Two-element interferometer for millimeter-wave solar flare observations

In this paper, we present the design and implementation of a two-element interferometer working in the millimeter wave band (39.5 GHz - 40 GHz) for observing solar radio emissions through nulling interference. The system is composed of two 50 cm aperture Cassegrain antennas mounted on a common equatorial mount, with a separation of 230 wavelengths. The cross-correlation of the received signals effectively cancels the quiet solar component of the large flux density (~3000 sfu) that reduces the detection limit due to atmospheric fluctuations. The system performance is obtained as follows: the noise factor of the AFE in the observation band is less than 2.1 dB, system sensitivity is approximately 12.4 K (~34 sfu) with an integration time constant of 0.1 ms (default), the frequency resolution is 153 kHz, and the dynamic range is larger than 30 dB. Through actual testing, the nulling interferometer observes a quiet sun with a low level of output fluctuations (of up to 50 sfu) and has a significantly lower radiation flux variability (of up to 190 sfu) than an equivalent single-antenna system, even under thick cloud cover. As a result, this new design can effectively improve observation sensitivity by reducing the impact of atmospheric and system fluctuations during observation

The Key Signals Integrity Simulation and Implementation of Portable Processing Terminal in the Special Environment

For this portable processing terminal in the special environment, we introduced the purpose and technical requirements concisely, analyzed the relationship between the reliability in hostile environment and signal integrity, discussed the key signals in the design of portable processing terminals, described the ways to ensure the stability of signal transmission via establishing SI and PI model. In the process of engineering design, the clock source, DDR signals integrity and power integrity were modeled and simulated through CADENCE IBIS to avoid some invisible problems existing in the design, optimize indicators of the signal integrity, and guide the actual design of the products. In the end, we did the actual test for the signal transmission of product through using high-performance oscilloscope, verified simulation design, and gave the effectiveness of the design and reliability of the product

Study of the Way to Firmware Program Upgrade in FPGA Reconfiguration of Distributed Geophysical Instruments

In the distributed geophysical instruments, it would lead to reduced reliability, increased manufacturing costs and low efficiency problem when firmware program upgrade of the high- end FPGA for control data processing of master station in using traditional methods, the direct updating FPGA configuration Flash chip firmware program proposed based on researching on the ways of the update the FPGA program. Using FPGA chip and the FPGA corresponding Flash chip, it directly design the FPGA configuration FLASH model interface by the logic resource, through this interface and the external interface bus between FPGA and computer receives remote firmware program and send it to the configuration FLASH, then complete FPGA firmware updated. Verified by experiments by Xilinx's V6 series FPGA, the method to download a FPGA program takes about 2.5 min, 10 times faster than other methods efficiency, avoiding the problems about use of third-party controllers disassemble and other methods to bring reliability, cost and technical complexity. This approach has a high practical significance

Subdivision Error Analysis and Compensation for Photoelectric Angle Encoder in a Telescope Control System

As the position sensor, photoelectric angle encoder affects the accuracy and stability of telescope control system (TCS). A TCS-based subdivision error compensation method for encoder is proposed. Six types of subdivision error sources are extracted through mathematical expressions of subdivision signals first. Then the period length relationships between subdivision signals and subdivision errors are deduced. And the error compensation algorithm only utilizing the shaft position of TCS is put forward, along with two control models; Model I is that the algorithm applies only to the speed loop of TCS and Model II is applied to both speed loop and position loop. Combined with actual project, elevation jittering phenomenon of the telescope is discussed to decide the necessity of DC-type subdivision error compensation. Low-speed elevation performance before and after error compensation is compared to help decide that Model II is preferred. In contrast to original performance, the maximum position error of the elevation with DC subdivision error compensation is reduced by approximately 47.9% from 1.42″ to 0.74″. The elevation gets a huge decrease in jitters. This method can compensate the encoder subdivision errors effectively and improve the stability of TCS

The First Flare Observation with a New Solar Microwave Spectrometer Working in 35–40 GHz

