RU2575209C2 - Method of calibrating receiving radio links of radio interferometer and device therefor - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: method of calibrating receiving radio links of a radio interferometer and a device therefor include monitoring and adjusting the amplitude and phase identity of the receiving radio links of the radio interferometer in a wide frequency range and at different distances between receiving antennae.

EFFECT: high accuracy of forming a calibration database and cutting the required number of cable links by half.

2 cl, 1 dwg

Description

The invention relates to radio engineering and can be used in radio interferometers and microwave range finders. The invention is applicable in stationary and mobile systems for determining the location of objects by radio emission of microwave transmitters on-board. The invention is intended to control and adjust the amplitude and phase non-identity of the receiving radio channels of the radio interferometer in a wide frequency band and at different distances between the receiving antennas.

Direction finding errors in the radio interferometer are largely determined by the imperfection of the receiving radio channels [1]. At the same time, the characteristics of the receiving radio channels are affected by weather conditions, aging of elements, etc. To compensate for systematic errors in the radio interferometer, a calibration mode for the receiving radio channels using the built-in monitoring tools is required. The calibration procedure should be carried out periodically.

A known method of calibration of the receiving paths of the radio interferometer [1], including:

the formation of a broadband pulse control signal (CS), the level of which is lower than the level of the receiver noise floor;

radiation from a separate calibration antenna to each receiving antenna of the radio interferometer;

KS reception by each channel;

digital to digital conversion;

correlation accumulation and processing of CS;

construction of amplitude and phase characteristics.

This calibration method allows you to combine calibration and operation, but has the following disadvantages:

there is no mechanism for taking into account the amplitude and phase non-identities of the transmission channels of the CS to the receiving paths, which is of particular importance with increasing distances between the receiving antennas of the radio interferometer;

the relative position of the receiving and calibration antennas, their individual characteristics and the influence of reflections are not taken into account;

the difference in the structure of the calibration signal and the working signals reduces the calibration efficiency;

as a result of the combination of operating modes and calibration, the signal-to-noise ratio is reduced.

Also known is a method of calibrating receiving paths [2], including:

formation of a broadband pulsed CS;

CS radiation from one antenna from a variety of azimuthal directions to all receiving antennas;

reception of signals by each channel;

digital signal conversion;

correlation extraction of signals of various rays and polarizations;

creation of a calibration database.

This calibration method includes receiving antennas along with receiving paths and can also be used for calibration, but this method also has disadvantages, which include:

the need to use the remote transmitter of the CS at a certain distance and to ensure transmission from various directions seems difficult, especially for stationary systems;

there is no mechanism for taking into account the amplitude and phase non-identities of the transmission channels of the CS to the receiving paths, which becomes especially important when the distances between the receiving antennas of the radio interferometer increase.

The above calibration methods do not provide the necessary accuracy and are not easy to implement, but there are other methods, one of which is the internal calibration of the radio channels with the receiving antennas turned off. Receiving antenna calibration is done separately.

Closest to the proposed method for calibrating the receiving radio channels of the interferometer by the totality of actions on the signal is the method adopted for the prototype [3], based on the transmission of the SC to the inputs of the receiving radio channels using a separate cable communication line (CLS).

According to this method:

1. Form a pulsed CS at various frequencies.

2. Commute the line of distribution of the COP to the transmission in the forward direction.

3. Receive a signal by each channel.

4. Synchronously convert the signal in each channel into a digital stream.

5. Calculate and store the relative amplitude and phase characteristics between the channels.

6. Commute the distribution line of the calibration signal to the transmission in the opposite direction.

7. Repeat paragraphs 3, 4, 5.

8. Based on the data of the two stages create a calibration database.

This method provides the ability to take into account the amplitude and phase non-identities of the transmission channels of the CS, however, it requires the use of a separate CLS for their transmission, which at large distances between the receiving antennas is a significant drawback. In addition, the method does not provide the maximum achievable calibration accuracy, because as the distance between the receiving antennas increases, the difference in the level of signals between the channels increases, and when using bi-directional amplifiers, the calibration accuracy decreases.

Closest to the proposed calibration device for the totality of features is a device adopted for the prototype [4], containing N receiving radio channels, respectively consisting of series-connected receiving antennas, omnidirectional communication elements, mixers and amplifiers of intermediate frequency (IF), a local oscillator and a control generator.

The disadvantages of the calibration device of the receiving paths of the radio interferometer are:

the inability to exclude the influence of signals present on the air on the calibration result;

the impossibility of maintaining an acceptable level of CS at all inputs of the receiving paths with increasing length of the CLS.

the need for an additional separate SC transmission line to each channel, which leads to a significant increase in the cost of creating a radio interferometer with increasing distances between the receiving antennas.

