JPH0367587B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radio direction finder for measuring the arrival direction of radio waves.

[Conventional technology]

As is well known in Patent Publication 1982-35828, by placing a large number of omnidirectional antennas at equal intervals on the circumference, sequentially switching and scanning reception of these antennas, and extracting the phase change of the received signal, the arrival direction of the radio wave can be determined. You can know. Methods for detecting phase changes in such Doppler radio direction finders include a frequency discriminator or a phase-locked circuit (PHASE LOCKED).
LOOP (hereinafter referred to as PLL) is used, and in principle both provide an output proportional to the phase change of the signal. A frequency discriminator responds over the spectral range of the slope of its characteristic and provides a constant DC output if the center frequency does not match that of the discriminator. If there is an amplitude change in the input signal, an output corresponding to the product of the phase change and the amplitude change is obtained.

In this way, in the frequency discriminator, if the center frequency of the signal does not perfectly match the center, a DC component will be superimposed on the demodulated output. In other words, depending on how the receiving frequency is tuned, this superimposed DC component always changes, which adversely affects direction measurement.

On the other hand, when using a PLL, as shown in Figure 1, a phase detector (PD) 1 detects the phase difference between the input signal, that is, the received signal, and the output of a voltage controlled oscillator (VCO) 3. The output obtained by detecting the
VCO 3 is controlled by the signal obtained by applying it to LPF 2 so that the phase difference between the two is 90°, that is, the output is 0, and the output of LPF 2 is applied to an integrator (called IO) 6 to output SIN. I am getting a wavy direction signal.

However, in this case, if there is a frequency difference between the free oscillation frequency of the VCO 3 and the input signal, the VCO control voltage corresponding to this frequency difference will come out as a DC component, causing the following inconvenience. It turns out.

(1) If the control range of the VCO is unbalanced and the phase suddenly changes in a narrow direction, the phenomenon of loss of control and loss of synchronization is likely to occur.

(2) In order to extract the azimuth signal, this VCO control voltage is integrated to obtain the periodic phase change component of the input signal, but if a DC component exists, the integration progresses in a fixed direction and the circuit becomes saturated. do. Therefore, since the direction signal component becomes invalid, it is necessary to remove this DC component before integration.

(3) When the signal is intermittent like _A1 radio waves, the DC component of the output disappears when the signal is interrupted, so the VCO undergoes free vibration and its phase is lower than when the signal is continuously input. It's getting more and more out of place. Therefore, the next time a signal is input, there will be a very large phase difference, and a very large transient phenomenon will occur until the PLL enters synchronization, causing a change in the output, which may cause a very large problem in direction measurement.

[Problem to be solved by the invention]

In order to remove the above DC component, the output of the LPF 2 is fed to a high pass filter (referred to as HPF) 5 as shown in Figure 1, but this gives a phase shift (orientation error) to the orientation signal. Especially when the signal is intermittent like _A1 radio waves,
Due to the above-mentioned reason, the DC component is also interrupted, and this passes through the HPF as a transient phenomenon and is superimposed on the orientation signal, causing the orientation to fluctuate significantly.

Therefore, there is a problem in that it is desired to provide something that eliminates the above-mentioned disadvantages without relying on HPF5.

[Means to solve the problem]

In this invention, the voltage controlled oscillator, that is, the VCO In addition to controlling
An azimuth for measuring the direction of arrival of radio waves based on the above-mentioned detection signal obtained by giving a received signal having an azimuth component due to a phase change to a phase synchronized circuit, that is, a PLL, which outputs the filtered signal as a detection signal. A radio direction finder that obtains a signal includes an integrating means that integrates the above-mentioned detected signal to obtain an integrated output, and controls the above-mentioned integrated output by giving it to a VCO in order to remove the DC component contained in the above-mentioned detected signal. VCO control means for providing the above-mentioned detection signal to the above-mentioned integration means; and cutoff switch means for providing a cutoff switch for cutting off the path for giving the above-mentioned detected signal to the _{above-mentioned} integration means; an interruption detection means for detecting this and obtaining an interruption signal; and in order to maintain the above-mentioned integral output in the state before interruption, an interruption signal is given to a cut-off switch to cut off the detection signal given to the above-mentioned integration means. The above problem can be solved by providing a blocking means or the like.

