Application of multi-layer structures of wafer-type made of composite materials for creating microwave antenna radomes

A new type of microwave antenna radome structure for aircrafts is suggested, which is a wafer radomes that possess improved characteristics if compared to traditional structures. Design peculiarities of such radome walls, wafer structures and their load-bearing elements made of dielectric composite materials are considered. A calculation model for such structures is justified and a methodology of selecting reasonable layer parameters according to radome’s level of radiolucency. A comparison of radio engineering characteristics of wafer and traditional three-layer structures of radome’s walls in a wide range of electromagnetic waves’ incidence angles in presence of mass limitations is conducted.     

The Generation of Bessel Beam and Its Application in Millimeter Wave Imaging

In this paper, the zero-order Bessel beam at W band is generated by using a diagonal horn, a convex lens, and an axicon. The generated Bessel beam has a beam spot size of 5.5mm and can propagate with a distance longer than 100mm. Several imaging experiments with the generated zero-order Bessel beam are done. The results show that the millimeter wave imaging system with the generated Bessel beam can be used to detect object as small as 1mm.     

A post-coding scheme for peak-to-average power ratio reduction in intensity modulated optical OFDM systems

An efficient post-coding strategy is proposed in this letter to reduce the peak-to-average power ratio （PAPR） of orthogonal frequency division multiplexing （OFDM） signals for optical intensity modulated direct detection （IM/DD） systems. The post-coding scheme based on discrete cgsine transform （DCT） is employed after the inverse fast Fourier transform （IFFT） in the transmitter to reduce the PAPR of OFDM signals. This method is different from the conventional pre-coding scheme which is employed before IFFT operation. Numerical simulations demonstrate that the new DCT post-coding strategy can significantly reduce the PAPR than the conventional pre-coding scheme. Meantime, the bit error rate （BER） performance of the proposed post-coding system can be improved compared with the conventional pre-coding scheme.     

Design and Implementation of An Active Multibeam Antenna System with 64 RF Channels and 256 Antenna Elements for Massive MIMO Application in 5G Wireless Communications

This paper focuses on the design and implementation of an active multibeam antenna system for massive MIMO applications in 5G wireless communications. The highly integrated active multibeam antenna system is designed and implemented at 5.8 GHz with 64 RF Channels and 256 antenna elements. The 64-channel highly integrated active multibeam antenna system provides a verification platform for digital beamforming algorithm and massive MIMO channel estimation for next generation wireless communications.     

NEW APPROACH TO ELECTROMAGNETIC SCATTERING FROM A CONDUCTIVE DISC-RING STRUCTURE

A one-dimensional modified integral equation for electromagnetic scattering from a metallic concentric disc-ring structure is derived by using Fourier expansion and separating the contribution of charge density from conventional EFIE. In the case of normal incidence, the derived equation is very simple and easy to be solved numerically regardless of the electric dimension of the structure. The comparison between the data of RCS of a disc by using this method and analytical method shows the effectiveness of this approach. Numerical results are also given for current distributions and the scattered fields for a disc-ring structure.     

Correlation between infrared,THz and microwave dielectric properties of vanadium doped antiferroelectric BiNbO4

Terahertz (THz) transmissivity and infrared (IR) reflectivity spectra of orthorhombic microwave (MW) ceramics Bi(Nb_1−xV_x)O₄ (0.002 < x < 0.032) were measured between 4 and 3000 cm⁻¹ (0.09–90 THz) at room temperature. A well underdamped mode, presumably the ferroelectric soft mode, was observed at 25 cm⁻¹. Complex permittivity spectra obtained from the fits to our data were extrapolated down to the MW range and compared with the dielectric data near 5 GHz. The linear extrapolation of dielectric losses from THz down to the MW range is in agreement with the experimental MW losses. Addition of 3.2% of vanadium reduces the sintering temperature to 850 °C and the dielectric properties (ɛ′ = 42.2, Q·f = 14,000 GHz, τ_f = +10 ppm/°C) remain at a level satisfactory for MW applications. Somewhat lower MW losses were observed in a sample sintered in the N₂ atmosphere.     

Measurement of built-in voltage of organic semiconductor devices

The built-in voltage in organic semiconductors is usually measured by electroabsorption measurements. In this paper, we show that for tris-(8-hydroxy quinolato)aluminium (Alq) devices, modulated photocurrent spectroscopy provides a simple viable alternative to measuring the built-in voltage. This is possible because the quantum efficiency for photoconductivity in Alq is independent of the electric field. We also examine the limitations of modulated photocurrent spectroscopy in obtaining the built-in electric field.     

Effect of condensed phase environment on luminescent properties of MEH-PPV thin films

We study sensitivity of photoluminescence emission properties to state of aggregation in MEH-PPV thin films, and its solution in chloroform and xylene (50:50) mixture from which these films are either spin-cast or drop-cast. The choice of composition of solvent is dictated by the ease of fabrication of devices. We demonstrate unambiguous correlation between relative peak heights of the two characteristic major peaks in steady state photoluminescence with processing parameters, such as spin speed, and show that their ratio can be used as a robust measure of degree of entangled packing both in films and solutions. In thin films, a small but discernible red shift of about 3–10 nm in PL peak positions, and increase in width of peaks is observed with changes in degree of packing. A comparison of PL decay dynamics at the 588 nm emission shows that the decay develops slower components with increase in entangled packing in the case of thin films as compared to the fast nearly exponential decay in the case of solution. The progressive slowing down of dynamics is attributed to shift in distribution of inter-chain species of excitons in thin films.     

The solution of end effects of microstrip line by open resonator model

An open resonator model is presented to analyze the end effects of microstrip. Both the reactance and radiation effects are taken into account. The numerical results are compared with the published data.     

一种改进的微波MESFET模拟器

本文介绍一种改进的基于器件物理参数的微波ＭＥＳＦＥＴ模拟器，它不仅可以模拟器件物理参数变化对ＭＥＳＦＥＴ特性（如等效电路元件、Ｓ参数、电流－电压特性）的影响，而且亦可以模拟ＭＥＳＦＥＴ特性随温度变化的情况。