RU44213U1 - MICROWAVE RECEIVER WITH DIGITAL AUTO-FREQUENCY FREQUENCY - Google Patents

Abstract

The device relates to radio engineering, in particular to microwave radio communication devices, and can be used for accurate frequency self-tuning, can also be used in weather radar devices to receive information from radiosondes. The technical task is to increase the efficiency of AGC and AFC adjustments in conditions of destabilizing factors (low signal-to-noise ratio, etc.) due to: constructing the proposed circuitry; technological transparency; low cost hardware. This goal is achieved by the fact that the microwave receiver has two channels: information, having only AGC and frequency, having only AFC, while the microcontroller finds in the useful signal a frequency that has a maximum amplitude or an energy maximum, this frequency is the one to be adjusted for AFC , due to this construction of the circuit, we have the optimal structure of the microwave receiver.

Description

The device relates to radio engineering, in particular to microwave radio communication devices, and can be used for accurate frequency self-tuning, can also be used in weather radar devices to receive information from radiosondes.

Professional radio receivers provide access to communication without searching and maintaining communication without manual adjustment. This problem is solved by increasing the frequency accuracy of the receiver and the use of automatic frequency control (AFC), which corrects the inaccuracy of the initial setting of the receiver tuning frequency and reduces the detuning that occurs during signal reception due to the instability of the receiver local oscillator and the transmitter frequency. The classical AFC circuit contains, in addition to the elements of the main path of the receiver, additional elements: a discriminator and a ruler. The discriminator is designed to determine the magnitude of the deviation of the frequency from its nominal value. The manager provides the necessary change in the frequency of the controlled generator, see "Radio receivers" V.D. Yakimov and K.M. Pavlov, M., Communication, 1975, pp. 344-338.

The disadvantages of this method are: low self-tuning coefficient due to the application of the analog principle; in microwave receivers this principle is generally ineffective (even when using a PLL), since a minor frequency can be captured; with a small signal-to-noise ratio, which is especially characteristic with a ratio of less than two, this method is almost inoperative.

Known pulsed AFCs that ensure the constancy of the intermediate frequency by adjusting the local oscillator frequency according to the received signal, see "Fundamentals of Radio Engineering", T. T. Mashkova and S. N. Stepanov, M., Radio and communications,

1992, p. 217.

The disadvantages of these AFCs are as follows: they require two detectors (frequency and peak); low noise immunity; the difficulty of using both automatic frequency response and automatic gain control (AGC).

Known synchronous heterodyne radio receiver with a phase-locked loop (PLL) (see application No. 93018635), in which the oscillations of the local oscillator are modulated at a low frequency, which allows the use of AC amplifiers, in addition, the AGC is used in the receiver, which ultimately increased stability, sensitivity and noise immunity.

Its disadvantages include: the complexity of the circuitry, requiring an additional low-frequency generator, modulator, etc .; the combination in one channel of the AFC and AGC, which determines the mutual influence of these adjustments on each other, and as a result on the news of the receiving path.

In modern receivers, digital AFC circuits working in conjunction with digital frequency indicators are used, see, for example, Radio Equipment of Aircraft, N. A. Safronov, M., Mechanical Engineering, 1978, in which the signal frequency at the AFC output is digitized and fed to a microprocessor , where it is compared with a given (written in RAM), and the resulting difference is used to adjust the local oscillator.

The disadvantages of such receivers are as follows: the AGC is also used in the path, and the combined use of these two adjustments, especially in the microwave range, can lead to (and leads to) the loss of a useful signal, if, for example, for connected receivers this is not particularly scary, then for meteo receivers -RADAR this leads to irreparable loss of information.

The closest technical solution is a digital local oscillator frequency control system using a digital frequency synthesizer, which uses a pulsed frequency detector, quartz

generator, reversible pulse counter, DAC, frequency divider with variable and fixed division coefficient, pulse shapers and local oscillators with corresponding connections, see "Radio receivers", ed. N.N. Fomina, M, P and S, 1996, pp. 373-378 - PROTOTYPE.

The disadvantages of the prototype include: the complexity of the circuit-technical solution, which still does not solve the problem - uniqueness in determining the synthesizing frequency, especially at low signal-to-noise ratios; further, the mutual influence of automatic AGC and AFC adjustments on each other, which negatively affects the quality of receiving useful information.

The technical task is to increase the efficiency of AGC and AFC adjustments in conditions of destabilizing factors (low signal-to-noise ratio, etc.) due to:

building the proposed circuitry;

technological transparency;

low cost hardware.

