Directive photonic-bandgap antennas

This paper introduces two new photonic bandgap (PBG) material applications for antennas, in which a photonic parabolic reflector is studied. It is composed of dielectric parabolic layers associated to obtain a PBG material. The frequency gap is used to reflect and focus the electromagnetic waves. This device has been designed using a finite-difference time-domain (FDTD) code. FDTD computations have provided the theoretical reflector's directivity. These results are in good agreement with measurements, and it appears that the PBG reflector presents the same directivity as a metallic parabola. A second application uses a defect PBG material mode associated with a metallic plate to increase the directivity of a patch antenna. We explain the design of such a device and propose experimental results to validate the theoretical analysis     

一维光子带隙光子晶体激光腔的特性分析

利用平面波展开法与时域有限差分法分析计算了一维光子带隙光子晶体腔的特性。得到了品质因子Q为2.2×106,模体积V为0.278(λ/n)3的一维带隙光子晶体腔。分析了渐变区、腔镜子区及缺陷区对腔品质因子Q和模式体积V的影响。引入渐变区、选择适量周期数及一定缺陷区长度都可以提高腔性能。该结论为设计优化一维光子带隙光子晶体腔提供了有效的理论分析依据与指导。     

平面带隙结构在微波和毫米波集成电路中的应用

介绍了平面带隙结构在微波集成电路应用方面的最新进展。光子带隙(PBG)结构是具有带阻特性的周期结构,最初应用于光学领域,后来扩展到其他领域。目前从可见光到红外都有研究,在微波和毫米波频段也有应用。PBG结构可以采用金属、介质、铁磁或铁电物质植入衬底材料,或者直接由各种材料周期性排列而成。目前国内外所提出的光子带隙结构多种多样,一维和二维的平面带隙结构由于易于实现且便于集成,因而在微波毫米波集成电路中得到了广泛的应用。     

UC-PBG结构创建准TEM波导的仿真分析

光子带隙(Photonic BandGap, PBG),是指人造的周期性电介质结构,它使得在一定频率范围内的电磁波是禁止传播的,而单平面紧凑型光子带隙结构(UC-PBG)是一种以微带基片为载体的周期性平面光子带隙结构。该文用UC-PBG结构置换标准矩形波导窄边,可在UC-PBG结构的谐振频率点附近将TE10模转变成准TEM模。通过对整个系统进行仿真计算,证实了此方法切实有效,在Ku波段转换带宽达到450 MHz。     

Experimental woodpile EBG waveguides, bends and power dividers at microwave frequencies

Experimental waveguides, bends and power dividers in the woodpile electromagnetic bandgap (EBG) material at Ku-band are demonstrated. Prototypes are fabricated from alumina, and use an efficient waveguide transition to enable high quality measurements. Low-loss transmission is demonstrated for a waveguide and a 90/spl deg/ bend, and near equal power division shown for a woodpile EBG waveguide power divider. The components have the potential to be scaled for applications at millimetre-wave and terahertz frequencies     

Polarization Transformation in Twisted Anisotropic Media

Polarization transformation of plane waves propagating in twisted anisotropic media is studied theoretically and numerically. It is shown that rotation of linear polarization is effected by such a medium when the anisotropy is of the order of 2 to 1 and twist rates commensurate with the relative value of the dielectric constants of the medium are used (less than 15/spl deg///spl lambda//sub 0/ for low dielectric constants and up to 90/spl deg///spl lambda//sub 0/ for dielectrics in the vicinity of 1000).     

Wide-Band Polarizer In Circular Waveguide Loaded with Dielectric Discs

A converter between linear and circular polarization has been designed in circular waveguide by the use of periodic loading with oblong dielectric discs. The disc loading increases the single-mode (TE-11) bandwidth relative to that of homogeneously filled circular waveguide. Moreover, periodic loading gives the designer freedom to adjust the disc thickness and shape to meet certain requirements. With the abutting disc-loaded waveguide as a reference, the dielectric loading is increased in one plane of polarization and decreased in the orthogonal plane. In a wide-band design, this differential loading gives nearly constant 90/spl deg/ difference in time phase between space-quadrature component waves, the condition for circular polarization. Such a polarizer has been constructed with four oblong discs. Across a frequency bandwidth of about 15 percent, the measured phase difference is within 2/spl deg/ of the desired value and the SWR is within 1.5 dB.     

