A data-gathering antenna array for transhorizon propagation research

A versatile vertical antenna array and receiving system have been developed for measuring relative phase and amplitude along the wavefront of anS-band transhorizon signal. The array, which operates at 3.200 GHz, consists of 12 parabolic antennas 1.22 meters (4 feet) in diameter which are spaced 1.39 meters apart on a tower for a total effective vertical aperture of 15.24 meters (162 lambda). The raw data outputs from the array are amplitude and differential phase successively sampled from the 12 elements. Data can be taken at variable rates of up to 100 passes per second over the 12 elements. The data are processed in a computer to form conventional uniformly illuminated array beams 0.3 degree wide with a grating lobe spacing of 3.9 degrees or to produce many combinations of correlation functions. A reference signal is used to cancel the effects of relative motion of the array support structure from the phase data. The array and receiving system and actual performance characteristics are described.     

A method for fast amplitude detection of variable period sinusoidal signals

In this work a method for fast detection of sinusoidal signal amplitude of variable period is proposed. Information for the signal amplitude is taken with several sample pulses in each half period with the aid of a multiplier and a differentiator. The sampled signal values are held and equalized with the signal amplitude by a weighting amplifier.     

移动卫星通信终端天线极化跟踪研究

针对移动通信终端天线的极化失配损失问题,利用两个正交线极化天线结合相应的馈电网络实现了任意方向的线极化波,用于移动状态下的天线极化跟踪。提出了通过控制两个正交线极化天线的相位差来接收任意线极化波的方法,并给出了相位差与极化角的关系。当两个正交线极化天线增益及其对应通道间的幅度和相位均相同时,接收到的信号强度随相位差的变化而作余弦,且当相位差ψ为2θ-π2时,信号强度有最大值。基于该方法进行理论仿真,并得到了极化跟踪曲线,与测试结果相比,吻合良好。将该方法应用到卫星通信移动终端,在运动过程中信号稳定,未出现明显极化失配现象,验证了该算法的有效性。     

用于室内无线通信的新型多波束天线阵列

本文提出了一种低剖面、低成本的多波束天线阵列的设计方法。与传统的切换多波束天线设计相比,新设计可以在不切换的情况下同时实现多个波束。多波束由一个简单的馈电网络实现,馈电网络的激励分配由最大功率传输效率法和加权对角矩阵确定。通过调整测试接收天线的加权系数,可以实现8个方向不同辐射强度的多个波束。天线的工作中心频率为5.8 GHz,天线系统主要由辐射部分和馈电部分组成,分别置于两个不同的堆叠基板上,通过同轴馈电。利用八波束共存的优势,可提供全面覆盖和改进链路预算,适用于双向隧道或室内使用的无线通信系统。     

相位加权阵列天线的互耦分析及补偿

采用分段正弦基函数Galerk in法计算了阵列天线的阻抗矩阵,利用互耦阻抗方程分析了相位加权阵列的幅相恶化程度,且用矩量法分析了互耦对两种相对加权阵列天线性能的影响。提出了一种互耦补偿的方法即网络分析法,仿真结果表明了这种补偿方法的正确性和有效性。     

Multiple-pattern linear antenna arrays with single prefixedamplitude distributions: modified Woodward-Lawson synthesis

The authors describe the design of linear antenna arrays that generate multiple radiation patterns by switching between different excitation phase distributions while maintaining a constant pre-established amplitude distribution. Examples are given of antennas with uniform or Gaussian amplitude distributions that, depending on their phase distribution, generate a sum pattern, a flat-topped beam or a cosec-squared pattern     

Photonic RF phase shifter and tunable photonic RF notch filter

A new photonic RF phase shifter structure for phased array antennas is presented. It is based on a single dual-output modulator and two optical switches and optical attenuators. This can realize continuous phase shifting of 0/spl deg/-360/spl deg/ without altering the signal amplitude. It has the advantages of wide bandwidth, fast response time, and fine tuning resolution. Experimental results demonstrate phase shifts over a 360/spl deg/ phase range, with RF signal power changes of less than 0.2 dB, which is in close agreement with predictions. A tunable photonic RF notch filter, which is based on the new phase shifter, is also presented. Experimental results demonstrate continuous tuning of the photonic notch filter over a wide tuning range, which covers the full free spectral range, which is in good agreement with predictions.     

一种TDM-MIMO雷达的运动目标相位补偿方法

汽车雷达主要使用时分复用多输入多输出技术(TDM-MIMO)增加其虚拟天线数量来提高角度分辨率。当目标与雷达之间存在相对运动时,由运动目标多普勒频率在不同发射天线切换时间内带来的相位变化量会耦合到各接收天线上,导致频谱出现散焦效应。这种相位变化会对目标的角度估计产生影响。针对这种问题,推导了TDM-MIMO信号模型,通过分析运动目标相位误差产生的原因,提出了一种相位补偿方法,该方法无需对目标速度进行预估,并且无需额外的硬件开销。通过仿真实验和实测数据证明了该方法可以使运动目标正常测角并且具有较低的时间复杂度。     

Circular polarised microstrip patch antennas for broadband and dual-band operation

A novel design of microstrip patch antennas for circular polarisation (CP) is proposed. As an example, two CP patch antennas are investigated: a broadband CP patch antenna and a dual-band CP patch antenna. The proposed structure can be achieved by embedding circular holes in the microstrip circular resonator. By changing the size and position of loaded holes, two orthogonal modes are simultaneously excited with equal amplitude and /spl plusmn/90/spl deg/ out of phase. Without any 90/spl deg/ phase-shifter, the proposed CP patch antennas are excited by single feed.     