〔Example〕

Examples will be described below with reference to figures.

In Figure 2, Figure 2 is a system diagram showing one embodiment of the present invention.
4 and 6 are the same as in FIG.
7 is a semiconductor switch, and 8 is an integrator ID for integrating the DC output of the LPF2. In the phase detection circuit shown in FIG. 1, the received signal obtained by sequentially switching each antenna (for convenience of explanation, an example is shown in which eight antennas are switched and received), that is,
When a receiver IF output signal whose phase changes as shown in the dotted line in Figure 5A is applied to the input, the output of LPF2 becomes a pulse wave whose amplitude changes in a sinusoidal manner at the time of antenna switching as shown in Figure 5B. This signal is integrated by the integrator IO, and an azimuth signal that changes in a stepped sinusoidal waveform centered on OV as shown in Fig. 5C is obtained.

If there is a frequency difference between the input signal and the VCO, a DC output corresponding to the frequency difference is generated at the LPF output, and the center point of the direction signal in Figure 5 C crosses OV and changes to the + or - side. do.

Furthermore, when the input signal is intermittent as shown in Figure 5 D (T is the period when the radio waves are interrupted), the LPF output becomes 0 when the signal is interrupted, and the free vibration frequency of the VCO gradually shifts. become. Then the signal
Since there is a frequency difference between the input signal and the VCO when it is turned ON, a large transient phenomenon will occur in the direction signal as shown in Figure 5 D before synchronization is started, and as a result, the above (1) ) The same inconveniences as mentioned in (2) and (3) will occur. Therefore, in this invention,
The LPF output is passed through the semiconductor switch 7 to the integrator ID.
Integrate by 8 and use the output to control the VCO.
It controls the DC component of the LPF output to zero.

In this way, if the VCO is controlled via the integrator ID provided separately for the DC output of LPF2, even if there is a minute DC component in the output of LPF2, it will be integrated and controlled so that the DC output becomes 0. Because,
The average value of the phase difference between the VCO and the input signal will be kept completely zero. Therefore, the PD can always operate at its center, and the HPF for cutting off the DC component, which was conventionally provided before the signal integrator 6, is no longer necessary, and transient phenomena due to phase shift of the azimuth signal or interruption of the input signal are eliminated. This makes it possible to prevent the direction from wandering due to the influence of

The function of the semiconductor switch 7 mentioned above is that if the input signal is interrupted, ideally the PD output (LPF output) will also be 0, so the VCO control will remain at 0 and nothing will happen, but in reality it is due to interference.・PD output (LPF output) is not necessarily 0 due to noise etc. These can be considered to have an average value of 0 over a sufficiently long period of time, but over a finite period of time they affect the integrator ID output, which causes the VCO frequency to change, and when the signal appears again, it becomes large as described above until it enters synchronization. Accompanied by transient phenomena.

For this reason, switch _S1 is provided at the integrator ID input,
If S ₁ is turned off at the same time as the input signal is turned off, the integrator output will remain at the previous value, so
The VCO frequency remains consistent with the signal, and when it appears again, it smoothly synchronizes, so the large transient phenomenon described above does not occur.

The control signal for the semiconductor switch _S1 may be obtained by providing a signal detection circuit as shown in FIG. 3, and detecting the signal by known means to supply the signal.

In Figure 3, A ₀ is a PLL/IC, A ₁ and A ₂ are operational amplifiers, S ₁ , S ₂ , S ₃ and S ₄ are semiconductor switches, and C
are oscillation capacitors, R ₁ , R ₂ , RA, RB, RC,
RL is a fixed resistor, CA, CC, CL are capacitors,
R ₃ is a variable resistor for frequency fine adjustment, and 9 is a signal detection circuit that detects an input signal and generates a control signal for causing the semiconductor switches S ₁ to _{S 4} to perform predetermined operations.

