K波段谱分析技术的微波辐射计方案设计

以探测大气中水汽吸收谱线为应用背景,系统设计了一种基于快速傅里叶变换(FFT)的宽带宽的谱分析技术的微波辐射计。阐述了谱分析技术的微波辐射计的设计原理,详细介绍了系统结构设计、接收机方案设计和谱仪的方案设计,并分析了系统的主要技术指标、正交接收机指标及谱仪的设计。该系统可实现的辐射计探测频率为22.235 GHz,设计带宽达到500 MHz,谱分辨力为60 kHz。     

Sensitivity of the Total Power Radiometer with Periodic Absolute Calibration

The total power radiometer is an attractive choice for imaging applications due to its high sensitivity and simple configuration. However, available theoretical results are inadequate to allow an accurate radiometer performance prediction in the presence of receiver gain fluctuations and other receiver characteristics with nonuniform fluctuation power spectra. An improved analysis of the total power radiometer Delta T is presented in terms of the receiver output fluctuation power spectral density and a transfer function due to postdetection filtering and periodic calibration. Verification of this analysis is obtained by measuring the fluctuation power spectrum of a 94-GHz receiver and comparing the predicted Delta T with a direct measurement. Numerical results including application to an example radiometer system are presented. These results indicate that the total power radiometer should function well in short integration time, periodically calibrated radiometer systems.     

Radiometric measurement of atmospheric absorption at 600 Gc/s

Atmospheric absorption in the 600-Gc/s region was measured throughout the actual atmosphere by means of a DICKE-type superheterodyne radiometer receiver using second harmonic mixing. The average measured value of horizontal attenuation was approximately 34 dB/km/g/m³. The variation of water vapor absorption with respect to water vapor density was also indicated in the measured results. The minimum detectable temperature difference (ΔT)MINwas obtained by calculating the rms value of output deflection and the use of the calibration curve for the radiometer. The best value achieved was 5.2°K. From this result, the radiometer receiver noise figure and the mixer conversion loss were able to be determined indirectly. The results were 33.2 dB and 26.4 dB, respectively. A thermal calibrator was used to adjust and calibrate the radiometer, and as a source of radiation for the measurement program.     

Performance characteristics of a 300-GHz radiometer and some atmospheric attenuation measurements

A 300-GHz Dicke-type superheterodyne radiometer receiver was used for measurements of atmospheric attenuation of electromagnetic waves over an open path at frequencies near 300 GHz. The average measured values of horizontal attenuation at 304 GHz and 316 GHz, presumably due to atmospheric water vapor absorption, were, respectively, 3.35 dB/km and 5.55 dB/km per g/m³of water vapor density. Absorption variations at 304 GHz with respect to water vapor density were shown in the measured results. The variation of the effective zenith sky temperature with respect to atmospheric water vapor density was also determined. The minimum detectable temperature difference(Delta T)_{min}, was obtained by measuring the rms value of noise in the receiver output. The best value achieved was3.16degK. Based on this result, the receiver noise figure and the mixer conversion loss were determined indirectly. The results were 31.4 dB and 22.9 dB, respectively. A blackbody radiation source served to calibrate the radiometer.     

8mm波段直接检波式接收机研究

以弹载被动毫米阵列探测系统为应用背景，提出一种8mm波段直接检波式接收机，在论述其系统工作原理的基础上，对相关系统参数进行了分析与设计，方案性试验研究结果表明：这种辐射计具有灵敏度高、探测精度高和体积小等优点。     

基于地基微波辐射计的大气参数廓线遥感探测

介绍了实时连续遥感探测大气温度廓线、湿度廓线和液态水含量廓线的地基微波辐射计。通过无线电气球探空测量的温度、湿度廓线、太阳辐射计测量的晴天水汽总量与微波辐射计探测结果的对比,证明该微波辐射计可以可靠地探测大气温度、湿度和水汽总量。通过对两个典型天气事件微波辐射计的观测数据分析表明：微波辐射计还可以监测云和天气变化的过程信息。     

微波辐射计接收机两点定标法误差分析及准确性验证

介绍了微波辐射计接收机两点定标法,并进行了误差分析.对自行研制的23.8GHz数字增益自动补偿微波辐射计进行了定标,计算定标误差范围.对接收机两点定标法得到的定标方程进行了验证实验,结果表明采用两点定标法对辐射计接收机进行定标有良好的准确性.     

