Jiadong Xu

Analysis of Doppler effect of moving conducting surfaces with Lorentz-FDTD method

To analyze scattering fields from moving conducting bodies, a novel Lorentz finite-difference time-domain (FDTD) method is proposed in this paper. The transformation formulas of electromagnetic field parts, space parts, and time variable are gained by using Lorentz transformation between the rest and the moving reference frame. To calculate the scattering fields from moving conducting bodies, the total-field–scattered-field boundary condition is set up to introduce an incident plane wave in the moving reference frame. Using the interpolation method, the relation between electromagnetic fields in the moving reference frame and that of the related grids in the rest is estimated. Using the proposed Lorentz-FDTD method analyze the scattering fields from one-dimensional moving conducting surface. Thus, variations of the amplitude and frequency of scattering fields with the moving conducting surface speed are considered. Caused by the moving conducting surface, the amplitude and frequency of incident plane wave suffer a modulation shift. Numerical results are in a good agreement with analytical results for the discussed case.

Design of Two-Arm Conical Spiral Antenna for Low Elevation Angle Communication

Conical Archimedes spiral antennas are designed to produce radiation patterns of cardoid or conical shapes for satellite applications. It is shown that the radiation pattern of this antenna can be easily shaped by setting the geometrical parameters of the conical spiral such as the cone angle and spiral constant. A minimized two-arm conical spiral antenna is presented for low elevation angle communication. The antenna has a beam with its highest gain at about 50° off zenith and its dip at zenith. The gain at 2492 MHz is more than 4.5 dBi from 35° and 65° off zenith. The Measured VSWR actually can satisfy the design request (≤ 1.2).

Designing and Measurement of a Single Layered Planar Gain-Enhanced Antenna Radome with Metamaterials

A novel single layer planar gain-enhanced antenna radome is presented to overcome the low gain disadvantage of microstrip antenna. Seven same microstrip complex structures were arranged as a planar centrosymmetric honeycombed shape and accordingly etched on the surface of FR4 substrate. By extracting the constitutive parameters of unit cell of the proposed antenna radome, the value of effective permittivity of unit cell turned out to be near zero at frequency f = 4.25 GHz. The proposed radome design is assessed by comparing the related simulation and measurement results. Gain of the antenna with the new radome design is enhanced with a growing range of 2.5 dB. Results offered in this paper validate the novel design of the proposed antenna radome.

Backscattering characteristics of millimeter wave radar in sand and dust storms

The backscatter properties of millimeter wave radar in sand and dust storms have been addressed. An expression for signal attenuation of millimeter wave radar is derived in terms of visibility and frequency. The results show that the values calculated by the proposed model are in good agreement with those obtained by Goldhirsh’s model and Alhaider’s formula. The general formulas of the backscatter power and equivalent scattering cross-section through sandstorms, suitable for any particle size distribution, are developed in terms of radar range, visibility, and wave attenuation. The results of the calculation show that the equivalent scattering cross-section increases with the increase of radar range less than 35 km, whereas the echo power decreases with the increase of radar range. It is confirmed that the equivalent scattering cross-section and echo power decrease rapidly as the radar range increases for the lower visibility, and decrease slowly with the increase of radar range for the bigger visibility. It is found that the particle size distribution is one major factor which will affect the backscattering properties of millimeter wave radar in sand and dust storms.

Graphical computational method for near-field backscattering problems

A graphical method for the computation of near-field scattering by electrically large scatterers is presented. A perspective transform is introduced for viewing point located in the near region of the scatterers so that the near-field effect is graphically represented. For efficient computation, a graphical algorithm of surface integration is implemented based on currently available graphics software. The concept of Generalized Radar Cross-Section (GRCS) is defined and theoretical results of GRCS of two typical scatterers are carried out.

A novel circular polarization antenna radome

This study presents the use of contiguous aperture radome as a method of generating circularly polarized signals from linear polarization antenna or antenna arrays which are covered by the structure. The experiment results of the novel structure with microstrip antenna are demonstrated for L-band operation. In addition, the structure is also built as a director which can greatly improve the directivity of the antenna.

One terminal improving method of open-circuit near-field antenna of UHF RFID system

A novel broadband dual-loop antenna is presented for the ultra high frequency (UHF) near-field radio frequency identification (RFID) applications. Owing to the novel structure, the current distribution along the loop is kept in phase, as well as the metal terminals exert less influence on the z-orientation magnetic field. The antenna with novel terminals is described and the principle of operation is explained. A comprehensive parametric study of the new model is carried out and the results are presented and discussed in detail. To prove the novel structure, a prototype is developed and fabricated. The measurement results demonstrate that the antenna could achieve a broad bandwidth and low gain, and produce a strong magnetic field with a relatively small z-orientation magnetic field empty hole in the near field. Hence, the work is very promising for UHF near-field RFID reader applications.

Fast Carrier Cancellation for UHF Near Field RFID Systems

Abstract A novel carrier cancelation circuit is presented for ultra high frequency (UHF) near field radio frequency identification applications.A directional coupler, logarithmic detector and controlling circuit are used for improving the sensitivity of the receiver. The cancelation circuit, which consists of vector multiplier and SCM (Single Chip Micyoco), can be adaptively tuned to generate an optimum canceling signal for carrier cancelation. In order to secure good and fast carrier cancelation, logarithmic detector is used as a feedback component to transmit power information of the tag signal channel. The implemented reconfigurable carrier cancelation exhibits good performance on reduction of carrier level in tag signal channel when the adaptive control voltage of SCM is applied. Furthermore, the carrier cancelation control system could be operated real time as well as applied for hopping-frequency systems.

Mutual coupling efficient analysis of rectangle microstrip circular polarization antenna array

Mutual coupling performance of the microstrip circular polarization (CP) antenna array is analyzed in this study. Compared with the single antenna application, in the antenna array, the S11, the radiation pattern, and the axial ratio will all be changed due to the mutual coupling and the axial ratio will be more sensitive. To further prove the concept and performance effect, a model of the microstrip antenna array is developed and analyzed in theory. The simulation and measurement results demonstrate that the relative position of antennas in the array exert different effect on the performances of the antenna. Thus, the study provides some very useful results of the CP antenna array.

Wideband ring-slot coupled patch antenna with enhanced gain

A wideband ring-slot coupled patch antenna is presented in this paper. A microstrip line feeding network is used for impedance matching. Additionally, in order to depress the backward radiation caused by the resonance of the ring-slot, a reflector is introduced to obtain unidirectional radiation patterns, while a dielectric cover is adopted to alleviate the deterioration in impedance caused by the reflector. A prototype is fabricated and measured. The measured results are in good agreement with those simulated, which indicates that the antenna operates well with a relative bandwidth of 55% for reflection coefficient less than −10 dB, an enhanced gain of 8–11 dBi, unidirectional radiation patterns, as well as low cross-polarization.