JPH08162834A - Adaptive array antenna - Google Patents

Abstract

PURPOSE: To attain a stable electronic tracking even when a very weak radio wave is received. CONSTITUTION: A signal received by an antenna unit 7 and frequency-converted by a 1st frequency converter 8 is given to a mixer 9-1, in which the signal is converted with a 2nd local oscillation signal generated from a high precision PLL oscillator 9-2 being a 2nd local oscillator into a 2nd intermediate frequency signal. The 2nd reference intermediate frequency signal is distributed into two by a distributer 10 via a BPF 9-3 and fed to mixers 3-3, 6-3, where phases are compared. Thus, the frequency and the phase of the 2nd intermediate frequency signal outputted from the mixers 3-1, 6-1 and those of the reference 2nd intermediate frequency signal are made coincident with each other. Thus, the signals are synthesized in phase at a synthesizer 1 to attain stable electronic tracking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive array antenna mounted on a mobile body for automatically tracking and receiving radio waves such as broadcast waves, and is particularly applied to a vehicle receiving system for receiving satellite broadcasting. Is suitable.

[0002]

2. Description of the Related Art When a terrestrial television broadcast is received on a moving body such as a vehicle while moving, multipath propagation may cause flicker or ghost interference, resulting in extremely low image quality. On the other hand, when the mobile body receives satellite broadcasting such as BS broadcasting while moving, if the broadcasting satellite can be directly viewed, it is less likely to be disturbed by the propagation and a good image can be obtained. Further, satellite broadcasting is suitable for mobile reception because the service area is wide. Thus, satellite broadcasting is suitable for mobile reception, and has already been put to practical use as media for buses, trains, ships, and aircraft.

In mobile reception, the beam direction of the receiving antenna loaded on the moving body and the arrival direction of the radio wave are deviated as the moving body moves. It is required to automatically turn to the direction of arrival of radio waves. As this receiving antenna, a receiving antenna called an adaptive array antenna, which can electronically direct the beam of the receiving antenna in the arrival direction of radio waves, has been conventionally proposed.

An example of the structure of this conventional adaptive array antenna is shown in FIG. In this figure, 101 and 1
02 is, for example, a planar antenna, 103 and 104
Transmits the radio waves received by the antennas 101 and 102 to the first
A frequency converter for converting to an intermediate frequency, 113 is a second local oscillator signal generated from the voltage variable local oscillator 115,
A mixer for converting the first intermediate frequency signal into a second intermediate frequency, and 114 is a second second oscillator generated from the fixed local oscillator.
It is a mixer that converts a first intermediate frequency signal into a second intermediate frequency by a local oscillation signal.

Further, 117 and 118 are bandpass filters for extracting the second intermediate frequency component and supplying it to the phase detector 119, and 119 is a phase detector for detecting the relative phase difference between the two input second intermediate frequency components. , 120 is a narrow band low-pass filter with a large time constant for filtering the detected phase difference signal, 121 is a wide band low-pass filter with a small time constant for filtering the detected phase difference signal, and 122 is a narrow band. Low-pass filter 120 or broadband low-pass filter 121
A switch for supplying any one of the outputs to the voltage variable local oscillator 115, and a ripple detector 123 for controlling the switch 122 by detecting the ripple voltage generated when the lock is released.

The operation of the adaptive array antenna configured as described above will be described. For example, a broadcast wave of 12 GHz band propagated from a broadcasting satellite is transmitted to the antennas 101 and 102.
Are respectively received by the frequency converters 103 and 104.
In, for example, the respective frequencies are converted into the first intermediate frequency in the 1 GHz band. Then, the first intermediate frequency signal converted by the frequency converter 104 is input to the mixer 114, mixed with the local oscillation signal from the fixed local oscillator 116, and, for example, the second intermediate frequency band of 300 to 600 MHz.
The frequency is converted to an intermediate frequency. The signal of the second intermediate frequency is supplied to the combiner 124 and also input to the bandpass filter 118.

Further, the first intermediate frequency signal converted by the frequency converter 103 is input to the mixer 113 and mixed with the local oscillation signal from the voltage variable local oscillator 115, for example, the second intermediate signal in the 300 to 600 MHz band. Frequency converted to frequency. The signal of the second intermediate frequency is supplied to the combiner 124, combined with the signal from the mixer 114, and input to the bandpass filter 117. Then, the bandpass filter 117 and the bandpass filter 1
The second intermediate frequency component extracted by 18 is input to the phase detector 119 and the phase difference between both signals is detected.
The detected phase difference signal is input to the narrow band low pass filter 120 and the wide band low pass filter 121. However, when the changeover switch 122 is switched to the narrow band low pass filter 120 side, the narrow band low pass filter. In accordance with the DC error voltage output from 120, the voltage variable local oscillator 1
The oscillation frequency and phase of 15 are controlled.

