Phased array calibration is crucial to ensure accurate array beam direction and radiation pattern. The calibration method can be divided into farfield calibration and near-field calibration according to the measurement distance. With the development trend of largescale array antennas, it is increasingly difficult for the anechoic chambers to meet the far-field requirements of array antennas. The applicability of far-field calibration methods gradually weakens, while the demand for nearfield calibration methods gradually increases. This article combs traditional near-field calibration methods and discusses the latest near-field calibration methods. The principles and features of different calibration methods are analyzed and compared, and finally an outlook for future development directions is proposed.

For the quadrotor UAV attitude adjustment process, the existence of parameter uncertainty and external environmental interference often cause certain difficulties to the attitude control. This paper studies and proposes a quadrotor attitude control method based on cascade linear active disturbance rejection. First, the dynamic attitude model of the quadrotor UAV was established, and a cascade PID dualloop control architecture was proposed to decompose the attitude control task into two internal and external loops. The Levant differentiator is used to extract control parameters to enhance tracking capabilities. In addition, the original linear active disturbance rejection controller is optimized to better eliminate the impact of external random disturbances on the system. The MATLAB Simulink environment was used to simulate the proposed control method. The results show that compared with traditional method, this method can better suppress the influence of the system caused by perturbations and enhance the tracking ability of the system to the desired signals, which significantly improves the precision and stability of the attitude adjustment of the quadcopter UAV, and improves the precision and robustness of the attitude control of the quadcopter UAV.

In order to ensure the communication security of users and improve the high latency of traditional solutions in the integrated network of space and ground. In this paper, we propose a lightweight certificateless key agreement scheme. Firstly, we analyze the certificateless key agreement protocol system model. Based on the characteristics of the integrated network of space and ground, it is proposed that the protocol needs to satisfy some security requirements such as two-way authentication, anti-replay, and integrity. Then, we choose a lightweight certificateless encryption scheme. Base on the encryption scheme, we propose a key agreement protocol to meet the resource and security requirements of the integrated network of space and earth. Finally, we prove the proposed key agreement protocol security conducted on the BAN logical analysis, and compare the protocol performance with software simulation. The results show that the solution not only meets the network security requirements, but also provides fast and efficient negotiation.

TT&C communication link of sun pointing satellite in sun-synchronous orbit is easy to be interrupted due to the gain pattern interference area of the satellite’s TT&C antennas which are placed in traditional way. In order to reduce this kind of communication link interruption, the antennas’ placement on the satellite should be optimized by taking advantage of the characteristic that the orbital plane of the sun-synchronous orbit and the solar vector maintain a relatively fixed. In this paper, the concrete realization process of TT&C antennas’ placement for sun pointing satellite in sun-synchronous orbit is given through a simulation example, and the recommended installation angle of the TT&C antennas for sun pointing satellites in different sun-synchronous orbit are also provided as a reference.

Digital beam forming technology is a key in the field of communication countermeasures. By controlling the signal amplitude and phase in the digital domain, multiple independent and controllable beams can be formed, with high precision and flexibility in beam pointing, and theoretically not limited by the number of beam forming. The article focuses on the requirements of large phased arrays, utilizes the principle of digital beam forming, and combines large-scale arrays signal synchronization technology and phased arrays amplitude-phase calibration technique, implements a multi-wave position beam search system that can simultaneously generate 180 biased beams. It can utilize the real-time scanning function of the beam group to achieve large-scale beam search and faster target angle positioning. The system has been applied in engineering and successfully executed a large-scale measurement and control task, achieves complete success.

