Channel Statistics-Based RF Pre-Processing with Antenna Selection

We introduce two novel joint radio-frequency (RF)-baseband designs for receivers in a MIMO system with N_t transmit antennas, N _r receive antennas, but only L < N_r RF chains at the receiver. The joint design introduces an RF pre-processing matrix that processes the signals from the different antennas, and is followed by selection (if necessary), down-conversion, and further processing in the baseband. The schemes are similar to conventional antenna selection in that they use fewer RF chains than antenna elements, but achieve superior performance by exploiting the spatial correlation of the received signals. The first of our proposed designs uses an L times N _r RF pre-processing matrix that outputs only L streams followed by baseband signal processing, and, thus, eliminates the need for a selection switch. The second one uses an N_r times N _r RF pre-processing matrix that outputs N_r streams and is followed by a switch that selects L streams for baseband signal processing. Both spatial diversity and spatial multiplexing systems are considered and the optimum pre-processing matrices are derived for all cases. To accommodate practical RF design constraints, which prefer a variable phase-shifter-based implementation, a sub-optimal phase approximation is also introduced. Performance better than conventional antenna selection and close to the full complexity receiver is observed in both single cluster and multi-cluster wireless channels. A beam-pattern-based geometric intuition is also developed to illustrate the effectiveness of the optimal solutions     

机载天线辐射与散射对射频特征的影响

机载天线除了对其自身工作辐射性能有要求外,还对其散射性能提出了高要求。由于飞机平台外形及材料具有不同的特性,导致天线在装机后产生不同程度的辐射畸变,从而影响传感器的辐射性能,直接影响其通信、探测、干扰等功能。同时从散射角度看,由于空间角域电磁辐射能量分布发生变化,导致其散射性能也发生变化。通过精确分析典型模型的天线辐射畸变、散射特性及有源对消等问题,分析了辐射畸变、散射及对消对机载平台射频特征的影响,最后提出了发展建议,对于机载天线工程设计具有很好的参考价值。     

Analysis of Single‐RF MIMO Receiver with Beam‐Switching Antenna

This paper proposes a single‐RF MIMO receiver that adopts a beam‐switching antenna (BSA) instead of a conventional array antenna. The beauty of the proposed single‐RF MIMO receiver with BSA is that it can be deployed in a very small physical space while achieving a full spatial multiplexing gain. Our analysis has revealed that the use of a BSA inevitably results in the spectrum spreading effect at the RF output, which in turn causes an SNR decrease and adjacent channel interference (ACI). Two novel receiver techniques are proposed to mitigate the issues of redundant sub‐band suppression and ACI avoidance. Numerical analysis results verify the performance improvement from the proposed receiver techniques.     

A photonic variable RF delay line for phased array antennas

It is shown that by applying spatial frequency-dependent phase compensation in an optical heterodyne process a variable RF delay line can be synthesized over a prescribed frequency band. Experimental results which demonstrate the performance of the delay line with regard to both maximum delay and resolution over a broad bandwidth are presented. A spatially integrated optical system is proposed for control of phased array antennas. The integrated system provides mechanical stability essentially eliminates the drift problems associated with freespace optical systems, and can provide high-packing density. The approach uses a class of spatial light modulator known as a deformable mirror device and leads to a steerable arbitrary antenna radiation pattern of the true time-delay type     

Packaging of optoelectronic and RF components with shared elements for dual-mode wireless communications

The development of a new hybrid packaging method is reported, where the front end radio frequency (RF) element, namely a modified quasi-Yagi antenna, is integrated with an optical transmitter and an optical receiver on single PCB for dual-mode, i.e. RF/free space optical communication. The VCSEL and the pin diode are placed on the antenna directors to share the common metal pads on the Duroid (RT 6010) board. The modules have demonstrated dual-mode wireless communication capability, i.e. RF and free space optics. Though the RF channel induces noise to the optical transmitter/receiver due to electromagnetic coupling between closely-spaced RF and optical circuits, a data rate of 2.5 Gbit/s is demonstrated for the optical channel.     