The feedback control in the loop composed of the mixer 113 or the voltage variable local oscillator 115 is performed so that the phase difference signal output from the phase detector 119 becomes zero, so that the feedback control outputs the output from the mixer 113. A second intermediate frequency signal,
The frequency and the phase of the second intermediate frequency signal output from the mixer 114 match. By the way, the phase of the second intermediate frequency signal output from the mixer 113 is
The phase of the second intermediate frequency signal output from the mixer 114 corresponds to the phase of the broadcast wave received by the antenna 101, and thus corresponds to the phase of the broadcast wave received by the antenna 102. The phase difference detected by 119 corresponds to the phase difference between the broadcast waves received by the antenna 101 and the antenna 102, that is, the deviation between the arrival direction of the broadcast wave and the beam formed by the antenna 101 and the antenna 102. It will be.

Therefore, if the phase difference detected by the phase detector 119 is set to zero by performing the above-mentioned feedback control, the beam formed by the antenna 101 and the antenna 102 coincides with the arrival direction of the broadcast wave. It will be. As described above, the conventional adaptive array antenna is capable of automatically matching the antenna beam with the arrival direction of the broadcast wave by electronically controlling.

The mixer 113 and the band pass filter 1
17, a phase detector 119, a narrow band low-pass filter 120,
When the feedback loop including the voltage variable local oscillator 115 is out of lock, the phase detector 11
Since the output of 9 includes the ripple, the ripple detector 1 connected to the wide band low pass filter 121
23 will detect the ripple. As a result, the ripple detector 123 switches the changeover switch 122 and applies the error voltage from the wide band low pass filter 121 to the voltage variable local oscillator 115. Then, since the time constant of the wide band low-pass filter 121 is made small, the pull-in range of the feedback loop becomes wide,
You will be pulled into the locked state quickly. And
In the locked state, the output of the phase detector 119 contains no ripple, so the ripple detector 123 does not detect the ripple, and the changeover switch 122 is switched to the narrow band low-pass filter 120 side.

By the way, the reason for providing the narrow band low-pass filter 120 and the wide band low-pass filter 121 is that the narrow band low-pass filter 120 has a large time constant.
Although the steady-state deviation can be reduced, the response speed is slow, and when the narrow band low-pass filter 120 is used, the pull-in range becomes narrow once the lock is released, and further it takes a long time to be locked. However, the influence of noise can be removed and the steady-state deviation becomes small. Further, since the wideband lowpass filter 121 has a small time constant, the response speed is fast, and by using the wideband lowpass filter 121, even if the lock is released, the locked state can be quickly returned. But,
It has the drawback of large steady-state deviation. Therefore, when the lock is released, the broadband low-pass filter 121 is used to quickly pull the lock state, and after the lock state, the narrow-band low-pass filter 120 is used to reduce the steady-state deviation. The control is done.

[0012]

However, the antenna of the mobile receiving apparatus cannot be a high antenna because the installation height of the object to be installed on the moving body is limited to, for example, 30 cm or less, and generally, at least. It is configured by being divided into two or more antenna units. In addition, since the direction of arrival of radio waves changes in various ways with the movement of mobile objects, the directivity of each antenna unit must be wide in order to perform electronic tracking with an adaptive array antenna so that it can be applied to this. There is a need to. Therefore, the antenna gain of each antenna unit is very small, and it is necessary to combine signals received by a large number of antenna units.

Therefore, the C / N in the received signal of each antenna unit becomes very low, and the phase detection accuracy decreases. Therefore, when electronic tracking is performed by in-phase combining the received signals, a frequency shift is captured. The range that I could do was narrow. Furthermore, in the conventional adaptive antenna, the frequency of the reference local oscillator moves due to variations in the electrical characteristics of the components and changes in the ambient temperature used, and the deviation of the intermediate frequency for in-phase synthesis increases. The frequency lock range of the phase locked loop has been exceeded, and due to the above-mentioned cause, there is a problem that in-phase synthesis for electronic tracking becomes difficult. In particular, when satellite broadcasting is received, it is a weak radio wave and the C / N of the input signal is low, so it was necessary to minimize the deviation between the reference frequency and the frequency of each antenna system.

