Yongshik Lee

Wideband Microstrip Patch Antenna With U-Shaped Parasitic Elements

A wideband U-shaped parasitic patch antenna is proposed. Two parasitic elements are incorporated into the radiating edges of a rectangular patch whose length and width are lambdag/2 and lambdag/4, respectively, in order to achieve wide bandwidth with relatively small size. Coupling between the main patch and U-shaped parasitic patches is realized by either horizontal or vertical gaps. These gaps are found to be the main factors of the wideband impedance matching. The proposed antenna is designed and fabricated on a small size ground plane (25 mmtimes30 mm) for application of compact transceivers. The fabricated antenna on a FR4 substrate shows an impedance bandwidth of 27.3% (1.5 GHz) at 5.5 GHz center frequency. The measured radiation patterns are similar to those of a conventional patch antenna with slightly higher gains of 6.4 dB and 5.2 dB at each resonant frequency

Package-level integrated antennas based on LTCC technology

We propose a novel package topology integrating multilayer miniaturized antennas. Such a functional package is suitable for the design of a system-on-chip device, or of system-on-package applications. A stacked patch antenna is designed and integrated in a package using a low temperature co-fired ceramic process. The overall size of the package is 10.3times10.3times1.3 mm3, and this package contains an 8.3times8.3times0.7 mm3 internal space for the integration of chip-scale packaged components. The package is mounted on a 20times20 mm2 ground plane to miniaturize the volume of the system. The antenna is designed to have two neighboring resonant frequencies at 5.264 and 5.355 GHz, resulting in a 140 MHz impedance bandwidth. However, the measured resonant frequencies occur at slightly higher frequencies due to manufacturing tolerances. Radiation patterns are similar to a conventional patch antenna. In addition, various parasitic effects rooted in the package size, ground size, antenna height, SMA connector, via misalignment, and the number of via holes and their locations are fully investigated

Improved thermal stability of Al2O3/HfO2/Al2O3 high-k gate dielectric stack on GaAs

Thermal stability of HfO2 high-k gate dielectric on GaAs is investigated. Compared to HfO2 gate dielectric, significant improvements in interfacial properties as well as electrical characteristics were found by constructing a Al2O3/HfO2/Al2O3 dielectric stack. At elevated temperatures, the amorphous Al2O3 layers were effective in inhibiting crystallization of HfO2. Since the passivating Al2O3 layers prevent interfacial oxide and trap charge formation, it aids in reducing the increasing rate of equivalent oxide thickness as well as capacitance-voltage hysteresis. Transmission electron microscopy and x-ray photoelectron spectroscopy data supported the improved electrical characteristic of GaAs metal-oxide-semiconductor capacitors with Al2O3/HfO2/Al2O3 gate dielectric stack.

A Design Method for Microstrip Directional Couplers Loaded With Shunt Inductors for Directivity Enhancement

An accurate design method is proposed for directivity enhancement of microstrip directional couplers loaded with shunt inductors. The parasitic effects of junction discontinuities in various parts of such microstrip directional couplers have critical effects especially on the directivity, and therefore they must be taken into account. Without proper modeling of these parasitic effects, directivity enhancement becomes extremely difficult especially for weak coupling levels. The demonstrated method of analysis can be applied to obtain exact designs of all previous microstrip directional couplers that are loaded symmetrically with series and/or shunt reactance for directivity enhancement, regardless of the coupling levels. Based on the proposed method, a 20-dB microstrip directional coupler is designed at 2.4 GHz. A maximum directivity of 56 dB has been measured, which is an improvement of 48 dB over a conventional microstrip directional coupler. A 16.3% bandwidth at 2.4 GHz has been measured in which the directivity remains above 20 dB, while the maximum variation in the coupling level is 0.5 dB. This is the first work to demonstrate directivity of more than 50 dB for a 20-dB microstrip directional coupler.

Fully micromachined finite-ground coplanar line-to-waveguide transitions for W-band applications

A fully micromachined finite-ground coplanar (FGC) line-to-waveguide transition for W-band applications has been designed, fabricated, and tested. The transition utilizes a printed E-plane probe, inserted into the broad sidewall of a micromachined waveguide. This type of transition plays an important role in many applications where coupling between the popular FGC line and a waveguide is required. Excellent performance across the entire W-band of such a transition is presented in this paper. The investigated waveguide, micromachined in silicon using the deep reactive ion etching technique, demonstrates its potential as an alternative to costly conventional waveguides at high frequencies. A similar transition with a micromachined waveguide formed via bulk micromachining using a wet etchant is also demonstrated. The free-standing probe utilized in this second transition proves the potential of such transitions to be applicable well into the submillimeter and terahertz range.

