基于DDS的有源相控阵天线

有源相控阵天线不仅能提高通信系统的性能,而且还能扩充其功能,所以在通信领域的应用越来越广泛.本文介绍一种没有高频移相器的8单元有源相控阵天线系统,它由平面天线阵、数字T/R组件、接收DBF和系统控制分析软件等组成.其基本原理是在发射模式下,利用直接数字合成(DDS)代替传统的高频移相器和衰减器.由于DDS的工作频率比较低,需要通过上变频到系统所需要的工作频率(2.0GHz).在发射模式下,通过控制DDS完成发射波束形成所必需的幅度、相位加权和上变频所必需的本振信号;在接收模式下,则利用DDS技术产生接收信号下变频所必需的本振信号,然后采用DBF技术形成接收波束.文中详细介绍了基于DDS的有源相控阵天线的实现方法和实验结果.通过8单元基于DDS的有源相控阵天线系统的研究,证实了DDS技术在相控阵天线中应用的显著优点和相控阵天线在通信领域具有潜在应用市场.     

一种基于压控移相技术的低成本相扫天线

研制了一种基于铁电体压控移相技术的低成本相扫天线阵列,该天线采用空间馈电透镜型式,省去复杂的馈电网络,减少移相器/TR组件数量,能显著降低相控阵天线的制造成本。介绍了空馈铁电体透镜相控阵天线系统的组成及其特点。对透镜天线关键部件的设计作了详细阐述,给出了12列铁电体空馈透镜天线阵列的实验结果,结果表明:在X波段,研制的铁电体透镜天线阵列在10%频带内可实现天线波束±45°的电控扫描,各扫描状态的输入驻波比小于1.4。     

Circularly symmetric RF commutator for cylindrical phased arrays

A new feed concept is described which greatly simplifies the problem of commutating the RF distribution system of a cylindrical phased array. The feed consists of a circular parallel-plate radial transmission line with a central set of probes and a ring of peripheral probes. The array of probes in the center can be phased to produce an amplitude distribution in the parallel-plate line in any given direction. Proper setting of only two phase shifters connected to the central probes can cause any sector of the peripheral probes to be excited with the proper amplitude distribution necessary to produce a directive pattern with low sidelobes as well as a monopulse difference pattern when the peripheral probes are connected, through collimating phase shifters, to the active radiating elements of a cylindrical array. The cylindrical array can be scanned through360degin fine increments by continued indexing of the amplitude distribution generated by the central probes. ExperimentalLband hardware, built to prove the feed technique, is described. Nine central probes in a 0.25-inch thick 21-in diameter model produced a cardioid distribution and an orthogonal figure-eight distribution which could be commutated together by adjustment of two phase shifters. Measured insertion loss between the central probes and 48 peripheral probes showed only 0.1-dB loss over a 6-percent band. Coupling measurements between the three available central terminals indicated isolation between the various ports of 23-35 dB. The minimum insertion loss and the corresponding transmission phase between the central feed and the peripheral probes was shown to be independent of the setting of the two control phase shifters which were set to have conjugate phase shift.     

Sidelobe-reduction techniques for phased arrays using digital phase shifters

Through the introduction of a new parameter the radiation pattern of a phased array using digital phase shifters for beam steering can be made periodic, and pattern considerations can be confined to a very narrow range of the scan angle. Arrays designed on the basis of a least mean-square pattern error are shown to require the smallest absolute values of a phase-index function. A systematic and easy-to-apply method is developed for reducing the peak sidelobes of nonreciprocal phased arrays by one-step phase adjustments in certain elements. The amount of possible sidelobe reduction depends on the scan angle and the size of phase-quantization steps. Typical examples for 4-bit phase shifters show that reductions in excess of 9 dB are possible for certain main-beam directions.     

宽带相控阵天线延迟线分析

采用频率无关移相器的相控阵天线的波束指向会随频率发生变化,实时延迟线是提高宽带相控阵天线波束指向精度的重要方法。分析了子阵级采用延迟线,单元级使用移相器的宽带相控阵天线副辫特性,发现当工作频率改变时,由于阵列存在周期相位误差导致天线副瓣电平抬高。针对此问题,提出单元级精细延迟线方案,消除周期相位误差对天线副瓣的影响。仿真结果表明,这种方法在扩展相控阵天线带宽的同时,明显改善了天线的副瓣特性。     

Genetic Algorithms for Design of Discrete Phase-only Reconfigurable Array Antennas with Fixed Dynamic Range Ratio

In this paper, we present a new method based on real-coded Genetic Algorithm (GA) with elitist model for optimal design of a reconfigurable symmetrical dual-beam uniformly spaced linear isotropic antenna array with phase-only control of quantized phase shifters. The problem is to find a common amplitude distribution that will generate a pencil beam with zero phases and a flat-top beam with discrete phases of a six-bit discrete phase shifter, without or with pre-fixing the value of dynamic range ratio (|I _max/I _min|) of excitation current amplitude distribution equal to or less than five.     

