JP2005175521A - Receiving apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that it takes a certain amount of time to decide a band, the optimum band is not instantly selected, and if a low-level signal is inputted during selecting a wide band, the signal cannot be captured because the widest band equipped in a receiving apparatus is firstly set to analyze the radio wave, and the optimum band is selected when receiving a radio wave having unidentified bandwidth. <P>SOLUTION: A received radio wave is distributed by a distributor 1, and inputted into three filters 2, 3, 4 having different bandwidths. The outputs of the filters 2, 3, 4 are detected with a detector 6, and an S/N ratio of each system is compared by an S/N ratio determining circuit 8. The determining circuit is previously caused to store a noise level at the time of no signal. A switch 9 is controlled so as to select a system having the highest S/N ratio. To prevent an input signal to pass through while the determining circuit is performing determination, a delay line 10 for delaying just for a delay time required for determining by the circuit 8 is inserted so that the signal may pass through after the switch 9 selects a system. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention mainly relates to a receiving apparatus such as a radar or an EW (Electronic Warfare = electronic warfare).

In a receiving apparatus that receives a radio signal, it is important to obtain a better reception state to know the radio frequency, its bandwidth, and modulation format. Of these, the frequency can be measured at the same time as reception, and the modulation format is often easily determined by simple analysis of the received signal.
In order to receive a weaker signal, if the signal communication partner is known in advance, or if it is clear that a signal of radio wave specifications based on a certain convention (standard) is transmitted, it is received On the receiving side, by reducing the reception bandwidth to a predetermined bandwidth, unnecessary noise signals are cut and the S / N is improved, so that the reception sensitivity can be further increased. However, in some cases, the bandwidth of the received signal may not be known. For example, this is the case when an untrusted radio wave whose source is unknown is intercepted.

  Some conventional radio wave receivers have a variable bandwidth, or have a plurality of bands for switching. In any case, the band is selected based on the result of analyzing the received radio wave. This is because the bandwidth suitable for receiving the signal differs depending on the pulse width and frequency of the modulation signal. Since signal analysis takes a certain amount of time, a certain amount of processing time is required until an optimal band is selected. Usually, the receiving apparatus selects the widest band equipped first, detects the signal, analyzes this, and then narrows the band to increase the sensitivity. At this time, if a low level signal is input during the wide band selection, the signal that could have been detected in the narrow band may not be detected.

The invention disclosed in Patent Document 1 transmits a transmission signal having the same content at a plurality of different frequencies and compares the reception / demodulation results at each frequency with each other to obtain an optimal demodulation result. This is a reference for the present invention.
JP 2000-357985.

  When the radio wave receiving apparatus is equipped with a receiving circuit capable of variably setting or selecting the bandwidth, the setting / selection of the bandwidth is performed based on the result of analyzing the received radio wave. This is because the bandwidth suitable for the signal differs depending on the pulse width and frequency. Since signal analysis takes time, a certain amount of processing time is required to select an optimal bandwidth. In general, first, wideband reception applicable to many signals is performed, and the narrowband is selected after the signals are detected and analyzed. However, wideband reception naturally has a problem that the noise level becomes high and the reception sensitivity cannot be increased. Therefore, when a low-level signal is input during the selection of a wide band, there is a problem that a signal that should have been detected in a narrow band may not be detected.

  The receiving device of the present invention includes a distributor for distributing an input signal, a plurality of filters connected to the distributor and having different bandwidths, and a plurality of detectors respectively connected to output terminals of the plurality of filters. An S / N ratio determination circuit for comparing S / N ratios of output signals of the plurality of detectors with each other, and one signal out of output signals of the plurality of filters based on a determination result of the S / N ratio determination circuit A switch for selecting is provided.

Since the optimal reception bandwidth can be selected instantaneously, reception quality is improved with less reception leakage.
The reception performance of the system can be utilized to the maximum.

Embodiment 1 FIG.
FIG. 1 shows a receiving apparatus according to the present invention that can instantly select an optimum receiving band. In the figure, different frequency bandwidths (hereinafter referred to as bandwidths or bands) connected to each system (three systems in this example) of the distributor 1 that distributes an input signal to a plurality of circuits and the output terminals of the distributor 1 are shown. Filters 2, 3 and 4, a coupler 5 for coupling signals for each system, a detector 6 for detecting the coupled signals of each system, and an A / D converter for A / D conversion of the detected signals A D converter 7, a determination circuit 8 that compares the S / N ratio of each system, and a switch 9 that selects one system from each system are included. The center frequencies of the filters 2, 3 and 4 have the same center frequency depending on the modulation format of the target signal (for example, when the signal is an amplitude-modulated wave) and have different frequencies (for example, the signal) Are selected so as to easily include the required signal band.

