillator, using an improved crystal unit, reaches a long term drift rate of less than 1×10-11 per day in a few days. The design includes precautions for reduction of effects of conducted electrical noise on the output frequency. Modular design of functional circuits provides ease of manufacture and uniformity of the product. Stabilized temperature control circuits have been utilized to provide improved oven performance. The oscillator has been tested for the effects on frequency and phase stability of power supply variation, changes in thermal environment, modulation by electrical noise, and mechanical vibration. Phase noise within the range of 100 Hz through 5.0 kHz varies from -120 dB to -125 dB.     

An Intercomparison of Hydrogen and Cesium Frequency Standards

Intercomparisons of average frequency and of frequency stability were made among one Hewlett-Packard 5060A cesium beam, two Varian Associates H-10 atomic hydrogen masers, and the National Bureau of Standards NBS III cesium beam designated as the United States Frequency Standard. Each of the standards displayed a white noise frequency fluctuation behavior with a transition into an approximate flicker of frequency fluctuation behavior for longer time intervals. The rms fractional frequency fluctuation between adjacent samples, ?(?, N = 2), was 6 × 10-11?-1/2 down to a flicker level of about 3×10-13 for the hp 5060A cesium beam (102 ? ? ? 104s), 1 × 10-11?-1/2 down to a flicker level of less than 1×10-13 for NBS III cesium beam (102 ? ? ? 104s), and 5×10-13?-1/2 down to a flicker level of about 1×10-14 for the H-10 hydrogen masers (1 ? ? ? 104s). The accuracy capabilities of NBS III and H-10 #4 are now 1.1×10-12 and 0.47×10-12, respectively (1? estimate). A discrepancy of only 1.1 parts in 1012 was observed between the average frequencies of the hp 5060A cesium beam and the NBS III cesium beam, with the former being higher in frequency. In terms of the frequency of the Cs133 hyperfine transition (F=4, mF = 0)?(F=3, mF = 0), defined as 9 192 631 770.0000 Hertz, the measured frequency of the H1 hyperfine transition (F=1, mF = 0) ?-F = 0, mF = 0) was vH=1 420 405 751.7864±0.0017 Hertz.     

RF Spectrum of a Signal after Frequency Multiplication; Measurement and Comparison with a Simple Calculation

A novel experimental technique is introduced and used to measure the effect of frequency multiplication on the RF spectrum of an oscillator. This technique makes it possible to produce the RF spectrum at X band?where measurements are relatively straightforward?that would have been produced by frequency multiplication of the 5-MHz source to any frequency from 9.2 GHz to 100 THz (1014 Hz). A simplified theory is developed and shown to reproduce the experimental results for the relative power in the carrier and noise pedestal, and the shape and the width of the carrier and noise pedestal, to within the measurement uncertainty of 2 or 3 dB, from 5 MHz to 10 THz. The calculations are easily made using analytical techniques from the measurement of the spectral density of phase fluctuations of the source, the effective input spectrum density and the bandwidth of the multiplier chain, and the frequency multiplication factor. It is shown that present 5-MHz-crystal-controlled oscillators are useful as a precision source to ~500 GHz. Suggestions for extending their range to ~100 THz are made.     

Model for excess noise in voltage-biased superconducting bolometers

We are developing superconducting transition-edge bolometers for far-infrared and millimeter wavelengths. The bolometers described here are suspended by thin legs of silicon nitride for thermal isolation. At frequencies between 200 mHz and 10-50 Hz these devices show white noise at their thermal fluctuation limit (NEP approximately 10(-17) W/ radicalHz). At higher frequencies a broad peak appears in the noise spectrum, which we attribute to a combination of thermal fluctuations in complex thermal circuits and electrothermal feedback. Detailed noise calculations fit the noise measured in three different devices that were specifically designed to test the model. We discuss how changes in bolometer materials can shift the noise peak above the frequency range of interest for most applications.     

Stability and phase noise tests of two cryo-cooled sapphire oscillators

A cryocooled compensated sapphire oscillator (CSO), developed for the Cassini Ka-band Radio Science experiment, and operating in the 7 K-10 K temperature range, was demonstrated to show ultra-high stability of sigma(y)=2.5x10(-15) for measuring times 200 seconds 相似文献