Jyh-Wen Sheen

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.

LTCC-MLC duplexer for DCS-1800

A low-temperature cofired-ceramic (LTCC) multilayer-ceramic (MLC) duplexer is presented in this paper. The duplexer is designed for a DCS-1800 handset. It is constructed using a multilayer laminated bandpass filter and a multilayer laminated bandstop filter. These two filters are capable of easy tuning after duplexer manufacture. The computer-aided design flowchart is also presented. Additionally, the tuning method and loss improvements of the duplexer are discussed. Measured results show the performance of the LTCC-MLC duplexer is acceptable for DCS-1800 applications.

Chip-type LTCC-MLC baluns using the stepped impedance method

A chip-type low-temperature co-fired ceramic (LTCC) multilayer ceramic (MLC) balun is presented in this paper. This balun is designed using the stepped impedance method. It uses a multilayer structure, meander lines, and multisection coupled lines. The use of multisection couple lines that have various characteristic impedance ratios can shrink the length of a quarter-wavelength coupled-transmission line and makes it very easy to match various impedances of balanced output. The proposed chip-type balun operates over a bandwidth of 2.25-2.65 GHz. The in-band phase and amplitude balances are excellent because of the symmetric structure and transmission-line trimming section. Measured results of the chip-type LTCC-MLC balun match well with the computer simulation.

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.

LTCC-MLC balun for WLAN/Bluetooth

A low temperature co-fired ceramic (LTCC) multi-layer ceramic balun is presented in this paper. This balun is designed in the ISM band for WLAN or Bluetooth use. It uses multi-layer structure, meander lines, and multi-section coupled-lines with various coupling coefficients. The characteristics of phase balance and amplitude balance are extremely excellent because of its symmetric structure and a transmission line trimming section. Measured results of the LTCC-MLC balun match well with the computer simulation.

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. >

Surface-wave leakage properties of coplanar strips

Propagation characteristics of coplanar strips (CPS), balanced transmission line widely used in uniplanar circuits, is investigated with the spectral domain analysis. Besides the conventional coplanar strips mode, an extra surfacewave-like dominant mode can be supported by coplanar strips in the lower frequency region. The bound modes evolve into a complex leaky mode in higher frequency region in a similar way to those of coplanar waveguide (CPW). No sharp and deep minima in leakage constants are found after the onset of the leakage, as in the coplanar waveguide case. Furthermore, the physical complex mode disappears in wider strip cases.<<ETX>>

A leaky-mode S-parameter extraction technique for efficient design of the microstrip line leaky-wave antenna

A leaky-mode S-parameter extraction technique is proposed in this paper. The proposed method can be employed in a numerical way or an experimental way. By properly arranging two circuits under test, the leaky-mode S-parameter can be de-embedded from the transmission line theory. Numerically, this method can avoid the problem of having to deal with a large-circuit-size structure when designing a leaky-wave antenna. The propagation constants of the leaky modes calculated by the full-wave spectral domain approach, and the experimental results of an aperture-coupled leaky-wave antenna are used to confirm the parameters extracted by this proposed technique. They all show good agreement. With appropriate modifications, the method can also be extended to extract and define the characteristic impedance of a leaky-wave antenna.