JPH02304384A - Azimuth measuring system - Google Patents

Abstract

PURPOSE:To improve the resolution by providing an arithmetic circuit for calculating a method to a transmitting antenna of a receiving antenna, based on position information of the transmitting antenna inputted from a code demodulating circuit. CONSTITUTION:A code demodulating circuit 27 inputs and decodes a code signal for showing antenna arrangement information contained in a reference signal 122 outputted from a reference wave separating circuit 23, and outputs the antenna position information 127 to a phase arithmetic circuit 26. The phase arithmetic circuit 26 inputs a phase signal 125 outputted from a phase detecting circuit 25 and calculates an azimuth to a transmitting antenna of a receiving antenna, based on position information of the transmitting antenna from the code demodulating circuit 27. In the case a receiving antenna of a airborne equipment 20 is at a distance enough against a transmitting antenna of a fixed equipment 10, an azimuth resolution theta4 of this system is proportional to ln/lambda. Also, a distance between each transmitting antenna is in inverse proportion to the maximum measured angle. Accordingly, when the distance between the transmitting antennas is constant, the resolution can be improved in proportion to the number of transmitting antennas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a system for measuring the azimuth position of a moving object, and particularly to a high-precision azimuth measurement system that can be applied to an aircraft position measurement system.

[Conventional technology]

Conventionally, the direction measurement system used in aircraft is
ADF (Automatic Direction Finder), VOR (VIIF
omnidirectional radio ran
ge).

ADF is a system that mechanically rotates a frame or atcox antenna to determine the arrival direction of radio waves from changes in reception output, and determines the position from the transmitting antenna.

VOR rotates directional radio waves in the VHF band at a speed of 30 times per second, and transmits a 30Hz signal synchronized with the rotation of the radio waves on top of these radio waves.
This system sends radio waves with a reference phase and compares the 3 Q Hz variable phase of the electric field strength change caused by the rotation of the directivity with the phase of the reference phase radio wave of <30 Hz on the aircraft to determine the direction of the transmitting station.

[Problem to be solved by the invention]

ADF has simple ground equipment and five onboard equipment, but has the disadvantage of large measurement errors. The measurement errors of the ADF are classified into instrument errors, proximate object scattering errors, and radio wave propagation errors. Equipment errors are errors in the antenna system or errors specific to the system. Near-object scattering error is an error that occurs when incoming radio waves are scattered by objects near the receiving antenna installation location, and anything such as structural objects near the antenna causes scattering and causes errors. Radio wave propagation errors vary depending on the wavelength used, but include coastline effects. With the ADF, not only the measurement accuracy decreases due to these errors, but also the measurement accuracy itself depends on the directivity of the antenna, so highly accurate azimuth measurement cannot be expected.

On the other hand, the accuracy of VOR is determined by the characteristics of the transmitting antenna, and has the disadvantage that the measurement accuracy is limited to approximately ±2.5°.

An object of the present invention is to eliminate these drawbacks and provide an azimuth measurement system with high measurement accuracy.

[Means for Solving the Problems] The direction measurement system of the present invention includes a plurality of transmitting antennas whose mounting positions are determined in advance, and radio waves from the transmitting circuit are switched in a predetermined switching procedure and supplied to the transmitting antennas. When the antenna switching circuit is connected to a specific transmitting antenna serving as a reference, the antenna switching circuit is connected to a feeding circuit that is adjusted so that the electrical distances between each transmitting antenna and the antenna switching circuit are all equal. Consists of a frequency-stable transmitting circuit that generates a radio wave that is modulated with a predetermined code that indicates that it is a reference wave and includes information about the antenna placement, and generates a continuous wave at other times. a receiving antenna, a frequency-stable receiving circuit that amplifies the signal received by this receiving antenna, and a reference signal based on the reference wave and other signals from the output signal of this receiving circuit. a reference wave separation circuit that oscillates, a phase-locked oscillation circuit that oscillates in phase with the reference signal output from the reference wave separation circuit, and information regarding the arrangement of antennas included in the reference signal output from the reference wave separation circuit. a code demodulation circuit for decoding the reference signal; a phase detection circuit for phase-detecting a signal other than the reference signal output from the reference wave separation circuit using the signal from the phase lock oscillation circuit; and a phase signal output from the phase detection circuit. and an arithmetic circuit that calculates the orientation of the receiving antenna with respect to the transmitting antenna based on the position information of the transmitting antenna input from the code demodulation circuit.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an azimuth measuring system that is an embodiment of the present invention. This orientation, measurement system is fixed equipment 1
0 and onboard equipment 20.

The fixed equipment 10 includes a transmitter 3 and an antenna switching circuit 2.
, a plurality of transmitting antennas 1, and a feeding circuit 101 electrically connecting each transmitting antenna 1 and the antenna switching circuit 2 at equal distances.

The mounting positions of the multiple transmitting antennas are determined in advance with high installation accuracy.

The antenna switching circuit 2 switches the radio waves from the transmitter 3 according to a predetermined switching procedure and supplies the radio waves to the transmitting antenna 1.