车载天线射频系统电磁干扰的仿真与抑制

整车平台上电子设备密集,通过电磁仿真得出射频天线系统间的干扰矩阵表,分析了系统间的干扰源、电磁干扰裕度,并利用空间隔离、添加滤波器、调整接收频谱等优化措施,抑制各射频天线系统间的干扰,降低车载射频设备的电磁兼容风险。     

射频隐身技术研究综述

机载用频设备的增加和截获接收技术的发展,导致航空器在电子对抗中的生存能力受到严重威胁。该文阐述了射频隐身的概念和基本原理,概括射频隐身技术的研究现状及主要矛盾。其次,重点以雷达射频辐射模型为主线,归纳了功率控制、波形设计、环境利用等时域、空域、频域、能量域的射频隐身技术,总结射频隐身领域的重要研究成果。最后,基于对已有算法和研究成果的分析,提出当前研究中存在的射频隐身技术局限性、评估指标单一性等问题,预测了射频隐身技术未来的研究方向。     

RF multiple-input multiple-output switchless front-end

RF multiple-input multiple-output circuits are normally implemented with the beam-forming network between the amplifier and antenna. Here the amplifier is placed between the beam-forming network and antenna, thus improving the performance in terms of power loss and noise figure as well as allowing operation for beam steering or spatial diversity     

RF characterization of an inflatable parabolic torus reflectorantenna for space-borne applications

Space-borne satellite applications provide a vast array of services extending from global connectivity to Earth observation systems. The soil moisture radiation mission is a proposed space-borne passive microwave system complementary to the existing Earth observing system operating at low microwave frequencies and requiring an antenna with multibeam, high-beam efficiency, and dual polarization capabilities. To achieve both the large reflector size and the multibeam pattern at the operational frequencies an innovative multibeam reflector antenna design was needed. The advances in inflatable antenna technology has been proposed to overcome the launch vehicle size and weight restrictions. This paper describes a novel offset parabolic torus reflector antenna design that produces the desired multibeam pattern and is compatible with the inflatable antenna technology. Using the system requirements of this mission as an example, the design process for an inflatable parabolic torus reflector antenna is outlined, the development of suitable distortion models is given, and representative RF characteristics are presented. These RF characteristics include far-field patterns, beam contour patterns, beam efficiency, and other key performance parameters. The development of an advanced analytical modeling/numerical tool in support of the design effort is also detailed     

雷达射频隐身技术研究与发展

在分析雷达及其对抗技术发展现状的基础上,阐述了雷达系统射频隐身技术的概念及其重要性;通过对射频隐身基本原理的研究,提出从雷达射频辐射的时、频、空和能等多维空间上进行控制,并与作战环境相融合等研究方向与方法,为开展具有隐身性能的雷达装备研制和技术研究提供参考。     

Package-Level Integrated LTCC Antenna for RF Package Application

This paper presents a compact antenna geometry to realize an radio frequency (RF) system in package (SIP) and discusses an antenna-integrated package for an IEEE 802.11a application. The proposed compact antenna is similar to a modified U-shaped slot antenna; however, its electrical properties are quite different. A fabricated antenna demonstrates bandwidth of 180 MHz at a center frequency of 5.8 GHz, and it may be used to implement antenna-integrated packages. An antenna-integrated package is proposed consisting of the antenna placed on the top surface, internal space for integration of other IC components, a conducting layer placed between the antenna and the internal space, and finally a bottom layer. In addition, from the parametric studies it is found that the size of the package, dielectric thickness of the antenna, package height, and the number as well as the position of via holes, are critical factors of antenna characteristics     

A method of accurate determination of azimuthal distribution of received RF power

In this paper, we introduce a method for the determination of directional distribution of received RF power, with angular resolution independent of receiving antenna radiation pattern. The proposed method is based on a series of measurements taken while rotating, at fixed predefined steps, a usual directional antenna of known radiation pattern on the azimuthal plain. It is proved that the resolution accuracy of the measurement method depends only on the angular step of the antenna rotation and it is independent of the antenna beamwidth. As a result of this feature, the proposed method allows the determination of the RF power angular distribution with fine resolution using a directional antenna of much wider beamwidth for the measurements. Copyright © 2001 John Wiley & Sons, Ltd.     

