Hung-Yu Yang

Gain enhancement methods for printed circuit antennas through multiple superstrates

Reciprocity and a transmission line model are used to determine the radiation properties of printed circuit antennas (PCAs) in a multilayered material configuration. It is demonstrated that extremely high directive gain may result at any scan angle, with practical materials, if the thickness of the substrate and multiple superstrate layers is chosen properly. This model is also used to analyze the radiation characteristics of printed circuit antennas in inhomogeneous substrates.

Photonic band-gap materials for high-gain printed circuit antennas

It is found through a vector integral-equation analysis and the reciprocity theorem that the gain of a microstrip antenna can be greatly enhanced with a photonic band-gap material layer either as the substrate or the superstrate. The beam angle is found to coincide with that of a leaky-wave mode of a planar-grating structure. This observation suggests that high gain is due to the excitation of strong leaky-wave fields.

Finite difference analysis of 2-D photonic crystals

In this paper, a finite difference method is developed to analyze the guided-wave properties of a class of two-dimensional photonic crystals (irregular dielectric rods). An efficient numerical scheme is developed to deal with the deterministic equations resulting from a set of finite difference equations for inhomogeneous periodic structures. Photonic band structures within an irreducible Brillouin zone are investigated for both in-plane and out-of-plane propagation. For out-of-plane propagation, the guided waves are hybrid modes; while for in-plane propagation, the guided waves are either TE or TM modes, and there exist photonic bandgaps within which wave propagation is prohibited. Photonic bandgap maps for squares, veins, and crosses are investigated to determine the effects of the filling factor, the dielectric contrast, and lattice constants, on the band-gap width and location. Possible applications of photonic bandgap materials are discussed.

A rigorous dispersive characterization of microstrip cross and T junctions

A full-wave spectral-domain analysis is applied to the characterization of multiport microstrip discontinuities. This approach uses the moment method to find the currents in the microstrip circuits and, subsequently, the scattering parameters of the junctions. In this approach, all the physical effects are considered, including radiation and surface waves. The numerical results for a tee and a cross junction are presented and agree well with the quasi-static values at low frequencies. The S-parameters of a tee junction are further compared with the measured results with excellent agreement. The utilization of a shaped T-junction as a broadband equal-power divider is also discussed. >

A Printed Crescent Patch Antenna for Ultrawideband Applications

A miniaturized crescent-shape microstrip antenna is proposed for ultrawideband (3-10 GHz) applications. The crescent antenna is evolved from an elliptical patch antenna by carving a circular hole inside symmetrically. The circular aperture introduces an additional antenna in-band resonance and provides wider bandwidth with more design flexibility. The radiation characteristics of this crescent antenna are investigated with full-wave electromagnetic simulations and compared with an elliptical antenna. A crescent antenna prototype that occupies only 60% area of the elliptical patch is fabricated and tested. Antenna pattern and impedance measurements show good performance over the 3-10 GHz band with consistent radiation patterns, low cross polarization, and a substantial gain. The design method is also described

Theory of line-source radiation from a metal-strip grating dielectric-slab structure

This paper describes the fundamental theory of line source radiation from a source on a dielectric slab backed by a metal-strip grating. A continuous phased-array (CPA) method is applied to treat the analytic and numerical problems of antenna interaction with periodic structures. Both TE and TM mode cases for a one-dimensional strip grating are investigated. It is found that the strip grating on the dielectric surface may result in surface wave elimination and may also be used to support leaky waves. It is shown that high-efficiency and high-gain antennas on a dielectric substrate are possible with such metal-strip gratings.

Basic blocks for high-frequency interconnects: theory and experiment

Proximity-coupled open-end microstrip transitions in double-layer planar structures are investigated through the method of moments solution of integral equations. Two types of EMC (electromagnetically coupled) microstrip lines are considered, namely, collinear lines and transverse lines. It is found that these transitions are broadband and provide a wide range of coupling coefficients. The theoretical model for the transverse microstrip transitions is in good agreement with measurements. >

A generalized method for distinguishing between radiation and surface-wave losses in microstrip discontinuities

A generalized method for calculating both radiation and surface-wave losses is developed for microstrip discontinuities. The losses are determined by a rigorous Poynting vector analysis where the current distribution over the microstrip discontinuities is a result of a full-wave moment method solution. The power loss mechanism of such microstrip discontinuities as open-end, right-angle-bend, gap and stub lines, EMC lines, and rectangular patches are investigated. A self-consistency check of the result based on power conservation is performed to confirm the numerical results. It is found that, above a certain frequency, the surface-wave loss becomes more important than the radiation loss. >

Microstrip open-end and gap discontinuities in a substrate-superstrate structure

The analysis and modeling of microstrip open-end and gap discontinuities in a substrate-superstrate structure using the numerical solution of integral equations is presented. Good accuracy is achieved by adopting semi-infinite subdomain mode expansion functions, with a transverse coordinate dependence obtained from a two-dimensional finite-line analysis. A parametric study of the material layer effects of radiation and surface wave losses and the fringing fields at the discontinuities is performed. >

Microstrip Patch Antennas on Tunable Electromagnetic Band-Gap Substrates

A tunable metamaterial in integrated circuit structures is investigated through an example of a microstrip patch antenna on a mushroom-type electromagnetic band-gap (EBG) structure. The patch antenna is designed as a half-wavelength resonator of an EBG loaded microstrip transmission line. The operating frequency of a patch antenna can be switched and controlled dynamically by loading diode switches in between vias and the ground plane. When the switches are on, the EBG surface is short to the ground and is at its on-state; while when the switches are turned off, the EBG surface is dc open and is at its off-state. It is found that the resulting patch antenna in-band resonant frequencies are very different at these two states. Antenna dual-band frequencies, gain, efficiency, and radiation patterns are characterized. The designed switchable EBG-patch antenna is fabricated and tested in these two states. The measurement is found in good agreement with simulation. An example is also given for the case of selected switches within the EBG elements to tune dynamically the resonant frequency.