Specifically, A ₀ is 4046 in PLL/IC. It outputs an output on the pin that is proportional to the phase difference between the two signals applied to the pin, including the VCO and PD. Furthermore, a resistor with an external pin output
In addition to the LPF consisting of RL and capacitor CL, it removes high frequency components. (pin input signal and pin
The output becomes 0 when the phase difference between the VCO input signals is 90°. )
The VCO outputs a signal to the pin with a frequency proportional to the oscillation capacitor C between the pins and the current in the pin. (VCO output) Also, the current flowing to the pin can be controlled by the voltage applied to the pin. So pin to pin and LPF
A PLL loop can be configured by connecting the output and pins respectively.

On the other hand, the LPF output is output by semiconductor switch S ₁ (e.g.
4066, etc.) and is integrated by an integrating amplifier consisting of A ₁ , RA, and CA, and its output connects the resistor.
Controls pin plus 12 pin current through RB. During normal operation where the input signal is continuously input, semiconductor switch _S1 is ON, and _{S2 S3 S4} is ON.
It is set to OFF.

In this state, the LPF output is kept completely at 0.
Even if there is a difference between the free oscillation frequency of the VCO and the input frequency, the voltage necessary to correct the difference and achieve complete phase synchronization is stored in the capacitor CA.

Immediately after the input signal is turned off, the signal detection circuit detects this and outputs drive signals for the semiconductor switches _S1 to _S4 , turning _S1 OFF and _S3 ON. Therefore,
Since the input of the integrator becomes 0, the voltage of CA remains unchanged and the oscillation frequency of the VCO continues to match the input frequency.

Next, when the signal is applied again, the voltage held at CA remains unchanged, so phase synchronization is quickly achieved smoothly and no unnecessary transient phenomena occur.

S ₃ is due to interference, noise, etc. when there is no signal.
This is a switch that shoots the output to prevent unnecessary output from appearing in the LPF and confusing the VCO system.

The operational amplifier A and the _2- resistor RC capacitor CC are an integrator circuit for the azimuth signal. Semiconductor switches S ₂ and S ₄ are used to prevent the integration circuit from drifting and becoming saturated when there is no signal for a long time. When there is no signal for a certain period of time or more in the signal detector, S ₂ and S ₄ are switched on. Cause a short circuit. (In this diagram, it is designed to operate with the power supply voltage ±V of PLLICA ₀ , but a single power supply of +V may also be used.
In this case, the DC average value of the LPF output is not OV but +
It becomes V/2.

[Modification example]

This invention can be modified and implemented as shown in FIG.

In FIG. 4, 1, 2, 3, 4, and 6 are the same as in FIG. A ₁ is an operational amplifier, S ₁ and S ₂ are semiconductor switches,
RA and RD are fixed resistances, CA is a capacitor, and is an integrator. Configure an integrator with A ₁ , RA, and CA,
RA and RB constitute a normal inverting amplifier.

This allows for normal fast phase changes.
PLL operation is performed for the DC component of the LPF output.
Integral operation is performed by RA and CA. Therefore, the Doppler component integrator I0 does not require a DC component blocking HPF.

〔Effect of the invention〕

According to this invention, as described above, even if a minute DC component exists in the output of the low-pass filter (LPF) 2, the DC component can be reduced to 0 by the integration of the integrator ID8. .

In addition, when there is a short interruption of the _A1 radio wave, the signal from the low-pass filter LPF2 that is applied to the integrator ID8 is blocked by the signal that detects this interruption, and the _A1 radio wave is interrupted by the switch _S1. The voltage controlled oscillator
The operation of VCO3 is also maintained.

