R EIEW A R TCLE Abstract As an emerging topic, photonic-assisted microwave measurements with distinct features such as wide frequency coverage, large instantaneous bandwidth, low frequencydependent loss, and immunity to electromagnetic interference, have been extensively studied recently. In this article, we provide a comprehensive overview of the latest advances in photonic microwave measurements, including microwave spectrum analysis, instantaneous frequency measurement, microwave channelization, Doppler frequency-shift measurement, angle-of-arrival detection, time–frequency analysis, compressive sensing, and phase-noise measurement. A photonic microwave radar, as a functional measurement system, is also reviewed. The performance of the photonic measurement solutions is evaluated and compared with the electronic solutions. Future prospects using photonic integrated circuits and software-defined architectures to further improve the measurement performance are also discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.201600019

Photonics for microwave measurements

As the only method for all-weather, all-time and long-distance target detection and recognition, radar has been intensively studied since it was invented, and is considered as an essential sensor for future intelligent society. In the past few decades, great efforts were devoted to improving radar's functionality, precision, and response time, of which the key is to generate, control and process a wideband signal with high speed. Thanks to the broad bandwidth, flat response, low loss transmission, multidimensional multiplexing, ultrafast analog signal processing and electromagnetic interference immunity provided by modern photonics, implementation of the radar in the optical domain can achieve better performance in terms of resolution, coverage, and speed which would be difficult (if not impossible) to implement using traditional, even state-of-the-art electronics. In this tutorial, we overview the distinct features of microwave photonics and some key microwave photonic technologies that are currently known to be attractive for radars. System architectures and their performance that may interest the radar society are emphasized. Emerging technologies in this area and possible future research directions are discussed.

/pdf/microwave-photonic-radars-1mv4ppmi12.pdf

Microwave Photonic Radars

A compact means to separate microwave and millimeter-wave optical signals by RF frequency in real time is demonstrated. The approach is to employ an integrated optical Bragg grating Fabry-Perot (BGFP) device to spatially separate optically modulated microwave signals with high resolution. The compactness is achieved through the use of an integrated optical hybrid diffractive lens beam expander to provide the required optical wavefront to the BGFP. A proof-of-principle measurement was performed from 1 to 23 GHz with peak finesse of 27. The theoretical analysis, fabrication procedure, experimental results, limitations, and improvements are described.

/pdf/a-microwave-channelizer-and-spectroscope-based-on-an-emz3qfi2rl.pdf

A microwave channelizer and spectroscope based on an integrated optical Bragg-grating Fabry-Perot and integrated hybrid Fresnel lens system

In this paper, a novel photonic-assisted broadband and high-resolution radio-frequency (RF) channelization scheme based on dual coherent optical frequency combs (OFCs), regular optical de-muxes, and I/Q demodulators is analyzed and experimentally demonstrated. The use of two coherent combs avoids precise optical alignment, and a numerical filter in digital signal processor (DSP) enables an ideal rectangular frequency response in each channel without any ultranarrow optical filters. Besides, due to the use of I/Q demodulators, ambiguous frequency estimate in direct detection is avoided. By using two coherent OFCs with the free spectrum range (FSR) of about 40 GHz, we experimentally demonstrate the channelization scheme with seven channels, 500-MHz channel spacing, and frequency coverage from 3.75 to 7.25 GHz. The input RF tones are accurately downconverted to an intermediate frequency (IF) with a maximum frequency error of 125 kHz. Meanwhile, the channel frequency response and crosstalk of the scheme are also evaluated experimentally.

Broadband Photonic RF Channelization Based on Coherent Optical Frequency Combs and I/Q Demodulators

An approach is presented to realizing a digital channelized receiver for signal intercept applications that provides a hardware efficient implementation of a uniform filter bank in which the number of filters K is greater than the decimation factor M. The proposed architecture allows simple channel arbitration logic to be used and provides reliable instantaneous frequency measurements, even in adjacent channel crossover regions. In the proposed implementation of the filter bank, K is related to M by K=FM where F is an integer. It is shown that the optimum selection of F allows the instantaneous frequency measurement to be made in the channel crossover region and the arbitration function to be based solely on the instantaneous frequency measurement. The development of a filter bank structure which combines the flexibility of the short-time Fourier transform (STFT) with the implementation efficiency of the polyphase filter bank decomposition, meeting these requirements and leading to a hardware-efficient implementation, is presented.

A hardware-efficient, multirate, digital channelized receiver architecture

An overview of the channelization function, the parallel signal processing techniques used in channelizers, the signal processing functions, and the critical channelizer parameters is given. Signal processing capabilities that use analog techniques suitable for channelized receivers are compared with those capabilities that can be obtained by using current or foreseen digital techniques. The receiver signal-processing needs are outlined, and the limitations of digital signal processing in terms of the overall receiver signal processing needs are discussed. Options and tradeoffs at the receiver and channelizer technology levels are discussed. Promising channelizer technologies, including components, that have been or potentially may be implemented with small volumes and moderate dynamic range are described. Parallel signal-processing methods, architectural techniques, and hardware for channelized receiver technologies that can be implemented in a small volume (tens of channels per in/sup 3/) with a moderately high dynamic range (>50 dB) are discussed. These include the surface-acoustic-wave (SAW), bulk-acoustic-wave (BAW), magnetostatic-wave (MSW), and acoustooptical (AO) channelizer technologies. The critical signal preprocessing functions required in channelized receivers before the needed information is passed on to the host computer, so that the host computer can be operated at a possible computation rate, are discussed, and the first successful monolithic integrated circuit preprocessor component for channelizers, is presented. >

Advanced channelization for RF, microwave, and millimeterwave applications

Advanced channelization technology for RF, microwave, and millimeterwave applications

An improved optical technique for electrical phase measurement has been developed at the Naval Research Laboratory under ARPA sponsorship. The approach has been demonstrated in an rf interferometer application and its performance evaluated under condition of direct rf injection and free-space irradiation. Test results indicate high-accuracy angle of arrival and low probability of ambiguity was achieved. This paper describes the phase measurement concept, implementation into the NRL Precision Direction Finding Receiver brassboard unit, calibration techniques, automated test software, and measurement results.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Superresolution precision direction-finding techniques and measurements

The Acousto-Optic Precision Direction Finding (AOPDF) system is a demonstration EW receiver in development at the Naval Research Laboratory as a DARPA sponsored activity. A two-dimensional Acousto-Optic processing element extracts frequency, angle of arrival (AOA), and time of arrival (TOA) on a pulse-by-pulse basis. Performance advantages achieved through use of Acousto-Optic technology include a wide instantaneous RF bandwidth, multiple simultaneous signal capture, and accurate AOA measurement over a quadrant field of view. This paper describes the conceptual design, system development, and evaluation of a demonstration unit based on the AOPDF concept.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Acousto-optic precision direction-finding system

The EW channelizer and PDF were developed under the ARPA TOPS program to satisfy broad electronic warfare systems demands. This paper describes EW system architectures and the functions the TOPS EW channelizer and PDF processor performs in these systems. EW system architectures examined includes Ships Early Warning, airborne Surveillance, Weapons, and Airborne Warning. In addition, functional descriptions of the EW and PDF processors are provided.

Electronic warfare (EW) channelizer and precision direction-finder(PDF) applications

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