To solve this problem, a microwave receiver with digital automatic frequency control is proposed, comprising: an input channel, a frequency channel and an information channel; the input channel contains a receiving antenna, a low-noise amplifier (LNA), the first and second mixers, the first and second oscillators and the first amplifier connected as follows: the receiving antenna, which is the input of the channel and the microwave receiver, is connected to the input of the LNA, the output of which is the same as the output the first local oscillator is connected to the inputs of the first mixer, the output of which through the first amplifier, as well as the output of the second local oscillator are connected to the inputs of the second mixer, the output of the latter is the information output of the input channel, and the output of the first amplifier is often you to exit the channel, the control input of the local oscillator is a frequency input of this channel; the information channel contains: a second amplifier, a bandpass filter, a frequency detector, a linear video amplifier

(TLD) with AGC, connected as follows: the input of the information channel (output of the second mixer of the input channel) through the second amplifier, a bandpass filter and a frequency detector connected in series, connected to the input of the TLD, the output of which is the output of the microwave receiver, the outputs of the AGC of the LVL are connected with control input UPCH 2 and control input LNA input channel; the frequency channel contains: a first and second synthesizer, a microcontroller, a third mixer, a local oscillator and a converter, an ADC, PLD and an external control circuit with the following connections: the input signal (output of the first converter of the input channel) is connected to the third mixer, the output of which is connected to ADC analog input, the digital output of which is connected via PLD to the internal RAM of the microcontroller, the outputs of which are connected to the first and second synthesizers, and the outputs of the latter are connected to the first (smooth auto-tuning) and third local oscillators (scan frequency control), the third local oscillator with its output is connected to the control input of the third mixer, the external control circuit is connected to the master inputs of the microcontroller, the output of which is connected to the control inputs of the ADC.

Figure 1 shows the structural diagram of the microwave receiver, figure 2 - the operation algorithm of finding the desired frequency, figure 3 - the frequency response of the frequency channel, the determined structural diagram has the following connections: antenna A, which is the input of the microwave receiver, through LNA 1 connected to one input of the first mixer 2, with the second input of which the output of the first local oscillator 8 is connected, the output of the first mixer through the first UPCH 5 is connected to one input of the second mixer 3, with the second input of which the output of the second local oscillator 9 is connected, the output of the second mixer through edovatelno included a second IF amplifier 6, a bandpass filter 15 and frequency detector 16 is connected to the linear accelerator 17, which on circuits negative feedback AGC one output coupled to the regulating input MSHU1, and by other output with a control input of the second IF amplifier 6, output of the linear accelerator is the output of the microwave receiver; the output of the first UPCH 5 is also connected to the third mixer

4, the output of which through the third amplifier 7 is connected to the analog input of the ADC 18, the digital output of which through PLD 19 is connected to the RAM 13, the last signal outputs are connected to the first and second synthesizers 11 and 12, respectively, the latter are connected to the control inputs of the first 8 and second 10 local oscillators, the outputs of which are connected to the first 2 and third 4 mixers, respectively, the output of the MK 13 control signals is connected to the ADC 18, and the external control circuit 14 is connected to the master input MK 22.

These nodes and blocks can be made on the following ERE and IC: LNA 1 is made, for example, on an integrated gallium arsenide IC type MGA-86563, see the Hewlett Packard catalog "Communications Components Designer's Catalog 1998", p.6-220; mixers 2, 3 and 4 can be performed on mixing diodes, for example, reverse tunnel diodes, varicaps, diodes with Schottky barriers (see "Microelectronic Microwave Devices", edited by G.I. Veselov, M., Higher School, 1988, pp. 226-227); UPCH 5, 6 and 7 can be performed, for example, on field-effect transistors with a piezoceramic filter, see "Radio receivers", V.D. Ekimov et al., M., Communication, 1975, p. 159; synthesizers 11 and 12 can be performed on the Philips UMA1020 IC, see "Product Specification", 1995, Jun 15, File under integrated Circuits; ADC 18 - high-speed 8-12 bit, for example, on the AD571KN IC with fpr = 40 MHz, see "Foreign Integrated Circuits", A. Nefedov et al., M., Energoatomizdat, 1989, p. 132; PLD 19 can be performed on a base matrix crystal, see g. Chip News, M., August 2000, pp. 18-21; microcontroller 13 can be implemented on the IC 80X196KS, see "Microcontrollers", ed. N.A. Kazachenko, M, 1997, article "Guidelines for the use in control systems of 16 bit MK Jntel in embedded control systems"; the frequency detector 16 can be performed according to the scheme see "Radio receivers", ed. N.N. Fomina, M., P and S, 1996, pp. 330-332; AGC according to the scheme, see "Radio receivers", ed. N.N. Fomina, M., P and C,

1996, pp. 402-404.

