A reflect-transmit-array antenna (RTA) with dual operating modes is proposed in this study. The proposed RTA, which has a three-layer structure without air layers, can achieve a reflectarray-mode (RAM) at 1114 GHz and a transmitarray-mode (TAM) at 1519 GHz. When the incident electromagnetic (EM) wave is Y-polarization, the RTA operates at RAM, and the reflected EM wave is Y-polarization. In comparison, the RTA operates at TAM and the transmitted EM wave is circular polarization (CP) when the incident EM wave is X-polarization. The dual-mode wideband reflect-transmit-array has been fabricated and measured to validate the design. The measured results indicate that 1-dB bandwidth of 15.7% (11.713.7 GHz) can be achieved in RAM and that the maximum aperture efficiency is 63% at 12.4 GHz. Furthermore, 1-dB bandwidth of 17.6% (15.518.5 GHz) can be achieved in TAM, and the axial ratio (AR) is less than 2.3 dB within the operating band. Our findings prove a RTA, which can produce different polarizations (linear polarization (LP) and CP) radiation at different modes with a simple architecture without an air layer.

The Chinese Ocean Salinity Satellite is dedicated to global sea surface salinity (SSS) mapping with two payloads onboard, which are the interferometric microwave radiometer (IMR) and the microwave imager combined active and passive (MICAP), both using the interferometric aperture synthesis radiometry. One of the payloads is an L-band interferometric radiometer system with a Y-shaped antenna array. The other one, MICAP, is a 1-D passive/active combined system, where the L-, C-, and K-band interferometric radiometers’ antenna arrays are arranged in a line, and the active device is an L-band scatterometer. Based on the payload configurations, a series of simulations is applied to analyze the payloads performance, including the brightness temperature (TB) characteristic, the SSS accuracy, and the effects of Sun and land contamination. The TB simulation results show that the IMR possesses a finer spatial resolution compared to the MICAP L-band radiometer, whereas the latter achieves a better TB radiometric resolution. With the assistance of the C- and K-band radiometers and the L-band scatterometer, the combined retrieval accuracy improves compared with the SSS retrieved using only L-band TB and auxiliary parameters. The best accuracy of SSS is achieved when considering all the available measurements from two payloads together in a combined retrieval. Finally, the results related to Sun and land contamination that endanger the interferometric radiometer measurements are presented and discussed. The performance simulation in this article has been used as a reference for the design phase of two payloads and will be updated with the development of payload manufacture.

The global sea surface salinity (SSS) can be accomplished by means of the L-band microwave radiometers from space, such as European Space Agencys SMOS (Soil Moisture and Ocean Salinity) and NASAs Aquarius/SAC-D. However, the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) in SMOS mission suffers from various errors and unexpected in-orbit phenomena, which degrade SSS accuracy. To further improve SSS accuracy, a Full Polarization Aperture Synthesis Microwave Radiometer (FPASMR) has been proposed for Chinas next generation Haiyang (HY) satellite program with two important improvements, which is composed by an L-band and X-band aperture synthesis radiometer (ASR) with two dimensions. One important improvement is that the sea surface roughness (SSR) and sea surface temperature (SST) are simultaneously measured by the full polarization X-band ASR, and another important improvement is that the microwave-optical receiving technology and in-orbit thermal control subsystem are employed to improve the stability of the FPASMR for reducing visibility phase errors. The system of the FPASMR is introduced in terms of L-band subsystem, X-band subsystem and the calibration subsystem. The main specifications of the FPASMR are analyzed in terms of field of view (FOV), angular resolution and radiometric sensitivity. In addition, the FPASMR calibration is also introduced. The FPASMR demonstrator has also been developed and a series of experiments is performed to assess the performance of the FPASMR demonstrator and the improvements in the FPASMR.

Sea surface salinity (SSS) in coastal zones with high temporal and spatial resolutions is also needed for scientific research and marine economy. However, one of the limitations of airborne L-band real-aperture microwave radiometers and synthesis aperture interferometric radiometers is high mass and volume or the high complexity of the system. To overcome the limitations, an L-band phased array radiometer is proposed as an alternative solution to monitor SSS in coastal zones from a small unmanned aerial vehicle (UAV). The L-band phased array radiometer is introduced, which only comprises a phased array and a single receiver. In addition, the calibration methods of the L-band phased array, radiometer that the external calibration method and the internal calibration method, are also introduced. A series of experiments was performed to assess the performance of the L-band phased array radiometer. The results indicate that the L-band phased array radiometer show a good performance in low pointing angles and low scanning angles. As a conclusion, the L-band phased array radiometer can be an alternative solution to monitor SSS in coastal zones with high temporal and spatial resolutions from a small UAV.

The effective calibration of systematic errors is a precondition for high-quality images from a synthetic aperture radiometer system. The receiving channel errors can be relatively well calibrated, but antenna errors cannot be calibrated effectively in-orbit. This paper proposes an in-orbit external antenna error calibration method for synthetic aperture radiometers using external calibration point sources on the ground. Simulation and experimental results demonstrate the accuracy and feasibility of the method. The layout of on-ground calibration point sources was then explored. Our results indicate that is sufficient to adjust the power of the calibration point sources when SNR is 30 dB, and that the calibration requirements can initially be met with three calibration point sources. If better calibration effect is required, eight calibration point sources are sufficient. Non-repeated and uniform azimuth angle schemes appear to be the optimal layout for operating the proposed method, but adjustments can be made as necessary to suit the situation at hand. Finally, a feasible implementation scheme was established. The proposed method has certain reference value in terms of image quality improvement and practical engineering applications.

Traditional specific emitter identification (SEI) systems often suffer significant performance degradation when confronted with previously unseen signal sources, underscoring the critical need for accurate detection and rejection of novel-class instances. To address this limitation, we propose an Integrated Deep Feature Representation and Isolation Forest (IDFIF) method for identifying novel-class radiation emitters. IDFIF begins by employing a convolutional neural network (CNN) to extract embedding features from raw In-phase/Quadrature (IQ) signals, enhancing inter-class separability while suppressing intra-class variability. These deep features are then used to construct an unsupervised iForest that learns the statistical distribution of known classes, enabling the effective detection of anomalies via a threshold-based scoring mechanism. Experiments conducted on a real-world ADS-B dataset demonstrate that the proposed method achieves a novel-class detection accuracy of over 94%, significantly outperforming comparative methods. Furthermore, the method exhibits low sensitivity to known-class samples, thereby ensuring robustness and generalization under open-set conditions. The proposed IDFIF method is promising for deployment in challenging electromagnetic environments.