RU101842U1 - BROADBAND RADIOMETER WITH RADIO INTERFERENCE SELECTION - Google Patents

Abstract

 1. Broadband radiometer containing a broadband receive-amplifier channel with an analog-to-digital converter, which is connected to a clock generator, a spectrum calculator on a programmable logic integrated circuit (FPGA) with an FPGA configuration device and an interface controller connected to a radio telescope computer, characterized in that (n-1) additional spectrum calculators on the FPGA, an n-channel demultiplexer, an n-channel spectrum adder, a signal processor connected to the interface controller and an annular n-element shift register connected to the mentioned clock generator, n-channel demultiplexer and all n spectrum calculators, the n-channel spectrum adder connected to the outputs of n spectrum calculators and to the signal processor, the outputs of the n-channel the demultiplexer is connected to all spectrum calculators, (n-1) additional spectrum calculators are connected to the FPGA configuration device, which is connected to the signal processor by the control inputs, and the output s with an n-channel spectrum adder. ! 2. The broadband radiometer according to claim 1, characterized in that the signal processor is connected to a gain modulator of the broadband receive-amplifier channel and to a modulated noise generator connected to the input of the radiometer.

Description

The utility model relates to radio astronomy systems and can be used, for example, for the reception and registration of very weak (much lower than the level of the noise of the radio telescope) radio signals from space sources of broadband radio emission. Using such systems — radiometers — the average values of the noise temperature T _{s of the} broadband radio signal of the cosmic radiation source in the passband of the receiving device Δf are measured. With a sufficiently wide band Δf (hundreds of megahertz), radiometers record broadband radio signals whose temperature is approximately 40 dB lower than the temperature T _{w of} the noise of the radio telescope (see, for example, the article by Finkelshtein AM, Ipatov A.V., Smolentseva S.G. Radio interferometric network " Quasar "- scientific tasks, technology and the future. // M .: Earth and the Universe No. 4, 2004, p.12-27.).

Almost all known radio astronomy radiometers are built according to the traditional scheme, in which there is a broadband receiving-amplifying path with a quadratic detector at the output and a narrow-band measuring path with an output recording device (see, for example, the book by N. Esepkina, D.V. Korolkova, Pariysky Yu.N. "Radio telescopes and radiometers" M. 1973, patent Lebedev V.S., Orlova I.Ya., Koshechkina V.A. "Modulation radiometer" (application No. 4916584/09 from 01.30.1991), Shesternev’s patent D.M., Filatova A.V. “Zero radiometer” (application No. 2003101276/09 of 01/17/2003), patent A. N. condition “Modulation radiometer using direct frequency conversion” (application No. 2008126303/22 dated 06/27/2008), article by Ipatova A.V., Koltsova N.E., Krokhaleva A.V. “Radiometric system of the RTF- radio telescope 32 ". Instruments and experimental equipment, No. 4, Moscow: Nauka, 2005, p.66-75). The disadvantage of such radiometers is their low protection against narrow-band radio interference created by radio communication systems and radio equipment for various purposes. Radio interference received by the antenna in an additive mixture with the studied broadband signal and the noise of the radio telescope is detected by a quadratic amplitude detector, thereby changing the output voltage of the radiometer and distorting the measurement results of the noise temperature T _{s of} the signal under study.

The closest in purpose and technical essence is a radiometric system without an amplitude quadratic detector, which is described in application for invention No. 2008108318/09 (008999) dated 03.03.2008 “Radiometric method for detecting weak broadband radio emission”.

This system (prototype) contains a broadband amplifier channel for the microwave range, a video converter, an analog-to-digital voltage converter (ADC) with a clock generator for reading signal samples, a spectral calculator on programmable logic integrated circuits (FPGA) and a computer that records the results of observations . Modulated noise generators (GS) can be connected to the input of a broadband amplifier channel, used when the radiometer is in modulation mode or when calibrating the radiometer's transmission coefficient, which is carried out by methods known in radio astronomy. Unlike radiometer with quadratic detectors, the device can operate effectively under the influence of narrowband interference, because there is noise broadband signal determined from the measured temperature and accumulated at a certain time interval t _n range from which the excluded components on radio frequencies.

