This paper proposes a novel and efficient design technique to achieve multifrequency impedance matching. The matching network is mainly constructed based on fragment discrete structure, which consists of regularly distributed metallic microstrip stubs, where some of them are connected whereas others are not. Different designs are generated by determining the interconnections between each two stubs. To facilitate the design procedure, a theory based on port impedance substitution is rigorously developed to calculate the resulted performance (reflection coefficient) of each design. Finally, the optimal design is obtained by using the derived formulas and genetic algorithm. The full optimization procedure is totally free of electromagnetic (EM) simulation and is quite timesaving. Three different examples of mismatched frequency-varying complex load are adopted to illustrate the steps and functionality of the proposed method. The accuracy of the proposed fast-calculation method is also verified by EM simulation and experimental results.
A numerical simulation of flow around rectangular 2-D prisms of different cross-sectional aspect ratios, ranging from 0.3 to 7.0, is conducted at a Reynolds number of 105. The large eddy simulation (LES) scheme is utilized to solve the 3-D Navier-Stokes equations using a finite volume method on a non-uniform grid, with the Smagorinsky closure model representing the subgrid scale viscosity. This study identifies the influence of aspect ratio on flow features of the velocity/pressure field, i.e., instantaneous vorticity/pressure contours, mean flow streamlines, mean/RMS pressure distribution around the prism, base pressure, mean/RMS drag/lift coefficients, spectral description of drag/lift time history, the associated wavelet based scalograms, wavelet instantaneous frequency spectra and the Strouhal number. Results exhibit salient features in the flow field and associated pressure/aerodynamic forces due to changes in the after body length, demonstrating good agreement with observations from wind tunnel experiments. Findings include identification of the critical depth/breadth ratio and fluctuations in the drag/lift forces, containing features that vary with aspect ratio. A time-frequency analysis is introduced to identify the transient nature of these fluctuations. Wavelet based signal processing schemes combined with instantaneous vorticity/pressure contours are utilized to further highlight temporal variations in the frequency contents of these fluctuations and their influence on the force coefficients.
This paper proposes a novel decoupling and matching technique to enhance port isolation and broaden their common operating bandwidth for asymmetric antenna arrays. The original antennas have strong mutual coupling and a large inconsistency of bandwidths. After adding the proposed network, the coupling has been suppressed and their operating bandwidths have been equalized. To verify this technique, a reference and proposed antenna arrays with element spacing of 0.1506 λ 0 (λ 0 is the wavelength in free space at the center frequency point) are simulated and fabricated. In the experiment, the port isolation is improved by about 23.7 dB at the center frequency. Their bandwidths with a reflection coefficient of −15 dB are also equalized. The common bandwidth is enhanced by about 110.63%. The proposed antenna array has potential application value in modern wireless communication.
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