Microwave digitally tuned frequency receiver operates as follows. First, it should be noted that the information signals arriving at the input of the receiver are (for the case of working with aerological radiosonde) microwave signals with the main carrier frequency and modulating frequencies, which are carriers of telemetry and radar information. The input microwave signal through the receiving antenna A goes to the LNA 1, designed to compensate for losses at the input of the LNA 1 to increase the signal-to-noise ratio of the entire receiver, to prevent spurious radiation from the radio frequency of the mixer 2 from penetrating into the receiving antenna A and to create optimal reception of signals of incoherent mode of operation. The difference signal of a frequency of 260 kHz allocated on the first mixer is amplified at the first amplifier 5, the second conversion again takes place at the second mixer 3 with the second local oscillator 9 to a frequency of 60 kHz, amplified at the second amplifier 6 (with a wide band pass Δf = 4 kHz), it is filtered out on a band-pass filter 15, it is detected by a frequency detector 16 and through the LVL 17 has a useful information signal; The AGC from the outputs of the TLV / AGC 17 with the purpose of the environmental protection system is connected with the second amplifier 6 with the full voltage value and part of this value with LNA 1 (“gentle” AGC) in the case of saturation of the LVL, i.e. when the signal at the input of the microwave receiver is very large, when the AGC on the second amplifier 6 does not “cope” with its value and the information signal is saturated. At the same time, the signal f = 260 kHz from the first amplifier 5 goes to the third mixer 4, where it is mixed with the signal from the third local oscillator 10 with f = 320 kHz and at the output we have a difference frequency of 60 kHz, the amplitude of which is digitized by the ADC 18 and supplied as a parallel code to PLD 19, in which the received signal value is converted into a form convenient for recording in RAM MK 13, i.e. the address part, data, time relationships between control signals, records, etc. are formed. These data are regularly recorded in RAM MK 13 with a sampling frequency of the ADC 18 (in our

case it is units of MHz). The program for finding the frequency with the maximum amplitude is recorded in the MK 13 ROM; according to this program, with the ADC 18 sampling frequency, we go through the frequency spectrum of the signal and determine the frequency whose amplitude is maximum, then controlling the synthesizers 11 and 12, at this frequency we obtain the maximum signal at the outputs UPCH 5 and 7; it is possible by this principle, but by a different algorithm, also written in the MK 13 ROM, to determine the frequency corresponding to the energy maximum of the signal, for which the area of the measured frequency response is determined and its “gravity” center (geometric center) is located, the frequency at which it is located and is the desired one. Thus, the desired frequency found determines the maximum signal at the outputs of the IFA 5 and 7. We see that with this construction of the circuit, the information channel 22 has its own gain control only (AGC), and the frequency channel 21 determines the frequency control, figuratively speaking, each channel does its job, but the frequency channel 21 in frequency offloads the information 22, leaving the latter with the function of only processing information. The external control circuit 14 serves to make changes to the program of work of MK 13 if necessary, for example, choosing the operation of the module of the frequency channel 21 of the AFC 18 in amplitude or energy maximum (determined based on the following conditions: we have high speed in amplitude, high in energy maximum efficiency or reliability, increased noise immunity, but lower performance).

On the frequency response (Fig. 3) it is seen that the actually taken characteristics (4 curves) have a very large convergence at different signal-to-noise ratios, i.e. deviations of the curves from each other are related to the difference in random noise implementations, and a small “hump” at a frequency of 1770 MHz can be taken by the device as the true unknown value when the frequency channel 21 is AFC, but this will not happen when working with the energy maximum, t. to. the entire frequency response area will be calculated and there will be no false capture.

Claims (1)

Microwave-tuned microwave receiver comprising an input channel, a frequency channel, and an information channel; the input channel contains a receiving antenna, a low noise amplifier (LNA), the first and second mixers, the first and second local oscillators and the first IF amplifier, connected as follows: the receiving antenna, which is the channel input and the microwave receiver, is connected to the LNA input, the output of which is the same as the output the first local oscillator is connected to the inputs of the first mixer, the output of which through the first amplifier, as well as the output of the second local oscillator are connected to the inputs of the second mixer, the output of the latter is the information output of the input channel, and the output of the first amplifier is often you to exit the channel, the control input of the local oscillator is a frequency input of this channel; the information channel contains: a second IF amplifier, a bandpass filter, a frequency detector, a linear video amplifier (LLL) with automatic gain control (AGC), connected as follows: the input of the information channel (the output of the second mixer of the input channel) through a second amplifier, a bandpass filter and a frequency detector, connected in series, connected to the input of the LVD, the output of which is the output of the microwave receiver, the outputs of the AGC of the LVU are connected to the control input of the UHF 2 and the regulatory input of the LNA of the input channel; the frequency channel contains: a first and second synthesizer, a microcontroller, a third mixer, a local oscillator and a converter, an ADC, PLD and an external control circuit with the following connections: the input signal (output of the first converter of the input channel) is connected to the third mixer, the output of which is connected to ADC analog input, the digital output of which is connected via PLD to the internal RAM of the microcontroller, the outputs of which are connected to the first and second synthesizers, and the outputs of the latter are connected to the first (smooth auto-tuning) and third local oscillators (scan frequency control), the third local oscillator with its output is connected to the control input of the third mixer, the external control circuit is connected to the master inputs of the microcontroller, the output of which is connected to the control inputs of the ADC.