A disadvantage of the known device (prototype) is the limited frequency band of reception and, accordingly, the limited sensitivity of the radiometer, which is determined by the bandwidth of the video converter and the maximum clock frequency for the spectrum calculator on the FPGA. In the known device, the maximum reception band when using two channels is 64 MHz. Although modern ADCs can digitize signals with a clock frequency of up to 5 GHz (for example, EV2AQ160 from e2v) and even if the bandwidth of the video converter is removed, it is known that for the most advanced FPGAs (for example, XC5VSX35 from Xilinx) the maximum clock frequency is 550 MHz, which limits the ability to register and process signals with a band of not more than 275 MHz.

For radiometric measurements of the weakest radio signals of space origin, wider bands of the receiving channel are needed, for example, 500, 900, or even 2000 MHz.

The purpose of the claimed utility model is to expand the frequency band of the reception and, accordingly, increase the sensitivity and accuracy of the measurement of energy parameters (noise temperature, power) of a broadband radio signal when exposed to narrow-band interference.

This goal is achieved by the fact that in a radiometer containing a broadband receive-amplifier channel with an analog-to-digital converter, which is connected to a clock frequency generator, a spectrum calculator on an FPGA, an FPGA configuration device and an interface controller connected to a radio telescope computer and to an FPGA configuration device, introduced (n-1) additional spectrum calculators on the FPGA, n-channel demultiplexer, n-channel spectrum adder, a signal processor connected to the mentioned interface controller, annular n-element shift register connected to the mentioned clock generator, n-channel demultiplexer and with all n spectrum calculators, and the n-channel spectrum adder is connected to the outputs of n spectrum calculators and to the signal processor, the outputs of the n-channel demultiplexer are connected to the inputs spectrum calculators, and (n-1) additional spectrum calculators are connected to the FPGA configuration device.

The introduction of an n-channel demultiplexer, (n-1) additional spectrum calculators, an n-channel adder, and an annular n-element shift register made it possible to distribute the processing of a broadband signal among n spectrum calculation channels operating at a clock frequency f _t = f _cf / n (where f _sc - the clock frequency of reading the samples of the signal, which for modern ADCs is much higher than the maximum frequency f _t allowed for FPGAs). This made it possible to record the energy parameters of a broadband noise signal in a band up to f _cf / 2, which on a modern element base can reach 5 GHz. Each spectrum calculator processes its part of the packet of signal samples and accumulates spectrum implementations in its internal memory (primary averaging). The spectra at the outputs of the spectrum calculators are the sum of the overlays of the Nyquist zones of the spectrum of the investigated broadband signal and the spectra of the received radio noise obtained at time instants that are phase shifted by 2π / n radians (from 0 to n-1). With sufficient accumulation, the spectra of narrowband radio interference are clearly defined as emissions on the smooth spectrum of a broadband signal and can be excluded from consideration. At the end of the accumulation cycle, the averaged spectra of each calculator are transmitted to the n-channel adder, where they are secondary componentwise averaged, and the dispersion of the spectral components decreases time. The signal processor receives the averaged spectrum from the n-channel adder, from which, according to the amplitude criterion, excludes the spectrum components at the radio noise frequencies, and then sums up all the remaining spectrum components in the storage register and transmits the obtained value to the registration device.

Figure 1 shows a block diagram of the inventive utility model. Figure 2 shows a block diagram of a modulation radiometer with a noise pilot based on the claimed utility model. Figure 3 shows a block diagram of the operation of the claimed utility model in the mode of a modulation radiometer with switching input.

In these figures is indicated:

1 - broadband receiving-amplifying channel (ShPC);

2 - High-speed analog-to-digital voltage converter (ADC);

3 - n-channel demultiplexer;

4 ₁ -4 _n - high-speed FPGA spectrum calculators (total of n calculators);

5 - n-channel adder of spectra on the FPGA;

6 - signal processor;

7 - controller interface with a computer;

8 - clock generator;

9 - ring n-element shift register;

10 - device configuration FPGA;

11 - gain modulator;

12 - antenna;

13 - noise generator;

14 - directional coupler;

15 - switch.

