Ultra-Low Phase Noise Frequency Division With Array of Direct Digital Synthesizers.

In this article, we present a four-channel direct digital synthesis (DDS) design that operates with a common clock ranging from 500 MHz to 24 GHz and generates output frequencies up to 1.75 GHz. A key feature of this board is its custom field-programmable gate array (FPGA)-based synchronization method, which ensures alignment accuracy of 170 ps between the channels, enabling precise frequency and phase relationship settings.

Ultralow PM and AM Noise Generation With an Ensemble of Phase-Coherent Oscillators.

This article investigates the performance of an array of multiple phase-coherent power-combined oscillators (PPOs) in terms of phase modulation (PM) noise and amplitude modulation (AM) noise. The array consists of six individual oscillator modules that generate three distinct frequencies: 10, 100 MHz, and 1 GHz. By meticulously aligning the phases, we observed a notable improvement of approximately 7.

Continuous-capture microwave imaging.

Light-in-flight sensing has emerged as a promising technique in image reconstruction applications at various wavelengths. We report a microwave imaging system that uses an array of transmitters and a single receiver operating in continuous transmit-receive mode. Captures take a few microseconds and the corresponding images cover a spatial range of tens of square meters with spatial resolution of 0.

W -Band Vibrometer for Noncontact Thermoacoustic Imaging.

Noncontact thermoacoustic imaging (TAI) has several desirable characteristics for applications such as explosive detection in high-water-content media. In this letter, we report a detection technique using millimeter-wave interferometry based on sensitive phase detection at W -band. The displacement sensitivity of the proposed W -band vibrometer at 95 GHz is of the order of 1 nm.

Phase noise measurements with a cryogenic power-splitter to minimize the cross-spectral collapse effect.

The cross-spectrum noise measurement technique enables enhanced resolution of spectral measurements. However, it has disadvantages, namely, increased complexity, inability of making real-time measurements, and bias due to the "cross-spectral collapse" (CSC) effect. The CSC can occur when the spectral density of a random process under investigation approaches the thermal noise of the power splitter.

Oscillator PM Noise Reduction From Correlated AM Noise.

We demonstrate a novel technique for reducing the phase modulation (PM) noise of an oscillator in a steady-state condition as well as under vibration. It utilizes correlation between PM noise and amplitude modulation (AM) noise that can originate from the oscillator's loop components. A control voltage proportional to the correlated AM noise is generated and utilized in a feedforward architecture to correct for the steady state as well as the vibration-induced PM noise.

PM noise measurement at W-band.

We report a high-performance 92 to 96 GHz cross-spectrum phase modulation (PM) noise measurement system. Utilizing this system, we measured residual PM noise of several amplifiers, mixers, and frequency multipliers. Data for the measurement system noise floor and the PM noise of W-band components are reported.

An integrated low phase noise radiation-pressure-driven optomechanical oscillator chipset.

High-quality frequency references are the cornerstones in position, navigation and timing applications of both scientific and commercial domains. Optomechanical oscillators, with direct coupling to continuous-wave light and non-material-limited f × Q product, are long regarded as a potential platform for frequency reference in radio-frequency-photonic architectures. However, one major challenge is the compatibility with standard CMOS fabrication processes while maintaining optomechanical high quality performance.

State-of-the-art RF signal generation from optical frequency division.

We present the design of a novel, ultralow-phase-noise frequency synthesizer implemented with extremely-low-noise regenerative frequency dividers. This synthesizer generates eight outputs, viz. 1.

Photonic microwave generation with high-power photodiodes.

We utilized and characterized high-power, high-linearity modified unitraveling carrier (MUTC) photodiodes for low-phase-noise photonic microwave generation based on optical frequency division (OFD). When illuminated with picosecond pulses from a repetition-rate-multiplied gigahertz Ti:sapphire modelocked laser, the photodiodes can achieve a 10 GHz signal power of +14 dBm. Using these diodes, we generated a 10 GHz microwave tone with less than 500 attoseconds absolute integrated timing jitter (1 Hz-10 MHz) and a phase noise floor of -177 dBc/Hz.

Ultra-low-noise regenerative frequency divider.

We designed ultra-low-noise regenerative divide-by- 2 circuits that operate at input frequencies of 10, 20, and 40 MHz. We achieved output-referred single-sideband residual phase noise equal to -164 dBc/Hz at 10 Hz offset and estimated residual Allan deviation, σ(y)(τ) less than 3 × 10(-15)τ(-1) for a single divider, which is, to our knowledge, the lowest noise of any divider ever reported at these frequencies. To measure such a low noise, we also built a cross-spectrum measurement system that has a noise floor of -175 dBc/Hz at 10 Hz offset from the carrier frequency.

Vibration-induced PM and AM noise in microwave components.

The performance of microwave components is sensitive to vibrations to some extent. Aside from the resonator, microwave cables, and connectors, bandpass filters, mechanical phase shifters, and some nonlinear components are the most sensitive. The local oscillator is one of the prime performance-limiting components in microwave systems ranging from simple RF receivers to advanced radars.

Merits of PM noise measurement over noise figure: a study at microwave frequencies.

This paper primarily addresses the usefulness of phase-modulation (PM) noise measurements versus noise figure (NF) measurements in characterizing the merit of an amplifier. The residual broadband (white PM) noise is used as the basis for estimating the NF of an amplifier. We have observed experimentally that many amplifiers show an increase in the broadband noise of 1 to 5 dB as the signal level through the amplifier increases.

High spectral purity microwave oscillator: design using conventional air-dielectric cavity.

We report exceptionally low PM noise levels from a microwave oscillator that uses a conventional air-dielectric cavity resonator as a frequency discriminator. Our approach is to increase the discriminator's intrinsic signal-to-noise ratio by use of a high-power carrier signal to interrogate an optimally coupled cavity, while the high-level of the carrier is suppressed before the phase detector. We developed and tested an accurate model of the expected PM noise that indicates, among other things, that a conventional air-dielectric resonator of moderate Q will exhibit less discriminator noise in this approach than do more esoteric and expensive dielectric resonators tuned to a high-order, high-Q mode and driven at the dielectric's optimum