Therefore, it is an object of the present invention to provide an adaptive array antenna capable of performing in-phase synthesis and stable electronic tracking even when receiving weak radio waves such as when receiving satellite broadcasting.

[0015]

In order to achieve the above object, an adaptive array antenna according to the present invention comprises an antenna composed of at least two or more antenna units and respective received signals received by the respective antenna units. The same number of first frequency converters as the number of the antenna units for frequency-converting to the first intermediate frequency signal and the same number of the antenna units for converting each of the first intermediate frequency signals to the second intermediate frequency signal are provided. Second
A frequency converter and a combiner that generates a reception signal by combining a plurality of the second intermediate frequency signals output from the second frequency converter, wherein a plurality of the second intermediate frequency signals are included. By controlling the phase of the second local oscillator provided in each of the other remaining systems with the phase of the second intermediate frequency signal of the system using the PLL oscillator as the second local oscillator as a reference, all the second intermediate frequencies are controlled. The phase of the frequency signal is in-phase, and in-phase synthesis is performed by the synthesizer.

In each of the remaining other systems of the adaptive antenna, a mixer, a bandpass filter for extracting a frequency component of the second intermediate frequency signal output from the mixer, and a bandpass filter A phase comparator that compares the phase of the output signal with the second intermediate frequency signal that is the reference, a low-pass filter with a large time constant that converts the phase comparison output from the phase comparator into an error voltage, and the low-pass filter. The phase is controlled by the error voltage from the filter, and a voltage controlled oscillator whose output is supplied to the mixer is provided.

[0017]

According to the present invention, since the PLL oscillator is used as the local oscillator of the reference system, since the oscillation frequency of the reference local oscillator does not substantially change, the frequency shift between the intermediate frequency signals to be in-phase synthesized. Can be made smaller. Therefore, the frequency acquisition range of the phase locked loop is not exceeded, in-phase synthesis can be performed even when the C / N of the input signal is low, and stable electronic tracking can be performed. Also, since the frequency shift between the intermediate frequency signals that are in-phase combined becomes small
It is not necessary to use two low-pass filters, a narrow-band low-pass filter and a wide-band low-pass filter, and it is possible to reliably perform in-phase synthesis only by using a narrow-band low-pass filter that can reduce steady-state deviation. become.

[0018]

1 is a block diagram showing the configuration of an embodiment of the adaptive array antenna of the present invention. In this figure, 1, 4, 7 are antenna units divided into three, for example, 2, 5, 8 are each antenna unit 1, 4,
A first frequency converter (first IF converter) that converts the frequency of the radio wave received by each of the first to seventh intermediate frequencies (first IF)
CONV), 3, 6, 9 are second frequency converters for converting the first intermediate frequency to the second intermediate frequency (second IF), 3
-1 or 6-1 changes the first intermediate frequency to the second intermediate frequency (second I2) by the second local oscillator signal generated from the voltage controlled local oscillator 3-5 or the voltage controlled local oscillator 6-5.
The mixer 3-2 or 6-2 for converting into the F) extracts the second intermediate frequency component and supplies it to the phase comparator 3-3 or the phase comparator 6-3.
3 and 6-3 are phase comparators for detecting a relative phase difference with reference to the second intermediate frequency signal supplied from the distributor 10, and 3-4 and 6-4 are for filtering the detected phase difference signal. Low-pass filter (LPF) with a large constant, 3
-5 or 6-5 is a voltage controlled local oscillator (VCO) whose frequency and phase are controlled by the error voltage output from the low pass filter 3-4 or the low pass filter 6-4.
Is.

Further, 9-1 is a mixer for converting the first intermediate frequency signal into the second intermediate frequency by the second local oscillator signal generated from the PLL oscillator 9-2, and 9-3 is the second intermediate frequency component. A bandpass filter (BPF) 10 for extracting the second intermediate frequency signal from the bandpass filter 9-3 is divided into two and supplied to the phase comparators 3-3 or 6-3, respectively, and 11 is a mixer. 3 is a combiner for in-phase combining the second intermediate frequency signals output from the mixer 6-1 and the mixer 9-1.