The scheme of the claimed utility model (Figure 1) contains a broadband receive-amplifier channel 1, ADC 2 (for example, an AT84AS008 chip operating at a clock frequency of up to 2.2 GHz), a demultiplexer 3 (for example, AT84CS001, which distributes the digital stream over 4 channels), n- FPGA spectrum calculators 4 ₁ -4 _n , n-channel spectrum adder 5 (e.g. based on XC4VLX100 FPGA), signal processor 6 (e.g. AD BF 600), interface controller 7 (e.g. CY7C68013 when using USB 2.0 as an interface between the signal processor 6 and the computer) and the recorder and (e.g., a radio telescope computer) that are connected in series. The reference frequency generator 8 is connected directly to the ADC 2 and through the annular n-element shift register 9 is connected to the demultiplexer 3 and all spectrum calculators on the FPGA 4 ₁ -4 _n . The clock inputs of the oscillator 8 and the local oscillators of the receive-amplifier channel 1 are usually connected to an external generator of a highly stable reference frequency f _sync (for example, to the hydrogen frequency standard on a radio telescope). The FPGA configuration device 10 with the control inputs is connected to the signal processor 6, and the outputs are connected to all spectrum calculators on the FPGA 4 ₁ -4 _n and with the n-channel spectrum adder 5.

The inventive utility model can operate in any of three modes widely used in radio astronomy: without modulating a radio receiver (the so-called compensation radiometer mode), when the signal is continuously accumulated during the observation time of the source t _obs , in modulation mode with input switching and in modulation mode with noise pilot signal, which minimized the influence of the noise level of instability T _w and the gain K in the receiving channel, but the signal is received and stored only in Techa s half of the observation time.

For the operation of the claimed utility model in the compensation radiometer mode, it is connected directly to the antenna 12.

To ensure operation in the modulation radiometer mode with a noise pilot signal (Figure 2), a gain modulator 11 is introduced into the receiving-amplifying channel 1 of the claimed utility model, and it itself is connected to the output of the directional coupler 14, the antenna 12 is connected to its first input, and to the second input - the output of the controlled noise generator 13. The control inputs of the noise generator 13 and the modulator 11 are connected to the output of the modulating voltage of the signal processor 6.

When operating in modulating mode with switching input (Figure 3), the claimed utility model is connected to the output of switch 15, the first input of which is connected to antenna 12, and to the second is the output of noise generator 13. The output of the modulating voltage of signal processor 6 is connected to the control input of switch 15 .

The operation of the claimed utility model in the compensation mode is as follows. When the power supply apparatus configuring FPGA 10 under control of the signal processor 6 reads from its internal memory the codes, which sets the configuration of the FPGA calculators spectra April ₁ -4 _n and n-channel spectra adder 5 by default. From the computer, through the interface controller 7, the initial data for signal registration is entered into the signal processor 6 — the operating mode code, according to which the FPGA configurations of devices 4 ₁ -4 _n and 5 are loaded to ensure operation in compensation, modulation or modulation modes with a pilot signal , and the time of reception and accumulation of the signal t _n .

A system prepared for operation in this way calculates the spectra and energy parameters of the signal cyclically.