实时定标微波辐射计

本文提出了一种新形式的微波辐射计,即实时定标微波辐射计。这种体制的微波辐射计具有的特点是:不受增益波动的影响,不受本机噪声变化的影响,能够提供连续的定标,动态范围宽等。制作了一台C波段实时定标微波辐射计,积分时间为0.2s,灵敏度为0.2K,线性度为0.9990,适应于地面、机载和星载微波遥感。     

A New Type of Digital Compensatory Millimeter Wave Radiometer

System gain and receiver noise are two main impact factors of total power millimeter wave (MMW) radiometer output. In this paper, a new method of using software to compensate system gain and receiver noise fluctuation is introduced. This method can keep the long-term stability and accuracy of the radiometer. At the same time, only one matching load is used as the reference source, which can prevent the trouble caused by using two cold and hot calibration sources in ground-based or airborne radiometer. The preliminary experiment proves the efficiency of the method.     

The Sensitivity Analysis of Full Digital Compensatory MMW Radiometer

The digital compensatory millimeter wave radiometer is a new type of radiometer, which uses the digital compensatory operator to compensate gain and receiver noise fluctuation. This paper aims at the full digital compensatory 8 MMW radiometer which was designed, proposing the analysis method of its sensitivity, obtaining the mathematical formulae of its equivalent integration time and the best sensitivity adjustment method by software.     

Calibration procedure of a microwave total-power radiometer

A total-power radiometer built in combination with a beacon receiver is being used for low-level attenuation measurements. This experimental receiver was built to measure atmospheric propagation impairments, using the ITALSAT satellite 50 GHz signal. The radiometer is mainly used to provide the reference level for the beacon measurements. Its precision should be better than ±3 K, for low attenuation levels, in order to have 0.1 dB accuracy in the attenuation measurements. A suitable calibration procedure is described     

A Gain-Stabilized Maser Radiometer for 13 cm (Correspondence)

A radiometer using noise from a neon discharge tube to effect gain stabilization of a 13-cm maser radiometer is described. A balancing technique is used to make the output insensitive to gain and bandwidth fluctuations. The output does, however, depend on the total system noise temperature, and the technique is best suited to a receiver using a low-noise traveling wave maser, whose effective noise temperature is inherently stable.     

Submillimeter-wave heterodyne spectroscopy with a compact solid state radiometer

A compact, solid state submillimeter-wave heterodyne radiometer has been developed and was used to measure spectral characteristics of a water vapor jet in a space simulation chamber. Features of the 557 GHz water vapor line profile were observed in significantly greater detail than in previous experiments through an increased sensitivity and improved frequency resolution (600 kHz). The local oscillator of the radiometer consisted of a frequency multiplication chain which was driven by an InP Gunn oscillator at 92.6 GHz, and which contained a frequency tripler and harmonic mixer in cascade. The front end of the receiver had a noise temperature of 4500 K (DSB) at 555 GHz, consumed 3 W and weighed 3 kg. This advance in technology is particularly relevant to submillimeter-wave radiometry from a space-based platform.     

