Phase Of Radio Frequency Signal Research Articles

Photonic-assisted RF phase difference detector with full 0° to 360° phase detection capability

A microwave photonic structure for detecting the phase difference of two radio frequency (RF) signals is presented. It is capable of determining the RF signal phase difference unambiguously over the full 0° to 360° range, which overcomes the 0° to 180° phase detection range limitation in the reported structures. The proposed RF phase detector is designed to generate two DC voltages with amplitudes depending on the phase difference of the two input RF signals. An RF signal phase difference in the 0° to 360° range can be obtained from the ratio of the two system output DC voltages. The proposed RF phase detector has a wide operating frequency range, as it is free of microwave components. It overcomes the drawbacks of complex structures, large phase detection errors, limited phase detection range, and limited operating frequency range in the reported photonics-based RF phase detectors. Experimental results are presented that demonstrate 0° to 360° phase difference detection with errors below ±3∘ for different input RF signal frequencies.

전자전 다중 위협 재밍을 위한 멀티빔 송수신장치용 광대역 고출력 송수신모듈 개발

An eight-channel transmit/receive module (TRM) was designed for a wideband electronic warfare multiple threat jamming transceiver. In the system, the TRM amplifies a multijamming signal from a multibeam transceiver module and a small radio frequency (RF) signal from an antenna. In TX mode, it has an output power of more than 43 dBm for a continuous wave. In RX mode, it has a gain of more than 10 dB and noise figure of less than 5 dB. The voltage standing wave ratio is less than 2:1, and the TX and RX path isolation is 50 dBc or more. The RF signal amplitude and phase variation are less than 2 dB and 10°, respectively. True time delay and a digital attenuator are used to compensate for the signal amplitude and phase for each channel.

Angling for angles

Researchers from Australia have presented their novel technique to estimate incoming radio-frequency (RF) signal angles of arrival (AOA), irrespective of the RF signal amplitude. Experimental results show that the AOA measurement can be achieved between 0°–63° with less than 3° of errors for a 15 GHz signal at varying power levels. Identifying the location of an object is extremely important for a number of different applications, including navigation, wireless communication and electronic warfare. The process of identifying an object involves a transmitter, for example a mobile phone or a radar unit, that transmits an RF signal, and a detector device to measure the RF signal. The RF signal reflects off an object and towards the detector. The detector unit can identify the difference in time or phase for the arriving RF signal to when it was transmitted – the angle of arrival. The AOA can then be used to identify the object's location. Chan (left) and Chen (right), authors of the published submission. Correlation between estimated (Y) and actual (X) AOA. The deviation above 60° can clearly be seen. Schematic of the proposed system. Using microwave photonics, the AOA of high-frequency RF signals can be determined, with a reduction in electromagnetic interference as well as system size, weight and power consumption. There are drawbacks to using microwave photonics, however, in that a calibration process involving measuring either system output power at a 0° AOA, or measuring the incoming RF signal amplitude, is necessary to eliminate the RF signal amplitude dependence in the system output prior to measuring the AOA. The work of Chan and Chen is useful because it allows for a measurement of the AOA without the need for measuring the incoming RF signal amplitude, simplifying the process. The new technique works by using a continuously laser-generated wave of light, which is split equally between two modules. Each module comprises one dual-drive Mach Zehnder modulator, an optical bandpass filter and a photodetector. After some phase shifting, the photodetectors eventually generate two DC photocurrents, which can be used to calculate a K value which is a function of the RF signal phase difference. K can then be used to derive the AOA without the need for information about the input RF signal amplitude. Further experiments were carried out using the system. An RF signal of 15 GHz was generated by a microwave signal generator, producing two RF signals with 3.2 dBm power level after the initial splitting between the two modules. It was found that the methodology performed well when the actual AOA was between 0° and ∼60°. The experiment was also repeated with different signal powers of −0.3 dBm and −3.6 dBm, with accurate results being obtained, proving that the AOA can be estimated independent of the RF signal amplitude. With a larger optical carrier suppression, it should be possible to accurately measure the RF signal AOA beyond 60°.

Ripple Suppression in Broadband Microwave Photonic Phase Shifter Frequency Response

This paper presents a detailed investigation on the cause of ripples in the frequency response of a microwave photonic phase shifter implemented using a 90° hybrid coupler. It was found that an unwanted radio frequency (RF) modulation sideband is generated at the modulator output due to the 90° hybrid coupler amplitude and phase imbalance. This resulted in phase shifter output RF signal amplitude variation and phase deviation. Experimental results demonstrated that incorporating an optical filter in the phase shifter structure can reduce the amplitude variation and phase deviation from 4.2 dB to 2.2 dB and from ±12° to ±3.8°, respectively, over a wide frequency range. A comparison of the loss and the dynamic range of the microwave photonic phase shifter implemented using a 90° hybrid coupler with a conventional fiber optic link is also presented.

