This paper studies a four-dimensional (4D) memristive system modified from the 3D chaotic system proposed by Lü and Chen. The new system keeps the symmetry and dissipativity of the original system and has an uncountable infinite number of stable and unstable equilibria. By varying the strength of the memristor, we find rich complex dynamics, such as limit cycles, torus, chaos, and hyperchaos, which can peacefully coexist with the stable equilibria. To explain such coexistence, we compute the unstable manifolds of the equilibria, find that the manifolds create a safe zone for the hyperchaotic attractor, and also find many heteroclinic orbits. To verify the existence of hyperchaos in the 4D memristive circuit, we carry out a computerassisted proof via a topological horseshoe with twodirectional expansions, as well as a circuit experiment on oscilloscope views.
So far, plenty of microwave power circuits such as microwave diode rectifiers are mainly designed and analyzed by conventional electromagnetic (EM) co-simulation method based on the semiconductor equivalent circuit models. However, the simplified equivalent circuit model may contribute to loss of precision at high frequencies or under high power. Compared with the equivalent circuit model, the semiconductor physical model provides a means for studying the physics of electron transport, and thus, better describes the semiconductor device. This paper explores analyzing microwave diode rectifiers by employing a physical model-based field-circuit co-simulation method. This method combines the physical model-based circuit simulation to the finite-difference time-domain (FDTD)-based field-circuit co-simulation and thus, achieves accurate and effective hybrid full-wave field-circuit co-simulation. For validation, two diode rectifiers working at S-and C-band, respectively, are simulated and analyzed by the proposed method. The simulation result agrees well with measurement and shows higher accuracy than the equivalent circuit model-based simulation.INDEX TERMS Microwave rectifier, Schottky diode, physical model, filed-circuit co-simulation.
A key open question in the aerial locating method is ensure that parameters that identify the location of the radio frequency interference (RFI) are monitored, and to make sure that the locating algorithm is unbiased. Furthermore, the transmission of parameters to the ground for real-time analysis and display of the RFI location is important as it provides insight into the performance advantages of the aerial location method. The main contributions of the article are four points: the first is the introduction of the angle of arrival (AOA) algorithm to civil aviation RFI location, and the integration of algorithm characteristics with unmanned aerial vehicle (UAV) operations proposing an aerial monitoring method for civil aviation RFI. Simulation results show that the two-point cross-location method obtains effective information on the location parameters of the RFI. The second is to build a UAV monitoring platform, which is as light as possible to make sure the direction finding and digital transmission devices meet the airworthiness requirements, so that the UAV can complete the data acquisition task within a safety margin. Thirdly, a ground analysis system was designed to receive information on the UAV’s parameters, enabling software manipulation to ensure safe operation under non-visual conditions. In addition to this, the monitoring data is processed in real time and algorithms are used to resolve the location of interference sources and display them on a map. The fourth one is to verify the implementation of the aerial positioning method by setting up different test scenarios. Compared with portable direction-finding equipment and ground monitoring, the test results show that the UAV-based RFI monitoring method performances better in monitoring radius and positioning accuracy with a small direction-finding error, and the advantages of the ground analysis system are highly integrated and intuitive display.
Electrically small antennas usually exhibit limited bandwidth and reduced efficiency. The aperture tuning technique offers a means to achieve broad frequency characteristics for such antennas. However, determining the optimal positioning of the tuning element can be challenging. Consequently, a novel wideband tuning method based on characteristic mode analysis is introduced. According to the analysis of modal significance and characteristic current distribution of the small loop antenna, a small slot is created at the location where the current of the primary resonant mode is strongest. Two varactors are then inserted in parallel within the slot and adjusted by using bias voltage. This method enables the originally narrowband resonant antenna to attain an ultra-wideband tuning capability. Experimental results confirm the feasibility and effectiveness of the method, revealing a relative tuning ultra-wideband bandwidth (VSWR < 3) is 53.6% (103 MHz to 178.5 MHz) and the gain is about -3.9 to -1.8 dBi within the bandwidth, Furthermore, the minimum electrical size is only 0.086 λ.
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