二维综合孔径微波辐射计误差分析

北航电磁工程实验室已经研制出的一套工作于8mm波段(34.07GHz)的10天线二维综合孔径微波辐射成像系统BHU-2D,其原理样机采用T形阵列.对其采用相关/不相关噪声注入法进行误差分析,实验结果表明:相关偏置的主要原因是采集板量化前的互相耦合;通道问相位不平衡误差为-53.89度,当积分时间为0.2秒时,其起伏不大于0.18度;由于采用数字解调,IQ非正交误差很小,可以忽略其影响,同时拟合出了条纹洗涤函数.     

A Double Detector for RFI Mitigation in Microwave Radiometers

A double detector (DD) for radio-frequency interference (RFI) in microwave radiometers is demonstrated in theory and practice. The detector is based on the principle of using kurtosis to detect the presence of non-Gaussian signals and is shown to approximate the kurtosis of input. Theoretical response to continuous wave and pulsed RFI is derived and tested in two experiments. The DD hardware comprises two microwave detectors, two integrator-amplifiers, and a wideband video amplifier. The technique is compatible with existing direct-detection radiometer designs and desirable for applications requiring low technological risk.     

Ground-Based Detection of Aircraft Icing Conditions Using Microwave Radiometers

The potential role of ground-based remote sensors in the detection of atmospheric conditions conducive to aircraft icing is evaluated. Zenith measurements of liquid water and profiles of atmospheric temperature were made by microwave radiometers located at Stapleton International Airport, Denver, Colorado. Radiometer data and sky cover observations for a two-year period were correlated with icing occurrences reported by aircraft pilots in the area. Data limitations in this study include the following: 1) the radiometer observations were made at one location and in the zenith direction only, whereas icing conditions may be highly variable in space; 2) because pilot reports vary greatly with time of day, aircraft route, etc., the reports do not systematically verify the presence of icing conditions in all situations. Given these limitations, it is concluded that the liquid measurement makes a critical contribution to the detection of icing conditions. This measurement is not generally available (e. g., from radiosondes), except from sensors like the radiometer.     

一种用于微波系统的输入电压控制电路

随着射频技术的不断发展,微波系统对功率密度、可靠性的重视程度不断提高。以氮化镓为基础的微波功率器件的应用取得了很大的进步,对微波系统的供电时序也提出了更高要求。根据微波系统对脉冲电压及电源时序控制的要求,设计了一种电压控制电路,实现直流输入电压的脉冲输出和上电、掉电时序的控制,并通过实验电路对设计原理进行了验证。     

Amplitude Stabilization of a Microwave Signal Source

Recent developments in the microwave field have provided new tools for use in regulating the output amplitude of a microwave signal source. An amplitude or power stabilizer has been constructed at the National Bureau of Standards Boulder Laboratories, using the recently developed self-balancing dc bolometer bridge and a commercially available, electrically controlled, ferrite attenuator which achieves power stabilities of a few parts in 10/sup 4/ per hour. Use of a high directivity directional coupler permits stabilization of the forward traveling component of the signal, thus providing the equivalent of a matched, stable generator. In practice, a broad-band source match of vswr less than 1.05 is achieved, and this figure may be further improved, at a given frequency, by suitable tuning. In addition, the device has applications as a precision broad-band attenuator, since known changes in power level may be achieved by switching certain of the associated dc components.     

IF Amplifier Section in 90 nm CMOS Technology for SoC Microwave Radiometers

In this letter a novel design solution in 90 nm CMOS technology is proposed for the IF amplifier, low-pass filter and square-law power detector of a system-on-chip (SoC) microwave radiometer. To minimize the number of off-chip components (just a single capacitor) the IF filter is based on an active $g_{m}C$ configuration, whereas the power detector exploits the MOS transistor non-linearity, i.e., avoiding the need for Schottky diodes. The fabricated IF chip features a sensitivity of 3 mV/nW, a linearity range of about 25 dB around the $-$60 dBm level, a noise equivalent bandwidth of 58 MHz and a current consumption of only 1.8 mA at 1.2 V supply. The core area is within a rectangle of $220 mu{rm m}times 540 mu{rm m}$. The proposed design solution is also compatible with SiGe BiCMOS processes and can be regarded as a further step toward the realization of microwave radiometric sensors fully integrated on silicon.      