A Discrete‐Amplitude Pulse Width Modulation for a High‐Efficiency Linear Power Amplifier

A new discrete‐amplitude pulse width modulation (DAPWM) scheme for a high‐efficiency linear power amplifier is proposed. A radio frequency (RF) input signal is divided into an envelope and a phase modulated carrier. The low‐frequency envelope is modulated so that it can be represented by a pulse whose area is proportional to its amplitude. The modulated pulse has at least two different pulse amplitude levels in order that the duty ratios of the pulse are kept large for small input. Then, an RF pulse train is generated by mixing the modulated envelope with the phase modulated carrier. The RF pulse train is amplified by a switching‐mode power amplifier, and the original RF input signal is restored by a band pass filter. Because duty ratios of the RF pulse train are kept large in spite of a small input envelope, the DAPWM technique can reduce loss from harmonic components. Furthermore, it reduces filtering efforts required to suppress harmonic components. Simulations show that the overall efficiency of the pulsed power amplifier with DAPWM is about 60.3% for a mobile WiMax signal. This is approximately a 73% increase compared to a pulsed power amplifier with PWM.     

相位量化DRFM性能分析

本文提出了一种数字射频存储器(DRFM)偏移相位量化方法,它是在传统相位量化方法的基础上通过增加一个相位偏移而得到.通过傅立叶分析,得到了其谐波寄生信号性能计算公式,结果表明,其性能与传统相位量化方法相同.其优点是,由于其良好的对称性,更适合于硬件电路实现.在此基础上,提出了一种用D/A变换器代替加权求和网络实现相位量化DRFM信号重构的新方法,解决了多位相位量化DRFM工程实现的困难.采用计算机仿真方法对由于D/A变换幅度量化引起的性能变化进行了分析,表明当D/A变换器位数接近于相位量化位数时就可以获得满意的效果.     

Scanning synthetic radiation pattern antennas

It is proposed conception of development of new type transmitting-receiving scanning antennas, which are called antennas with synthetic radiation pattern. It is based on application of movement of radiating (receiving) element together with synthesizing of radiation pattern (RP) by means of SAR for processing of recorded information about radiated and received signals. Physical radiator movement can be real or virtual (switching of radiation phase center) due to switching in turns of radiators of one-dimension antenna array (AA) to single-channel transmitter-receiver. There are represented two applications of this approach realization, such as spiral-waveguide slot and tape-slot scanning synthetic RP antennas for registration of radio images and radiofilms in 8-mm wavelength band.     

多载频MIMO-SAR对消处理抗欺骗干扰

 根据多发多收合成孔径雷达(MIMO-SAR)的特点,提出在重叠等效相位中心(EPC)处采用对消处理抑制欺骗干扰的方法.MIMO-SAR采用收发同置天线配置可形成多组位置相同的等效相位中心;发射多载频线性调频(LFM)信号将使每组位置重叠等效相位中心处的回波相位有所差异.利用此特点,可以在子回波相位补偿后采用对消处理对欺骗干扰进行抑制.文中给出了收发同置MIMO-SAR的系统模型,分析了欺骗干扰下的回波特点,指出在位置重叠等效相位中心处的欺骗干扰信号对间仅存在相位差异,给出了对消处理完成欺骗干扰抑制的信号流程,实验结果证明了本文方法的有效性.     

Nonuniform sampling techniques for antenna applications

Recent investigations have demonstrated that uniform sampling techniques can be effectively applied for construction of far-field patterns of antennas. There are, however, many circumstances for which it may not be practical to directly utilize uniform sampling techniques. A two-dimensional sampling technique which can employ irregularly (nonuniformly) spaced samples (amplitude and phase) in order to generate the complete far-field patterns is presented. The technique implements a matrix inversion algorithm which depends only on the nonuniform sampled data point locations and with no dependence on the actual field values at these points. A powerful simulation algorithm is presented to allow a real-life simulation of many reflector/feed configurations and to determine the usefulness of the nonuniform sampling technique for the co-polar and cross-polar patterns. Additionally, an overlapped window concept and a generalized error simulation model are discussed to identify the stability of the technique for recovering the field data among the nonuniform sampled data. Numerical results are tailored for the pattern reconstruction of a 20-m offset reflector antenna operating atL-band. This reflector is planned to be used in a proposed measurement concept of large antennas aboard the space shuttle, whereby it would be almost impractical to accurately control the movement of the shuttle with respect to the radio frequency (RF) source in prescribed directions in order to generate uniform (u, v) sampled points. Also, application of the nonuniform sampling technique to patterns obtained using near-field measured data is demonstrated. Finally, results of an actual far-field measurement are presented for the construction of patterns of a reflector antenna from a set of nonuniformly distributed measured amplitude and phase data.     

