Donglin Su

On the Performance of Printed Dipole Antenna With Novel Composite Corrugated-Reflectors for Low-Profile Ultrawideband Applications

An investigation of the performance of printed dipole antenna with finite periodically corrugated-reflectors for low-profile ultrawideband (UWB) applications is presented. According to the relative orientations of the linear-polarized source antenna and the corrugated-reflectors, the problem could be divided into H and E cases. Their fundamental differences and design guidelines are discussed in detail. A novel composite corrugated-reflector based on the combinations of H-type and E-type ones is proposed for the first time, and fully characterized with a UWB source dipole which was optimized in the free space for better comparisons. An example antenna with only 21 mm core profile, composed of a printed UWB dipole, a microstrip balun and a composite corrugated-reflector, has an impedance bandwidth of 2.75 GHz to 8.35 GHz. Both numerical and experimental results show that the example antenna also has stable uni-directional radiation patterns and a realized gain of over 6 dB within the frequency band from 2.3 to 6.0 GHz, which could be a decent alternative to the EBG antennas due to significant improvements on pattern and gain bandwidth.

A Novel Reversed T-Match Antenna With Compact Size and Low Profile for Ultrawideband Applications

A new unidirectional antenna composed of a reversed T-match dipole, a microstrip feeding line and a ground plane is presented for low-profile ultra-wideband (UWB) applications. This antenna is an improvement over the folded dipole antenna, as it achieves a compact size and a low profile through the introduction of shorting branches on the opposite layer. Detailed descriptions of the structure and design are presented. The antenna occupies an area of 23 mm × 32 mm, and the height above the ground plane is 18 mm (about a quarter of a wavelength at mid-band). Simulated and measured results are studied and compared, which show that the proposed antenna has stable directional radiation patterns, a wide bandwidth from 2.89 GHz to 6.50 GHz, and a gain of 6.0 dBi to 9.4 dBi.

An Unconditionally Stable Radial Point Interpolation Meshless Method With Laguerre Polynomials

The time-domain radial point interpolation (RPI) meshless method has the advantage of conformal modeling of a structure with non-uniformly distributed nodes; however, the time step used is still restricted by the stability condition or distances between the nodes. The time step has to be small and computational time can be long when the distances between nodes are small. In this paper, an unconditionally stable scheme using the weighted Laguerre Polynomials is introduced into the (RPI) meshless method. The result is an always-stable RPI meshless method; it retains the advantages of both the node-based meshless method and the unconditionally stable scheme with the weighted Laguerre Polynomials. The unconditional stability, numerical accuracy and efficiency of the proposed method are verified and confirmed through numerical examples. In the case of the numerical examples computed, CPU time saving can be more than 99% in comparisons with the CPU time used with the conventional conditionally stable meshless method.

Equivalent Circuit for Dipole Antennas in a Lossy Medium

A lumped-parameter equivalent circuit for an uninsulated antenna in a lossy medium is derived from the impedance of the same antenna in air. Consisting of four frequency-independent elements and four elements related to loss tangent and frequency, the equivalent circuit is sufficiently accurate for a broadband simulation including the resonant frequency at which antennas are generally designed to operate. Acceptable relative errors are demonstrated by comparing the results of the equivalent circuit with simulated data obtained from a full wave analysis. The equivalent circuit can be used to replace complex antenna models in lossy media and quantify the effect of the loss on antenna performance.

Equivalent Circuit With Frequency-Independent Lumped Elements for Coated Wire Antennas

A 7-element lumped-parameter equivalent circuit is derived for wire antennas coated with a thin dielectric and/or magnetic material. The derivation is based on a method for transforming any coating to an equivalent magnetic coating on a wire with a different radius. The derived circuit is composed of a five-element sub-circuit for bare wire antennas plus a two-element parallel circuit for modeling magnetic coatings. Compared to full-wave simulations and measurements, this equivalent circuit provides reasonably accurate results over a broad frequency range that includes the first resonance. It can be used to estimate the input impedance of a coated antenna without requiring an EM solver. It can also be used to model coated antennas in circuit simulations.

Stability Analysis and Improvement of the Conformal ADI-FDTD Methods

In order to model curved conducting boundaries with high accuracy, conformal alternating direction implicit finite-difference time-domain (ADI-FDTD) methods have been developed with applications of Dey-Mittras and Yu-Mittras conformal techniques. We show that the conformal ADI-FDTD methods developed as such lose the unconditional stability although it is expected with the ADI schemes. We present the theoretical analysis and numerical experiments that proves our findings. We then present a modified conformal ADI-FDTD technique with better stability than those based on Yu-Mittras and Dey-Mittras conformal techniques.

Reduction in Out-of-Band Antenna Coupling Using Characteristic Mode Analysis

Out-of-band interference by antenna coupling is frequently encountered and difficult to compensate. In this paper, it is studied for the first time using characteristic mode analysis (CMA). Mutual coupling between two antennas is separated into several fundamental modes, and the contribution of each mode is evaluated through modal mutual admittance (MMA). Some higher order modes, which contribute little to the in-band radiation but much to the out-of-band coupling, are discriminated and controlled by means of inductive loadings. The placement of loadings is suggested by the distribution of eigencurrents and optimum values are obtained by evaluating the MMA. Numerical and experimental results are presented for verification.

Prediction of the HF Ionospheric Channel Stability Based on the Modified ITS Model

Since the narrowband ionospheric channel model is applicable only to a limited set of actual conditions, in 1997 the Institute for Telecommunication Science (ITS) (Vogler and Hoffmeyer) developed a wideband HF ionospheric model, the so-called ITS model. However, the widely used ITS model has some restrictions in application: the parameters are complex and difficult to obtain; only the undisturbed situation is considered; and the multipath delay is fixed and cannot represent the stochastic behavior of the ionosphere. In this paper, the ITS model is modified by introducing the International Reference Ionosphere (IRI) and adding a parameter amending module to provide more accurate parameters, and based on the ITS mathematical and modeling structures, a wideband HF random time-varying ionosphere channel model is presented. With this model, the characteristics of the ionospheric channel under different conditions have been analyzed, and the simulation results show that it can represent the ionospheric channel more accurately and has good consistence with the measured data.

Errata to “The HF Channel EM Parameters Estimation Under a Complex Environment Using the Modified IRI and IGRF Model” [May 11 1778-1783]

In the above paper (ibid., vol. 59, no. 5, pp. 1778-1783, May 2011), the authors affiliation was incorrectly shown as Beijing University. It should have read Beihang University. The IEEE regrets this error.