The technical result of the invention is to increase the accuracy of measuring the amplitude and phase identity of the receiving radio channels of the radio interferometer at significant distances between the receiving antennas in a wide frequency band, as well as increasing the accuracy of forming the calibration data base and combining the CLS functions for transmitting received and calibration signals.

The technical result is achieved by the fact that in the method of calibrating the receiving radio channels of the microwave range interferometer, including the formation of a radio pulse control signal (KS), tunable at a variety of calibration frequencies, transmitting it to the inputs of the receiving paths, synchronizing the digital transmission of the received receiving channels of the KS and determining the difference in electrical the lengths of the receiving channels for each n-th calibration frequency as a result of measurements of the delays of the SC at two stages of its direct and reverse transmission, according to According to the invention, at the first calibration stage, the antenna outputs are turned off and the SCs are transmitted to the inputs of the receiving paths via cable communication lines (CLS), which switch through time τ to the reverse transmission through the receiving paths, and at the second calibration stage, close the CLSs at the inputs of the receiving paths and receive the reflected CL moreover, a pulse CS is formed, the pulse duration of which is less than the signal propagation time in the input circuits of the receiving paths.

The method is implemented by a device for calibrating radio channels. Another technical result of the invention is to simplify the design of the device by combining the functions of the CLS for transmitting received and calibration signals, as well as eliminating calibration errors due to the influence of external signals.

The technical result is achieved by the fact that the first, second and third switches, amplifiers, first and second lines are introduced in the device for implementing the method of calibrating the radio channels of the radio interferometer, consisting of N receiving radio channels, including receiving antennas, a calibration signal generator, a control and processing unit, according to the invention delays, first and second directional couplers, gate generators and combiners, the outputs of the first switches through amplifiers connected to the inputs of the first delay lines, output which are connected to the third inputs of the second switches, the second outputs of the second switches are connected to the first inputs of the first switches, and the inputs and outputs of the second switches are connected through the second delay lines to the inputs and outputs of the first directional couplers, the outputs of which are connected to the control inputs of the second switches through gate formers, the other inputs and outputs of the first couplers are connected to the inputs and outputs of the third switches, the outputs of which through adders are connected to the control and processing unit, and the inputs etih switches via second directional couplers connected to the outputs of the calibration signal generator which is also connected to the control input of the third switch, the other output of the second directional couplers via the adders are connected to a control and processing unit.

The drawing shows a structural diagram of a device for calibrating the radio channels of a radio interferometer.

For clarity, the structural diagram is shown for two channels and can be expanded to an arbitrary number of channels.

The device consists of series-connected receiving antennas, the first switches 1-1, 1-2, amplifiers 2-1, 2-2, the first delay lines 3-1, 3-2, the second switches 4-1, 4-2, delay lines 5-1, 5-2, first directional couplers 6-1, 6-2, gate formers 7-1, 7-2, third switches 8-1, 8-2, adders 9-1, 9-2, control unit and processing 10, the second directional couplers 11-1, 11-2, the calibration signal generator 12. The signal from the antennas is fed to the second inputs of the first switches 1-1, 1-2, the outputs of which are connected through amplifiers 2-1, 2-2 to first line inputs th delay 3-1, 3-2, the outputs of which are connected to the third inputs of the second switches 4-1, 4-2, the second outputs of which are connected to the first inputs of the first switches 1-1, 1-2, and the inputs and outputs of the second switches 4 -1, 4-2 through the second delay lines 5-1, 5-2 are connected to the inputs and outputs of the first directional couplers 6-1, 6-2, the outputs of which through the formers of the gates 7-1, 7-2 are connected to the control inputs of the second switches 4-1, 4-2, the other inputs and outputs of the first couplers 6-1, 6-2 are connected to the inputs and outputs of the third switches 8-1, 8-2, the outputs of which are through the adder S 9-1, 9-2 are connected to the control and processing unit 10, and the inputs of the third switches 8-1, 8-2 through the second directional couplers 11-1, 11-2 are connected to the outputs of the calibration signal generator 12, which is also connected to the control input of the third switches 8-1, 8-2, the other output of the second directional couplers 11-1, 11-2 through the adders 9-1, 9-2 is connected to the control and processing unit 10.

The device operates as follows.

The amplitude and phase identity of the receiving radio channels is measured in two stages, which differ in the order of operation of the switches.