The microwave spectrum contains valuable information about solar flares. Yet, the present spectral coverage is far from complete and broad data gaps exist above 20 GHz. Here we report the first flare (the X2.2 flare on 2022 April 20) observation of the newly built Chashan Broadband Solar millimeter spectrometer (CBS) working from 35 to 40 GHz. We use the CBS data of the new Moon to calibrate, and the simultaneous NoRP data at 35 GHz to cross-calibrate. The impulsive stage has three local peaks with the middle one being the strongest and the maximum flux density reaches ∼9300 solar flux unit at 35–40 GHz. The spectral index of the CBS data ( α _C ) for the major peak is mostly positive, indicating the gyrosynchrotron turnover frequency ( ν _t ) goes beyond 35–40 GHz. The frequency ν _t is smaller yet still larger than 20 GHz for most of the other two peaks according to the spectral fittings with NoRP-CBS data. The CBS index manifests the general rapid-hardening-then-softening trend for each peak and gradual hardening during the decay stage, agreeing with the fitted optically thin spectral index ( α _tn ) for ν _t < 35 GHz. In addition, the obtained turnover frequency ( ν _t ) during the whole impulsive stage correlates well with the corresponding intensity ( I _t ) according to a power-law dependence ( ${I}_{t}\propto {\nu }_{t}^{4.8}$ ) with a correlation coefficient of 0.82. This agrees with earlier studies on flares with low turnover frequency (≤17 GHz), yet it is being reported for the first time for events with a high turnover frequency (≥20 GHz)

The Calibration of the 35–40 GHz Solar Radio Spectrometer with the New Moon and a Noise Source

Calibrating solar radio flux has always been a concern in the solar community. Previously, fluxes were calibrated by matching load or the new Moon for relative calibration, and at times with the assistance of other stations’ data. Moreover, the frequency coverage seldom exceeded 26 GHz. This paper reports the upgraded and calibrated Chashan Broadband Solar millimeter spectrometer (CBS) working from 35 to 40 GHz at the Chashan Solar Observatory (CSO). Initially, the calibration of the solar radiation brightness temperature is accomplished using the new Moon as the definitive source. Subsequently, the 35–40 GHz standard flux is achieved by establishing the correlation between the solar radio flux, brightness temperature, and frequency. Finally, the calibration of the solar radio flux is implemented by utilizing a constant temperature-controlled noise source as a reference. The calibration in 2023 February and March reveals that the solar brightness temperature is 11,636 K at 37.25 GHz with a standard deviation (STD) of 652 K. The solar radio flux’s intensity is ∼3000–4000 solar flux units (SFU) in the range of 35–40 GHz with a consistency bias of ±5.3%. The system sensitivity is about ∼5–8 SFU by a rough evaluation, a noise factor of about 200 K, and the coefficient of variation of the system transmission slope of 6.5% @ 12 hr at 37.25 GHz. It is expected that the upgraded CBS will capture more activity during the upcoming solar cycle

A Dual-Band High-Gain Subwavelength Cavity Antenna with Artificial Magnetic Conductor Metamaterial Microstructures

This paper presents dual-band high-gain subwavelength cavity antennas with artificial magnetic conductor (AMC) metamaterial microstructures. We developed an AMC metamaterial plate that can be equivalent to mu-negative metamaterials (MNMs) at two frequencies using periodic microstructure unit cells. A cavity antenna was constructed using the dual-band AMC metamaterial plate as the covering layer and utilizing a feed patch antenna with slot loading as the radiation source. The antenna was fabricated with a printed circuit board (PCB) process and measured in an anechoic chamber. The |S11| of the antenna was −26.8 dB and −23.2 dB at 3.75 GHz and 5.66 GHz, respectively, and the realized gain was 15.2 dBi and 18.8 dBi at two resonant frequencies. The thickness of the cavity, a sub-wavelength thickness cavity, was 15 mm, less than one fifth of the long resonant wavelength and less than one third of the short resonant wavelength. This new antenna has the advantages of low profile, light weight, dual-frequency capability, high gain, and easy processing

Large area subwavelength cavity antenna with planar metamaterials

We present a kind of large area subwavelength cavity antenna with artificial permeability-negative metamaterials at GHz range. The antenna has the advantages of flatness, ultra-thin thickness, high gain and good directivity. The optimal receiving area of the antenna is mainly determined by the size of the radiation source. Its directivity and sidelobe cancellation mainly depend on the patterns of the patch array as the radiation source. It is found that the antenna with non-uniform distributed patch array as the radiation source has better performance than that with uniform distributed patch array patterns. Otherwise, this type of metamaterial antenna has nearly the same performance compared to that of parabolic antenna with equal radiation aperture, so it has potential applications to replace the traditional large aperture parabolic antenna