For the last 20 years, the time-reversal (TR) process has been successfully applied to focus pulses in the microwave frequency range and in complex media. Here we examine the specific conditions to obtain the same results but in the sub-THz frequency range. Because of the stronger attenuation at this much higher frequency, it is more challenging to exploit the TR self-focusing property. The TR of pulses is studied in two kinds of complex media: metallic waveguide and leaky reverberating cavity. For each medium, we propose one or two models to assess the quality of the focusing. For the waveguide, we show that the angle of incidence is an important parameter. Based on these results, we perform TR experiments at 273 GHz with a bandwidth that can be as large as 2 GHz. TR experiments are successfully first conducted in a 1 m long and 10 mm diameter straight hollow cylinder and then in a 5 m long and 12 mm diameter curved waveguide. Finally, we present results obtained in a cavity of 72 cm³ that leaks through a copper grid. The best focusing is observed with the longer waveguide.....

In this work, we present numerical results regarding the effects of temperature on the omnidirectional photonic band gap (OPBG) of ternary 1DPC containing metal (Ag) layer or graphene layer. By periodically introducing layer metal (Ag) or graphene into 1DPC, the width of OPBG has been increased. As the temperature increases, the photonic band gap of the OPBG becomes wider. Compared to the conventional OPBG in ternary 1DPC containing Ag, the OPBG in 1DPC containing graphene with temperature T = 1000˚K is greatly broadened by 2.04 times. The theoretical basis of our study adopts the transfer matrix method TMM. In fact, these broad omnidirectional and thermally tunable OPBGs will offer many prospects for omnidirectional mirrors, temperature sensing device, optical filters, polarizer, and other optical devices.....

Reconfigurable intelligent surface (RIS) has been suggested as a promising solution to prevent wireless communication systems from transmission blockage. In this paper, the performance of reconfigurable intelligent surface in cooperative decode-and-forward relaying for hybrid radio frequency (RF)/free space optical (FSO) system is evaluated where parallel transmission of information occurs on the system downlink. In this network, the RF links in the system are assumed to follow Nakagami-m distributions while the FSO link is subjected to Gamma-Gamma distribution. Thus, the exact closed-form expressions of the system outage probability and average bit error rate are obtained to quantify the system performance. The accuracy of these expressions is justified by the Monte-Carlo simulations. Also, to get more physical insight from the derived outage probability expression, the asymptotic outage probability under the condition of higher signal-to-noise ratio (SNR) is provided. In addition, the results illustrate that the system and channel parameters significantly affect the performance of the concerned system. Furthermore, the results show that RIS-hybrid downlink system offers better performance than hybrid downlink system without RIS. Under the RIS system, the results demonstrate that RIS-hybrid downlink system outperforms RIS-FSO downlink system.....

A dual-band hexagon shape substrate integrated waveguide (SIW) based band pass filter with single loop complementary spilt ring resonators (CSRRs) is introduced in this paper. The design parameters of this filter are optimized by using artificial neural networks (ANNs). Especially error back propagation multilayer perceptron (EBP-MLP) neural network with Levenberg-Marquart (LM) algorithm is used. A physical prototype of the proposed model is fabricated and tested. In the lower passband from 10.2 to 10.6 GHz, the insertion loss is about -0.8 dB with a fractional bandwidth of 3.85%, and in the upper passband from 12.11 to 13.31 GHz, the insertion loss is about -0.8 dB with a fractional bandwidth of 9.56%. It is observed that the insertion loss is same in both the passbands. The obtained experimental results are in good agreement with the estimated results using full-wave analysis and ANN optimization.....