Based on the alternating direction implicit finite-difference time-domain (ADI-FDTD) algorithm, a higher order perfectly matched layer (HO-PML) is proposed to solve the problems in a three-dimensional computational domain. The proposed scheme can not only take advantage of the HO-PML for improving the absorbing performance but also has the advantage of the ADI-FDTD algorithm in terms of the unconditional stability. A dielectric resonator antenna example is carried out to validate its effectiveness. The results show that the Courant-Friedrich-Levy limit can be eliminated and the absorbing performance can be further enhanced.

Based upon the approximate Crank-Nicolson (CN) algorithms and the higher order concept, unconditionally stable perfectly matched layer (PML) implementations are proposed for electromagnetic problems in the finite-difference time-domain (FDTD) lattice. The approximate CN algorithms include the CN direct-splitting (CNDS) and CN approximate-factorizationsplitting (CNAFS). The proposed schemes take advantages of the approximate CN algorithms in terms of eliminating the Courant-Friedrichs-Levy stability condition and maintaining the computational accuracy. By introducing the higher order concept to the PML formulation, the absorbing performance can be enhanced during the simulation. Furthermore, to cope with the existence of half time step problems in simulating the anisotropic magnetized plasma, a modified ADE method is proposed at the integer time step. Thus, the modified ADE method can be directly employed to the approximate CN algorithms. Numerical examples and experiments are carried out to demonstrate the effectiveness, efficiency and performance. Through the results, it can be observed that the computational efficiency and the absorbing performance can be significantly improved. Meanwhile, it can be concluded that the CNAFS-PML and CNDS-PML algorithms show higher accuracy and considerable efficiency, respectively, when the time step surpasses far beyond the CFL condition.

Most terahertz (THz) radar systems can only work in the near-field region, because the THz source power is limited and the size of the target scattered near field is up to tens of kilometers. Such conditions will result in the conventional radar range equation being unsuitable. Therefore, the near-field radar cross section (RCS) formula is given according to the numerical simulation on different targets. By modifying the parameters in the near field, including the gain of radar antennas and the RCS of targets, the generalized radar range equation is proposed. The THz radar working efficiency in the whole range and the simulation of the near-field RCS simulation model were employed to validate its effectiveness. Through comparison with the radar range equation, it can be concluded that the calculation results of the proposed equation are smaller in the near field, and the outcomes in the far field are identical. The proposed generalized radar range equation can be applied to the whole radiation area including the near field and the far field. Furthermore, more complicated real targets are calculated according to the generalized radar range equation and it can be extended from the submillimeter wave band to a much wider band range. Finally, the near-field radar theory is established, which shows its potential application to the radar cross section estimation in the extremely high frequency and fine design of THz radar systems.

We propose a collaborative simulation method for evaluation of passive intermodulation (PIM) on mesh reflector antenna. The electric field on the surface of reflector can be simulated exactly and conveniently by multiscale equivalent method and finite element (FEM) solver. Meanwhile, the coefficients in the nonlinear model of PIM characteristic on mesh structure are determined from the experiment results on mesh reflector sample, so that the PIM of mesh reflector antenna with the same braided form and working conditions can be calculated using the same nonlinear model. In simulation, the PIM calculations of mesh reflector samples based on the actual woven form and with dimensions of 0.25 × 0.25m 2at C-band and Ku-band have been established, indicating basically consistent to the measured results and validating the effectiveness of this method. Moreover, the PIM prediction of a mesh reflector antenna with the same woven structure is also given. These results show that this method can be utilized to predict PIM level of the mesh reflector antenna under conditions of the precise PIM measurement of mesh reflector sample, also providing reference for designing the low PIM microwave components.

In the sub-millimeter-wave band, the wave is transmitted between two aperture antennas merely in the near-field region because of high working frequency and large space transmission loss. The antenna gain defined in the far-field region is no longer applicable under certain circumstance. Therefore, the near-field gain, one of the most important parameters of the sub-millimeter-wave antenna, should be defined. Based on the transmission equation and near-field transmission efficiency formulation, the near-field gain expression for the aperture antenna is proposed. The proposed expression can be applied to the entire radiation area, including not only the near field but also the far field. From the perspective of the theoretical derivation and numerical simulation, the results of the near-field gain for the aperture antenna are obtained in the sub-millimeter-wave band. Through a comparison with the published research, it can be concluded that the proposed expression is reasonable, indicating the theoretical establishment of the near-field gain and its potential application to the sub-millimeter-wave antenna design and sub-millimeter-wave radar theory.

In this article, two ferrite circulators with wedge-shaped cross section geometry have been designed, manufactured, and tested. Inclination angle of wedge-shaped geometry for two circulators is different. First, the electrical performance of the ferrite circulators is optimized using high-frequency electromagnetic simulation software (HFSS), and then measurements of the electrical performance are completed. Also, the two ferrite circulators have equivalent electrical characteristic. The isolation is greater than 20 dB, and the bandwidth is 15%. Finally, the multipactor thresholds of the circulators involved in this article are simulated using particle solver in CST simulation software and the actual measurement experiment is also performed. The simulation and measurement results show that the circulator with a larger wedge angle has a larger multipactor threshold. So, this structure can provide a reference for the design of multipactor-free ferrite circulator.