Statistical analysis on ambient RF energy harvesting for low‐power wireless applications

Renewable energy sources from the earth constitute another option apart from the available ones for wellspring of energy for economizing on cost of power supply. The energy obtained from ambient sources is called energy harvesting. Energy‐harvesting low‐power systems have acquired a remarkable consideration as a viable hotspot for expanding both energy efficiency and spectral efficiency. Radio frequency (RF) energy harvesting from ambient source is a promising technique for fulfilling the irreplaceable power prerequisites for powering the low‐power devices. Hence, it requires the development of an antenna for harvesting RF energy. In this paper, a coplanar waveguide (CPW) antenna has been designed and fabricated using FR4 lossy substrate. This CPW antenna covers frequency bands from the most important RF patrons (GSM 900, GSM 1800, 3G, and Wi‐Fi) within the frequency range from (0.58 to 3 GHz) with a percentage fractional bandwidth of 116% with the center frequency of 1.65 GHz. The fabricated antenna then has been experimentally validated at SSN College of Engineering campus. The effects on the RF power density level for CPW antenna are examined by statistical approach known as Taguchi method. The L9 and L8 orthogonal arrays and analysis of variance are implemented to analyze the execution qualities. The CPW antenna control factors are distance, time, and number of receivers. Then, statistical test (P) are used to determine the significant factors on RF power density.     

λ/64‐spaced compact ESPAR antenna via analog RF switches for a single RF chain MIMO system

In this study, an electronically steerable parasitic array radiator (ESPAR) antenna via analog radio frequency (RF) switches for a single RF chain MIMO system is presented. The proposed antenna elements are spaced at λ/64, and the antenna size is miniaturized via a dielectric radome. The optimum reactance load value is calculated via the beamforming load search algorithm. A switch simplifies the design and implementation of the reactance loads and does not require additional complex antenna matching circuits. The measured impedance bandwidth of the proposed ESPAR antenna is 1,500 MHz (1.75 GHz–3.25 GHz). The proposed antenna exhibits a beam pattern that is reconfigurable at 2.48 GHz due to changes in the reactance value, and the measured peak antenna gain is 4.8 dBi. The reception performance is measured by using a 4  4 BPSK signal. The measured average SNR is 17 dB when using the proposed ESPAR antenna as a transmitter, and the average SNR is 16.7 dB when using a four‐conventional monopole antenna.     

A reconfigurable wideband MIMO antenna combines RF energy harvesting

This article introduces a novel and groundbreaking approach combining multiple-input-multiple-output (MIMO) technology with radio frequency (RF) energy harvesting. The proposed antenna consists of two semi-circular monopole antenna components, optimized with dimensions of 89 × 51.02 × 1.6 mm³, that share a common ground plane to achieve MIMO characteristics. A series of split-ring resonators on the ground plane significantly enhances the isolation between the two radiating components. Band-notched features are performed in the 3.5 GHz WiMAX and 5.5 GHz WLAN bands through modified C-shaped slots in the radiating patch and two rectangular split-ring resonators serving as parasitic devices near the feed line. The reconfiguration of band-notching is made possible by controlling the modes of the embedded PIN diodes. The two antenna elements maintain mutual coupling below −18 dB from 1.5–13 GHz, achieving an impressive 158.62% impedance bandwidth. The antenna's efficiency and gain experience significant drop, indicating effective interference suppression at the center frequencies of the notch bands, and its performance in MIMO systems is assessed through parameters including envelope correlation coefficient, port isolation, radiation patterns, efficiency, gain, and diversity gain. The simulated properties of the designed antenna closely align with the measured outcomes, demonstrating its reliability and consistency. Moreover, the article evaluates the antenna's potential for RF energy harvesting, achieving a maximum harvested energy of 4.88 V. This proposed antenna can be used in multiple applications, like wideband, band-notching MIMO, and RF energy harvesting. This proposed antenna is an efficient, reconfigurable wideband MIMO antenna with novel RF energy harvesting capability.     