Simultaneous analysis of downlink beacon dynamics and skybrightness temperature. Part II. Extraction of amplitude scintillations

This paper addresses the long-standing problem of separating the tropospheric amplitude scintillations from the dominant trend of atmospheric attenuation in a satellite downlink. Following extensive theoretical and experimental work, it is shown how the use of a radiometer coaxial with the communications beacon receiver constitutes an excellent tool for an optimum separation regardless of the meteorological conditions along the propagation path and avoids the use of the long-traditional high-pass filter approach. The experimental and theoretical work has revealed that the angular resolution of the radiometer together with the dynamics of rain attenuation and tropospheric scintillations determine the success of the extraction. This is because fast fadings require large radiometer antennas in order to resolve the sky temperature fluctuations. The dynamic behavior of rain attenuation has been reanalyzed and adapted for this study with special focus on the Maseng-Bakken (MB) model and the impact of the slant path on attenuation dynamics. The importance of the antenna pattern in the time response of the radiometer is studied in detail and permits to derive the maximum Fourier component observable for a given antenna size. The theoretical work has been verified by means of extensive experimental results obtained using a dual radiometer system and a beacon receiver tracking the ITALSAT 39.5 GHz F40 beacon. Finally, because of its importance and direct relevance to future communication systems benefiting from fade countermeasure strategies, the minimum size of the radiometer antenna for a successful extraction of amplitude scintillations is determined as a function of the elevation angle and carrier frequency     

基于BP神经网络辅助的车载组合导航算法研究

针对INS/GPS组合导航系统在GPS信号被遮挡时,GPS接收机失锁导致导航精度迅速下降的问题,提出了基于BP神经网络辅助的组合导航算法。即在GPS信号锁定的时候,采用卡尔曼滤波对INS/GPS信号进行数据融合得到实时的精确位置,同时利用组合导航输出信息对BP神经网络进行实时在线训练;一旦GPS失锁,利用之前训练好的神经网络对INS系统进行误差补偿,解决精度迅速下降问题。通过跑车实验证明,速度精度在0.2m/s以内,位置精度为25m以内,该算法对INS/GPS组合导航系统有效。     

Low-Noise Receiver Design Trends Using State-of-the-Art Building Blocks

The current state-of-the-art and the various design tradeoffs encompassing the variety of low-noise microwave and millimeter-wave receiver "building blocks" which have evolved during the past two decades are described. Key examples of these are the high-idler non-cryogenic parametric amplifier, the gallium arsenide field-effect transistor (GaAs FET) amplifier, and the image-enhanced Schottky-diode mixer. It is then shown how this inventory of building blocks can best be integrated into optimum receiver configurations for application in a multiplicity of future and present microwave and miltimeter-wave communications, RADAR, and radiometer systems.     

Stable differential radiometer

A differential radiometer using a balanced receiver is described. The radiometer has good immunity to fast gain variations and atmospheric fluctuations.<>     

周期两点定标微波辐射计原理研究

根据热辐射理论,任何温度处于绝对零度以上的物体都存在热辐射。通常用亮度温度来表征物体的辐射强度,其取决于物体本身的几何特性与介电特性。微波辐射计是用于测量物体微波辐射能量的被动遥感仪器,在军事、环境科学上都有重要的作用。阐述了微波辐射计的定标原理,介绍了周期两点定标方法,并简要描述了某毫米波成像辐射计的结构组成和工作原理。     

噪声相加比较式微波辐射计体制研究

在微波辐射计的应用中,系统增益长期稳定性是一个重要设计指标。本文给出了一种噪声相加比较式微波辐射计体制。通过实验证明此体制具有测量的准确度与系统的增益变化无关、输出与接收机噪声温度无关的优点。     

The Low-Noise 115-GHz Receiver on the Columbia-GISS 4-ft Radio Telescope

The superheterodyne millimeter-wave radiometer on the Columbia-GISS 4-ft telescope is described. This receiver uses a room-temperature Schottky diode mixer, with a resonant-ring filter as LO diplexer. The diplexer has low signal loss, efficient LO power coupling, and suppresses most of the LO noise at both sidebands. The receiver IF section has a parametric amplifier as its first stage with sufficient gain to overcome the second-stage amplifier noise. A broad-banded quarter-wave impedance transformer minimizes the mismatch between mixer and paramp. At 115 GHz, the SSB receiver noise temperature is 860 K, which is believed to be the lowest figure so far reported for a room-temperature receiver at this frequency.