Furthermore, when the received signal becomes a no-signal state, the signal detecting the no-signal state operates a switch S3 that short-circuits the output of the low-pass filter LPF2, and also operates a switch _S3 that short-circuits the output of the low-pass filter LPF2. Since the switch _S2 is operated to provide a predetermined constant voltage instead of the integral output as the control voltage given to the VCO3, inputs that would cause the voltage controlled oscillator VCO3 to operate in a chaotic manner are suppressed.
These suppressing operations have the advantage of providing stable azimuth measurement.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a phase detection circuit in a conventional Doppler radio direction finder. FIG. 2 is a system diagram showing one embodiment of the phase detection circuit according to the present invention. Third
FIG. 4 is a diagram showing one embodiment of the phase detection circuit according to the present invention. FIG. 5 is a waveform diagram showing the operation. 1... Phase detector (PD), 2... Low pass filter (LPF), 3... Voltage controlled oscillator (VCO),
4...Phase locked loop (PLL), 5...High pass filter (HPF), 6...Direction signal integrator (I0),
7...Semiconductor switch, 8...DC integrator, 9...
...Signal detector, A ₀ ... PLL/IC, A ₁ , A ₂ ... Operational amplifier, C ... Oscillation capacitor, CA, CC,
CL……Capacitor, R ₁ , R ₂ , RA, RB, RC,
RD, RL...Fixed resistor, R3 _... Variable resistor for frequency fine adjustment, _S1 , _S2 , _S3 , _S4 ...Semiconductor switch, T...Radio wave interruption period, M...Amplitude of transient phenomenon , t ₀ ...Time of one cycle of direction signal.

Claims (1)

[Claims] 1. The voltage controlled oscillator (hereinafter referred to as VCO Based on the detected signal obtained by feeding a received signal with a phase-changing azimuth component to a phase-locked loop (hereinafter referred to as PLL) that outputs the filtered signal as a detected signal, A radio direction finder (hereinafter referred to as a device) that obtains an azimuth signal for measuring the direction of arrival, comprising: a. an integrating means for integrating the detected signal to obtain an integral output; b. a DC component included in the detected signal. c) a cutoff switch means provided with a cutoff switch for cutting off a path for feeding the detected signal to the integration means; d) the above. Interruption detection means for obtaining an interruption signal by detecting that the received signal is interrupted for a short period of time equivalent to the interruption of _A1 radio waves; and a cutoff means for giving a signal to the cutoff switch to cut off the detection signal given to the integrating means. 2. Controlling the voltage controlled oscillator (hereinafter referred to as VCO) with a filtered signal obtained by applying the output obtained by detecting the phase difference between the input signal and the output signal of the voltage controlled oscillator using a phase detector to a low-pass filter, and A method for measuring the direction of arrival of radio waves based on the detected signal obtained by applying a received signal having a direction component due to a phase change to a phase locked loop (hereinafter referred to as PLL) that outputs the filtered signal as a detected signal. A radio direction finder (hereinafter referred to as a device) for obtaining an azimuth signal, comprising: a. an integrating means for integrating the detected signal to obtain an integral output; b. VCO control means for controlling the VCO by giving an integral output to the VCO; c. cutoff switch means provided with a cutoff switch for cutting off a path for giving the detected signal to the integrating means; d. when the received signal is an _A1 radio wave. Interruption detection means for detecting an interruption for a short period of time to obtain an interruption signal; f. short-circuiting switch means for short-circuiting the output circuit of the low-pass filter in order to short-circuit the filtered signal and not outputting it; and g. A predetermined constant voltage is used instead of the output.
a predetermined voltage switch means provided with a predetermined voltage switch to be applied to the VCO; h a no-signal state detection means for detecting that the received signal is no signal for a predetermined period of time or longer to obtain a no-signal state signal; i the predetermined voltage. The above when there is no signal for more than an hour
In order not to confuse the behavior related to the VCO,
It is characterized by comprising a no-signal state operating means for applying the no-signal state signal to the short-circuiting switch and the predetermined voltage switch to short-circuit the filtered signal and operating the VCO in a predetermined state. Device.