应用在相控阵雷达上的光学实时延迟线

相控阵天线是雷达技术的重要发展方向之一。电子相控阵雷达所遇到的问题是天线阵列孔径效应限制了雷达信号的瞬时带宽,使其不能满足通信和雷达技术的发展需要。光学实时延迟技术,可以解决这一问题。介绍了相控阵天线光实时延迟控制原理。并对几种典型的光实时延迟线的工作原理和技术特点作了简要的分析。     

All chirped fiber grating based true-time delay for phased-array antenna beam forming

We have demonstrated a continuous phased-array antenna beam former based on a variable photonics true-timedelay unit consisting of four chirped gratings. The system is suitable for the phased-array antenna beam forming at frequencies up to 20 GHz.This revised version was published online in August 2005 with a corrected cover date.     

Statistical characteristics of adaptive antenna arrays

Using the method of successive approximations, we obtain expressions for the spectral and correlation characteristics of the output signal of adaptive antenna arrays under the stationary operation regime in the first-order approximation, which is also called Born’s approximation. We show that the fluctuations of the weight coefficients result in distortions of the output-signal spectrum, such as its broadening and the appearance of a “trough” in a band that is somewhat narrower than the input-signal spectrum width. N. I. Lobachevsky State University, Nizhniy Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 10, pp. 1013–1024, October 1999.     

X-band continuously variable true-time delay lines using air-guiding photonic bandgap fibers and a broadband light source

We propose a novel implementation of true-time delay (TTD) using air-guiding photonic bandgap fibers (PBGFs) and a broadband light source. The air-guiding PBGFs are experimentally studied and used in the TTD module for the first time, to the best of our knowledge. The proposed approach shows the advantages of simple architecture, compact size, larger dispersion, low-temperature sensitivity, and high immunity to nonlinear effects in our experiments. The PBGFs were spliced with single-mode fibers with a 2 dB loss, and the characteristics of the PBGFs were measured. The PBGF-TTD with a continuously tunable time delays from 0 to 500 ps was demonstrated using the amplified spontaneous emission light of an erbium-doped filter amplifier as a broadband light source.     

Wide-band nulling system for antenna array based on a photonic microwave filter and optical delay lines

A nulling system for phased array antennas with broad bandwidth and reduced complexity is presented. The system is based on combining the output of an optical beamforming network with an optical transversal filter steered in the angle where a null is desired in a configuration that reduces the number of optoelectronic conversion compared to previous proposals. Preliminary experimental results to show the feasibility of the concept are provided between 2 and 6 GHz, showing null depths of 22, 10 and 19 dB at 2, 5 and 6 GHz, respectively.     

Efficiency of signal processing for spatially distributed sources in adaptive antenna arrays

The potential efficiency of signal processing for spatially distributed noise sources in adaptive antenna arrays is analyzed. The behavior of the output signal-to-noise ratio is studied as a function of the transverse space correlation radius, the antenna aperture, and the noise power.Nizhni Novgorod State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 6, pp. 512–519, June, 1993.     

Stable wavelength tunable fiber ring laser for true-time delay system

In this paper, we propose and experimentally demonstrate a novel wavelength tunable fiber ring laser source for a photonic beamforming system to control phased-array antenna. In this fabrication, a Sagnac loop composed of a polarization-maintaining (PM) coupler and a piece of high-birefringence (Hi-Bi) PM fiber is acted as a comb filter to make the frequency spacing equal. The wavelength of the output signal is controlled by the tunable filter outside the Sagnac loop. The intensities of the output signals with different wavelengths increased or decreased at the same frequency spacing are equal. A five-channel true-time delay system consisting of this tunable fiber source and five grating delay lines for discrete beamsteering has been demonstrated. In the experiment, the output signals of the tunable fiber ring with the equal frequency spacing have the same intensity of about 5.9 dBm and the same high signal to noise ratio (SNR) of 40 dB. If the tunable filter in this laser is replaced by a micro-electro-mechanical systems (MEMS) tunable filter, the speed of switching wavelength will increase rapidly.     

Analysis of interference cancellation techniques in OFDMA systems employing adaptive antenna arrays

We analyze the problem of interference cancellation in OFDMA cellular communication systems employing adaptive antenna arrays at the receiver and operating in the channels with frequency-selective fading and interference from the neighboring base stations. This problem is very important for modern broadband cellular systems operating with a low coefficient of multiple use of frequencies. Under such conditions of the network deployment, the system efficiency is restricted by the level of intrachannel interference from the neighboring base stations transmitting in the same frequency channel. In this work, we analyze different methods for measuring the interference characteristics and using them for spatial processing of received signals. Five different methods for signal processing in an adaptive antenna array of the receiver are discussed. Each approach (reception method) has its own interference immunity and complexity degree. Comparative analysis of the interference immunity of the considered receivers has been performed for different frequency-channel loads and different numbers of interfering stations. Recommendations for using the considered receivers are given.     

Photonic crystal fiber design for broadband directional coupling

A novel design for a broadband directional coupler based on a photonic crystal fiber is investigated numerically. It is shown that suitable index-depressing doping of the core regions in an index-guiding twin-core photonic crystal fiber can stabilize the coupling coefficient between the cores over an extremely broad (octave-spanning) frequency range.     

Weight vector fluctuations in adaptive antenna arrays with nonlinear function in a feedback loop

We present the results of statistical analysis of adaptive antenna arrays with nonlinear function in the feedback loop, which are adjusted by an algorithm for recurrent inversion of a sample estimate of the input-signal correlation matrix with allowance for the weight-coefficient fluctuations. Using the perturbation-theory methods in the first (Born) approximation, we obtain expressions for the correlation function and power of the output signal of an adaptive antenna array and a formula for the covariance matrix of the weight-coefficient vector. The weight-coefficient fluctuations are shown to result in signal distortions at the antenna-array output and appearance of additional terms in the statistical characteristics of the antenna array. These terms are second-order infinitesimals with respect to adaptation coefficient. Fluctuations are first-order infinitesimals and, thus, are much greater in an antenna array without nonlinear function in the feedback loop. It is also shown that the weight-vector fluctuations are anisotropic, i.e., they are absent in the constraint direction, minimal in the interference direction, and maximal in all other directions. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 2, pp. 164–172, February 2006.     

Optimal array pattern synthesis for broadband arrays

Broadband beamformers with constant mainlobe response over the frequency of interest are desirable in many applications including underwater acoustics, ultrasonics, acoustic imaging and communications, and so on. Solutions to this problem have been presented for specific array geometry often requiring a larger number of sensors. And the array pattern synthesis error minimization is employed for the whole field of view, which leads to suboptimal designs. In this paper, a broadband array pattern synthesis approach to designing time-domain constant mainlobe response beamformer is proposed. By imposing constraints both on the mainlobe spatial response variation over frequency and on the sidelobes of the beamformer, several optimization criteria are presented and the corresponding convex second-order cone programming implementations are given. In this approach, no preliminary desired beampattern is required and the beam responses variation minimization is employed only in the mainlobe region and not in the sidelobe regions, which improves the beamformer mainlobe synthesis accuracy. Equally, one can obtain lower sidelobes at the same mainlobe synthesis accuracy. This approach is applicable to arrays with arbitrary geometry. Simulation and experimental results are presented to illustrate the effectiveness of this approach. Performance comparisons of the proposed beamformers and the existing beamformer are also provided.     

Determining direction to a source of correlated signals,using adaptive antenna arrays

Gor'kii State University. Translated from Izvestiya Vysshikh Zavedenii, Radiofizika, Vol. 33, No. 6, pp. 719–725, June, 1990.