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This article presents an unequal Gysel power divider (UGPD) based on circuit transformation, which is converted from a Pto a T-type circuit. The P-type circuit of a conventional unequal Gysel divider consists of two different value resistors and its connection transmission line. In the proposed T-type circuit, the dummy transmission line and the other transmission line with shunt resistor at center position is connected in parallel. Theoretical analysis was performed to derive the design equations for the proposed circuit conversion. For the validation of the circuit transformation, the UGPD using a T-type circuit at the center frequency of 2 GHz was fabricated and measured. The measured characteristics agreed well with the simulation results. V C 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1529-1531, 2015; View this article online at wileyonlinelibrary.com.ABSTRACT: An electromagnetic band gap resonator antenna (ERA) with an extremely small footprint is presented. The proposed ERA has a peak measured gain of 15.6 dBi and an excellent measured 3dB gainbandwidth of 27%. The four-layer composite superstructure used in this ERA takes the shape of a circular disc with the ground plane radius equal to that of the superstructure. Its footprint area is only 1.7k 0 2 at the lowest operating frequency. The average measured aperture efficiency of this ERA is nearly 90%. The side lobe levels are well below 212 dB over most of the operating bandwidth and the cross polarization levels are below 217 dB. V C 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1531-1535, 2015; View this article online at wileyonlinelibrary.com.

We report that vanadium dioxide films patterned with λ/100000 nanogaps exhibit an anomalous transition behavior at millimeter wavelengths. Most of the hybrid structure's switching actions occur well below the insulator to metal transition temperature, starting from 25 °C, so that the hysteresis curves completely separate themselves from their bare film counterparts. It is found that thermally excited intrinsic carriers are responsible for this behavior by introducing enough loss in the context of the radically modified electromagnetic environment in the vicinity of the nanogaps. This phenomenon newly extends the versatility of insulator to metal transition devices to encompass their semiconductor properties.

The implementation of connection boundary for the hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) method is discussed in this article. It shows that the incident field of the HIE-FDTD method must be split into two time steps. Compared with the implementation method commonly used in the conventionalThe finite-difference time-domain (FDTD) method [1] has been proven to be an effective means that provides accurate predictions of field behaviors for varieties of electromagnetic interaction problems. However, as it is based on an explicit finitedifference algorithm, the Courant-Friedrich-Levy (CFL) condition [2] must be satisfied when this method is used. Therefore, a maximum time-step size is limited by minimum cell size in a computational domain, which makes this method inefficient for the problems where fine scale dimensions are used.To overcome the Courant limit on the time-step size of the FDTD method, unconditionally stable methods such as the alternating-direction implicit FDTD (ADI-FDTD) scheme [3][4][5] have been studied extensively. Although the time-step size in the ADI-FDTD simulation is no longer bounded by the CFL criterion, the method exhibits a splitting error [6,7] that is proportional to the square of the time-step size and the spatial derivatives of the field. When field variation and/or the timestep size is large, the splitting error becomes pronounced. The accuracy of the ADI-FDTD method is limited. Besides, in the ADI-FDTD scheme, three time steps are used for defining the field components, and two subiterations are required for field advancement. It must solve six tridiagonal matrices and six explicit update for one full update cycle, which makes the ADI-FDTD computationally inefficient.Based on the theory of ADI-FDTD method, a novel threedimensional hybrid implicit-explicit finite-difference time-domain (HIE-FDTD) method has been developed recently [8][9][10][11][12][13]. In this method, the CFL condition is not removed totally, being weaker than that of the conventional FDTD method. The time step in this scheme is only determined by two space discretizations, which is extremely useful for problems where a very fine mesh is needed in one direction. In the HIE-FDTD method, only a single iteration (with two tridiagonal matrices and four explicit update) is needed for the field development. The HIE-FDTD method has better accuracy and higher computation efficiency than the ADI-FDTD method, especially for larger field variation. When the same timestep size is maintained, the CPU time for the HIE-FDTD method can be reduced to about half of that for the ADI-FDTD method [10].Because of the important impact of HIE-FDTD method on the electromagnetic computation, an accurate and efficient connection boundary condition must be developed to simulate electromagnetic interaction. This article gives two implementation strategies of the connection boundary, one uses split incident field and the other does not. By comparing the two implementation strategies, it shows that the split in...