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Aiming at the limited space and resources of the UAV platform, the inaccurate target labeling and excessive calculation amount of high-resolution SAR image detection, a rapid detection method for UAV-borne high-resolution SAR image targets is proposed. Firstly, a bilateral filter is used to suppress the coherent speckle noise and non-uniform undulation inside the target in the high-resolution SAR image. Then, a large-scale SLIC segmentation is performed, and a small-scale SLIC segmentation is performed on the superpixel unit with under segmentation problem by analyzing the roughness of the superpixel unit. Finally, the over-segmented superpixel units are combined to obtain the target detection results. The experimental results show that this method can not only improve the detection efficiency of high-resolution SAR image targets, improve the SAR image target extraction ability, but also help to find small targets that are easily missed by some manual methods, and has good engineering application value.

Focus on the poor navigation precision when the aircraft suffers from the loss of satellite signals, the navigation method of the Synthetic Aperture Radar (SAR) platform based on Inertial Navigation System (INS), satellite positioning and scene matching is proposed. First, the corresponding equations of measurements are formed by the models of the INS, satellite positioning and scene matching points, respectively. And then applying the Kalman Filter (KF), the corresponding filter processes are established according to the different equations of measurements. The Extended Kalman Filter (EKF) is used to linearize the equations of satellite positioning and scene matching measurements. The proposed method can be executed when the satellites are not enough to provide the positioning information of the aircraft. In numeral simulations, when the satellite signals are partially missing, the proposed method can obtain lower absolute positioning errors than the INS and satellite-based method, and the proposed method obtains better precisian than the INS and satellite-based method when the satellite signals always exist. The simulation results prove the effectiveness and the superior performance of the proposed method.

In this study, a novel high‐performance balanced dual‐band bandpass filter (BPF) with controllable bandwidth and frequency ratio is proposed. The symmetrical dual‐band bandpass characteristics on both sides of the center frequency f0 can be achieved by cascading two one‐wavelength edge‐coupled ring resonators through coupling. To suppress the common‐mode (CM) noises, a high‐performance balanced dual‐band BPF is designed and analyzed. The elements affecting the controllable filtering bandwidth and frequency ratio are discussed. For practical verification, a microstrip prototype for GPS applications is manufactured and measured with great out‐of‐band rejection and excellent CM suppression. [ABSTRACT FROM AUTHOR]

The anti-intereference ability can be strengthened and the BER can be decreased when space-time block code (STBC) is applied to MIMO systems. The existing quasi-orthogonal code TBH can effectively improve the system capacity, but the effect is not good at high signal-to-noise ratio (SNR). In this paper, we introduce an improved quasi-orthogonal code, derive system capacity formula not with space-time coding but with TBH and improved quasi-orthogonal STBC, and simulate the relationship curve of the SNR and capacity in these systems based on MATLAB. The simulation shows that the system capacity with the improved code is bad in low SNR, but much better than that of the existed code with the increasing SNR, and the advantage on increasing capacity is outstanding, especially when the SNR is high. [ABSTRACT FROM AUTHOR]

Biological species can walk, swim, fly, jump, and climb with fast response speeds and motion complexity. These remarkable functions are accomplished by means of soft actuation organisms, which are commonly composed of muscle tissue systems. To achieve the creation of their biomimetic artificial counterparts, various biomimetic stimuli-responsive materials have been synthesized and developed in recent decades. They can respond to various external stimuli in the form of structural or morphological transformations by actively or passively converting input energy into mechanical energy. They are the core element of soft actuators for typical smart devices like soft robots, artificial muscles, intelligent sensors and nanogenerators. Significant progress has been made in the development of bioinspired stimuli-responsive materials. However, these materials have not been comprehensively summarized with specific actuation mechanisms in the literature. In this review, we will discuss recent advances in biomimetic stimuli-responsive materials that are instrumental for soft actuators. Firstly, different stimuli-responsive principles for soft actuators are discussed, including fluidic, electrical, thermal, magnetic, light, and chemical stimuli. We further summarize the state-of-the-art stimuli-responsive materials for soft actuators and explore the advantages and disadvantages of using electroactive polymers, magnetic soft composites, photo-thermal responsive polymers, shape memory alloys and other responsive soft materials. Finally, we provide a critical outlook on the field of stimuli-responsive soft actuators and emphasize the challenges in the process of their implementation to various industries. [ABSTRACT FROM AUTHOR]

In the paper, a wideband tunable 4 × 4 Nolen matrix is proposed. By using the presented topology of the Nolen matrix, tunable output port phase differences can be realized by inserting one type of tunable phase shifters (T-PS). Besides, the in-band phase deviation error is minimized by adding compensation phase shifters (C-PSs) to the output ports of the Nolen matrix. Analytical design methods based on signal flow graphs and complex exponential signal are given to obtain the rigorous relationships of the coupling and phase shifts in the Nolen matrix. Besides, a detailed method for output ports phase slope compensation is provided. For validation, a prototype centered at 5.8 GHz is designed and fabricated. Measurement results agree well with the simulated ones. By using only one voltage to control the phase shifts of the T-PS in a 90° range for each input excitation of the Nolen matrix, a full 360° range of the progressive phase difference is realized by switching four input ports. The measured fractional bandwidth under 10 dB return loss and isolation is larger than 24.5% with the in − band ± 1.5 dB amplitude imbalance and ±15° phase deviation error for ports 1-4 excitations. Besides, for a more strict criterion of ±1 dB amplitude imbalance and 10° phase deviation error, the measured bandwidths are larger than 15% for all port excitations. [ABSTRACT FROM AUTHOR]

In the paper, a wideband miniaturized impedance-transforming quadrature four-feed network with a flat output phase difference is presented and applied to the design of an active integrated GNSS antenna where no extra impedance matching circuit is needed. The features of impedance transformation and flat output phase difference are achieved by the proposed miniaturized rat-race coupler. When combining the proposed rat-race coupler with two trans-directional (TRD) couplers, a four-feed network with stable sequential quadrature phase shifts is obtained in the whole GNSS band. Since the quadrature four-feed network has the feature of impedance transformation, integration with a low-noise amplifier (LNA) can be realized without extra impedance matching circuits, which reduce the overall size and losses. For validation, a simple rectangular patch is applied as the radiator, and the active prototype is fabricated. Measurement results show that over the entire GNSS band from 1.164 GHz to 1.610 GHz, the miniaturized integrated antenna exhibits a return loss of more than 10 dB, an axial ratio of less than 3 dB axial ratio, and a gain of greater than 16 dBic. [ABSTRACT FROM AUTHOR]