Optimum Strategies and Performance for the Remote Sensing of Path-Delay using Ground-Based Microwave Radiometers

Computer simulations have been used to study the accuracy with which excess radio-propagation path delay due to atmospheric water vapor can be determined using a microwave remote-sensing technique. A number of strategies were investigated for the remote sensing of path delay with the objective of providing a broad foundation for the development and use of water-vapor radiometers (WVR's) for geodetic applications. A data base of nearly 10 000 radiosondes from a variety of climatological regions was used for the study. Strategies were judged by their "retrieval performance" on this data base; i.e., by the rms difference between simulations of "retrieved" path delay and "true" path delay, at the zenith, averaged over a radiosonde data base. An observing approach using the frequency set 20.7/22.2/31.4 GHz was found to be close to optimum. A statistical retrieval approach using retrieval coefficients stratified for clear and cloudy weather and for individual location was found to offer a substantial improvement over the use of a single all-weather set of retrieval coefficients. It was found that a reasonably well optimized WVR, with an estimated calibration uncertainty of 0.5 K, can achieve an overall retrieval performance of: 0.27 cm, clear; 0.51 cm, cloudy; and 0.38 cm, all weather average. The weather-averaged retrieval performance for individual locations was found to vary by no more than 14 percent from the average for all locations, in spite of the fact that the mean path delay for these locations ranged from 5 to 26 cm.     

Determination of Cloud Liquid and Precipitable Water Vapor by Ground-Based Microwave Radiometers

An algorithm has been developed for determining cloud liquid in the monsoon period from ground-based microwave radiometric observations over New Delhi. For cloud liquid measurements, 11- and 17.47-GHz frequencies are used. Calculations show that liquid content changes from 0.1 × 103 to 6.1 × 103 g/m2 and water vapor from 3 × 104 to 6 × 104 g/m2 in the monsoon period over New Delhi. Cloud liquid is found to be highly variable on a time scale and shows poor correlation (0.4) with water vapor content. The average liquid water density of cumulonimbus clouds is obtained as 1.2 g/m3 from these observations.     

A New Sidelobe Correction Algorithm for Microwave Radiometers: Application to the Envisat Instrument

The antenna temperature measured by a microwave radiometer is converted in brightness temperature (TB) by removing the different contributions that do not come from the main lobe of the antenna. Among them, the Earth contribution in the sidelobes may be significant as for the Environmental Satellite mission due to the antenna position on the platform. In such a case, simple corrections commonly applied on previous altimetry missions are inadequate, and a more accurate correction should be determined. We propose in this paper a new method based on global seasonal tables of contamination. This allows application of an accurate sidelobe correction in space and time in the retrieved TB computation     

An Investigation of the Use of Microwave Radiation for Pulmonary Diagnostics

This communication describes a new technique in which penetrating microwave radiation is used for the diagnosis and monitoring of pathological cardiopulmonary conditions, such as pulmonary edema. Edema causes changes in the electromagnetic characteristics of the lung tissue, which in turn produces a change in the reflected and transmitted microwave radiation. Both the amplitude and phase changes of the microwave signals are measured.     

Stabilization Scheme for Hot-Electron Bolometer Receivers Using Microwave Radiation

We present the results of a stabilization scheme for terahertz receivers based on NbN hot-electron bolometer (HEB) mixers that uses microwave radiation with a frequency much lower than the gap frequency of NbN to compensate for mixer current fluctuations. A feedback control loop, which actively controls the power level of the injected microwave radiation, has successfully been implemented to stabilize the operating point of the HEB mixer. This allows us to increase the receiver Allan time to 10 s and also improve the temperature resolution of the receiver by about 30% in the total power mode of operation.     

Frequency Stabilization of a Microwave Oscillator with an External Cavity

This paper describes a procedure by which a cavity stabilizer may be designed for a microwave oscillator. Formulas are derived for the following essential design parameters: 1) stabilization factor; 2) stabilization range; 3) vswr of the stabilizer circuit with cavity tuned; 4) vswr of the stabilizer circuit with the cavity detuned; and 5) insertion loss of the cavity assembly. The validity of designing with the derived relations has been experimentally confirmed.     