Chip-Based Brillouin Processing for Phase Control of RF Signals

Manipulating radio frequency (RF) signals in integrated photonic devices has recently emerged as a new paradigm for wireless communications, enabling high-frequency signal processing and broadband frequency agility in miniaturized photonic platforms. These advances are crucial for space and airborne applications which are weight and size sensitive. Recent progress in on-chip stimulated Brillouin scattering (SBS) using high gain has shown great potentials for RF photonic signal processing, owing to its inherent advantages of high resolution, high reconfigurability, and flexible programmability. On-chip SBS serves as a versatile and high-performance toolbox to process and manipulate the amplitude and phase of RF signals in the optical domain. In this paper, we provide a brief overview of recent advances achieved using SBS in planar waveguides, with a focus on applications requiring phase control of RF signals, including phase shifters, delay lines, and separate carrier tuning. We introduce a power-efficient scheme based on the concept of phase amplification to improve Brillouin-based phase processing capability.

FBG wavelength demodulation based on a radio frequency optical true time delay method.

A new fiber Bragg grating (FBG) wavelength shift demodulation method based on optical true time delay microwave phase detection is proposed. We used a microwave photonic link (MPL) to transport a radio frequency (RF) signal over a dispersion compensation fiber (DCF). The wavelength shift of the FBG will cause the time delay change of the optical carrier that propagates in an optical fiber with chromatic dispersion, which will result in the variation of the RF signal phase. A long DCF was adopted to enlarge the RF signal phase variation. An IQ mixer was used to measure the RF phase variation of the RF signal propagating in the MPL, and the wavelength shift of the FBG can be obtained by the measured RF signal phase variation. The experimental results showed that the wavelength shift measurement resolution is 2pm when the group velocity dispersion of the DCF is 79.5ps/nm and the frequency of the RF signal is 18GHz. The demodulation time is as short as 0.1ms. The measurement resolution can be improved simply by using a higher frequency of the RF signal and a longer DCF or larger chromatic dispersion value of the DCF.

Dual-Polarization Dual-Parallel MZM and Optical Phase Shifter Based Microwave Photonic Phase Controller

A new microwave photonic phase controlling structure that can realize a continuously tunable 0 $^{\circ}$ to 360 $^{\circ}$ phase shift using only one DC voltage control is presented. Unlike other phase controlling structures, the radio-frequency (RF) signal phase shift produced by the new phase controller has a predefined linear relationship with the control voltage. This enables users to easily determine the control voltage needed to realize the desired RF signal phase shift. The microwave photonic phase controller is based on an integrated dual-polarization dual-parallel Mach–Zehnder modulator (DPMZM) and a polarization-dependent optical phase shifter. It is suitable for realizing multiple RF signal phase shifts, which are required in beamforming applications. Experimental results are presented which demonstrate the realization of a continuously tunable $-$ 180 $^{\circ}$ to 180 $^{\circ}$ phase shift with little phase and amplitude variations over a wide frequency range, as well as a linear RF signal phase shift to control voltage relationship.

Radio Frequency Beamforming Based on a Complex Domain Frontend

The state-of-the-art phased array-based digital beamforming systems suffer from disadvantages of high power consumption, high cost, and system complexity due to the massive use of transmitter/receiver (T/R) modules and high-speed digital and digital–analog mixed devices. In this paper, we point out that by proposing a new concept “complex domain” radio frequency (RF) frontend, the relatively slowly changed waveform delay information required to accomplish adaptive beamforming can be separated from wideband RF signals, based on which a self-contained beamforming system can be implemented with a low-speed baseband. By introducing vector RF multipliers in the proposed frontend, the amplitude and phase of RF signals can be simultaneously controlled by the real and imaginary parts of complex numbers, such that beamforming algorithms derived in complex domain can be directly applied without any form of transformation. By doing so, the massive use of conventional T/R modules and high-speed baseband devices can be avoided. Theoretical analysis and experimental demonstration based on commercial components have validated the proposed approach. Our method is able to significantly simplify the realization and decrease the cost of wideband digital beamforming systems, and can be widely used in low cost, power efficient beamforming applications.

