Influence of the amplitude and phase nonlinearity of a spin-wave delay line on the wideband chaotic microwave generation

Regimes of wideband chaotic microwave generation have been studied in a self-oscillating ring system with a nonlinear delay line, in which magnetostatic backward volume waves (MSBVWs) are excited. It is established that a change in length of the delay line influences on its amplitude and phase nonlineartity, thus making it possible to control the characteristics of the chaotic microwave signal generated in the ring. It is demonstrated for the first time that a wideband chaotic microwave signal with a continuous spectrum and a nearly Gaussian probability density distribution can be generated by exciting MSBVWs in a self-oscillating ring system with a nonlinear delay line based on single ferromagnetic film.     

Generation of chaotic microwave pulses in broadband self-oscillating ring system with ferromagnetic film under the action of external pulse-modulated microwave signal

We have experimentally studied specific features of the generation of chaotic microwave pulse trains in a self-oscillating ring system with nonlinear delay line on surface magnetostatic waves, bandpass filter, and power amplifier on GaAs field-effect transistors under the action of an external pulse-modulated microwave signal occurring outside the band of the generated chaotic signal. It is established that a decrease in the off/duty ratio in the external pulse-modulated microwave signal leads to an increase in this ratio for the chaotic microwave pulses. The integral power of the chaotic microwave signal generated under the pulsed external signal action is increased as compared to the power of signal generated in the autonomous regime.     

Planar resonator and integrated oscillator using magnetostatic waves

A simple planar resonator using a magnetostatic wave (MSW) excited by aluminum finger electrodes with two bonding pads was realized on YIG/GGG (yttrium-iron-garnet film on a gadolinium-gallium-garnet crystal) substrate with two reflection edges. The tunable MSW resonator chip (2 mm×5 mm) exhibited a sharp notch filter response, as deep as 20-35 dB, and a high loaded Q up to 2000, which was tunable over the microwave frequency range from 2 to 4 GHz. A small tunable oscillator (8 cm³) was experimentally demonstrated using the MSW planar resonator and a silicon bipolar transistor integrated on a ceramic microwave circuit substrate. Microwave oscillation with spectral purity, at the same level as that of YIG sphere technology, was observed at 3 GHz. The experimental results indicate the technical areas where improvement must be made to realize a practical oscillator configuration     

A microwave photonic generator of chaotic and noise signals

The transition to chaos in a microwave photonic generator has been experimentally studied for the first time, and the generated broadband chaotic microwave signal has been analyzed. The generator represented a ring circuit with the microwave tract containing a low-pass filter and a microwave amplifier. The optical tract comprised a fiber delay line. The possibility of generating chaotic oscillations with uniform spectral power density in a 3–8 GHz range is demonstrated.     

Analysis of Modulation Method for Measuring Atomic Resonant Frequency

In microwave spectroscopy and in atomic frequency standards, the atomic resonant frequency is often determied by the use of harmonic frequency modulation of a microwave signal. The effects of line asymmetry and modulating-signal nonlinear distortions are investigated by the use of an analytic approximation of the resonance line by means of an algebraic polynomial. The coefficients of the polynomial are determined experimentally and also derived theoretically. Detailed numerical results for a Ramsey resonance line in a cesium clock are given.     

Optimum filtration of microwave signals by a multiband spin-wave ring resonator

The optimum filtration of pulsed microwave signals by a multiband active spin-wave ring resonator has been studied for the first time. The ring resonator, which comprises a spin-wave delay line based on a ferromagnetic single crystal film of yttrium iron garnet with a microwave amplifier in the feedback chain, possesses a comblike amplitude-frequency characteristic with a large number of pass bands. It is established that the best filtration of a periodic train of rectangular microwave pulses is achieved provided that harmonics of the signal coincide with the positions of the resonator pass bands. Thus, an active spin-wave ring resonator can be used as the optimum filter for periodic pulsed microwave signals.     

An ultrawideband spin-wave medium-power chaos generator based on field-effect transistors

A prototype of an ultrawideband (UWB) microwave chaos generator based on a nonlinear spin-wave transmission line, a multistage transistor amplifier with an output amplifier based on GaAs field-effect transistors, and a microstrip bandpass filter was constructed. The possibility of autonomous generation of a UWB chaotic microwave signal with a central frequency of 3 GHz and a total power of about 4 W in a frequency band exceeding 30% was demonstrated. The proposed chaos generator is characterized by a fairly high efficiency of about 20%.     

Atomic Clock Using Microwave Pulse-Coherent Techniques

In order to eliminate the light shifts and to increase the stability of gas-cell atomic clocks using optical pumping of the alkali atoms, the detection of a microwave pulse-induced coherent emission is used as the correction signal to lock a crystal oscillator to the atomic transition. Also, the line width of the O-O hyperfine transition is artificially narrowed by subjecting the atoms in the cell to two phase-coherent microwave pulses. In this case the resonance line has a width characteristic of the pulse-repetition frequency which can be made several times smaller than the natural line width in the cell. Proper timing of the sequence of microwave pulses and light pulses for optical pumping is necessary to conserve phase coherence and to obtain a well-defined Ramsey pattern. Results of the tests on a laboratory model using Rubidium-87 atoms show the elimination of the light shifts and an improvement of the short-term stability of the crystal oscillator by one order of magnitude.     

