Radar echo level calibration system

Abstract

Provided is a radar echo level calibration system capable of accurately determining the magnitude of a received echo by calibrating the entire receiver chain using a measured value of the noise level of the receiver chain. A radar echo level calibration system (100) comprises: an antenna having an observation period during which transmission and reception of radio waves are performed, and a non-observation period during which the transmission and reception of radio waves are not performed; a measurement means for measuring a reception gain and a noise temperature by measuring the noise level during the non-observation period while alternately generating two noise temperatures having a temperature difference periodically or aperiodically; a noise temperature calculation means for obtaining an antenna noise temperature by observing noise received in the period during which transmission of radio waves from the antenna is stopped; and a power calculation means for calculating the power of an echo of interest from the ratio between the power value of the noise level and the power value of the echo of interest by performing digital-level calibration using the noise level.

Description

Radar echo level calibration system

[0001] The present invention relates to a radar echo level calibration system that calibrates noise levels, transmission power levels, etc. in order to accurately measure radar reflectivity factors of weather radars and the like.

[0002] Conventionally, there have been radars that calibrate the gain and noise figure (NF) of the receiving system by measuring them using a transmission power monitor or a noise source. There have also been radars, such as pulse radars, that attempt calibration by injecting a pseudo signal generated in the transmitting system into the receiving system.

[0003] For example, Patent Document 1 discloses an antenna and an antenna structure for millimeter wave communication, and a technology for a wireless communication device that uses the antenna and the antenna structure for communication of wireless signals.

[0004] Patent No. 7441269

[0005] However, the technology of Patent Document 1 does not calibrate the noise level, which changes depending on temperature, etc., and therefore may not be able to accurately measure the radar reflectivity factor of weather radar, etc.

[0006] Therefore, the present invention has been made in consideration of the above-mentioned problems, and has as its main object to provide a radar echo level calibration system that can accurately determine the magnitude of a received echo by calibrating the entire receiving system using a measured value of the noise level of the receiving system.

[0007] In order to solve the above problems, the radar echo level calibration system according to the present invention includes an antenna that has an observation period during which radio waves are transmitted and received and a non-observation period during which the radio waves are not transmitted or received, a measurement means that measures the reception gain and the noise figure by alternately generating two noise temperatures with a temperature difference between them periodically or non-periodically during the non-observation period and measuring the noise level, a noise temperature calculation means that observes the noise received from the antenna during the period when transmission of the radio waves from the antenna is stopped and obtains the antenna noise temperature, and a power calculation means that performs digital level calibration using the noise level and calculates the power of the target echo from the ratio of the power value of the noise level to the power value of the target echo.

[0008] According to the radar echo level calibration system of the present invention, the magnitude of the received echo can be accurately determined by calibrating the entire receiving system using the measured noise level of the receiving system. Note that the effects described here are not necessarily limited to this range and may be any of the effects described in this specification.

[0009] 1 is a block diagram showing a configuration example of a radar echo level calibration system according to a first embodiment of the present invention, and FIG. 2 is a block diagram showing a configuration example of a radar echo level calibration system according to a second embodiment of the present invention.

[0010] Preferred embodiments for carrying out the present invention will be described below with reference to the drawings. Note that the embodiments described below are examples of typical embodiments of the present invention, and do not limit the scope of the present invention, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention.

[0011] 1. First Embodiment A radar echo level calibration system according to a first embodiment of the present invention will be described with reference to FIG.

[0012] <1-1. Configuration of radar echo level calibration system> First, an example of the configuration of a radar echo level calibration system 100 according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a block diagram showing an example of the configuration of the radar echo level calibration system 100 according to this embodiment. The radar echo level calibration system 100 shows a configuration in which the antenna is separated into a transmission system and a reception system.

[0013] The radar echo level calibration system 100 calibrates the entire receiving system by measuring the gain and noise figure (NF) of the receiving system using a noise source and the noise level of the receiving system at a specific elevation angle, and accurately measures the noise level of the receiving system based on the measured value.The radar echo level calibration system 100 is a system that accurately determines the magnitude of the received echo using the measured noise level of the receiving system as a reference and also using the monitored results of the transmission power.