In the embodiment configured as described above, the second intermediate frequency converter 3 of the tracking system 1 outputs the second intermediate frequency converter 3 based on the second intermediate frequency signal output by the second intermediate frequency converter 9. By performing feedback control of the frequency and phase of the intermediate frequency signal and feedback control of the frequency and phase of the second intermediate frequency signal output from the second intermediate frequency converter 6 of the tracking system 2, the second intermediate frequency converter is obtained. The phase of the second intermediate frequency signal output from the second intermediate frequency converter 3 and the phase of the second intermediate frequency signal output from the second intermediate frequency converter 6 with respect to the second intermediate frequency signal output from 9 As in-phase, combiner 1
In-phase synthesis is carried out by 1.

The operation will be described below.
For example, the broadcast waves in the 12 GHz band propagated from the broadcasting satellite are received by the antenna units 1, 4, and 7, respectively, and are transmitted by the first frequency converters 2, 5 and 8 to, for example, 1 GHz.
Each of the frequencies is converted into a first intermediate frequency (first IF) in the Hz band. Then, the first intermediate frequency signal converted by the first frequency converter 8 is input to the mixer 9-1 and mixed with the local oscillation signal from the PLL oscillator 9-2, and the second intermediate frequency signal in the 300 to 600 MHz band, for example. The frequency is converted to an intermediate frequency (second IF). The converted second intermediate frequency signal is supplied to the combiner 11 and
The second intermediate frequency component input to the bandpass filter 9-3 and extracted by the bandpass filter 9-3 is divided into two by the divider 10.

The first intermediate frequency signal converted by the first frequency converter 2 is input to the mixer 3-1 and mixed with the local oscillation signal from the voltage controlled local oscillator 3-5, for example, 300-. The frequency is converted to the second intermediate frequency in the 600 MHz band. The signal of the second intermediate frequency is supplied to the combiner 11 and the bandpass filter 3-
2 is supplied. Similarly, the first intermediate frequency signal converted by the first frequency converter 5 is input to the mixer 6-1 and mixed with the local oscillation signal from the voltage-controlled local oscillator 6-5, for example, in the 300 to 600 MHz band. Second
The frequency is converted to an intermediate frequency. The signal of the second intermediate frequency is supplied to the combiner 11 and the bandpass filter 6-2.

Then, the second intermediate frequency component extracted by the band filter 3-2 and the band filter 6-2 is
The phase difference from the reference second intermediate frequency supplied to the phase comparator 3-3 or the phase comparator 6-3, respectively, and distributed by the distributor 10 is detected.
Each of the detected phase difference signals has a low-pass filter 3-
4 or a low-pass filter 6-4, which is filtered (integrated) to form a DC error voltage, which is supplied to the voltage-controlled local oscillator 3-5 or the voltage-controlled local oscillator 6-5 to generate a local oscillation signal. The frequency and phase of is controlled.

The feedback control of the voltage controlled local oscillator 3-5 and the voltage controlled local oscillator 6-5 is performed so that the phase difference signal output from the phase comparator 3-3 or the phase comparator 6-3 becomes zero. Therefore, the phase of the reference second intermediate frequency signal output from the mixer 9-1 and the second intermediate frequency signal output from the mixer 3-1 and the mixer 6-1 match due to the feedback control. .

By the way, the phase of the second intermediate frequency signal output from the mixers 3-1 and 6-1 corresponds to the phase of the broadcast wave received by the antenna units 1 and 4, and the mixer 9-
The phase of the second intermediate frequency signal output from 1 corresponds to the phase of the broadcast wave received by the antenna unit 7. Therefore, setting the phase differences detected by the phase comparators 3-3 and 6-3 to zero means that the phase differences between the broadcast waves arriving at the antenna unit 1, the antenna unit 4, and the antenna unit 7 become zero. In response to this, as described above, the antenna beam formed by the antenna units 1, 4, and 7 is directed in the arrival direction of the broadcast wave.

Therefore, in the second frequency converter 3 and the second frequency converter 6, feedback control is performed so that the phase difference detected by the phase comparators 3-3 and 6-3 becomes zero, whereby the antennas are Units 1, 4, 7
Thus, the antenna beam formed by can be automatically matched with the arrival direction of the broadcast wave. For this reason, even if the moving body on which the antenna including the antenna units 1, 4, and 7 is mounted moves, the beam of the antenna can be always aligned with the arrival direction of the radio wave, and a good reception state can be maintained. As described above, the adaptive array antenna of the present invention performs tracking electronically,
The antenna beam can be automatically matched with the arrival direction of the broadcast wave.

