5:15 PM - 6:45 PM
[PEM16-P03] Development of a digital multi-beamformer for a next-generation solar wind observation system
Keywords:solar wind, phased array, beamformer, radio telescope
The solar wind that has the speeds of which is 300km/s to 800km/s is continuously flowing into interplanetary space as the plasma flow from the solar corona, which is the outermost solar atmosphere where the temperature is over 1 million Kelvin. The solar wind interacts with the Earth's magnetosphere. Disturbances of the solar wind can affect social infrastructure by causing troubles with spacecraft, generating geomagnetically induced currents, and destroying power transmission lines on the ground. For these reasons, the space weather forecasting is being noticed, but there are many issues that need to be solved.
If the solar wind and/or coronal mass ejection (CME), which is a phenomenon that part of the sun's atmosphere is blown into space caused by eruptions at solar corona, cross within line of sight of a radio telescope when it observes radio sources outside the heliosphere, the radio waves are scattered by density disturbances of solar wind and CME. As a result, radio telescopes observes time variations of the strength and phase of received radio waves. This fluctuation in received radio waves is called the Interplanetary Scintillation (IPS) phenomenon and observing the IPS phenomenon is called IPS observation.
Nagoya University has detected disturbances of the solar wind efficiently by using IPS observation system composed of 3 cylindrical parabolic antennas at 327MHz. The observation system currently in operation observes up to 100 objects per day, with each object being observed for approximately 200 seconds. By using data obtained from our IPS observations, the accuracy of solar wind disturbance arrival forecasts can be improved. However, there is currently a lack of IPS observation data to improve the accuracy of space weather forecasts.
Therefore, Nagoya University has been developing a next-generation solar wind observation system (hereinafter, this is called "new system") which can generate approximately 10 times more solar wind speed data compared to the conventional observation systems. The new system is composed of 2D phased array antennas and implemented a multi-beam system. The new system can observe up to 1,000 radio sources per day with 1,024 analog inputs, and about 4,000-square-meter aperture array at 327MHz. To achieve this goal, multi-beam systems and wide field antenna systems must be developed.
A digital backend system that realizes a large-scale phased array has been developed. For the first step, an array that corresponds to approximately 5 to 10% of the full system will be constructed. A 64 channel digital backend, which is part of this system, has already been developed.
The AD conversion module has 8 channels of analog input, and each signal can be digitized with 12bit and 100Msps. By using under sampling technique, it is also possible to support signal input from 300MHz to 350MHz. The beamformer uses many FPGAs, and the number of beams can be selected ether 8-beam mode (8192-points FFT) or 4-beam mode (16384-points FFT). The maximum elevation angle of the synthesized beam is 60 degrees. The output of the AD converter module is 16 bits, and data storage interval is 8 milliseconds. All connections between the AD converter modules and the control computer are made using optical cables.
In this research, the 64 channel digital backend that has already been developed is tested about calibration, linearity, grating lobe, filter curve, and Allan dispersion. At present, antennas for 64 channels have not been installed for observation of radio sources yet. Hence, the test of this system is conducted by using a test signal generated by white noise source in the laboratory.
As the first step of this research, a prototype instrument of the new system was tested to establish the test methods of the beamformer. This prototype instrument has 8 channels of analog input and synthesizes 4 beam. This prototype instrument has signal synthesis sequences, which are also installed in the new system.
The calibration sequences and the linearity of the prototype instrument were derived by using a test signal using a white noise source. As a result, the dynamic range of the prototype instrument was approximately 50dBm (between -95 dBm and -45 dBm). The grating lobes was confirmed in tests using sine waves generated by signal generator.
If the solar wind and/or coronal mass ejection (CME), which is a phenomenon that part of the sun's atmosphere is blown into space caused by eruptions at solar corona, cross within line of sight of a radio telescope when it observes radio sources outside the heliosphere, the radio waves are scattered by density disturbances of solar wind and CME. As a result, radio telescopes observes time variations of the strength and phase of received radio waves. This fluctuation in received radio waves is called the Interplanetary Scintillation (IPS) phenomenon and observing the IPS phenomenon is called IPS observation.
Nagoya University has detected disturbances of the solar wind efficiently by using IPS observation system composed of 3 cylindrical parabolic antennas at 327MHz. The observation system currently in operation observes up to 100 objects per day, with each object being observed for approximately 200 seconds. By using data obtained from our IPS observations, the accuracy of solar wind disturbance arrival forecasts can be improved. However, there is currently a lack of IPS observation data to improve the accuracy of space weather forecasts.
Therefore, Nagoya University has been developing a next-generation solar wind observation system (hereinafter, this is called "new system") which can generate approximately 10 times more solar wind speed data compared to the conventional observation systems. The new system is composed of 2D phased array antennas and implemented a multi-beam system. The new system can observe up to 1,000 radio sources per day with 1,024 analog inputs, and about 4,000-square-meter aperture array at 327MHz. To achieve this goal, multi-beam systems and wide field antenna systems must be developed.
A digital backend system that realizes a large-scale phased array has been developed. For the first step, an array that corresponds to approximately 5 to 10% of the full system will be constructed. A 64 channel digital backend, which is part of this system, has already been developed.
The AD conversion module has 8 channels of analog input, and each signal can be digitized with 12bit and 100Msps. By using under sampling technique, it is also possible to support signal input from 300MHz to 350MHz. The beamformer uses many FPGAs, and the number of beams can be selected ether 8-beam mode (8192-points FFT) or 4-beam mode (16384-points FFT). The maximum elevation angle of the synthesized beam is 60 degrees. The output of the AD converter module is 16 bits, and data storage interval is 8 milliseconds. All connections between the AD converter modules and the control computer are made using optical cables.
In this research, the 64 channel digital backend that has already been developed is tested about calibration, linearity, grating lobe, filter curve, and Allan dispersion. At present, antennas for 64 channels have not been installed for observation of radio sources yet. Hence, the test of this system is conducted by using a test signal generated by white noise source in the laboratory.
As the first step of this research, a prototype instrument of the new system was tested to establish the test methods of the beamformer. This prototype instrument has 8 channels of analog input and synthesizes 4 beam. This prototype instrument has signal synthesis sequences, which are also installed in the new system.
The calibration sequences and the linearity of the prototype instrument were derived by using a test signal using a white noise source. As a result, the dynamic range of the prototype instrument was approximately 50dBm (between -95 dBm and -45 dBm). The grating lobes was confirmed in tests using sine waves generated by signal generator.