Before describing the operation, the relationship between the bandwidth and the S / N ratio will be described with reference to FIG.
The horizontal axis in FIG. 2 indicates the bandwidth of the filter that the receiving apparatus has. When the bandwidth is changed, the noise component 21 with respect to the received signal or the detection signal increases almost in proportion to the bandwidth. On the other hand, although the signal component 22 cannot be generally specified depending on the type of signal or the modulation method, it increases monotonously up to the optimum bandwidth f0, but the signal component 22 does not increase even if the bandwidth becomes larger than f0. Therefore, the S / N ratio 23 with respect to the change in the bandwidth of the filter becomes maximum when the bandwidth is f0, and the S / N ratio is lowered regardless of whether the bandwidth is larger or smaller.

Next, the operation will be described. First, the input signal is distributed by the distributor 1 (divided into three in the figure), and is simultaneously input to the three filters 2, 3 and 4 in different bands (the center frequencies are the same). The signal having the highest S / N ratio can be obtained from the filter having the most suitable passband among the three filters, with respect to the bandwidth determined by the frequency and pulse width of the input signal. For each system, an input signal is extracted by the coupler 5 at the same time, and each signal detected by the detector 6 at the same time is A / D converted by the A / D converter 7. The A / D converted signal is compared with the S / N ratio of each system by the S / N ratio determination circuit 8.
As described above, the S / N ratio determination circuit 8 simultaneously measures and compares the S / N ratios of the three signals.
The noise level N may be stored in advance in the determination circuit when there is no signal. Since the system with the highest S / N ratio is the optimum band, the switch 9 is controlled to select the system.

Note that the switch 9 may not be selected until the determination result of the S / N ratio determination circuit 8 is output, or any of predetermined filters, for example, three filters may be selected. Alternatively, the output of the filter with the widest (or narrowest) bandwidth may be selected. In FIG. 1, the coupler 5 may be a simple branch circuit. The detector 6 may switch the type according to the modulation format of the received signal. Since the A / D converter 7 is necessary when the S / N ratio determination circuit 8 performs digital processing, it is not always necessary when the S / N ratio determination circuit 8 performs analog processing. Absent. In FIG. 1, the number of distribution circuits has been described as three, but it may be two or more.
If one bandwidth variable filter is used instead of a plurality of filters, the analysis of the S / N ratio for each different bandwidth must be performed in series in time, and the time required for the analysis becomes longer. In addition, there is a problem that the S / N ratio cannot be compared using the same signal for each different bandwidth.
Of course, if a slight delay in operation is allowed, for example, a memory is provided for each of the outputs of the plurality of detectors 6 and the output signals from all the detectors are stored at the same time. In comparison, the one having the maximum S / N ratio may be obtained.

Embodiment 2. FIG.
FIG. 3 shows the configuration of the receiving apparatus of this embodiment. In the configuration of the first embodiment, at least the optimum filter is not selected until the determination result of the S / N ratio determination circuit 8 is output. Therefore, the signal received during this period is useful. There is a fear of not becoming. Therefore, as shown in FIG. 2, a delay line 10 for delaying the signal for a time longer than the time taken for the determination by the S / N ratio determination circuit 8 is inserted between the filter and the switch 9, and the S / N ratio is determined. The determination circuit 8 outputs a determination result and the switch 9 selects the system so that the signal passes.
The operation will be described with reference to FIG. The horizontal axis in FIG. 4 is the time axis. In the circuit of FIG. 3, the determination result output 32 of the S / N ratio determination circuit 8 is output after the time T1 from the output signal 31 of the distributor 1. Further, the output signal 33 of the delay line 10 is output after the time T2. An arbitrary filter 35 before selection is selected before the determination result output 32 (may be a state where nothing is selected), and an optimum filter 36 is selected after the determination result output 32. Since the obtained signal 34 is output after the optimum filter is selected, it is a good signal received with the optimum bandwidth.

Embodiment 3 FIG.
FIG. 5 is a block diagram of the third embodiment. In the first or second embodiment, since the frequency of the input signal to the distributor 1 may be unknown or fluctuate, it does not necessarily fall within the bandwidth of the prepared filters 2, 3, 4. Therefore, the input signal is always within the bandwidth of the filters 2, 3, 4 (when the center of the bandwidth is preferable depending on the modulation format of the signal, and preferably at the end of the bandwidth) A circuit described below is provided. That is, the output of the mixer 11 that converts the frequency of the received signal is extracted by the coupler 12 and input to the F / V converter 13. The F / V converter outputs a voltage that changes according to the frequency, and the output frequency of the local oscillator 13 is controlled by this voltage. Then, the frequency is controlled so that the output frequency of the mixer 11 (referred to as an intermediate frequency to distinguish from the reception frequency) falls within the bandwidth of the prepared filters 2, 3, 4.

Embodiment 4 FIG.
FIG. 6 shows a receiving apparatus according to Embodiment 4 of the present invention, which is coupled by a mixer 11 that converts the frequency of a received signal to an intermediate frequency, a coupler 12 that couples the frequency-converted input signal, and a coupler 12. The F / V conversion circuit 13 that performs F / V conversion of the received signal, the local oscillator 14 that is controlled by the output voltage of the F / V converter, and the intermediate frequency input signal output from the mixer 11 are distributed to a plurality of circuits. Filters 2, 3, and 4 having different bandwidths (center frequencies as described in the first embodiment) connected to distributor 1 and each system (3 in this example) of the output of distributor 1, A coupler 5 for coupling a signal for each system, a detector 6 for detecting the coupled signal of each system, an A / D converter 7 for A / D converting the detected signal, Size to compare S / N ratio The circuit 8, and a delay line 10 for delaying the signal for each passage system of the coupler 5, and a switch 9 for selecting one system from the system provided after the delay line 10.