ADC 2, connected directly to the output of the broadband receive-amplifier channel, reads signal samples with a frequency f _cf = 2f _max , where f _max = (f _n + Δf) is the upper cutoff frequency of the broadband channel bandwidth, f _n is the lower border of the passband broadband channel. Digital signal samples taken by ADC 2 with a readout frequency are distributed circularly using a demultiplexer 3 over n spectrum calculators 4 ₁ -4 _n , each of which calculates spectrum implementations in a band f _max / n with a clock frequency using n-thinned signal sample packets f _t = 2 _max / n and accumulates (averages) them over a given time interval t _n . Spectrum calculators 4 ₁ -4 _n work according to the principles described in the patent of the Russian Federation for utility model No. 64386 dated 01/31/2007 newsletter No. 18. (Grenkov S.A., Ipatov A.V., Koltsov N.E. “System for the analysis of the spectra of narrow-band cosmic radio emissions”). ADC 2 operates at a frequency which is 2 times the maximum frequency of the input signal, and n-calculators spectrum calculated realization of the spectrum by the method of Fast Fourier Transform (FFT), operate at f frequency _t = f _sch / n, where n - number of demultiplexer channels. For each of the spectrum calculators 4 ₁ -4 _n, signals of the clock frequency f _cf / n, phase shifted relative to each other by 2π / n, are obtained, which are obtained using a circular n-element shift register. From the output of each spectrum calculator 4 ₁ -4 _{n, the} n-channel adder reads the averaged spectrum implementations, which are the sum of the overlays of the Nyquist spectra of the studied broadband signal and the received radio noise received at time instants that are phase-shifted by 2π / n radians . Further, the i-channel adder on FPGA 5 sums up these spectra element-wise (secondary averages), while the variance of the spectrum samples decreases in times ( = 2 when using the AT84CS001 as a demultiplexer). As a result of the secondary averaging of the spectra, narrow-band interference can be distinguished against the background of a smooth spectrum of the intrinsic noise of the receiving system and the signal under study and excluded from consideration, which is what signal processor 6 does according to the amplitude criterion. The exclusion from consideration of the spectrum components at frequencies occupied by radio noise and summing up the remaining components gives the total power of the studied signal and the noise of the radio telescope in the band Δf ₁ = Δf-Δf _x , where Δf _x is the total frequency band occupied by narrow-band interference. Subtracting from the received power the power of the own noise of the radio telescope in the same band, we obtain the power or noise temperature T _{s of the} investigated signal in the band Δf ₁ . In this case, the influence of any narrow-band radio interference is excluded, regardless of their duration and type of modulation. The result of the calculations through the controller interface 7 is transmitted to the registration device. Since all digital packets of signal samples obtained for the frequency band Δf of the broadband receiving channel are taken into account in the calculations, the energy parameters of the noise signal are determined for the same band and, accordingly, the sensitivity and accuracy of radiometric measurements of the energy parameters of broadband radio emission are increased. For narrowband radio interference Δf _x << Δf, the narrowing of the frequency band to Δf ₁ = Δf-Δf _x compared to the original band Δf is small and almost does not affect the sensitivity of the radiometer. The transition from power to noise temperatures is carried out by standard methods for radio astronomy using amplitude calibration of the receiving-amplifying channel. After calibration, you can calculate the power when tuning to the signal and during the detuning from it, and then find the noise temperature T _{s of the} received broadband signal from the difference in the measured powers.

The signal processor 6 also performs the function of decoding the commands received from the computer through the interface controller 7, when exchanging data between the computer and the n-channel adder of spectra 5. From the computer through the interface controller 7, the initial data for data recording is entered into the signal processor 6 - operating mode compensation mode, modulation mode, modulation mode with a noise pilot signal), and the time of reception and accumulation of signal T.

The operation of the device in the modulation radiometer mode with a noise pilot signal (Figure 2) differs in that the FPGAs of the spectrum calculators are configured and controlled in such a way that the spectra are accumulated when the noise generator 13 is turned on and the modulator 11 is closed, and the noise generator 12 is turned off and the modulator is open 11 were accumulated in separate memory blocks of the corresponding drives of spectrum calculators 4 ₁ -4 _n . Analog-to-digital converter 2 and demultiplexer 3 work in the same way as compensation mode. The signal processor 6, in contrast to the compensation mode, here, in addition to performing all the above functions, generates a modulation voltage - either the meander, or the signal is on or the signal is off, and the edges of the meander are synchronized with the spectrum calculation cycles. A ready-to-use system calculates the spectra cyclically. The signal processor 6 delivers a logic zero voltage (log 0) to the noise generator 13 and modulator 11, at which the ADC 2 is affected by a mixture of the signal received by the antenna and the intrinsic noise of the radio telescope with a temperature of T _s . Spectrum calculators 4 ₁ -4 _n calculate and accumulate spectra with the noise generator turned off and store the averaged spectrum in memory blocks 1. Then, upon completion of the modulation half-cycle, the signal processor 6 changes the voltage at the modulation output from log.0 to log.1. In this case, the noise generator 13 is turned on, and the modulator 11 is closed and the noise mixture of the noise generator 13 is affected by the ADC 2 input. The obtained spectral implementations are accumulated in the memory blocks of 2 spectrum calculators 4 ₁ -4 _n . Further, the cycles of variation of the modulation voltage are repeated. After accumulating implementation spectrum over a predetermined time interval t _n is performed element-wise subtraction of the spectra with and without the noise generator with subsequent transfer to the n-channel adder 5 spectra.

When operating in the mode of a modulated radiometer with input switching (Figure 3), the difference from the operation according to the above scheme (Figure 2) is that the signal processor 6 controls the switch 15 so that the outputs of the antenna 12 and alternately are connected to the input of the broadband channel 1 noise generator 13. In this case, the calculated spectrum implementations, as well as when operating in the modulation radiometer mode with a noise pilot signal, are accumulated and averaged separately for half-periods of modulation, during which it takes I analyzed signal (the switch are switched to the output antenna 12), and for half-periods during which the incoming signal from the antenna substituted equivalent antenna noise (switch are switched to the output of the noise generator 13). Comparison (subtraction) of the spectra obtained after averaging gives the energy spectrum of the signal received by the radio telescope antenna, which is transmitted to the signal processor 6 to eliminate the components of the interference spectrum.

