Shanjia Xu

A millimeter-wave omnidirectional circular dielectric rod grating antenna

A millimetre-wave omnidirectional circular dielectric rod grating antenna is investigated theoretically and experimentally. As an eigenvalue problem, the antenna is analyzed with the rigorous mode matching method. The radiation characteristics of the antenna are calculated and measured in the Ka-band frequency range. A comparison between the experimental results and the theoretical predictions is made and good agreement is found. The practicality of the omnidirectional antenna and the effectiveness of the theory are thus justified. >

Characteristics and design consideration of leaky-wave NRD-guides for use as millimeter-wave antenna

Leaky-wave characteristics of a class of nonradiative dielectric (NRD)-guides with various shapes of trapezoidal cross section are systematically studied for their potential applications in low-cost millimeter-wave antennas. A numerical technique is applied to model these irregular structures. The technique is formulated by effectively combining a multimode network theory with a mode-matching method. Our emphasis in this work is on the investigation of parametric effects in connection with the trapezoidal dimensions on leakage properties of the NRD-guide. Extensive results are presented to derive some useful guidelines for the design considerations of new types of NRD-guide leaky-wave antennas.

A millimeter-wave omnidirectional dielectric rod metallic grating antenna

A new millimeter-wave omnidirectional dielectric rod metallic grating antenna is investigated theoretically and experimentally, in this paper. The radiation characteristics of the antenna are carefully investigated by a rigorous formulation for the TE/sub 01/-mode and TM/sub 01/-mode excitation in the Ka-band frequency range. Based on the analysis, an omnidirectional antenna excited by the TE/sub 01/ mode is designed and measured. The measured results are compared with theoretical predictions and good agreement is found. Extensive numerical results are given to establish some useful guidelines for the design of the omnidirectional antenna.

Hybrid-mode analysis of planar transmission lines with arbitrary metallization cross sections

The problem of planar transmission lines of arbitrary metallization cross sections is solved by using the generalized transverse resonance technique combined with the mode-matching procedure. Analyses are carried out on the dispersion characteristics of microstrip lines, finlines and coplanar waveguides with trapezoidal strip cross sections. Numerical results verify the versatility and accuracy of this method, and show that the profiles of the metallizations in miniaturized MMIC guiding structures have marked effects on the transmission properties. >

DESIGN OF A 1 × 20 SERIES FEED NETWORK WITH COMPOSITE RIGHT/LEFT-HANDED TRANSMISSION LINE

Based on composite right/left-handed (CRLH) transmis- sion line (TL),a novel series feed network for microstrip arrays is pro- posed and its theoretical analysis and experimental results are pre- sented. In the present structure,power dividers and open-ended stubs are employed to even the amplitude distributions among different out- put ports,while CRLH TLs and short meandering lines are used to compensate the phase delay caused by the different lengths of right- handed (RH) TLs. Finally,an X-band series feed network is designed and fabricated as an example. The simulated and measured results indicate that the present design can achieve even amplitude and phase distributions among different output ports in the range of 8.8-9.6 GHz. And it has other advantages such as a compact size of 350 mm ×50 mm and good return loss which is higher than 22 dB in the operation fre- quency.

Modal analysis of open groove guide with arbitrary groove profile

A modal analysis method is proposed for groove guide with arbitrary groove profile. The formulation is versatile, efficient, and rigorous, except for the step approximation process of the groove profile. Numerical results have shown excellent agreement with previous data.<<ETX>>

Properties of guided modes on open structures near the cutoff region using a new version of complex effective dielectric constant

Radiation region for open guiding structures is known to be further divided into antenna- and reactive-mode regions, and there is no clear cutoff point defined between the two regions. For a leaky-wave antenna, it is crucial that the antenna is designed to operate in the antenna-mode region so as to increase radiation efficiency, whereas in integrated circuits, the leakage should be suppressed to avoid unwanted coupling among circuits. Therefore, a reasonable definition of the two above-mentioned mode regions is necessary. In this paper, we propose a simple, but good alternative to define these two regions by means of a new version of complex effective dielectric constant, where the complex nature is due to leakage rather than dielectric or metal losses, as is customary. With the new approach, the reactive-mode region is found to be consistent with the conventional concept, and our results are similar to those in the literature. The present technique, however, helps in a better understanding of the results in a much easier way. Furthermore, we find for the first time that the attenuation constant in the deep reactive-mode region can be divided into two separate parts, one is due to the cutoff effect, while the other is caused by the leakage effect. Simple closed-form expressions are derived to determine the two kinds of effects. One can, therefore, gain some insight into the leakage effect in the reactive-mode region. A nonradiative-guide leaky-wave antenna is then investigated as a showcase and low radiation efficiency is observed in the reactive-mode region.

Transverse scattering matrix formulation for a class of waveguide eigenvalue problems

Based on the mode-matching procedure, a unified transverse scattering matrix formulation is presented for the characterization of a class of waveguide eigenvalue problems, which include not only closed but also open structures. As examples, calculations are carried out on the dispersion characteristics of ridged waveguides and their variations, nonradiative dielectric (NRD) waveguides, groove guides, microstrip lines, finlines and coplanar waveguides. Comparisons with published data are made and verify the versatility and accuracy of the method. Besides its generality, this approach is also superior to some other techniques in simplicity and numerical efficiency. >

Design of time delay lines with periodic microstrip line and composite right/left-handed transmission line

Based on the sharp relationship between Ang(S21) of CRLH-TLs and working frequency, CRLH-TLs TDLs with large time delays are proposed. Meanwhile, sawtooth-shaped PMLs are selected to realize tiny time delays. Finally, a 9-bit time delay module consisting of CRLH-TLs, sawtooth-shaped PMLs and OMLs as well as eighteen SPDTs is designed and fabricated. By selecting different states of SPDTs, time delays from 1.2ps up to 613.2ps can be achieved. The comparisons of simulation and experimental results validated the present design. Besides, the present time delay module possesses other advantages such as compactness, low loss, precise and easy fabrication.

An efficient high-order mixed-edge rectangular-element method for lossy anisotropic dielectric waveguides

A new efficient high-order mixed-edge rectangular element method is proposed for the analysis of lossy anisotropic dielectric waveguides. The space construction of the high-order mixed-edge rectangular element is investigated and the explicit form of the shape function is given. The high-order mixed-edge element yields higher accuracy and faster convergence than the lowest order mixed-edge rectangular elements without spurious solutions, and is more efficient compared to the high-order covariant projection element. The computations of the propagation constants in the rectangular waveguide and the slab loaded waveguide show that the accuracy of this high-order mixed-edge element is about one order higher than that of the lowest order one, and the nodes used in the calculation are only two-thirds as many as those used in the high-order covariant projection element having the same accuracy. The calculations of the dispersion curves for the dominant mode in the waveguide loaded with the lossy anisotropic dielectric block verify the accuracy and efficiency of the present method.