[0014] 1, the radar echo level calibration system 100 includes a transmission / reception control unit 101. The radar echo level calibration system 100 also includes a transmission signal generation unit 102, an up-converter circuit 103, a power amplifier (PA) 104, a coupler 105, a detection unit 106, and an analog-to-digital conversion circuit (ADC circuit) 107 as a transmission circuit for transmitting radio waves.

[0015] The transmission / reception control unit 101 is connected to the transmission circuit and the reception circuit and controls the transmission and reception of radio waves. The transmission / reception control unit 101 also calibrates the noise level and transmission power level, which change with temperature, etc., in order to accurately measure the radar reflection factor of a weather radar, for example. The notation "transmission control / reception and calibration equipment" for the reference numeral 101 in Figures 1 and 2 will be read as "transmission / reception control unit."

[0016] The transmission signal generation unit 102 is connected to the transmission / reception control unit 101 , receives a command signal from the transmission / reception control unit 101 , generates a radio wave transmission signal, and outputs the generated transmission signal to the up-converter circuit 103 .

[0017] The upconverter circuit 103 is connected to the transmission signal generator 102 and the power amplifier 104. The upconverter circuit 103 converts a low-frequency video signal into a high-frequency radio wave signal and transmits the converted radio wave to, for example, a weather radar under test.

[0018] The power amplifier 104 is connected to the upconverter circuit 103 , converts the low-voltage signal transmitted from the upconverter circuit 103 into a high-power signal, and outputs the high-power signal to the transmitting antenna 121 .

[0019] The coupler 105 is a connection unit that connects the power amplifier 104 and the detection unit 106, and allows a portion of the power of the transmission circuit to flow from the power amplifier 104 to the detection unit 106. The coupler 105 can allow, for example, approximately 1 / 10,000 of the power of the transmission circuit to flow into the detection unit 106.

[0020] The detector 106 is connected to the coupler 105 and the ADC circuit 107, and detects a portion of the power of the transmission circuit that flows in from the power amplifier 104 via the coupler 105. The power detected by the detector 106 can be, for example, approximately 1 / 10,000 of the power of the transmission circuit.

[0021] The ADC circuit 107 is an electronic circuit that is connected to the detection unit 106 and the transmission / reception control unit 101, converts the analog electrical signal input from the detection unit 106 into a digital electrical signal, and outputs the digital signal to the transmission / reception control unit 101. The coupler 105, the detection unit 106, and the ADC circuit 107 form a transmission power monitor.

[0022] The radar echo level calibration system 100 also includes, as a receiving circuit for receiving radio waves, a low noise amplifier (LNA) 108, a downconverter circuit 109, and a receiving unit 110. The radar echo level calibration system 100 also includes, as part of the calibration circuit, a noise source 111, a temperature sensor 112, and a changeover switch 113.

[0023] The low-noise amplifier 108 is connected to the receiving antenna 122 or the noise source 111 via the changeover switch 113 , and amplifies the weak signal input from the receiving antenna 122 or the noise source 111 and outputs the amplified signal to the down-converter circuit 109 .

[0024] The downconverter circuit 109 is connected to the low-noise amplifier 108 and the receiving unit 110, and is a circuit that receives radio waves, for example, from the weather radar being tested, converts the high-frequency signal of the received radio waves into a low-frequency signal, and outputs it to the receiving unit 110.

[0025] The receiving section 110 is connected to the downconverter circuit 109 and the transmission / reception control section 101 , receives a signal input from the downconverter circuit 109 , and outputs the signal to the transmission / reception control section 101 .

[0026] The noise source 111 is connected to the low-noise amplifier 108 via the transmission / reception control unit 101 and the changeover switch 113. The noise source 111 is connected to the low-noise amplifier 108 periodically or aperiodically during non-observation times, such as the time until the transmitting antenna 121 moves to the measurement start position. The noise source 111 and transmission / reception control unit 101 function as a measurement means that measures the receiving gain and the noise figure of the receiving circuit by, for example, alternately generating two noise temperatures, HOT and COLD, which have a temperature difference, and measuring the noise level from the two noise temperatures.