Next, FIG. 2 is a block diagram showing the configuration of the PLL oscillator 9-2. PLL oscillator 9- shown in this figure
2, a voltage controlled oscillator (VC) whose oscillation frequency is controlled by an error voltage from a low pass filter (LPF) 22.
O) 21 generates a local oscillation signal which is generated by the reference oscillator 2
The frequency is divided by the frequency divider 25 so that the frequency becomes approximately equal to the reference oscillation frequency generated by the frequency division circuit 4. Then, the frequency-divided local oscillation signal and the reference frequency generated by the reference oscillator 24 are compared in phase by the phase comparator 23. The phase difference signal detected by the phase comparator 23 is filtered by the low pass filter (LPF) 22 and applied to the voltage controlled oscillator 21 as an error voltage. The frequency divided by the frequency divider 25 is a frequency in a band where phase comparison is easy.

Since the reference oscillator 24 is composed of a crystal oscillator capable of maintaining a highly accurate oscillation frequency even when the environment such as temperature changes, the frequency of the local oscillation signal generated from the voltage controlled oscillator 21 is Even if the environment such as temperature changes, it hardly changes and high accuracy can be maintained. Therefore, the second frequency converters 3 and 6 of the tracking system
The frequency acquisition range is not exceeded and stable in-phase synthesis can be performed by the synthesizer 11. Further, since the frequency acquisition range of the second frequency converters 3 and 6 of the tracking system is not exceeded, the low-pass filter 3-4 and the low-pass filter 3-4 that have a narrow band (enlarged time constant) that can reduce the steady deviation are provided. The band-pass filter 6-4 can be used, and stable in-phase synthesis can be performed.

In the above description, an example in which the antenna unit is divided into three antenna units has been shown, but the present invention is not limited to this.
You may make it use the antenna unit divided into 2 or 4 or more. Further, if each antenna unit is a planar antenna composed of a large number of patches, it can be downsized and is suitable for a moving body.

[0030]

As described above, according to the present invention, since the high-precision PLL oscillator is used as the local oscillator of the reference system, the frequency of the reference local oscillator does not fluctuate and the in-phase synthesis is performed. The frequency shift between the intermediate frequency signals can be reduced. Therefore, since the frequency acquisition range of the phase-locked loop is not exceeded, in-phase synthesis can be reliably performed even when the C / N of the input signal is low, and stable electronic tracking can be performed. Further, since the frequency shift between the intermediate frequency signals to be in-phase synthesized becomes small, it is not necessary to use two low-pass filters, that is, a narrow-band low-pass filter and a wide-band low-pass filter. It becomes possible to perform stable in-phase synthesis using only the low-pass filter.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an adaptive array antenna of the present invention.

FIG. 2 is a block diagram showing a configuration of a PLL oscillation circuit.

FIG. 3 is a block diagram showing a configuration of a conventional adaptive array antenna.

[Explanation of Codes] 1, 4, 7 Antenna Units 2, 5, 8 First Frequency Converter 3, 6, 9 Second Frequency Converter 3-1, 6-1, 9-1 Mixer 3-2, 6- 2, 9-3 Band-pass filter (BPF) 3-3, 6-3 Phase comparator 3-4, 6-4 Low-pass filter 3-5, 6-5 Voltage controlled oscillator 9-2 PLL circuit 10 Distribution circuit 11 Synthesis vessel

Claims (2)

[Claims] 1. An antenna comprising at least two or more antenna units, and first frequencies provided in the same number as the antenna units for frequency-converting respective reception signals received by the respective antenna units into first intermediate frequency signals. A converter, second frequency converters provided in the same number as the antenna units for respectively converting the first intermediate frequency signals into second intermediate frequency signals, and a plurality of the second frequency converters output from the second frequency converters. And a combiner for generating a reception signal by combining two intermediate frequency signals, wherein the phase of the second intermediate frequency signal of the system in which the PLL oscillator is the second local oscillator among the plurality of second intermediate frequency signals is As a reference, by controlling the phase of the second local oscillator provided in each of the other remaining systems, all the second local oscillators are controlled.
An adaptive array antenna, wherein the phase of the intermediate frequency signal is in-phase and the in-phase combination is performed by the combiner. 2. In each of the remaining other systems,
A mixer, a bandpass filter for extracting the frequency component of the second intermediate frequency signal output from the mixer, an output signal from the bandpass filter, and the second reference
A phase comparator that compares the phase of the intermediate frequency signal, a low-pass filter that lowers the cutoff frequency that converts the phase comparison output from the phase comparator into an error voltage, and the phase is controlled by the error voltage from the low-pass filter. The adaptive array antenna according to claim 1, further comprising a voltage controlled oscillator whose output is supplied to the mixer.