Next, the operation will be described. First, the output of the mixer 11 that performs frequency conversion so that the received signal becomes the center of the bandwidth of the filter is extracted by the coupler 12 and input to the F / V converter 13. The voltage output from the F / V converter changes according to the change in frequency, and the transmission frequency is controlled so that the local oscillator 13 of the mixer 11 comes to the center of the filters 2, 3 and 4 prepared. The output signal of the mixer 11 is distributed (distributed into three in the figure) by the distributor 1 and input to the three filters 2, 3, 4 in different bands (the center frequencies are the same). The signal having the highest S / N ratio can be obtained from the filter having the most suitable passband among the three filters, with respect to the bandwidth determined by the frequency and pulse width of the input signal. An input signal is extracted by the coupler 5 for each system, and each signal detected by the detector 6 is A / D converted by the A / D converter 7. The A / D converted signal is compared with the S / N ratio of each system by the S / N ratio determination circuit 8. The noise level is stored in advance in the determination circuit when there is no signal. Since the system with the highest S / N ratio is the optimum band, the switch 9 is controlled to select the system.
At this time, since the input signal passes even during the determination by the S / N ratio determination circuit 8, the delay for delaying each system by the time required for the determination by the S / N ratio determination circuit 8. Line 10 is inserted so that the signal passes after switch 9 selects the system.

Embodiment 5 FIG.
In the above description, the S / N ratio comparison operation has been described as if it was performed only before the start of reception. However, the bandwidth with the maximum S / N ratio is not invariant once determined. For example, when another signal that interferes with communication appears near the end of the bandwidth, the S / N ratio is improved by reducing the bandwidth and removing the interference wave.
Therefore, while continuing reception with the determined bandwidth, the S / N ratio is repeatedly monitored at a predetermined timing, and the S / N ratio falls below a predetermined limit, or S of other bandwidths When the / N ratio becomes higher than the S / N ratio of the currently selected bandwidth, or every predetermined repetition time, the bandwidth selection operation described in the first and subsequent embodiments is performed again. Also good. A circuit for instructing the S / N ratio determination circuit 8 to redo the bandwidth selection operation described in the first and subsequent embodiments at predetermined predetermined repetition times is referred to as a repetition instruction circuit.

  The receiving apparatus according to the present invention can be used in general receivers that switch and receive various radio signals having different bandwidths, as well as radar apparatuses and EW receiving apparatuses.

3 is a block diagram of a receiving apparatus according to Embodiment 1. FIG. It is S / N ratio characteristic explanatory drawing explaining the operation | movement of FIG. 6 is a block diagram of a receiving apparatus according to Embodiment 2. FIG. 3 is a timing chart for explaining the operation of FIG. 2. 10 is a block diagram of a receiving apparatus according to Embodiment 3. FIG. FIG. 10 is a block diagram of a receiving device according to a fourth embodiment.

Explanation of symbols

1 Distributor, 2 Filter 1, 3 Filter 2, 4 Filter 3,
5 coupler, 6 detector, 7 A / D converter,
8 S / N ratio judgment circuit, 9 switch, 10 delay line, 11 mixer,
12 couplers, 13 F / V converters, 14 local oscillators,
21 noise level, 22 signal level, 23 S / N ratio,
31 received signal, 32 judgment result output, 33 delayed signal,
34 Switch output signal, 35 Filter before selection,
36 Filter after selection.

Claims (6)

A distributor for distributing an input signal to a plurality of output terminals;
A plurality of filters connected to each of the plurality of output terminals and having different bandwidths;
A plurality of detectors connected to each of the output terminals of the plurality of filters;
An S / N ratio determination circuit for comparing S / N ratios of output signals of the plurality of detectors with each other;
A receiving apparatus comprising: a switch for selecting one signal from output signals of the plurality of filters based on a determination result of the S / N ratio determination circuit. A mixer that frequency-converts a received signal to a predetermined intermediate frequency and inputs it as the input signal;
The receiving apparatus according to claim 1, further comprising a local oscillator that controls an oscillation frequency in accordance with a frequency change of the input signal and constantly controls the intermediate frequency within a predetermined range.   2. A delay line inserted between each of the output terminals of the plurality of filters and the switch, and having a delay time longer than a determination operation time of the S / N ratio determination circuit. 2. The receiving device according to 2.   The receiving apparatus according to claim 1, wherein center frequencies of the plurality of filters are the same.   The receiving apparatus according to claim 1, wherein the S / N ratio determination circuit compares output signals at the same time from the plurality of detectors.   A repeat command circuit that commands the S / N ratio determination circuit at predetermined time intervals to compare the S / N ratios of the outputs of the plurality of detectors with each other and selects the switch based on the determination result The receiving apparatus according to claim 1, further comprising:

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