The feeding circuit 101 is adjusted so that the electrical distances between the respective transmitting antennas 1 and the antenna switching circuits 2 are all equal.

The code generation circuit 4 generates a predetermined modulation signal indicating that the wave is a reference wave and includes information regarding the arrangement of the antenna when the antenna switching circuit 2 is connected to a specific transmitting antenna serving as a reference. .

The transmitter 3 is composed of a frequency-stable transmitting circuit that generates radio waves modulated by the output signal of the code generating circuit 4.

In the fixed equipment 10 as described above, the most basic antenna arrangement method is to arrange each antenna on a straight line at equal distances. In this case, all antennas have the same electrical characteristics. Then, one of these antennas is used for transmitting a reference signal.

FIG. 4 shows the state of signals transmitted from each antenna.

Note that the transmitting antenna 1 includes (N+1) transmitting antennas A
0 to A, and the transmitting antenna A0 is for transmitting the reference signal.

The reference signal is modulated with a special signal a that can be identified as a reference signal on the receiving side, and a code indicating antenna arrangement information. This reference signal is the transmitting antenna A0
TI from transmitting antenna A1 to T
During this period, signals are transmitted one after another from transmitting antenna A2 to T2. The transmitter 3 and the antenna switching circuit 2 operate during periods T o, T + , T z, . . .
The reference signal is generated and the antenna is switched in synchronization with the However, the transmitter 3 generates an unmodulated wave with a stable frequency, except that the signal is modulated with a code indicating the reference signal and antenna arrangement information at the beginning of the period T0.

The onboard equipment 20 includes a receiving antenna 21, a receiving section 22, a reference wave separation circuit 23, and a phase-locked oscillation circuit (PLO) 2.
4. It is composed of a phase detection circuit 25, a code demodulation circuit 27, and a phase calculation circuit 26.

The receiving section 22 is constituted by a frequency-stable receiving circuit that amplifies the signal received by the receiving antenna 21 and supplies the signal to the next reference wave separation circuit 23.

The reference wave separation circuit 23 separates the reference signal 122 and other signals 123 from the output signal 121 of the receiving section 22 .

The phase lock oscillation circuit 24 oscillates in phase with the reference signal 122 output from the reference wave separation circuit 23,
The oscillation signal 124 is output to the phase detection circuit 25.

The phase detection circuit 25 phase-detects the signal 123 other than the reference signal output from the reference wave separation circuit 23 using the signal 124 from the phase lock oscillation circuit 24, and converts the phase signal 12
5 is output to the phase calculation circuit 26.

The code demodulation circuit 27 manually decodes the code signal indicating antenna placement information included in the reference signal 122 output from the reference wave separation circuit 23 and outputs antenna position information 127 to the phase calculation circuit 26.

The phase calculation circuit 26 inputs the phase signal 125 output from the phase detection circuit 25 and calculates the orientation of the receiving antenna with respect to the transmitting antenna based on the position information of the transmitting antenna from the code demodulating circuit 27.

In the above-described onboard stage [20], the signal transmitted from the fixed equipment 10 is received by the receiving antenna 21, and the receiving section 22 performs amplification and appropriate intermediate frequency conversion to become the receiving section output signal 121. . The reference wave separation circuit 23 manually inputs the receiver output signal 121, and when a modulated signal representing a reference wave is input, a signal T containing the modulated wave is input. From the signal between pJ1, a code signal indicating antenna arrangement information is output to the code demodulation circuit 27, and an unmodulated reference wave signal is output to the phase lock oscillation circuit 24. Other signals are output to the phase detection circuit 25.

When the output signal 122 of the reference wave separation circuit 23 is input, the phase lock oscillation circuit 24 locks the phase to the signal, and when the output of the reference wave separation circuit 23 disappears,
It oscillates continuously at that frequency. The phase detection circuit 25 performs phase detection on the output 123 of the reference wave separation circuit 23 using the output 124 of the phase lock oscillation circuit 24 as a reference signal. The output of the phase detection circuit 25 is input as a complex signal indicating the phase to the phase calculation circuit 25, and the direction of the transmitting antenna is determined by calculation using the antenna arrangement information of the output 127 of the code demodulation circuit 27.

FIG. 2 shows a case where the receiving antenna of the onboard equipment 20 is sufficiently far away from the transmitting antenna of the fixed installation 10.

Generally, if the wavelength of the signal is λ and the maximum distance between the receiving antennas A0 and ○ is iN, then the distance R between the transmitting antenna and the receiving antenna is R≧2ffiN”/λ (1)
It is expressed as

As shown in FIG. 2, when the receiving antennas A0 to AN are in the plane formed by the antenna array and the normal line of the antenna, and the angle between the normal line and the azimuth angle is θ, each transmitting antenna A
, -A, are in phase with respect to the signal transmitted from antenna A0, as shown in Fig. 2, respectively.
8 late. In this case, the following holds true. However, in equation (1), i=1 to N. If the transmitting antenna A0 is the antenna that transmits the reference signal, this phase delay φ5 is expressed as the output of the phase detection circuit 25 of the onboard equipment 20.

