This paper presents a high-precision, hardware-efficient FFT processor for an on-board SAR (synthetic aperture radar) imaging system. To meet the high resolution imaging and big data granularity processing requirements, a radix-2k mixed FFT algorithm is proposed. The mixed radix FFT algorithm reduces the number of complex multiplication and the size of twiddle factor memory. To further reduce hardware resource and improve FFT precision, sufficient fixed-point simulation is performed for the fixed-point FFT processor design. As a proof of concept, a 32768-point fixed-point processor is implemented on XC6VCX240T FPGA platform. The proposed pipelined FFT processor achieves a signal-to-quantization noise ratio (SQNR) of 47.3 dB at 18-bit internal wordlength. Compared with Xilinx FFT v7.1 IP core, the results demonstrate that our design saves at least 11% memory and 57% arithmetic elements.
This paper presents closed-form expressions of optimal loads that achieve the maximum efficiency for inductive power transfer (IPT) system with multiple receivers. We model the system as a passive N-port network and jointly optimize both reactive and resistive components of the loads. The derived expression allows one to predict RF-to-RF efficiency of IPT system with any number of receivers, under any coupling condition and through any type of media.
A novel all-optical feedforward automatic gain control scheme for pump power shared erbium-doped fiber amplifiers has been proposed. Dynamic gain excursion characteristics of the amplifier using the scheme have been experimentally clarified. The maximum absolute value of the gain excursion has been significantly reduced from 7.3 dB without control to 0.47 dB with the control scheme.
In this paper, circular substrate integrated waveguide (CSIW) filters are presented. Π-shape slots etched along the electric walls of the CSIW on the upper layer are proposed firstly, which enhance the magnetic coupling parameters between two CSIW cavities. Meanwhile, S-shape slots as the electric coupling structure are firstly used on CSIW filters. With both magnetic and electric coupling, the third-order and fourth-order cross-coupled bandpass filters based on circular substrate integrated waveguide resonator (CSIWR) are designed, which possess one transmission zero (TZ) and two transmission zeros, respectively. Measured results of these filters with a high selectivity agree well with simulated ones.
By introducing the effects of bound electric and magnetic charges, the mechanical interaction between waves and a chiral cylinder is investigated with the auxiliary differential equations finite-difference time-domain method. The trapping Lorentz force density distributions of an active chiral cylinder, as well as a core-shell cylinder consisting of a chiral shell and a dielectric core illuminated by a normally incident plane wave are simulated. Numerical results show that the working principle is based on gradient forces generated by the continuously coupled cross-polarized waves. This finding may provide a promising avenue in chirality detection and sorting chiral particles from achiral ones.
This paper presents the design and development of a 190 GHz Schottky-diode frequency doubler (×2 multiplier) which can handle up to 260 mW input power. In order to increase the power handling capability, a modeling approach incorporating computer-aided design (CAD) load-pull techniques to characterize the diode performance is proposed. By the use of this approach, effects of several critical diode parameters on the power handling issue are quantitatively investigated and based on the analysis, a discrete diode chip is designed for the doubler. To ensure rapid heat sink in the doubler circuitry, low cost aluminum nitride ceramic (AlN) is selected as the dielectric material of the circuit substrate, which has significantly better thermal conductivity compared with currently widely-used fused quartz. The doubler circuitry is based on a balanced configuration, which brings a merit of avoiding the use of a filter for the input and output signal isolation. The doubler circuit is optimized by co-simulation using ANSYS’s HFSS and Keysight’s ADS. The measurements show that the doubler can handle up to 260 mW input power with a power conversion efficiency of nearly 8%, resulting in 20 mW output power at 193 GHz.
We fabricated the Bi2Gd1Fe5O12 thin films on glass substrates with the Gd3Fe5O12 buffer layer by the metal organic decomposition (MOD) method. We found an optimum thickness of the Gd3Fe5O12 buffer layer and annealing temperature for crystallization giving the maximum Faraday rotation. The optimum sample showed Faraday rotation of as high as 36.3 deg./µm at the wavelength λ = 500 nm, which is 23 times larger than the sample without the Gd3Fe5O12 buffer layer, and as high as 90.1% of the single crystalline Bi2Gd1Fe5O12 thin films on an (111) SGGG single crystal substrate. These results are promising for applications in optical waveguide isolators and magneto-optic spatial light modulators.