Xiang-yin Zeng

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.

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.

Leaky-wave characteristics of trapezoidally shaped NRD-guide suitable for design of millimeter-wave antenna

Leaky-wave characteristics of NRD guide with various shapes of trapezoidal cross section are systematically modeled and analyzed by a method which combines effectively a multimode network theory with a mode-matching technique. Emphasis is laid on the investigation of parametric effect of trapezoidal dimensions on the leakage of NRD guide. Extensive numerical results are given to establish some useful guidelines for the design of a new type of NRD-guide leaky-wave antennas.

A novel leaky NRD guide with a double-layer dielectric slab

A new leaky nonradiative dielectric guide with a double-layer dielectric slab is investigated in this paper by combining a multimode network theory with a mode-matching method. Numerical results show that proper selection of the permittivities can vary the leakage constant over a wide range. A leakage constant larger than 10% of free-space wavenumber can be obtained easily without entering the cutoff region. Leaky-wave antennas with shorter length and medium gain can thus be developed. In addition, the present leaky guide possesses the advantages of simple fabrication and physical stability. Extensive numerical results are provided to guide the antenna designs.

Low-loss millimeter-wave propagation characteristics of NRD-guide surface-mounted on planar substrate for hybrid integrated circuit

We present a new guided-wave structure, which consists of a non-radiative dielectric (NRD) guide surface-mounted on the top of a relatively thin dielectric substrate. This new structure allows a direct hybrid integration of planar microstrip circuits with NRD-guide without resorting to our reported aperture-coupling scheme. This waveguide is, however, no longer a conventional NRD-guide because its asymmetry may generate unwanted leakage loss. Our present work shows that one of its most interesting features is that it can still preserve a great deal of the desired properties of the conventional NRD-guide under certain circumstances. It is expected to provide an alternative circuit building block to a class of 3-D multilayered millimeter-wave circuits and systems.

Revisiting guided-wave and leakage-wave modal properties in near cutoff region with the concept of complex effective dielectric constant

A simple but good alternative way is given to define the antenna-mode and reactive-mode regions for open dielectric guiding structures by means of the concept of complex effective dielectric constant. The attenuation constant is clearly divided for the first time into two separate parts due to cutoff and leakage effect respectively. Simple closed-form expressions are derived to determine the two parts.

Radiation and leakage characteristics of transverse slot in NRD-guide operating in LSE/sub 00/ mode

Characteristics of a transverse slot in the upper plate of a nonradiative dielectric guide operating in the dominant LSE/sub 00/ mode have been analyzed. A fundamental radiation phenomenon due to the open property of the guiding structure is observed theoretically. It is found that the propagation direction of the leakage covers the whole angular spectrum in the plane parallel to the metallic plates. An explanation to its physical existence is given. A simple, but efficient method is developed to determine its angular power density. Numerical computation shows that the leakage is substantially high when the slot is near resonance.

A new asymmetrically grooved NRD guide leaky-wave antenna for millimeter-wave application

A new asymmetrically grooved nonradiative dielectric (AGNRD) guide leaky-wave antenna is proposed and investigated theoretically and experimentally for practical use in the 60 GHz frequency band. The AGNRD antenna structure overcomes the difficulty in precision assembling of the dielectric strip while preserving the simplicity of the original NRD guide structure. Leaky-wave characteristics of the new AGNRD guide are studied with a rigorous method that combines multimode network theory with a mode matching technique. Satisfactory agreement between theoretical and experimental results is obtained.

A systematic investigation on leaky characteristics for NRD guide with arbitrary profile of cross-section

The leaky characteristics of the NRD guide with arbitarary profile of cross section are systematically studied by a method which combines staircase approximation with multimode network theory and mode-matching procedure. Emphasis is laid on the investigation of the effect of the different profile dimensions on the leakage characteristics of the NRD guide. Extensive numerical results are given to establish useful guidelines for the design of some new types of NRD guide leaky wave antennas.

Analysis of leaky characteristics for NRD guide with arbitrary profile of cross-section

The leaky wave characteristics of a nonradiative dielectric waveguide (NRD) guide having irregular cross-section profile are known to be not amenable to an exact field analysis, even for a relatively simple geometric profile. Therefore, one must resort to an approximate but accurate modal analysis. In particular, a method is required that should be generally applicable to different profiles of the structure. A method using the staircase approximation and combining multimode network theory with the mode-matching procedure can be effectively applied to the analysis of leaky wave structures of any profile. In the analysis, the arbitrary continuous profile is discretised by a staircase approximation; evidently, in the limit of vanishing step size, the piecewise constant profile will approach the continuous one. With such an approximation, mathematical analysis and physical interpretation of the potential mode coupling phenomena related to the leaky wave structure can be kept simple and clear. The new antenna structures with an arbitrary profile of cross-section provide more degree of freedom for the design of a leaky wave antenna by flexibly changing the geometric dimensions of the structures. On the other hand, these antennas may be more practical because keeping an exact regular shape in manufacturing sometimes is very difficult. The analysis given thus permits one to gain an insight into the qualitative effects produced by some geometric size and also to determine how large the size change can be acceptable before it influences significantly the transmission properties of the NRD guide when used as a millimeter wave guiding structure.