一种用于数字D类功放的伪自然采样算法

该文针对均匀采样脉冲宽度调制(UPWM)型数字D类功放,提出了一种新的伪自然采样算法以校正其在开关信号调制时产生的谐波失真。该算法融合了三阶和一阶拉格朗日插值法,并结合伪自然采样点位置判断法而形成,可在计算复杂度较低的同时,达到较好的谐波失真校正效果。该文使用FPGA搭建了一个基于该算法以及其它同类算法的开关信号调制器测试系统。测试结果表明,相比同类算法,该算法基本消除了谐波失真且硬件消耗适中,显示了更大的优越性。     

Characteristics of a small planar loop antenna

Small planar-type loop antennas used in pagers have fixed directivity patterns. As a result, the received signal strength depends on the orientation of the antenna. A new type of small planar loop antenna (PLA) is, therefore, proposed. The position of the conductor posts can be changed and MOSFETs are adopted for switching the conductor posts. If the positions of the posts can be switched at will, then the dependence of the received signal on the orientation of the antenna can be minimized. Fundamental experiments were performed in order to investigate the characteristics of polarization switching. Polarization directivity was measured while switching each conductor alternately. The receiving characteristics are affected by a cable connected to the receiver. Therefore, the transmission characteristics are measured by using an internal oscillator. As a result, meaningful results were obtained and the possibility of polarization diversity was shown     

Phase shifter based on DDS-driven offset-PLL

A new topology for phase-shift control in the transmitter module of phased array antennas is introduced. The proposed structure is based on a hybrid DDS-PLL approach. An offset-PLL evolution is proposed in order to preserve phase resolution, along with a maximum phase shift of 360deg. Experimental results obtained by a prototype are reported, validating the architecture potentialities     

Some Designs of Full Rate Space–Time Codes With Nonvanishing Determinant

In this correspondence, we first present a transformation technique to improve the normalized diversity product for a full rate algebraic space-time block code (STBC) by balancing the signal mean powers at different transmit antennas. After rewriting a cyclic division algebra structure into a multilayer structure for a full rate code, we show that the normalized diversity product of the transformed code with the multilayer structure is better than the one of the transformed code with the cyclic division algebra structure. We then present a new full rate algebraic STBC with multilayer structure with nonvanishing determinant (NVD) for three transmit antennas when signal constellation is carved from QAM. We show that the new code has larger normalized diversity product than the existing 3 times 3 NVD full rate STBC for quadrature amplitude modulation (QAM) signals, and we also show that it has the largest normalized diversity product in a family of full rate STBC.     

Low delay coder (< 25 ms) of wideband audio (20 Hz-15 kHz) scalable from 64 to 32 kbit/s

A low delay coder for speech and music signals sampled at 32kHz is described. Its algorithmic delay does not exceed 25 ms which enables audioconferencing applications without echo cancellation. Its bit rate is scalable between 64 and 32 kbit/s by steps of 8 kbit/s. The transmitter issues the binary code at 64 kbit/s with lower bit rate codes embedded in it. The receiver may operate at lower bit rates with gradual loss of quality. The proposed coder is based on a mixed scheme : the adopted solution contains elements from the CELP speech coder and frequency domain music coders. The perceptual signal is obtained in the time domain, then transformed to the frequency domain where bit allocation is calculated and transform coefficients are quantized. A first solution based on the dft is discussed, then a second solution based on a mdct with small overlap is applied. The quantization of these coefficients is done in the following way. First, a prediction of the whole spectrum is applied. Then, a mean- removed gain- shape split vq is used for amplitude spectrum quantization and a hierarchical 2- dimensional vq is used for phase spectrum quantization with amplitude correction. At the phase quantization stage, each codeword describing the selected vector index is split into parts corresponding to different bit rates. Due to the hierarchical codebook structure, truncated indices may be used, without much affecting the signal quality. Simulation results are presented and the robustness of the proposed coder is examined.     

A polarization-amplitude-phase modulation scheme for improving the power amplifier energy efficiency

To improve the power amplifier (PA) energy efficiency, a polarization–amplitude–phase modulation (PAPM) scheme in wireless communication is proposed. The proposed scheme introduces the signal’s polarization state (PS), amplitude, and phase as the information-bearing parameters. Thus, the data rate can be further enhanced on the basis of the traditional amplitude–phase modulation. Also, since the transmitted signal’s PS completely manipulated by orthogonally dual-polarized antennas is unaffected by PA, PAPM can let PA work in its nonlinear region to acquire high PA efficiency. To further optimize the PA energy efficiency based on PAPM, a constrained optimization problem regarding the output back-off value and the ratio between the data carried by the PS and the amplitude–phase is formulated, and the distribution of the optimum solutions is presented. The simulation results show that PAPM can improve the PA energy efficiency significantly.