The calculation performed by the phase calculation circuit 26 when the transmitting antenna is arranged as shown in FIG. 2 will be explained with reference to FIG.

FIG. 5(a) shows an example of the configuration of the phase calculation circuit 26.

This phase calculation circuit includes a distance detection circuit 51, a phase correction function generation circuit 52, a phase multiplier 53, and a fast Fourier transformer (FFT) 54.

In the phase calculation circuit 26 having such a configuration, the output 125 of the phase detection circuit 25 is input to the distance detection circuit 51,
The distance detection circuit 51 determines whether the distance R between the transmitting antenna and the receiving antenna is sufficiently large. When the receiving antenna is sufficiently far away, that is, when the condition of equation (1) is satisfied, the phase of the signal from each transmitting antenna A0 to AN changes linearly. At this time, the distance detection circuit 51
The output signal 151 indicates an infinite distance, and the phase correction function 152 generated by the phase correction function generation circuit 52 is a constant. Therefore, the output 125 of the phase detection circuit 25 appears as a through signal at the output of the phase multiplier 53. A fast Fourier transformer (FFT) 54 outputs this phase change as a frequency spectrum, converts it into an angle, and displays it. Figure 5 (
b) shows the frequency spectrum of the phase change converted to angle.

When the distance between the transmitting antenna and the receiving antenna does not satisfy equation (1), that is, when the receiving antenna is close to the transmitting antenna, it is necessary to consider as shown in FIG. 3. At this time, the phase delay φ1 of the signal from each transmitting antenna of the output 125 of the phase detection circuit 25 changes almost quadratically. And the closer the distance, the more drastic the changes. Distance detection circuit 5
1, the distance can be determined by measuring the spectrum spread of the input signal. Based on the distance signal 151 from the distance detection circuit 51, a phase correction function generation circuit 52 generates a phase correction function 152 expressed as a quadratic function, and the phase is corrected by a phase multiplier 53. After that, the direction is determined in the same way as in the case of distant locations.

In the case of the installation method shown in FIG. 2, the azimuth resolution θ6 of this system is proportional to (e8/λ). Further, the distance between each transmitting antenna is inversely proportional to the maximum measurement angle. Therefore, if the distance between transmitting antennas is kept constant, resolution can be improved in proportion to the number of transmitting antennas.

〔Effect of the invention〕

As explained above, the present invention can freely realize the necessary azimuth resolution by changing the installation method of the transmitting antenna. In conventional systems, there was a limit to the resolution that could be achieved due to the physical characteristics of the transmitting antenna or receiving antenna, but with this system, it is possible to improve the resolution by increasing the number of transmitting antennas.

Furthermore, when there are multiple ground facilities with different antenna arrangements, the onboard equipment can automatically decipher the antenna arrangement information included in each reference signal and determine the correct orientation.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention; Fig. 2 is an explanatory diagram when the receiving antenna is located sufficiently far away in the embodiment of the present invention; Fig. 3 is an explanatory diagram when the receiving antenna is nearby; FIG. 4 is a diagram showing temporal changes in the transmission signal from the transmitting antenna, and FIG. 5 is a diagram showing the calculation contents of the phase calculation circuit. 1...Transmission antenna 2...Antenna switching circuit 3...Transmitter 4...Code generation circuit 10...Fixed equipment 20...Onboard Equipment 21...Receiving antenna 22...Receiving section 23...Reference wave separation circuit 24...Phase rotor oscillation circuit 25...
Phase detection circuit 26...Phase calculation circuit 27...Code demodulation circuit Representative Patent attorney Yoshiyuki Iwasa 8 + 5 g = rule (~ Figure 4 4■ 1゜■ □

Claims (1)

[Claims] (1) Multiple transmitting antennas whose mounting positions are determined in advance, an antenna switching circuit that switches radio waves from the transmitting circuit according to a predetermined switching procedure and supplies them to the transmitting antennas, and each transmitting antenna and antenna switching circuit. When the antenna switching circuit is connected to a feeding circuit that has been adjusted so that the electrical distances between them are all equal, and a specific transmitting antenna that serves as a reference, it indicates that it is a reference wave and also provides information regarding the antenna placement. Fixed equipment consisting of a frequency-stable transmitting circuit that generates radio waves modulated by a predetermined code, and generates continuous waves at other times, a receiving antenna, and this receiving antenna. A receiving circuit with a stable frequency that amplifies the received signal, a reference wave separation circuit that separates a reference signal based on the reference wave and other signals from the output signal of this receiving circuit, and an output from this reference wave separation circuit. a phase-locked oscillator circuit that oscillates in phase with the reference signal output from the reference signal, and a code demodulation circuit that decodes information regarding the antenna arrangement contained in the reference signal output from the reference wave separation circuit;
a phase detection circuit that detects the phase of a signal other than the reference signal output from the reference wave separation circuit using a signal from the phase lock oscillation circuit; and a code demodulation circuit that inputs the phase signal output from the phase detection circuit. 1. An azimuth measurement system comprising: onboard equipment comprising an arithmetic circuit that calculates the azimuth of a receiving antenna with respect to a transmitting antenna based on positional information of the transmitting antenna input from the aircraft.