A dual-polarized antenna based on vector synthetic mechanism is demonstrated in this paper. It mainly embraces four radiators, a feed structure and a reflector. All the radiators participle in the synthesis process, and there is almost no cross polarization current on the radiators. Hence, the antenna element could cover 3.3-3.6 GHz with high port isolation and low cross polarization. A prototype of the antenna element is also experimentally studied. Then, the antenna element is extended to an array. By assigning different weighting factor and phase for each element's port, the antenna array can generate different pattern to meet the multi-mode requirements of the communication network. High isolation, low cross polarization, low side lobes and high front to back ratio can still be obtained. Having such merits, the MIMO antenna would find its wide application in the future 5G base station application.

This letter describes the integration of microstrip slot array antenna with amorphous silicon solar cells. To appraise the antenna, a 2×2 circularly polarized microstrip slot array antenna integrated with amorphous silicon solar cells using a stacked design method was measured. The results show that the gain of the antenna is almost unchanged after the integration of the amorphous silicon solar cells and the axial ratio decreases to 1.4 dB. The amorphous silicon solar cells and the microstrip slot array antenna are perfectly combined, the interference between the solar cells and the antenna is minimal. The integration saves a lot of space, and has the ability to self-sustaining power generation, thus providing reliable and long-term communication for various satellite communication systems.

During hypersonic flight, the communication link is affected by the multipath effect and plasma sheath. As a result, envelopes and phases of the wireless signals fluctuate with time. In this paper, an integrated channel model is proposed based on geometric propagation theory. The statistical characteristics of the plasma sheath channel are carefully studied. The probability density functions (PDF), the correlation coefficient between envelope and phase, the autocorrelation function (ACF), the level-crossing rate (LCR) and the average fade duration (AFD) are derived and detailed based on electromagnetic propagation theory. Two numerical examples are also used to demonstrate the effectiveness of the model. All statistical curves agree with the theoretical curves. The proposed model comprehensively considers the multipath effect, the Doppler effect and the plasma sheath effect. It is crucial to plausibly understand the blackout problem to facilitate performance evaluations of hypersonic vehicle communication systems.

Orthogonal time frequency space (OTFS) modulation has been confirmed to provide significant performance advantages against Doppler in high-mobility scenarios. The core feature of OTFS is that the time-variant channel is converted into a non-fading 2D channel in the delay-Doppler (DD) domain so that all symbols experience the same channel gain. In available literature, the channel is assumed to be quasi-static over an OTFS frame. As for more practical scenarios, the Doppler shift is dynamic and the channel gain could be time-variant as the environment or medium changes. In this paper, we analyze the characterizations of OTFS modulation over a more general multipath channel, where the signal in each propagation path has experienced a unique rapid fading. First, we derive the explicit input-output relationship of OTFS in the DD domain for the case of ideal pulse and rectangular pulse. It is shown that the rapid fading will produce extra Doppler dispersion without impact on delay domain. We next demonstrate that OTFS can be interpreted as an efficient time diversity technology that combines space-time encoding and interleaving against the rapid fading. Simulation results reveal that OTFS is insensitive to rapid fading and still outperforms conventional multicarrier systems in these channels.

A three-dimensional (3-D) total-field/scattered-field (TF/SF) plane-wave source was developed for the analysis of the plane wave propagation characteristics in the reentry plasma sheath. Owing to the dynamic variation in the surrounding flow field, the plasma sheath during the reentry process presents various 3-D inhomogeneous structures, such as dynamic plasma turbulence and considerable metal ablation particles. The proposed 3-D model can be efficiently applied to simulate the scattering effects of the 3-D inhomogeneous structures on the EM signals. The proposed model utilizes a 3-D TF/SF boundary to introduce the plane wave source into the simulation domain, and six pairs of twodimensional (2-D) auxiliary propagators are created to generate the incident field on the TF/SF boundary based on the phase matching and the current density convolution finite-difference time-domain (JEC-FDTD) method. The uniaxial anisotropy perfectly matched layer (UPML) is modified as the absorbing boundary condition of the 2-D propagators. Implementation issues such as stability and dispersion are also discussed. The accuracy and efficiency of the proposed scheme are validated by admirable numerical simulation results and excellent agreement with the transmission line analogy method.

The high velocity of the re-entry object causes its surface to be enveloped with a plasma sheath. In the process of target detection of re-entry objects, the plasma sheath with fluid characteristics results in multiple reflected signals in the radar echo. Multiple targets appear in the 1-D range profile following pulse compression processing of a multicomponent echo signal. We refer to targets different from the real target as interference targets. The appearance of interference targets seriously affects the radar detection of re-entry objects, resulting in positioning failure or even tracking loss. In this article, by establishing the physical model of radar echo with multiple reference points and multiple velocity parameters of the re-entry object under plasma sheath, the multitarget phenomenon of the re-entry target echo signal on the 1-D range profile is simulated. A target detection method based on Doppler frequency compensation and nonuniform plasma sheath reflection model is proposed, which can effectively suppress false targets and realize reliable detection of targets under plasma sheath. The feasibility of detecting a target enveloped by a plasma sheath is verified by simulation, laying the foundation for the precise detection and tracking of targets.