At the first stage, the amplitude and phase identity of the receiving radio channels is measured together with the transmission circuits of the CS. To do this, the first switches 1-1 and 1-2 are put into calibration mode by disconnecting the antennas and connecting them to the second switches 4-1, 4-2. The calibration signal generator 12 is started in the pulse generation mode. The period and duration of the pulses is selected based on the length of the CLS to exclude the imposition of pulses, the frequency is tuned within the range, but within the pulse the frequency remains constant. CS from the generator of calibration signals 12 through the second directional couplers 11-1 and 11-2 and the third switches 8-1 and 8-2, controlled by the generator 12, are transmitted to the CLS, and then to the first directional couplers 6-1, 6-2, from where the CS is transmitted to the gate formers 7-1, 7-2, controlling the three-position switches 4-1, 4-2. At the first stage, when the KS passes from the CLS to the directional couplers 6-1, 6-2, the second switches 4-1 and 4-2 are transferred to the middle position, which ensures the transmission of the KS through the first switches 1-1, 1-2, amplifiers 2 -1, 2-2 and delay lines 3-1 and 3-2. Then, the gate formers 7-1 and 7-2 transfer the three-position switches 4-1, 4-2 to the position that ensures the transmission of the SC through the CLS to the third switches 8-1, 8-2, adders 9-1, 9-2 and the control unit and processing 10, where the measurement of the difference in electrical lengths of communication lines.

At the second stage, the amplitude and phase characteristics of the CLS are measured, for this, the three-position switches 4-1 and 4-2 are moved to the position providing the short circuit mode, and the calibration signal generator 12 is started in the pulse generation mode. The period and duration of the pulses is selected based on the delay in the propagation of the CS in the CLS to exclude the imposition of pulses, the frequency is tuned within the range, but within the pulse the frequency remains constant. The third switches 8-1 and 8-2, controlled by the calibration signal generator 12, during the passage of the SC transmit pulses through the directional couplers 11-1 and 11-2 to the directional couplers 6-1 and 6-2, passing the SC through the CLS of the receiving path in the direct and after reflection from the second switches 4-1 and 4-2 in the opposite direction. When the CS returns, the third switches 8-1 and 8-2 are moved to a position that ensures the transmission of the CS through the adders 9-1 and 9-2 to the control and processing unit 10, where complex cross-correlation processing of pulses transmitted through the CLS in the forward and reverse is performed directions, and pulses, which through directional couplers 11-1, 11-2 and adders 9-1 and 9-2 are directly transmitted to the control and processing unit 10.

The proposed method allows for high accuracy of measuring the difference in the electrical lengths of the receiving paths in a wide frequency band and at arbitrary distances between the antennas, and the device for its implementation provides almost complete compensation for the systematic error due to the non-identity of the receiving radio channels of the radio interferometer. The error in measuring the difference in the electrical lengths of the receiving radio channels did not exceed the accuracy of the measuring instruments.

The method and device can reduce the total length of the CLS by half and equalize the levels of the CS in all the receiving radio channels, which is especially important when creating radio interferometers with a large base.

INFORMATION SOURCES

1. Dyatlov A.P., Dyatlov P.A. Radio interferometer with calibration of receiving paths. Special equipment, 2010, No. 4, p. 26-32.

2. RU, patent, 2476986, IPC 7: G01S 11/00, G01S 11/02, G01S 11/10, 2013.

3. US patent 4,494,118, IPC 7: G01S 5/02, 1985.

4. RU, patent, 2269791, IPC 7: G01S 3/10, G01S 7/40, 2004

Claims (2)

1. A method for calibrating the receiving radio channels of a microwave range interferometer, including generating a radio pulse control signal (KS) tunable to a plurality of calibration frequencies, transmitting it to the inputs of the receiving radio channels, synchronously converting the received radio channels of the KS into digital form and determining the difference in the electrical lengths of the receiving radio channels for each n-th calibration frequency as a result of measurements of the delays of the CS at two stages of its direct and reverse transmission, characterized in that at the first stage calibrations turn off the antenna outputs and transmit the KS to the inputs of the receiving radio channels via cable communication lines (CLS), which switch through time τ to the reverse transmission through the receiving radio channels, and at the second calibration stage, close the CLS at the inputs of the receiving radio channels and receive the reflected CS, and form a pulse CS, the pulse duration of which is less than the signal propagation time in the input circuits of the receiving radio channels. 2. A device for implementing a method for calibrating receiving radio channels of a radio interferometer according to claim 1, consisting of N receiving radio channels, including receiving antennas, a calibration signal generator, a control and processing unit, characterized in that the first, second and third are introduced into each of the N receiving radio channels switches, amplifier, first and second delay lines, first and second directional couplers, gate driver and adder, and in each receiving radio channel, the first input of the first switch is connected to the output antenna, the output of the first switch through the amplifier is connected to the input of the first delay line, the output of which is connected to the third input of the second switch, the second output of the second switch is connected to the second input of the first switch, the input-output of the second switch through the second delay line is connected to the input-output of the first directional coupler, the output of which through the gate generator is connected to the control input of the second switch, the other input-output of the first coupler is connected to the input-output of the third switch , the output of the third switch of each receiving radio channel through an adder is connected to the control and processing unit, while the input of the third switch of each receiving radio channel through a second directional coupler is connected to the outputs of the calibration signal generator, which is also connected to the control input of the third switch, the other output of the second directional coupler each receiving radio channel through the adder is connected to the control and processing unit.

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