星载DBF Tx射频通道幅相误差校正

为了实现精确的多波束形成,该文提出了一种补偿卫星通信多波束系统发射通道幅相误差的校正方法,该方法在发射通道中同时注入多路正交码变换的校正测试信号,通过接收多路发射机的输出信号和,在基带校正算法单元利用正交码的时间相关性和IDFT并行处理的方法,同时得到多路射频通道的校正因子,并对得到的校正因子进行了归一化处理,消除了对通道中非线性器件的影响.仿真结果表明,该方法可以有效地补偿射频通道间的幅相不一致性,校正后的波束方向图接近理想的波束方向图.     

多功能射频综合系统中的电磁协同北大核心CSCD

限定时空条件下,射频综合系统有效发挥多功能效应的实质是实现系统多功能协同高效运行,而制约其协同高效运行的瓶颈是特定时空条件下可用的电磁资源。电磁资源的高效利用依赖电磁协同,是按照任务要求及限定条件,在时间、频率、空间、能量多个维度寻求构建电磁协同自组织结构的最优解,并确定具体任务时空下有序运行自组织结构的驱动方式,按照求解出的电磁资源动态分配结果,执行任务,使系统电磁效应在任务牵引下受控。电磁协同服务于多功能射频综合系统融合,可以有效利用、管理战场电磁环境,高效提升多功能射频综合系统的运行效率。本文从多功能射频综合系统融合运行之瓶颈、电磁协同概念和电磁协同方法三个方面论述电磁协同的核心要点,期望为实现多功能射频综合系统融合运行提供可行的技术途径。     

Statistical patterns of a general array

The present analysis considers the effects of Gaussian errors upon the antenna pattern of any array of elements. Analytical solutions for an average pattern and the standard deviation about this average are found. The errors are described in terms of the rms amplitude and phase errors at each element, with a correlation function relating errors in neighboring elements. The results are applied to the case of an array consisting of a sector of a circular array, with the resulting statistical patterns plotted. Then the problem of assigning probabilities to statements about the actual antenna pattern, based upon the statistical plots, is discussed.     

Performance of Time Domain Migration Influenced by Non-Ideal UWB Antennas

The antennas in ultrawideband (UWB) systems act as filters in both frequency domain and the spatial domain. This means that the antenna influence on a received signal varies with the wave incidence angle. This is particulary important for imaging systems, which make use of the time information of the received signals. However, since the incidence angles of the signals are not a priori known it is difficult to remove this effect from the measured data. To asses the antenna impact on the performance of the imaging system, in this work, simulated scattered signals are used as input for time domain migration algorithm. Then the image features like position errors, shape of the target image, resolution and coverage of an imaging system are extracted and compared for different real UWB antennas.      

Compact antenna test range without reflector edge treatment and RF anechoic chamber

There are several types of CATRs (compact antenna test ranges) used in antenna-pattern measurements. An offset reflector is generally used to generate the quiet zone of a CATR. Serrated edges, rolled edges, or R-cards are generally chosen along the reflector's edge to reduce the edge-diffraction field inside the quiet zone of the CATR. In order to reduce stray signals from the environment, a high-quality RF anechoic chamber is required for a CATR. In this paper, a new type of CATR, without either a reflector edge treatment or an RF anechoic chamber, is developed. A commercially available DBS (direct-broadcast satellite) reflector antenna, without edge treatment, is used as the reflector antenna of the CATR to generate the quiet zone of the antenna test range. In order to improve the quiet zone's performance, the fields due to feed spillover, edge diffractions, and other stray signals are gated out by the ITDAMS (impulse time-domain antenna measurement system). The RF interference in the environment can also be reduced by time synchronization and pulse integration of the impulse time-domain antenna measurement system. In order to verify the capabilities of the proposed CATR, three kinds of antennas (a low-directivity horn antenna, a high-directivity 60 cm direct-broadcast satellite reflector antenna, and a 25 cm Ka-band Cassegrain LMDS - local microwave distribution system - antenna) were measured by the proposed CATR. The antenna-pattern results agreed quite well with those of a near-field range and a far-field range.