Directional Modulation Technique for Phased Arrays

A directional modulation (DM) technique using a phased array to produce the modulation is presented. By phase shifting each element correctly, the desired amplitude and phase of each symbol in a digital modulation scheme can be produced in a given direction with data rates determined by the switching speed of the phase shifters. Because this signal is direction-dependent, the technique offers security, as the signal can be purposely distorted in other directions. DM also enables an array to send independent data in multiple directions. When using an array with driven elements, the phase shifts can be determined from simple calculations rather than time-consuming simulations or measurements. Mathematical analysis and experimental results are presented.     

A comparison of methods for randomizing phase quantization errors in phased arrays

Beamsteering for phased arrays normally employs electronically switchable digital phase shifters. These can only approximate to the desired phase distribution across the array, and if a straightforward rounding off is used, a periodic phase error arises which causes a pointing deviation of the main beam and introduces a parasitic sidelobe. Various methods have been given in the literature for randomizing the phase errors to reduce these problems. Here a general formula is derived to evaluate the parasitic sidelobe level for different methods. The various methods are compared with reference to 1) the parasitic sidelobe level, 2) the variances of the field pattern and the pointing direction, 3) gain reduction, and 4) any extra array hardware requirements and beamsteering unit resources.     

相控阵雷达反演口径分布实现方位超分辨

为了实现普通相控阵雷达的方位超分辨,需要知道天线阵面的幅相分布。通过对相控阵天线单元进行时序Ｗａｌｓｈ－Ｈａｄａｍａｒｄ相位权重可以反演该天线阵面的幅相分布。在此基础上再采用超分辨算法就可以得到目标的超分辨方位信息。所采用的超分辨算法是抗噪性和鲁棒性均较好的逐次逼近算法。为了得到平缓的相位分布,减少相位权重次数,对于不在正常方的目标采用了附加线性相位分布波阵面地准的方法,经数值仿真,对于一个Ｘ波段     

Pattern synthesis of the offset reflector antenna system with lesscomplicated phased array feed

The performance degradation of an offset reflector antenna with off-axis scanning feed and distorted reflector surface can be improved by using a phased array feed. Generally, both analog attenuators and phase shifters are used in phased array feed. Yet, it seems to make the feed system very complicated. In this paper, a phase-only gradient search (POGS) algorithm is developed to optimize the performance of offset reflector antenna systems using phased array feed that is equipped with phase shifters only. This technique not only can greatly simplify the complexity of phased array feed, but also can provide the reflector antenna with better antenna gain and sidelobe level control capability. Simulation and experimental results are presented to illustrate the excellent performance of offset reflector, with limited beam scanning capability, can be obtained by using this less complicated phased array feed     

Radar wideband digital beamforming based on time delay and phase compensation

In conventional phased array radars, analogue time delay devices and phase shifters have been used for wideband beamforming. These methods suffer from insertion losses, gain mismatches and delay variations, and they occupy a large chip area. To solve these problems, a compact architecture of digital array antennas based on subarrays was considered. In this study, the receiving beam patterns of wideband linear frequency modulation (LFM) signals were constructed by applying analogue stretch processing via mixing with delayed reference signals at the subarray level. Subsequently, narrowband digital time delaying and phase compensation of the tone signals were implemented with reduced arithmetic complexity. Due to the differences in amplitudes, phases and time delays between channels, severe performance degradation of the beam patterns occurred without corrections. To achieve good beamforming performance, array calibration was performed in each channel to adjust the amplitude, frequency and phase of the tone signal. Using a field-programmable gate array, wideband LFM signals and finite impulse response filters with continuously adjustable time delays were implemented in a polyphase structure. Simulations and experiments verified the feasibility and effectiveness of the proposed digital beamformer.     

Visualization of radiation-pattern characteristics of phased arrays using digital phase shifters

This article presents graphical investigations of the array factor of phased arrays with digital phase shifters. A software program, based on basic antenna array theory, has been developed in MATLAB to obtain the main array characteristics (array factor and directivity). The array factors of linear arrays of different sizes with different types of phase shifters have been studied as a function of the number of bits and the frequency. Unconventional two-dimensional color graphical representations are used to identify some characteristics of the array factor of arrays with digital phase shifters that can not be so clearly and quickly visualized with conventional graphical representations. In particular, the effects of quantization on the array factor for arrays of different sizes and for phase shifters with different numbers of bits, over scanning, and frequency ranges, are shown using this representation. Numerous data are also provided.     

