Yu-De Lin

Broadband tapered microstrip leaky-wave antenna

This study proposes a novel scheme based on the characteristics of leaky-wave antennas for the empirical design of broadband tapered microstrip leaky-wave antennas. This scheme can explain and approximately model the radiation characteristics of a linearly tapered leaky-wave microstrip antenna. A broadband feeding structure that uses the balanced and the inverted balanced microstrip lines to form a pair of broadband baluns is also presented. The measured return loss of the inverted balanced microstrip lines has a VSWR/spl les/2 from dc to 18.6 GHz and that of the back-to-back feeding structures has a VSWR/spl les/2 from 2.2 to 18.6 GHz. This feeding structure can be used to feed a broadband planar leaky-wave antenna with a fixed mainbeam that uses the tapered microstrip structure. The measured bandwidth of the antenna for a VSWR/spl les/2 exceeds 2.3:1.

Mode distinction and radiation-efficiency analysis of planar leaky-wave line source

Using the first microstrip-line higher order mode as an example, mode distinction and radiation efficiency of leaky-wave line sources in the radiation region are presented in this paper. The spectral-domain approach is used to calculate complex power flows, leaving the line source in the transverse directions and those guided down the line source. By observing the behavior of these complex power flows in different frequency regions, the leaky-wave line source can be distinguished into the antenna mode and the reactive mode in the radiation region. Experimental results are shown to confirm this mode distinction. Moreover, by comparing the power carried away by the surface and the space waves, radiation efficiency of the first microstrip-line higher order mode of various structural parameters is analyzed. The microstrip line is more efficient as a leaky-wave line source when its substrate is thin, the dielectric constant of the substrate is low, and the antenna main beam is away from the end-fire direction.

Propagation characteristics of the slotline first higher order mode

The propagation characteristics of the slotline first higher order mode are presented in detail in this paper. It is found that the attenuation constants and the radiation band of this first higher order mode are larger than those of the microstripline first higher order mode. Dependence of the propagation characteristics on structural parameters and the effect of finite-conductor planes are analyzed. The propagation characteristics of the surface-wave-like modes are also discussed. In order to avoid inadvertent excitation of these surface-wave-like modes in antenna applications, the current and field distributions of the slotline first higher order mode and the surface-wave-like modes are compared and discussed. Excitation of the slotline first higher order mode was conducted by feeding the slotline with a coplanar waveguide and microstrip line. Experimental results show good agreement with our numerical results, and also confirm the existence of the slotline first higher order mode.

Microstrip-fed microstrip second higher order leaky-mode antenna

With the appropriate placement of the slots and via holes, the microstrip second higher order leaky-mode antenna fed by a microstrip is presented. Two main beams with titled angles from the strip are measured in the predicted radiation leaky band. The leaky band of the microstrip second higher order mode is deduced from the characteristics of the propagation constants that are calculated by the spectral domain analysis. The proposed feeding method provides a direct connection with the circuits based on the microstrip line.

Analysis and design of feeding structures for microstrip leaky wave antenna

Two methods to excite the microstrip leaky wave antenna are proposed and investigated in this paper. A full-wave spectral domain integral equation method combined with fundamental mode sampling technique is applied to determine the reflection coefficient of the excitation source. Dependence on structural parameters such as line width, overlap length and line spacing is fully analyzed to obtain the optimum excitation for microstrip leaky wave antenna. Also, an experimental setup is performed to check the validity of our numerical results and identify the radiation nature of the microstrip line higher order modes. >

Wide Band Tapered Microstrip Leaky-Wave Antenna

In this paper, we propose an efficient method to widen the radiation bandwidth of the microstrip leaky-wave antenna. In order to achieve this objective, a broad band feeding structure and a tapered microstrip line are proposed. The tapered microstrip line is employed to make the different radiation bands distribute in different areas of the microstrip line. The simulation results and the experimental data show the proposed method is feasible.

Simultaneous Determination of Complex Permittivity and Permeability of Columnar Materials With Arbitrarily Shaped Cross Section

An effective simultaneous evaluation method for the complex permittivity and permeability of lossy materials is proposed by applying it to an arbitrarily shaped cross-sectional post placed in a rectangular waveguide. We use one sample and only measure S 21 parameters for two different locations of the sample. The measurement of complex reflection parameter S 11 is not required in this evaluation method. The scheme of electromagnetic field analysis for the evaluation is based on the extended spectral-domain approach combined with the mode-matching method, which is accurate and efficient, and can be flexibly used for the iterative fitting operation for the estimation of material parameters. Sample preparation and setting is significantly easier in this method compared to conventional methods. The error caused by deviations in the setting of a sample is investigated. The estimated values for the sample material by this procedure show good agreement with the results obtained using the conventional method over the X-band.

Variational method of coupled strip lines with an inclined dielectric substrate

A variational method is presented for the analysis of coupled strip lines with an inclined dielectric substrate for the first time. The stationary expressions of the line capacitance matrix elements are derived based on extended spectral domain approach combined with mode-matching method (ESDMM). Numerical computations are based on Galerkins procedure and the basis functions for the unknown aperture fields take the edge singularities into consideration. The accurate numerical values can be obtained by using a small number of basis functions.

Characterization and Design of Cylindrical Microstrip Leaky-Wave Antennas

The spectral-domain approach is applied for the analysis and the design of the cylindrical microstrip leaky-wave antenna. The first higher-order leaky-mode is thoroughly investigated. We perform the well-known spectral-domain approach and Galerkins method to acquire the complex propagation constants of leaky modes, which are verified with results obtained by the scattering-parameter extraction technique. Two practical antennas are designed and implemented. Measured return loss and radiation patterns show a good performance of these cylindrical antennas, compared to that of the planar ones.

A Novel Dual Circularly Polarized Microstrip Antenna

In this paper, we propose a novel design of dual circularly polarized microstrip antenna of the cogwheel-like annular ring structure. The microstrip sector stubs are added periodically in the outer and inner edges of the microstrip annular ring and an additional microstrip line as a diameter is also placed across the inner circle to enhance performance of the axial ratio. When operated in TM11 mode, this cogwheel-like microstrip annular ring antenna has a relatively wider bandwidth and a relatively smaller size than those of the traditional microstrip annular ring antenna. The three-wire transmission line and branch-line hybrid is employed as the feeding network to excite the righted-handed or left-handed direction of circular polarization