Wideband Branch-Line Couplers With Single-Section Quarter-Wave Transformers for Arbitrary Coupling Levels

Wideband branch-line couplers with arbitrary coupling levels are demonstrated. By integrating single-section quarter-wave transformers at each port, wideband characteristic with excellent coupling flatness is achieved. Also, a method is demonstrated that introduces intentional mismatch for a further enhancement in bandwidth. Superior structural and design simplicity outperform previous wideband couplers. Branch-line couplers at 3 GHz are demonstrated experimentally that maintain the coupling level within 0.5 dB from the specified 10 dB in as much as a 50.9% bandwidth, with minimum return loss and isolation of 16.3 and 18.7 dB, respectively.

Bandwidth-Compensation Method for Miniaturized Parallel Coupled-Line Filters

This paper proposes a bandwidth-compensation method for miniaturized filters based on short-ended parallel coupled lines. Capacitive loading of such coupled lines is a relatively simple means of reducing the line lengths. In this study, a method is developed that predicts exactly the degree of reduction in the fractional bandwidth due to miniaturization. Using this method, the fractional bandwidth of the prototype coupled line filter can be adjusted, enabling miniaturized filters to maintain the targeted fractional bandwidth. The proposed bandwidth-compensation method applies for any type of filters with coupled lines realized with various transmission lines, with uniform or nonuniform line lengths. Experimental results are also presented that verify the validity of the method.

A finite ground coplanar line-to-silicon micromachined waveguide transition

Circuits operating in the terahertz frequency range have traditionally been developed using hollow metal waveguides, which, due to the small wavelength at these operating frequencies, must be correspondingly small in cross section. As a result of the high cost of conventional precision machining of such small waveguides, alternate fabrication methods continue to be explored. Silicon micromachining has been suggested as a potential means to produce waveguides in a more cost-effective manner for operation at these frequencies. This paper presents a transition structure that couples the popular finite ground coplanar transmission line to a W-band silicon micromachined waveguide, forming a fully micromachined module. The waveguide is formed via bulk micromachining using a wet etchant, resulting in a diamond cross section. The consequences of utilizing a diamond waveguide in place of the more common rectangular waveguide are considered and potential means of developing rectangular-walled waveguides in silicon are noted. A Ka-band microwave model of a similar transition to a conventional rectangular waveguide is also demonstrated.

Dual-Polarization Slot Antenna With High Cross-Polarization Discrimination for Indoor Small-Cell MIMO Systems

We demonstrate a dual-polarization slot antenna for indoor small-cell multiple-input-multiple-output (MIMO) systems. The symmetric structure and differential feeding promotes destructive interference of cross-polarized radiation in the far field to achieve high cross-polarization discrimination (XPD) in all directions. In addition, a very similar radiation pattern is observed not only between the major planes of each polarization but also between the two polarization orientations. Therefore, the proposed antenna can be considered as a stronger candidate for indoor small-cell MIMO systems. With an average XPD of 26.4 dB in all directions, the 3-D ray-tracing simulation results show a more than 22% increase in the system throughput compared to previous dual-polarization antennas for a single-user MIMO system in a typical indoor environment.

High-efficiency W-band GaAs monolithic frequency multipliers

High efficiency monolithic frequency multipliers have been designed, fabricated, and tested in the W-band. In microwave monolithic integrated circuits (MMICs), transmission lines with various impedances are used not only to transfer the input and output signals, but also to match the impedances of active devices to those of the input and output ports, with open and/or short stubs. Thus, loss in the transmission lines is one of the major limiting factors on circuit efficiencies. This paper presents high-efficiency MMIC frequency doublers with a balanced pair of GaAs Schottky barrier planar diodes operating in the W-band. The geometries of transmission lines were optimized to reduce the loss and thus to improve the efficiency. The demonstrated efficiency of 36.1% is the highest efficiency reported for a diode-based MMIC frequency multiplier in the W-band.