Concept of an interlaced phased array for beam switching

A novel concept is described for feeding and phasing a large linear array of N antenna elements using only three or five feed points and phase shifters and still achieving beam switching. The idea consists of drastically reducing the number of input points by interlacing a small numer of serially fed subarrays which are suitably phased. This so-called interlaced phased array (IPA) concept was tested using an array of 15 four-element Yagi antennas with a spacing equal to 0.8 wavelengths and found feasible. Some of the distinct advantages of the IPA in comparison with a conventional system of beam switching are reduced power loss, reduced phasing errors, reduced cost, increased reliability resulting from greatly reduced number of phase shifters, and better symmetry of off-zenith beams     

An antenna beam steering technique comprised of constant-phase array elements

Beam steering is normally achieved by the use of phase shifters at each element of an array. The phase taper thereby produced causes a shift of the far-field pattern in sin θ space. An alternate approach to beam steering is presented in which a pair of interleaved arrays are employed. One array of the pair is fed entirely by currents of zero phase, while the other array is fed entirely by currents of quadrature phase. Beam steering is done by control of amplitude at each element. An example of this technique is presented and discussed.     

雷达数字波束形成及其数学分析

从相控阵雷达波束形成原理逐步引出了数字波束形成技术,并就其数字配相和幅度加权进行了详细的数学分析。给出了一种数字波束形成器的实现结构,也客观地指出了目前在工程实现中仍需注意的一些问题。     

Improvement for the steering performance of liquid crystal phased array

Optical phased array technology is introduced and the steering performances of liquid crystal phased array are discussed, several factors affecting the beam steering performances are analyzed completely, also simple models for some typical factors are developed. Then, a new method based on iterating and modifying the output phase pattern of liquid crystal phase shifters is proposed. Using this method, the modified voltages applied on electrodes of liquid crystal phase shifters can be obtained, after applying the voltages, the influence of factors can be compensated to some extent; the steering angle accuracy and efficiency with liquid crystal phased array can be improved. Through the simulation for the angle range from 0° to -1 °, the error of steering angle can be reduced three orders of magnitude, and the efficiency can be increased almost 30% after several iterations.     

Comparison of random phasing methods for reducing beam pointing errors in phased array

Beamsteering for phased arrays normally causes a pointing deviation of the main beam due to the periodic phase quantization error across the array. This deviation occurs due to the use of digital phase shifters. We modify the random phasing methods into appropriate random phasing methods, in which the accuracy of the pointing direction in phased arrays is improved. The word "appropriate" means that, for the phase quantization error, the rounding to the nearest bit method is not always to be applied, nor is the random phasing method. An appropriate mean phase error equal-to-zero method (AMPEEZ), an appropriate two probable value method (A2PV) and an appropriate phase-added method (APAM) are proposed. These methods are simulated and compared with the nonappropriate ones.     

Conceptual Study of Analog Baseband Beam Forming: Design and Measurement of an Eight-by-Eight Phased Array

We report on the design and measurement of an eight-by-eight modular phased array that uses analog quadrature baseband phase shifters. The array is designed for 2.4 GHz and has a few MHz of bandwidth. Though for such frequency, bandwidth and number of elements, digital beam forming is still feasible with contemporary analog-to-digital converters (ADC), the design is a proof of concept for analog baseband beam forming and shows that this technique will work at frequencies and bandwidths beyond ADCs capabilities. Besides covering the architecture, implementation and the measurement of the array, the calibration is discussed extensively, as this is an inevitable step in activating the antenna.      

A flat four-beam compact phased array antenna

This paper presents a flat four-beam compact phased array antenna. The low-cost and compact phased array antenna is designed using a circular array of four circular microstrip antennas made of low-cost material and four 1-bit phase shifters. The main beam of the antenna can be switched in four directions with the gain of about 4 dBi in each main-beam direction. More than 90° half-power beamwidth and over 10 dB F/B ratio are obtained. In addition, the diversity performance is considered and the diversity performance of this antenna can be provided with the envelope correlation about 0.6     

一种轻巧型接收数字波束雷达系统的实现

针对数字波束相控阵雷达多通道问题,提出利用多路复用技术实现全数字阵接收多波束相控阵雷达的一种解决方案。天线阵列直接采用高频二相调制,将接收多通道直接模拟合成一路传输处理,基带提取各个天线单元回波数据信号、相位幅度加权,基带实现任意接收数字多波束。该技术突破单通道数字波束相控阵雷达接收技术,使天线体积大幅度减小,雷达系统轻巧,低成本;灵活软件配置阵列,降低调试、测试、工艺、加工复杂难度,有利于雷达综合性能提升。