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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 The antenna gain defined in the far-field region is no longer applicable under certain circumstance.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.

For bandpass simulation of nonreciprocal devices with fine and complex structures, hybrid implicit–explicit (HIE) perfectly matched layer (PML) which is incorporated with the higher order concept and complex envelope (CE) method is proposed in finite-difference time-domain (FDTD) lattice. The proposed implementation shows advantages in terms of efficiency, accuracy, and absorption. The effectiveness is demonstrated through the simulation and measurement of ferrite circulator. Through numerical results, the proposed scheme can obtain considerable efficiency and enhanced absorption. From the measurement results, it can be seen that the proposed scheme impacts entire performance in bandpass nonreciprocal simulation.

For the simulation of gyrotropic plasma structure with fine geometry details along a single direction in open regions, the hybrid implicit-explicit (HIE) algorithm with improved absorbing boundary condition is modified based on the finite-difference time-domain (FDTD) algorithm. More precisely, incorporating the perfectly matched layer (PML) formulation, the higher order concept and the HIE procedure, the proposed implementation shows its significant superiority in terms of efficiency, accuracy and absorption. To simulate the unique anisotropic characteristic inside the gyrotropic plasma regions, the bilinear transform (BT) method is employed during the calculation. The effectiveness can be further demonstrated theoretically and numerically. Through the results, it can be concluded that the proposed scheme exhibits remarkable behaviors in the gyrotropic plasma open region problems. It can not only obtain considerable accuracy compared with the theoretical solution but also receive better absorption and efficiency compared with the published work. In addition, the results also indicate that the proposed scheme can maintain the stability of the algorithm with dissatisfaction of the Courant-Friedrichs-Levy condition between time step and mesh size.

By incorporating the complex envelope (CE) method and the higher order concept, unconditionally stable perfectly matched layer (PML) is proposed based on the Crank–Nicolson approximate-factorization-splitting (CNAFS) algorithm to simulate the bandpass problems in finite-difference time-domain lattice. The proposed algorithm has the advantages of the CNAFS algorithm, higher order PML concept, and CE method in terms of improving efficiency, enhancing absorbing performance, and simulating bandpass problems. A patched antenna model is carried to investigate effectiveness and efficiency.

Based on the alternating direction implicit (ADI) procedure, the complex envelope (CE) method, and the higher order (HO) concept, an unconditionally stable performance-enhanced convolutional perfectly matched layer (CPML) is proposed to efficiently simulate bandpass electromagnetic (EM) devices and signals in the finite-difference time-domain (FDTD) lattice. Through the numerical example, the proposed scheme shows the advantages of the unconditionally stable ADI procedure, HO-CPML scheme, and CE method in terms of absorbing performance, computational efficiency, and bandpass EM simulation.

In this paper, the effects of multi-radiators on the electromagnetic scattering characteristics of coated flat plate in half space are investigated. The electromagnetic scattering characterization of coated flat plate are represented by active radar cross section (ARCS) under multi-radiators. Simulations were conducted to research the effect of radar absorbing materials (RAM) and multi-radiators on the electromagnetic scattering characteristics of flat plate in half space. Through the resultants, it can be concluded that the electromagnetic scattering characteristics are significantly influenced by RAM and multi-radiators.

Based on the bilinear transform (BT) method and the Crank-Nicolson-approximate-decoupling (CNAD) algorithm, an efficient unconditionally stable implementation of the stretched coordinate perfectly matched layer (SC-PML) is proposed to truncate anisotropic magnetized plasma. The dispersive magnetized plasma can be calculated by the modified auxiliary differential equation (ADE) method. The proposed SC-PML formulations not only have the advantage of the conventional PML in terms of the absorbing performances but also take the advantage of unconditional stability of the original CN algorithm. In this paper, numerical examples are provided in the two-dimensional domain with anisotropic magnetized plasma to validate the effectiveness of the algorithm. The results show that the proposed SC-PML is an unconditionally stable scheme for the time step which surpasses the Courant–Friedrichs–Lewy (CFL) condition and it has considerable absorbing performance.

In this letter, an unconditionally stable and efficient implementation of the complex frequency-shifted perfectly matched layer (CFS-PML) based on the Crank–Nicolson-approximate-decoupling (CNAD) finite-difference time-domain method (FDTD) scheme and the bilinear transform method is developed for terminating anisotropic magnetic plasma. The dispersive and anisotropic magnetic plasma can be simulated by the auxiliary differential equation method. The proposed CFS-PML implementation can not only attenuate evanescent waves but also reduce late-time reflections. Furthermore, the proposed algorithm not only has the advantage of the conventional FDTD method in terms of absorbing electromagnetic waves but also takes advantage of the unconditional stability of the origin CN-FDTD scheme in terms of reducing the computational time. A numerical example is provided in the 2-D computational domain to indicate the effectiveness of the proposed CFS-PML scheme. The results show that the proposed CFS-PML is unconditionally stable for the time step, which surpasses the Courant limit, and it is suitable for truncating the anisotropic magnetic plasma.

According to the two-dimensional aperture principle, directivity and gain are expected to be proportional to the aperture area of an antenna or antenna array. Our simulations and measurements of an end-fire radiation antenna array overturn this conventional wisdom. The gain of an end-fire antenna array is found to be much higher than that calculated by the two-dimensional aperture principle. We introduce a length component into the two-dimensional aperture principle and propose a three-dimensional aperture principle. A four-element end-fire antenna array is designed and measured to verify the correctness of this new principle. The three-dimensional aperture principle opens a pathway to novel types of aperture utilization.

In order to investigate the influence of multi-radiators, active scattering characteristics, which can be reflected by the active radar cross section (ARCS), are investigated by incorporating the multi-radiators with the radar-radiator. The proposed implementation takes advantage of the ARCS concept in terms of considerable accuracy and close to reality especially in the complex electromagnetic environment. The metal sphere model is analyzed to demonstrate the effectiveness of the proposed implementation. Several procedures are employed during the investigation. The ARCS of the metal sphere model is compared with its radar cross section with a single radar-radiator. The frequency characteristic of the ARCS for a metal sphere model with multi-radiators is calculated. The changes in the ARCS with different phases, field intensities, field polarization directions are given. An example is given to illustrate the change in the maximum detection range caused by multi-radiators. Through the results, it can be concluded that the active scattering characteristics of the metal sphere model can be significantly influenced by the multi-radiators.

By incorporating a complex envelope (CE) method, higher order formulation, and approximate Crank–Nicolson (CN) procedure, unconditionally stable complex frequency shifted perfectly matched layer (CFS-PML) implementation is proposed for anisotropic gyrotropic plasma bandpass simulation in open region problems. More precisely, the CE based higher order CN approximate-factorization-splitting (AFS) PML implementation is introduced to terminate the unbounded finite-difference time-domain (FDTD) lattice. The proposed implementation can not only improve computational efficiency but also enhance the absorption at boundaries during the whole bandpass simulation. Numerical examples which include plasma slab models and ridge waveguide structures are introduced to further demonstrate accuracy, absorption, and efficiency. It can be concluded in the results that our proposal can achieve considerable performance in modeling bandpass signals, improving computational efficiency, enhancing absorption, and maintaining remarkable accuracy. Meanwhile, it can be observed that the proposed implementation is stable when the time step surpasses far beyond the Courant–Friedrichs–Lewy condition.