An electroacoustic method for measuring the intensity of high-powermicrowave pulses

A microwave electric field intensity meter for single high-power radiowave pulses is described. A surface acoustic wave (SAW) dielectric acoustic line is used which has nonlinear electroacoustic properties and is comprised of two transducers. The first (nonlinear) transducer is affected by a microwave electric field and provides the SAW excitation due to nonlinear effects. A delayed SAW signal, carrying information about the electric field strength, is received by a linear interdigital transducer     

Design of a microwave multisine source using allpass functionsestimated in the Richards domain

In this paper a low-crest-factor microwave multisine source is developed. This is a broadband, periodic signal with a low crest factor (peak factor to effective value ratio). The design method consists of generating a pulse with a broad spectrum, amplitude filtering to get the desired power spectrum, and phase filtering for lowering the crest factor. A new technique to realize microwave phase filters is described. First, the properties of a rational allpass function in the Richards variable are examined. This enables us to estimate the coefficients using a nonlinear optimization technique, The function is realized with coupled transmission line filters. Using this general technique, a microwave multisine consisting of 20 components in the band [100 MHz, 2 GHz] is realized with a crest factor of 2     

Broadband spin-wave delay lines with slot antennas

A planar spin-wave delay line with slot antennas based on an yttrium iron garnet (YIG) film has been experimentally studied. A specific feature of the proposed device is a relatively large (about 1.8 GHz) microwave bandwidth. Within this band, the signal delay time can be smoothly controlled from 4 to 18 ns. The central frequency can be tuned by an external magnetic field within 5–9 GHz. It is demonstrated that, using slot antennas and relatively thick ferromagnetic films, it is possible to achieve a significant increase in the microwave bandwidth of spin-wave devices.     

Recent Results of a New Microwave SQUID Multiplexer

We present recent results of a prototype microwave SQUID multiplexer containing four SQUIDs coupled to GHz frequency resonant circuits and fed with a single microwave readout line. The system is operating at a readout frequency range of 8–10 GHz. All four SQUIDs share a common DC bias and modulation lines. A new modulation scheme is tested to eliminate the need for individual flux biasing of the SQUIDs, which extends the dynamic range of the readout. In this scheme a common modulation signal is imposed on each SQUID and the received signal is demodulated at one and two times the modulation frequency to maintain sensitivity at any flux state. We also demonstrated a microwave RF bias scheme eliminating the necessity of the DC current bias to the SQUID. Our preliminary performance tests at 4.2 K show that the input noise of the device is ∼5 pA/ .      

Switching atomic fountain clock microwave interrogation signal and high-resolution phase measurements

This paper focuses on the development of tools aiming to solve several problems related to the microwave interrogation signal in atomic fountains. We first consider the problem related to cycle synchronous phase transients caused by the sequential operation of the atomic fountain. To search for such systematic phase variations deeply buried in the microwave synthesizer phase noise, we have developed a novel triggered-phase transient analyzer capable of processing the microwave signal to extract the phase in a synchronous manner even in the presence of frequency modulation. With this device we check in vivo the LNE-SYRTE fountain's interrogation signals with a resolution approaching 1 microradian. In addition, using this device, we investigate an innovative approach to solve a second problem, namely, the shift caused by microwave leakage in the fountain. Our approach consists of switching off the fountain microwave interrogation signal when atoms are outside the microwave cavity. To do that, we have developed a switch that is almost free of phase transients and is thus able to eliminate the frequency shift caused by microwave leakage without inducing significant phase transients on the interrogation signal.     

A TDMA Hybrid SQUID Multiplexer

We have developed a multiplexed read-out for transition-edge sensors (TES) based on a hybrid time- and frequency-domain basis set, similar to that used in time-division multiple-access (TDMA) mobile phones. The hybrid basis set uses bandwidth more efficiently than microwave frequency-division SQUID multiplexing, making it possible to multiplex more detectors in each output line. The high open-loop bandwidth provided by our SQUID TDMA system also makes it possible to multiplex large arrays of fast, high dynamic range detectors such as fast x-ray calorimeters. In this approach, we embed the second-stage SQUID amplifier of our standard time-division multiplexer in an impedance matching circuit coupled to a broadband cryogenic high electron mobility transistor (HEMT) in a microwave reflectometer configuration. The input signals are flux coupled into the first-stage SQUID amplifiers whose signals are time-division multiplexed into the second-stage SQUID. At room temperature, the signal from the HEMT is mixed down to dc for analysis and further signal processing.      