[0027] The temperature sensor 112 is connected to the transmission / reception control unit 101 , measures the temperature of the receiving circuit, and outputs the measured temperature to the transmission / reception control unit 101 .

[0028] The radar echo level calibration system 100 includes a noise temperature calculation means that aims the transmitting antenna 121 at outer space (vertically upward in clear weather for ground radar) and observes the noise received during non-observation times when transmission is stopped, and calculates the antenna noise temperature. Note that, in clear weather, even a relatively low elevation angle can be used if the antenna noise temperature is known in advance. In this embodiment, noise is observed by the low-noise amplifier 108, down-converter circuit 109, and receiving unit 110, and the transmission / reception control unit 101 functions as the noise temperature calculation means.

[0029] The radar echo level calibration system 100 uses the noise level to calibrate the digital level (in mV units of the ADC circuit 107), initially measures the noise level, and calculates the final power value of the received noise level from the relational expression between the mV of the ADC circuit 107 and the voltage. The system is equipped with a power calculation means, which calculates the power of the target echo from the ratio of that power value to the target echo power value. In this embodiment, the transmission / reception control unit 101 plays the role of the noise temperature calculation means.

[0030] 1-2. Operation of the Radar Echo Level Calibration System Next, an example of the operation of the radar echo level calibration system 100 will be described with reference to Fig. 1. First, the radio wave transmission operation will be described.

[0031] First, the transmission / reception control unit 101 outputs a command signal to the transmission signal generation unit 102 to generate a radio wave transmission signal.

[0032] Secondly, the transmission signal generation unit 102 receives the command signal from the transmission / reception control unit 101 , generates a radio wave transmission signal, and outputs the generated transmission signal to the up-converter circuit 103 .

[0033] Third, the upconverter circuit 103 converts the low-frequency transmission signal input from the transmission signal generation unit 102 into a high-frequency radio wave signal, and outputs the converted radio wave signal to the power amplifier 104 .

[0034] Fourth, the power amplifier 104 converts the low-voltage radio wave signal input from the upconverter circuit 103 into a high-power radio wave signal and outputs the converted high-power radio wave signal to the transmitting antenna 121. After that, the radio waves are transmitted from the transmitting antenna 121 toward a target.

[0035] Fifth, the coupler 105 allows a portion of the power of the transmission circuit to flow from the power amplifier 104 to the detection unit 106 .

[0036] Sixth, the detector 106 detects a portion of the power of the transmission circuit that has flowed in from the power amplifier 104 via the coupler 105 , and outputs the detected power to the ADC circuit 107 .

[0037] Seventh, the transmission / reception control unit 101 calculates the monitored result of the transmission power based on the power input from the ADC circuit 107. This makes it possible to grasp and calibrate the transmission power level.

[0038] Next, the operation of receiving radio waves and noise observation using the noise source 111 will be described.

[0039] First, the transmission / reception control unit 101 outputs a command signal to the noise source 111 to generate a noise temperature.

[0040] Second, the noise source 111 alternately generates two noise temperatures, HOT and COLD, which have a temperature difference, and the transmission / reception control unit 101 measures the noise level from the two noise temperatures to measure the reception gain and the noise figure of the reception circuit.

[0041] Third, the low-noise amplifier 108 amplifies a weak signal input from the receiving antenna 122 or the noise source 111 and outputs the amplified signal to the down-converter circuit 109. Here, the receiving circuit has three modes for reception: (1) normal radio wave reception operation, (2) noise level observation during non-observation time when no radio waves are being transmitted, and (3) gain and noise figure measurement operation using the noise source 111.

[0042] Fourth, the downconverter circuit 109 receives the output signal from the low-noise amplifier 108 , converts the received high-frequency signal into a low-frequency signal, and outputs the converted signal to the receiving unit 110 .

[0043] Fifth, the receiving unit 110 receives the signal input from the downconverter circuit 109 and outputs it to the transmission / reception control unit 101 .

[0044] Sixth, the transmission / reception control unit 101 observes the noise signal received from the receiving unit 110 and calculates the antenna noise temperature.

