有源相控阵雷达天线测试实现与优化

天线测试设计是有源相控阵雷达设计中重要组成部分。相较于传统的无源天线测试设计,有源相控阵雷达天线测试是雷达与采样系统异源同步测试过程,需要解决移相码测试和两个系统间时序同步的问题。本文分析和实现了有源相控阵雷达的测试并对其进行优化。使用优化前后两种方法对同一型号雷达进行实测,测试结果基本一致,优化方法测试时间仅为原方法的11%。

平面阵相控阵天线的阵面指向角度算法实现

对平面阵相控阵天线的阵面指向角度算法进行了研究。通过坐标转换及空中载体位置矢量和卫星位置矢量,计算卫星在天线本体坐标中的表示,并依此进一步计算天线方位角、俯仰角;根据平面阵移相码计算公式计算出最终的移相码发给T组件,使得天线能够实时指向中继星,完成遥测信号的传输。研究对空中载体使用相控阵天线传输遥测信号有一定的参考价值。

DIFFERENTIAL AMPLITUDE PHASE SHIFT KEYING: A NEW MODULATION METHOD FOR TURBO CODE IN DIGITAL RADIO BROADCASTING

The multilevel modulation techniques nf M-Differential Amplitude Phase Shift Keying (DAPSK) have been proposed in combination with Turbo code scheme for digital radio broadcasting bands below 30 MHz radio channel. Comparison of this modulation method with channel coding in an Additive White Gaussian Noise (AWGN) and multi-path fading channels has been presented. The analysis provides an iterative decoding of the Turbo code.

Multiple phase detector of M-ary phase shift keying symbols in code division multiple access systems

A novel iterative technique, the phase descent search detection was proposed. This technique constrained the solution （PDS） algorithm, for M-ary phase shift keying （M-PSK） symbols to have a unit magnitude and it was based on coordinate descent iterations where coordinates were the unknown symbol phases. The PDS algorithm, together with a descent local search （also implemented as a version of the PDS algorithm）, was used multiple times with different initializations in a proposed multiple phase detector; the solution with the minimum cost was then chosen as the final solution. The simulation results show that for highly loaded multiuser scenarios, the proposed technique has a detection performance that is close to the single-user bound. The results also show that the multiple phase detector allows detection in highly overloaded scenarios and it exhibits near-far resistance. In particular, the detector has a performance that is significantly better, and complexity that is significantly lower, than that of the detector based on semi-definite relaxation.

THE PHASE-OFFSET OVERLAPPED WAVE TECHNIQUE

A new digital communication technology based on the Phase-Offset Overlapped Waves (POOW) has been introduced in this letter. The waves can be considered as a special multicarrier different from traditional ones. The sub-waves in a coded word's period of the POOW are sine waves and have the same frequencies, but different starting phases. The most important characteristic is that these sub-waves are the piecewise functions and not orthogonal in a code word period. The decoding can be implemented by solving a linear equation group. This code has very high efficiency and thus the data transmission rate is increased greatly.

RADAR HRR PROFILING FOR GROUND MOVING TARGET USING PHASE-CODED AND HOPPED-FREQUENCY WAVEFORMS

To obtain the radar High Range Resolution (HRR) profile of the slowly moving ground target in strong clutter background, the Phase-Coded Hopped-Frequency (PCHF) waveform is proposed. By multiple-bursts coherent processing, the HRR profile synthesis, target velocity compensation and clutter compression can be accomplished simultaneously. The new waveform is shown to have good ability to suppress ground clutter and good Electronic Counter-CounterMeasures (ECCM) ability as well. The clutter compression performance of the proposed method is verified by the numerical results.

Multiparameter least-squares reverse time migration for acoustic–elastic coupling media based on ocean bottom cable data

In marine seismic exploration,ocean bottom cable technology can record multicomponent seismic data for multiparameter inversion and imaging.This study proposes an elastic multiparameter lease-squares reverse time migration based on the ocean bottom cable technology.Herein,the wavefield continuation operators are mixed equations:the acoustic wave equations are used to calculate seismic wave propagation in the seawater medium,whereas in the solid media below the seabed,the wavefields are obtained by P-and S-wave separated vector elastic wave equations.At the seabed interface,acoustic–elastic coupling control equations are used to combine the two types of equations.P-and S-wave separated elastic migration operators,demigration operators,and gradient equations are derived to realize the elastic least-squares reverse time migration based on the P-and S-wave mode separation.The model tests verify that the proposed method can obtain high-quality images in both the P-and S-velocity components.In comparison with the traditional elastic least-squares reverse time migration method,the proposed method can readily suppress imaging crosstalk noise from multiparameter coupling.

Generalized Maximum Likelihood Noncoherent Block Detection for Decode-and-Forward Relay Systems

This paper considers noncoherent cooperative decode-and-forward(DF) halfduplex multi-branch relay systems.Each relay branch is modeled as a probabilistic transition system at the last hop,and thus it can be considered as a relaying chain comprising multi-hop relays.An approximation to the generalized maximum likelihood(ML) noncoherent block detection is derived for uncoded M-ary modulation in a faded noisy environment.In particular,the derived noncoherent block detection in a noiseless case is equivalent to a multichannel reception with full diversity.Furthermore,the generalized detection is extended specifically to block coded M-ary phase shift keying(MPSK) modulation.For a DF three node relay system using block coded quadrature phase shift keying(QPSK),simulation results are provided to examine the end-to-end error performance of the noncoherent detection with considering the effects of network geometry and power allocation,respectively.It is shown that under a fixed power allocation,a proper relay placement can yield near full diversity for large signal-to-noise ratio.

Performance of M-QAM, M-DPSK and M-PSK with MRC diversity in a Nakagami-m fading channel

The nature of a wireless communication channel is very unpredictable. To design a good communication link, it is required to know the statistical model of the channel accurately. The average symbol error probability(ASER) was analyzed for different modulation schemes. A unified analytical framework was presented to obtain closed-form solutions for calculating the ASER of M-ary differential phase-shift keying(M-DPSK), coherent M-ary phase-shift keying(M-PSK), and quadrature amplitude modulation(QAM) over single or multiple Nakagami-m fading channels. Moreover, the ASER was estimated and evaluated by using the maximal ratio-combining(MRC) diversity technique. Simulation results show that an error rate of the fading channel typically depends on Nakagami parameters(m), space diversity(N), and symbol rate(M). A comparison between M-PSK, M-DPSK, and M-QAM modulation schemes was shown, and the results prove that M-ary QAM(M-QAM) demonstrates better performance compared to M-DPSK and M-PSK under all fading and non-fading conditions.

Measuring the kinetic parameters of saltating sand grains using a high-speed digital camera

A high-speed digital camera is used to record the saltation of three sand samples(diameter range:300–500,200–300 and100–125μm).This is followed by an overlapping particle tracking algorithm to reconstruct the saltating trajectory and the differential scheme to abstract the kinetic parameters of saltating grains.The velocity results confirm the propagating feature of saltation in maintaining near-face aeolian sand transport.Moreover,the acceleration of saltating sand grains was obtained directly from the reconstructed trajectory,and the results reveal that the climbing stage of the saltating trajectory represents an critical process of energy transfer while the sand grains travel through air.