Generation of single chaotic microwave pulses in a self-oscillating ring system with ferromagnetic film under the action of external noise

The generation of single chaotic microwave pulses in a self-oscillating ring system with ferromagnetic film under the action of external narrow-band noise microwave signal occurring outside the band of frequencies of the chaotic microwave signal was observed. Chaotic generation emerged due to the parametric instability of the magnetostatic surface wave in the ferromagnetic film, whereas formation of single chaotic microwave pulses was caused by the absence of complete suppression of chaos under the action of narrowband noise.     

Photonic generation of tunable microwave signal using Brillouin fiber laser

A simple approach to generate two bands of tunable microwave signal is proposed and demonstrated. In this scheme, two single-mode fibers with optimized Brillouin frequency shift spacing have been chosen as the scattering medium in two cascaded ring cavities. Two bands of tunable microwave signal from 390 to 453 MHz and 10.863 to 11.076 GHz can be obtained through adjusting the temperature of the fiber and the pump wavelength. The tunable frequency range can be further expanded by using a temperature controller with a wider adjustment range. The generated microwave signal exhibits high stability on frequency.     

Tunable multi-tap microwave photonic filter with complex coefficients using a dual-parallel Mach–Zehnder modulator

We propose and demonstrate a tunable multi-tap microwave photonic filter (MPF) with complex coefficients. It is based on addition of carrier suppressed single sideband (CS-SSB) signal and phase-controllable optical carrier. Instead of using the technique of optical filtering, the CS-SSB signal is generated by a dual-parallel Mach–Zehnder modulator (DPMZM) in our scheme. Frequency tuning of the filter is achieved by changing the phase of the optical carrier, which can be controlled by a variable optical delay line (VDL). The proposed structure features high flexibility and wideband RF response, and the experimental results demonstrate that it can be tuned continuously over one free spectral range (FSR) without changing the spectral shape of the filter.     

A Portable Microwave Phase and Amplitude Test Set

Phase alignment at microwave frequencies may be made to 0.1° or less, and amplitude balance to 0.1 dB may be made simultaneously with this fully solid-state test set which is designed to be comparable in size and weight to a Tektronix oscilloscope. Provisions are incorporated for testing with either pulsed or CW signals. Present means of measuring phase and amplitude differences at microwave frequencies require either rack size equipments or a group of various pieces of test equipment such as RF generators, standing wave indicators, and slotted lines. Standard procedures are to utilize slotted lines with VSWR sampling points using a short-circuited line or line-swapping arrangement. While these methods are versatile, all have limitations in resolution and accuracy while requiring long setup times and a high degree of skill by the operator. Operating at a single-crystal-controlled microwave frequency, this test set provides a means of continuously comparing two signals, one a reference or standard; the other a signal to be adjusted. The phase and amplitude difference between these two signals may be reduced to a null by adjusting the module under test while observing two zero-center balance meters. The signals may be read to ±3 dB and ±3.0° or ±90° full scale. Accuracy is better than 5 per cent for all scales, and the null resolution is ±0.05 dB and ±0.05°. A self-contained solid-state reference signal generator produces up to 3-watts power output from a balanced varactor double stage at 1296 Mc.     

Effect of MSW source-classified collection on the emission of PCDDs/Fs and heavy metals from incineration in China

Municipal solid waste (MSW) source-classified collection represents a change in MSW management in China and other developing countries. Comparative experiments were performed to evaluate the effect of a newly established MSW source-classified collection system on the emission of PCDDs/Fs (polychlorinated dibenzo-p-dioxins and dibenzofurans) and heavy metals (HMs) from a full-scale incinerator in China. As a result of presorting and dewatering, the chlorine level, heavy metal and water content were lower, but heat value was higher in the source-classified MSW (classified MSW) as compared with the conventionally mixed collected MSW (mixed MSW). The generation of PCDDs/Fs in flue gas from the classified MSW incineration was 9.28 ng I-TEQ/Nm(3), only 69.4% of that from the mixed MSW incineration, and the final emission of PCDDs/Fs was only 0.12 ng I-TEQ/Nm(3), although activated carbon injection was reduced by 20%. The level of PCDDs/Fs in fly ash from the bag filter was 0.27 ng I-TEQ/g. These results indicated that the source-classified collection with pretreatment could improve the characteristics of MSW for incineration, and significantly decrease formation of PCDDs/Fs in MSW incineration. Furthermore, distributions of HMs such as Cd, Pb, Cu, Zn, Cr, As, Ni, Hg in bottom ash and fly ash were investigated to assess the need for treatment of residual ash.     

Microwave losses in electrodes of distributed and lumped ferroelectric-based elements

The microwave losses in electrodes of a ferroelectric-based transmission line and a lumped ferroelectric-based element have been theoretically analyzed. The results of calculations of the effective loss tangent for the transmission line are confirmed by a two-dimensional electrodynamic model analysis and by experiments with a coplanar phase shifter. It is established that the use of microwave devices based on ferroelectric lumped elements is expedient in the 1–50 GHz frequency range (that is, in most microwave applications). The microwave losses in electrodes are significantly lower for lumped elements than for a long transmission line. These losses are determined by the ratio of the depth of electromagnetic field penetration into a conductor (superconductor) to the interelectrode gap width and are independent of the dielectric permittivity.