[0045] Seventh, the temperature sensor 112 measures the temperature of the receiving circuit and outputs the result to the transmission / reception control unit 101 .

[0046] Eighth, the transmission / reception control unit 101 calibrates the digital level using the noise level, and finally calculates the power value of the received noise level from the relationship between the LSB of the ADC circuit 107 and the voltage, which was initially measured.

[0047] Ninth, the transmission / reception control unit 101 calculates the power of the target echo from the ratio between the calculated power value of the noise level and the power value of the target echo.

[0048] where the noise level of the receiving system, P N can be calculated using the following equation (1) using the Boltzmann constant k, the antenna noise temperature Ta, the narrowest equivalent noise bandwidth B, the receiving system gain Gsys, the receiving circuit temperature Tr, and the noise figure NFsys of the entire receiving circuit.

[0049] P N = kTaBGsys+kTr(NFsys-1)BGsys (1)

[0050] Here, the Boltzmann constant k is a constant, and the equivalent noise bandwidth B can be measured in advance, so it can be seen that the antenna noise temperature Ta, receiving system gain Gsys, receiving circuit temperature Tr, and noise figure NFsys are values ​​to be calibrated.

[0051] The receiving system gain Gsys and noise figure NFsys can be obtained by measurements using a noise source 111, and the receiving circuit temperature Tr can be measured by a temperature sensor 112. Furthermore, the noise level P N can be determined by measuring background noise radiation, so the antenna noise temperature Ta can be calculated conversely using the above values.

[0052] Next, the reason for determining the antenna noise temperature Ta will be described below.

[0053] In conventional radar, the noise level P N In the case of directly measuring the noise level P N Fluctuation of δP NWhen the temperature of the noise source 111 is measured, it is assumed that the receiving system gain Gsys has changed in equation (1). In addition, in a radar that measures the temperature of the noise source 111 and recalculates the noise figure NFsys, the change δNFsys of the noise figure NFsys is first calculated, and the difference δNFsys and δP N In other words, the contribution of δTa, which changes with the elevation angle, was not taken into consideration, so δGsys could not be calculated accurately.

[0054] In this system, the value of the antenna noise temperature Ta at each elevation angle is obtained in advance, so the fluctuation δTa in the antenna noise temperature Ta due to conversion of the elevation angle can be taken into account, allowing for a more accurate calculation of δGsys and a more accurate calibration overall.

[0055] According to the radar echo level calibration system 100 of this embodiment, the radar reflection factor of the transmission system can be accurately determined and calibrated by monitoring the transmission power. Furthermore, the noise temperature of the reception system must be determined and calibrated, which can be achieved by accurately determining and calibrating the gain of the entire reception system, the NF of the entire reception system, and the antenna noise temperature Ta.

[0056] As described above, the radar echo level calibration system 100 enables calibration of the receiving system and determination of an accurate system noise level. Furthermore, since the accurate output level can be determined by the transmission power monitor during transmission, the level of the received echo can be accurately calibrated.

[0057] The radar echo level calibration system 100 is not limited to use in weather radars, but can also be applied to radars that require precise calibration of the reception level, such as radar cross section (RCS) measurement systems.

[0058] 2. Second Embodiment A radar echo level calibration system according to a second embodiment of the present invention will be described with reference to Fig. 2. Fig. 2 is a block diagram showing an example of the configuration of a radar echo level calibration system 200 according to this embodiment.

[0059] 2-1. Configuration of Radar Echo Level Calibration System The radar echo level calibration system 200 shows an example in which a transmission system and a reception system are configured with one antenna.

[0060] As shown in FIG. 2, the radar echo level calibration system 200 differs from the radar echo level calibration system 100 according to the first embodiment in that the transmitting / receiving antenna 211 is connected to the power amplifier 104 and the changeover switch 113 via a transmitting / receiving system switching unit 201.

[0061] The transmission / reception switching unit 201 switches the connection between the transmission / reception antenna 211 and the transmission circuit or the reception circuit. The transmission / reception switching unit 201 can be configured by a circulator, a changeover switch, or a combination of these.