A Review of Ground-Based Remote Sensing of Temperature and Moisture by Passive Microwave Radiometers

Remote sounding of atmospheric variables by groundbased microwave radiometers has proved to be useful for several applications. These radiometers are used to measure profiles or integrated values of temperature, water vapor, and cloud liquid. The information provided is useful in meteorology, astronomy, geodesy, communication, for correction of space observations, for atmospheric research, etc. It may be possible to combine ground-based radiometers, satellite-borne radiometers, and VHF radars to form a meteorological network which provides profiles of temperature, humidity, and wind continuously in time. This paper will review some of the developments in this area, describe basic principles and results of field experiments, including the recent ONSAM-experiment, and summarize two years' performance of the NOAA Profiler.     

Remote Control of Standby Engine Generator Sets Over a Microwave System

Experience in actual operation of microwave relay systems throughout the country has shown that involuntary outages have been caused principally by failure of the input power to the microwave equipment. Where substantially continuous service is required of the microwave system the common practice is to have emergency standby power available. This emergency power is supplied by an emergency generator set at the microwave station site. Failure of the normal input power supply initiates starting the engine generator set to supply a particular microwave station with power. This paper describes the units used to improve reliability of engine generators in microwave applications.     

微波硫灯的研究与实现

微波硫灯是新型环保的绿色光源,具有光效高、无污染和寿命长等优点。微波硫灯与一般的光源不同,它具有独特的工作原理和发光机理。微波硫灯由电源、磁控管、高频传输系统和硫泡等部件组成,这里主要介绍了电源、高频传输系统和硫泡的制作过程和自制各部件的实物图。最后对自制不同填充物的硫灯和外购硫灯做了测试,可以看出自制硫灯的系统光效达到55．34lm／W,高于外购硫灯,红光比高于外购硫灯,这就弥补了以前硫灯光色偏绿的缺陷。分析了光参数随不同填充物的变化趋势,得出了最佳填充量为硫粉17mg和氩气为532Pa左右。     

基于先验信息的综合孔径辐射计误差校正方法

误差会严重影响综合孔径微波辐射计的成像性能,需要进行校正.但是,随着系统工作频率的提高和阵列尺寸的扩大,校正难度越来越大.文中提出一种基于先验信息的综合孔径微波辐射计误差校正方法.该校正方法包括一个基于先验信息的校正矩阵以及一种基于先验信息的CLEAN算法.首先,该校正方法将含有误差的系统响应作为先验信息构造校正矩阵,并校正得到初步的反演图像;然后,利用上述先验信息估计系统的阵列因子并代入基于先验信息的CLEAN算法,校正图像中剩余的误差.仿真和实验结果表明该校正方法能有效提高综合孔径微波辐射计的成像质量.该校正方法可以在图像反演过程中全面校正综合孔径微波辐射计的误差,降低对校正系统的硬件性能要求,适用于大阵列毫米波综合孔径微波辐射计的校正误差.     

微波发射机控制与保护系统监控软件设计

由一微波发射机工作在强辐射、强干扰的环境中,必须要有相应的控制保护系统来保证其可靠性和安全性。文章介绍了微波发射机控制保护系统的监控软件的结构和设计,以及用ＢｏｒｌａｎｄＣ＋＋设计中文界面的方法。     

基于模糊控制的自适应激光功率稳定系统研究

研究了一种基于模糊控制的嵌入式激光功率稳定系统,用声光调制器作为功率稳定的外部环路反馈器件,采用模数转换器和数模转换器以及数字信号处理芯片组成数控功率稳定电路。用模糊控制方案解决了传统比例-积分-微分(PID)的超调问题,反馈环路的稳定时间为1.8 ms。有效抑制了激光功率在低频部分的相对强度噪声,在1 Hz处从-88 dBc/Hz改善至-110 dBc/Hz。激光功率的相对起伏由0.29%降低至0.035%。相比于传统PID,模糊PID可以根据系统所处状态实时调整参数,从而达到自适应的效果。     

控制系统中的一种抗干扰方法

本文介绍了一种控制系统的抗干扰方法。其主要思想是硬件看门狗和软件实时纪录系统状态相结合。