Accurate measurement of underwater terrain in coastal areas is the key to human activities in the ocean. Synthetic aperture radar (SAR) provides a new means for the detection of shallow sea terrain. TerraSAR-X bunching mode can obtain highresolution SAR data with a long integration time, so that the seabed terrain of shallow sea can be inverted more accurately. Traditional SAR image underwater terrain detection is based on the assumption of constant wave period, which not only needs to know the initial water depth to solve the wave period, but also brings some errors to the detection results. In this paper, an underwater terrain detection method based on subaperture images is proposed. A SAR image is decomposed into subaperture images with fixed multiscene time intervals, and the time interval between subaperture images is used to solve the changing wave period, so as to obtain more accurate underwater terrain. The TerraSAR-X data of Wuzhizhou Island in Hainan Province was used to verify the feasibility of this method. The results obtained by inversion of this method were compared with the GEBCO data, and it was found that the two were in good agreement（the MAE was 2.8m and the MRE was 23.91%）. It is proved that this method has great potential for retrieving water depth in shallow sea.

The phased array wave spectrometer is a Ku-band real aperture radar that illuminates the sea surface at small incidence angles to receive sea surface echo power. It extracts three-dimensional sea surface information by removing radar-related factors like EIRP（Effective Isotropically Radiated Power）, antenna patterns, and system loss, which can be measured in a microwave anechoic chamber. However, the antenna pattern's precision is limited, leading to the 'concave' anomaly in the backscatter coefficient profile that hinders wave spectrum inversion. To address this, the paper uses particle swarm optimization to correct integral antenna gain. Validation with flight test data shows a 12% improvement in data reliability, supporting operational wave spectrum production.

With the continuous progress of satellite internet and China's aerospace TT&C technology, aerospace TT&C networks are developing towards intelligence and integration, making great progress in autonomous TT&C, resource allocation, and other aspects. Therefore, establishing an intelligent space-ground integrated network is an important goal for the future development of China's aerospace industry. In this paper, the relevant principles and technologies of tracking orbit, telemetry, and telecommand in intelligent space TT&C network are introduced. At the same time, combined with the space data link standard protocol proposed by CCSDS, TM, TC, AOS, Proximity-1, and USLP standards are introduced in detail, and the technology and practical application of different standards are analyzed. This paper introduces the working principle and technical requirements of space TT&C system from the view of the data link layer and physical layer, and provides reference and prospects for the research of the intelligent space-ground integrated satellite TT&C communication network in China.

The sum and difference channels of Kaband dual channel telemetry equipment have phase differences, which can vary with environmental changes. Phase correction is required at the baseband terminal to achieve phase difference correction and ultimately achieve autonomous tracking of the target. In the shooting range, baseband phase calibration was usually achieved by setting up calibration rods, which can achieve the purpose of phase calibration. However, with the expansion of telemetry equipment in the field of combat, it has expanded to areas such as deep sea and plateau. Due to the various limitations of these special location environments on setting up calibration rods, this article focuses on studying how to achieve the purpose of calibrating the phase zero value of the differential channel, without setting up calibration rods, transmit signals through biased antennas in plateau environments. This article presents the principle and method of rodless calibration based on biased antennas, and verifies the effectiveness of the proposed method through experiments.

Accurate prediction of ionospheric clutter is of great significance in improving the target detection performance of high-frequency surface wave radar. This paper proposes a short-term prediction model of ionospheric clutter using the Opposite Artificial Rabbits Optimization optimized Gated Recurrent Unit (OARO-GRU) network. Firstly, based on the a priori knowledge that ionospheric clutter received by high-frequency surface wave radar has chaotic characteristics, the input and output sample sets of the GRU network are constructed using the phase space reconstruction technique. Then, two improvement strategies, namely, the opposition-based learning and the Cauchy-based mutation, are incorporated to enhance the optimization capability of the original ARO, which is used to optimizthe GRU network with the values of three hyperparameters including the number of hidden layer nodes, the initial learning rate, and the maximum number of iterations. Finally, the optimized GRU network is retrained and fed into the test sample set for testing. The model is evaluated based on the given evaluation metrics. The experimental results show that compared with the other seven comparison forecast models, the proposed OARO-GRU network model has obvious superiority in prediction accuracy and reliability, and provides a new idea and method for effectively improving the target detection performance of high-frequency surface wave radar.