When using the AT84AS008 chip as an ADC 2, and the AT84CS001 chip as a demultiplexer 3, for example, the generator 8 can be tuned to a frequency f _sc = 2000 MHz, which allows signals to be recorded in the band up to 1000 MHz. The AT84CS001 demultiplexer contains a built-in annular and-element shift register. Therefore, the n-channel demultiplexer 3 and the i-element shift register 9 can be performed on a single chip (AT84CS001). The frequency f _sc and the number of discrete frequencies N in the spectrum determine the spread ν = f _sc / 2N of discrete frequencies in the analysis band, where N is a fixed number of discrete frequencies in one channel of spectrum calculators 4 ₁ -4 _n . The number N is determined by the FPGA configurations and is limited by the amount of memory blocks and multipliers built into them. For example, when using the XC4VSX55 FPGA, you can set N = 8192 or less. FPGA configurations provides FFT spectral calculations in parallel with reading the signal without additional time loss (the so-called conveyor method). The calculation time t of one spectrum realization is determined only by the read time of 2N samples of the signal and is equal to t _cf = 1 / ν. The registration and recording of signals can be performed by a conventional computer.

According to the proposed scheme, RELTA CJSC made a model of the proposed utility model, which was installed on a 32-meter radio telescope at the Badary Observatory and tested by the Institute of Applied Astronomy of the Russian Academy of Sciences. The system was tested both in laboratory conditions and with real observations of space sources of radio emission. As a result of the tests, the effectiveness of the proposed broadband radiometer with radio interference selection was fully confirmed, namely, an increase in sensitivity and accuracy due to the expansion of the frequency band was achieved. The positive effect is especially noticeable when analyzing weak sources under the influence of radio interference. During the experiment, the spectrum accumulation time in the layout of the broadband radiometer was chosen to be 1 s, and the number of discrete frequencies in the spectrum with a band of 500 MHz was N = 8192. With the relation “interference amplitude / system noise” = -5 dB, in the absence of accumulation, interference is not visible (the noise of the receiving system in power calibration in noise temperature units was 67 K, and the maximum interference amplitude with a band of about 4.2 MHz was 20 K ) When carrying out radiometric measurements of a useful signal, the amplitude of which is 0.6 K, under the influence of such interference with a conventional radiometer with an amplitude quadratic detector, the measured value diverges from the desired value by 0.168 K, that is, the relative measurement error is 28%, which is a lot. When accumulating for 1 s in the prototype of a broadband radiometer with interference selection, the interference spectrum is clearly visible on a smooth spectrum of a mixture of noise of the receiving system and the useful signal. After eliminating the interference, the difference between the measured value and the sought one was only 0.001 K (or 0.16% in relative values).

The advantages of a spectrally selective radiometer are obvious. You can select both pulsed and continuous interference. Since the operation of excluding the spectral components is preceded by the accumulation and averaging of the spectrum, even relatively weak radio interference (under the intrinsic noise of the radio telescope) is detected and eliminated.

Claims (2)

1. Broadband radiometer containing a broadband receive-amplifier channel with an analog-to-digital converter, which is connected to a clock generator, a spectrum calculator on a programmable logic integrated circuit (FPGA) with an FPGA configuration device and an interface controller connected to a radio telescope computer, characterized in that (n-1) additional spectrum calculators on the FPGA, an n-channel demultiplexer, an n-channel spectrum adder, a signal processor connected to the interface controller and an annular n-element shift register connected to the mentioned clock generator, n-channel demultiplexer and all n spectrum calculators, the n-channel spectrum adder connected to the outputs of n spectrum calculators and to the signal processor, the outputs of the n-channel the demultiplexer is connected to all spectrum calculators, (n-1) additional spectrum calculators are connected to the FPGA configuration device, which is connected to the signal processor by the control inputs, and the output s with an n-channel spectrum adder. 2. The broadband radiometer according to claim 1, characterized in that the signal processor is connected to a gain modulator of the broadband receive-amplifier channel and to a modulated noise generator connected to the input of the radiometer.