[0062] <2-2. Operation of the radar echo level calibration system> The operation of the radar echo level calibration system 200 is the same as the operation of the radar echo level calibration system 100 according to the first embodiment, except that the transmission / reception system switching unit 201 switches between transmission and reception.

[0063] According to the radar echo level calibration system 200 of this embodiment, similar to the radar echo level calibration system 100 of the first embodiment, it is possible to calibrate the receiving system and obtain an accurate system noise level. Furthermore, since the accurate output level can be determined by the transmission power monitor during transmission, it is possible to accurately calibrate the level of the received echo.

[0064] The present invention may have the following configuration: (1) A radar echo level calibration system comprising: an antenna having an observation period during which radio waves are transmitted and received and a non-observation period during which the radio waves are not transmitted or received, a measurement means for measuring a reception gain and a noise figure by alternately generating two noise temperatures with a temperature difference between them periodically or non-periodically during the non-observation period and measuring the noise level, a noise temperature calculation means for observing noise received from the antenna during the period when transmission of the radio waves from the antenna is stopped and determining the antenna noise temperature, and a power calculation means for performing digital level calibration using the noise level and calculating the power of a target echo from the ratio of the power value of the noise level to the power value of a target echo. (2) The radar echo level calibration system according to (1), comprising: a transmission circuit that transmits the radio waves; a receiving circuit that receives the radio waves; and a transmission / reception control unit that controls the transmission and reception of the radio waves and has the noise temperature calculation means and the power calculation means, wherein the transmission circuit has a transmission signal generation unit that generates a transmission signal for the radio waves, the receiving circuit has a reception unit that receives the radio waves and outputs the received radio waves to the transmission / reception control unit as a received wave, and the measurement unit has a noise source connected to the transmission / reception control unit and the reception unit. (3) The radar echo level calibration system according to (2), further comprising a temperature sensor that measures the temperature of the reception circuit. (4) The radar echo level calibration system according to (2) or (3), wherein the transmission circuit has a detection unit that detects a portion of the power of the transmission circuit via a coupler, and an analog-to-digital conversion circuit connected to the detection unit and the transmission / reception control unit.

[0065] 100, 200 Radar echo level calibration system 101 Transmission / reception control unit 102 Transmission signal generation unit 103 Up-converter circuit 104 Power amplifier 105 Coupler 106 Detection unit 107 Analog-to-digital conversion circuit 108 Low-noise amplifier 109 Down-converter circuit 110 Receiving unit 111 Noise source 112 Temperature sensor 113 Change-over switch 121 Transmission antenna 122 Receiving antenna 201 Transmission / reception system switching unit 211 Transmission / reception antenna

Claims

1. A radar echo level calibration system comprising: an antenna that has an observation period during which radio waves are transmitted and received and a non-observation period during which the radio waves are not transmitted or received; a measurement means that measures the reception gain and noise figure by alternately generating two noise temperatures with a temperature difference periodically or non-periodically during the non-observation period and measuring the noise level; a noise temperature calculation means that observes the noise received from the antenna during the period when transmission of the radio waves from the antenna is stopped and obtains the antenna noise temperature; and a power calculation means that performs digital level calibration using the noise level and calculates the power of the target echo from the ratio of the power value of the noise level to the power value of the target echo.

2. A radar echo level calibration system as described in claim 1, comprising: a transmission circuit that transmits the radio waves; a receiving circuit that receives the radio waves; and a transmission / reception control unit that controls the transmission and reception of the radio waves and has the noise temperature calculation means and the power calculation means, wherein the transmission circuit has a transmission signal generation unit that generates a transmission signal for the radio waves, the receiving circuit has a reception unit that receives the radio waves and outputs the received radio waves to the transmission / reception control unit as a received wave, and the measurement means has a noise source connected to the transmission / reception control unit and the reception unit.

3. The radar echo level calibration system according to claim 2, further comprising a temperature sensor for measuring the temperature of the receiving circuit.

4. A radar echo level calibration system as described in claim 2 or 3, wherein the transmission circuit has a detection unit that detects a portion of the power of the transmission circuit via a coupler, and an analog-to-digital conversion circuit connected to the detection unit and the transmission / reception control unit.

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