Ji Yicai

A Wideband SMM Antenna with Gap and Dielectric Loadings

A wideband four-arm spiral mode micro strip (SMM) antenna, which is loaded by dielectric and gap, is introduced in this paper. This antenna, which operates at mode 0, uses a shallow back cavity to suppress back radiation. Gap-loading and dielectric-loading are used to decrease the voltage standing wave ratio (vswr) of the antenna. A capacitive gap is introduced by a metal ring strip around the spiral, and a nylon disk is attached to the supporting substrate to introduce dielectric-loading. Measured results show that vswr of the antenna is noticeably lowered by dielectric- and gap-loading (fractional bandwidth of vswr

Application of complex cepstrum filter in TDR waveform analysis

Accurate measurement of traveling time on TDR probe is important to apparent permittivity test in TDR measurement system. TDR measurement waveform is composed of first main reflection and multi-reflections. Complex cepsturm filter can separate the first main reflection from the echo like multi-reflection waveforms of the original data. In this paper, multi-reflection model of TDR measurement system is illustrated and the TDR waveform is analyzed in complex cepstrum domain. After filtered in cepstrum domain, the first main reflection of TDR measurement is separated from original waveform. The simulated waveforms is calculated by TDR main reflection and multi-reflection model. The simulated waveform is close to the original waveform measured by TDR device. The experiment results of tap water, alcohol and soil sample show that filtering in cepstrum domain can achieve accurate apparent permittivity.

Numerical Analysis of Electromagnetic Fields in Multiscale Model

Modeling technique for electromagnetic fields excited by antennas is an important topic in computational electromagnetics, which is concerned with the numerical solution of Maxwells equations. In this paper, a novel hybrid technique that combines method of moments (MoM) with finite-difference time-domain (FDTD) method is presented to handle the problem. This approach employed Huygens principle to realize the hybridization of the two classical numerical algorithms. For wideband electromagnetic data, the interpolation scheme is used in the MoM based on the dyadic Greens function. On the other hand, with the help of equivalence principle, the scattered electric and magnetic fields on the Huygens surface calculated by MoM are taken as the sources for FDTD. Therefore, the electromagnetic fields in the environment can be obtained by employing finite-difference time-domain method. Finally, numerical results show the validity of the proposed technique by analyzing two canonical samples.