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УДК 621.396.96
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Abstract
The algorithm for optimal signal processing in the single-channel radiometer of modulation-com- pensating type is synthesized using the maximum likelihood method. It is shown that a possible tech- nical realization of the resulting algorithm can be implemented in a way similar to the Dicke radiom- eter. Based on the analysis of the inverse Fisher ma- trix, was given estimates of the potential accuracy of measurements of the sources of thermal radia- tion.
Key words: optimal algorithm for radiometric sig- nal processing, single-channel radiometer modula- tion-compensating type, the potential accuracy of the estimates
D+&C B'&EG'>EHHCI E B'&ED+BEFDEI EDBDHE*
© !", 2011
Павликов В.В. —Кандидат технических наук, докторант Национального аэрокосмического университета им. Н. Е. Жуковского (ХАИ), Украина
E-mail: [email protected]
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1. Dicke R.H. The Measurement of Thermal Radiation at Microwave Frequencies // Review of Scienti c Instruments. 1946. Vol. 17. P. 268–275.
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STATISTICAL SYNTHESIS OF OPTIMAL STRUCTURE OF ULTRAWIDEBAND RADIOMETER
OF MODULATION-COMPENSATING TYPE
Pavlikov V.V.
In radiometry uses a lot of different types radiometers: modulation radiometer, compensation radiometer, correlation radiometer and their modi cations. Such a variety of receivers due to the lack of an acceptable technical realization of optimum radiometer, assuming a quadratic detection and signal accumulation. The main dif culties in its realization of are due to changes in the gain of the receiving channel radiometer in time that it requires constant control and calibration. Technical solutions to reduce the marked disadvantage, it was proposed in 1946 by Prof. Dicke, and was to introduce the operation of modulation of the input process before noisy elements radio receiver. This heuristic approach allows subsequent processing to separate the useful signal from the internal receiver noise. Usually in practice using the modulating function in the form of square wave, which corresponds to a simple unlocking or locking of the radiometer’s input. At times, when the antenna is disconnected from the radiometer to its input may further apply the reference signal. In this case, within one half to the input of the radiometer affects the additive mixture of useful process and internal noise of radiometer, and the next half-period — or internal noise of receiver, or additive mixture of the reference signal and the internal receiver noise. It is known that the further processing of the input process has such important operations as gain, quadratic detection, resonant ltering and synchronous detection. If alternately to the input of this scheme to connect the signals from the antenna and the reference channel, the output of such a scheme receive a signal proportional to the difference in their intensities. The sensitivity of these radiometers are lower and depends on the modulation function. However, the advantages of this type radiometers are the possibility of sharing useful component and internal receiver noise, as well as reducing the inZ uence of instability of the gain on the evaluation results. This causes their widespread use for solving scienti c and economic problems.
Interest is the solution to the problem of statistical synthesis of optimal processing algorithm, the radiometric signals in single-channel ultrawideband radiometers of modulation-compensating type. Analysis of the results obtained allow the development of quasioptimal technical implementation of the radiometer and compare it with existing ones.
The solution of the problem is obtained by the method of maximum likelihood. From the analysis of the synthesized of the algorithm an optimal processing of radiometric signals that the basic operations of the optimal treatment are: whitewashing the input sequence; quadratic detection bleached consistency and integration, subtraction of the measured intensities at neighboring Intervals input and reference signals.
Examine the possible technical implementation of the radiometer, which realizes the algorithm obtained. The proposed scheme is similar to the well-known realization of a modulation radiometer Dicke, with the difference in the presence of the resulting scheme whitening lter, the frequency characteristics depend on the signal to noise ratio. Accordingly, for processing signals from the antenna and the reference source is necessary to use two whitening lter connection which must be carried out simultaneously with the ling of these signals to the input of the radiometer.
Based on the analysis of the matrix inverse of the Fisher matrix estimates are given for the potential accuracy of measurements of the investigated sources of thermal radiation. The value of the limiting error is twice larger than that of the radiometer without modulation. This is because the time parameter estimation due to modulation halved. It is important to note that the quality of the estimation of the parameters affect the time of observation, the band radiometer operating frequencies and signal to noise ratio. In this frequency band is determined after the whitening lter, which extends the input band radiometer. From this it follows that whatever we do not have a wide frequency band, it still needs to be broadened in order to reduce potential errors in measurement.