2π Low Drift Phase Detector for High-Precision Measurements

In modern particle accelerators, radio frequency (RF) phase detectors have to fulfill high demands on stability and accuracy to meet the goals of state-of-the-art synchronization systems. Especially challenging are those cases where the RF signal phase shift accuracy must be measured with fs accuracy for several hours over the full $2 {\pi }$ phase detection range. In these cases special measures on the component’s nonlinearities and RF channel isolation have to be taken. The long-term stability of the phase detector is mostly affected by temperature and humidity variations. To meet the synchronization goals, we have built a phase detector that incorporates a high-speed dual analog-to-digital converter (ADC) with a special circuit for continuous phase drift calibration. In the calibration circuit we successfully combined the RF signal with an RF calibration signal (second tone) to compensate common phase drift that occurs in the microstrip lines, the RF transformers, and the ADC. The second-tone RF signals are directly converted to the digital domain by the fast ADC and, based on signal processing in the field-programmable gate array, are used to calculate the RF signal phase shift correction caused by detector drifts. In this paper, potential error sources of the analog and the digital part of the so-called two-tone calibration technique that limit the phase detector precision are discussed. Finally, the experimental results are presented showing a long-term phase measurement stability better than 0.01 ^\circ \hbox {pk}-\hbox {pk} $ evaluated at an RF frequency of 1.3 GHz over a few days.

Control of the optical carrier to sideband ratio in optical double/single sideband modulation by the phase variation of RF signals

We propose and experimentally demonstrate a novel approach to realize tunable optical carrier-to-sideband ratio (OCSR) by introducing two radiofrequency (RF) signals with phase difference to drive a Mach-Zehnder modulator. Stimulated Brillouin scattering is adopted to remove the undesirable sideband, converting double sideband (DSB) to single sideband (SSB). By altering RF signal phase difference, wide ranges of OCSR from −23 to 44dB and −21 to 44dB are obtained for the DSB and SSB modulation, respectively. The operation frequency bandwidth covers from 5 to 42.3GHz. The optimum OCSR to maximize the output RF power is also presented for the best transmission behavior. The proposed approach will be vital for optimizing the transmission performance by improving modulation efficiency and receiver sensitivity.

Stable fiber delivery of radio-frequency signal based on passive phase correction.

A novel passive phase correction method for stable fiber transfer of radio-frequency (RF) signal is proposed and demonstrated. By employing only one local oscillator and two frequency mixers in the local station, an RF signal received by an optical remote antenna unit is transmitted to the local station with very small phase jitter. An experiment is performed. When a 6GHz RF signal is delivered through a 20km single-mode fiber, effective cancellation of the RF signal's phase jitter induced by environmental perturbations is achieved. The residual jitter is less than 1.33ps (about 0.05rad). The proposed scheme requires no active mechanism to compensate the fiber-length fluctuations, and is thus compact, cost-effective, and easy to implement.

FPGA-based amplitude and phase detection in DLLRF

The new generation particle accelerator requires a highly stable radio frequency (RF) system. The stability of the RF system is realized by the Low Level RF (LLRF) subsystem which controls the amplitude and phase of the RF signal. The detection of the RF signal's amplitude and phase is fundamental to LLRF controls. High-speed ADC (Analog to Digital Converter), DAC (Digital to Analog Converter) and FPGA (Field Programmable Gate Array) play very important roles in digital LLRF control systems. This paper describes the implementation of real-time amplitude and phase detection based of the FPGA with an analysis of the main factors that affect the detection accuracy such as jitter, algorithm's defects and non-linearity of devices, which is helpful for future work on high precision detection and control.

전기광학폴리머 변조기틀 이용한 집적광학적 RF 위상변환기

본 논문에서는 두 개의 중첩된 Mach-Zehnder 구조의 변조기를 이용한 집적광학형 RF 위상변환기를 제안하고, 새로운 전기광학폴리머를 이용하여 제작하였다. 구현된 소자는 RF신호의 위상을 전압에 의하여 연속적으로 제어할 수 있는 특징을 갖는다. 본 논문에서는 16 GHz RF신호의 경우에 대해, 7.8 <TEX>$V_{pp}$</TEX> 제어 전압을 인가하여 약 108<TEX>$^{\circ}$</TEX>범위에서 RF신호의 위상을 거의 선형적으로 변환시킬 수 있었다.다. An integrated photonic radio frequency (RF) phase shifter has been proposed and fabricated using a nested dual Mach-Zehnder modulator configuration in a new electro-optic polymer. The fabricated device shows a continuous voltage control of the RF signal phase. A near-linear phase shift exceeding 108<TEX>$^{\circ}$</TEX>was obtained for a 16-GHz microwave signal by tuning the do control voltage over a 7.8- <TEX>$V_{pp}$</TEX> range.e.