Periodic Cylinder Arrays as Transmission Lines

Periodic structures of conducting cylinders have been used as radiators (Yagi antennas), and, more recently, as slow-wave lines in traveling-wave tubes and masers. In this report it is shown that a nonresonant structure may have interesting capabilities as an open surface-wave transmission line. By means of a relatively simple matching network, efficient excitation of a surface wave on the periodic line is obtained. Response is flat over a 20 per cent frequency range at X band for several combinations of cylinder lengths and spacings. Total insertion losses are less than 3 db and largely independent of length of transmission line. Conducting cylinders are embedded in styrofoam. The effects of bends and twists in the line have also been investigated. It is shown experimentally that a guided wave on this periodic structure can follow a circular path having 1.5/spl lambda/ radius of curvature with very little loss. The plane of polarization can be rotated 90/spl deg/ by inserting a short twisted section. By terminating the transmission line with short circuits at both ends, a discrete series of transmission maxima is observed. Since these resonant peaks of transmission are of high Q factor, the dispersion characteristic of the line is obtained with very good accuracy. This type of open transmission line may offer advantages over heavy-weight and bulky conventional waveguides for some specialized applications.     

Silicon micromachined EBG resonator and two-pole filter with improved performance characteristics

A novel micromachined resonator at 45 GHz based on a defect in a periodic electromagnetic bandgap structure (EBG) and a two-pole Tchebyshev filter with 1.4% 0.15 dB equiripple bandwidth and 2.3 dB loss employing this resonator are presented in this letter. The periodic bandgap structure is realized on a 400 /spl mu/m thick high-resistivity silicon wafer using deep reactive ion etching techniques. The resonator and filter can be accessed via coplanar waveguide feeds.     

Estimation of polarization crosstalk at a micro-bend in Si-photonic wire waveguide

The singlemode Si-photonic wire waveguide allows sharp bends, which significantly expands the design flexibility of optical devices and circuits. Here, the suppression of the polarization crosstalk at a sharp bend will be an important issue, since a large crosstalk affects the performance of devices and circuits. In this study, the three-dimensional (3-D) finite-difference time-domain (FDTD) simulation showed that the crosstalk at a 90/spl deg/-bend with a radius of 0.35-1.75 /spl mu/m is less than -25 dB at a wavelength of 1.55 /spl mu/m. In the experiment, the crosstalk from TE-like to TM-like polarization was evaluated to be -13 dB to -10 dB. This large value was explained by a small tilt of waveguide sidewalls, which seriously increased the crosstalk. In addition, it was found in the calculation that some combinations of bends increase or decrease the crosstalk, and that a U-shape bend is the most effective for the suppression of the crosstalk.     

Magneto-dielectrics in electromagnetics: concept and applications

In this paper, the unique features of periodic magneto-dielectric meta-materials in electromagnetics are addressed. These materials, which are arranged in periodic configurations, are applied for the design of novel EM structures with applications in the VHF-UHF bands. The utility of these materials is demonstrated by considering two challenging problems, namely, design of miniaturized electromagnetic band-gap (EBG) structures and antennas in the VHF-UHF bands. A woodpile EBG made up of magneto-dielectric material is proposed. It is shown that the magneto-dielectric woodpile not only exhibits band-gap rejection values much higher than the ordinary dielectric woodpile, but also for the same physical dimensions it shows a rejection band at a much lower frequency. The higher rejection is a result of higher effective impedance contrasts between consecutive layers of the magneto-dielectric woodpile structure. Composite magneto-dielectrics are also shown to provide certain advantages when used as substrates for planar antennas. These substrates are used to miniaturize antennas while maintaining a relatively high bandwidth and efficiency. An artificial anisotropic meta-substrate having /spl mu//sub r/>/spl epsiv//sub r/, made up of layered magneto-dielectric and dielectric materials is designed to maximize the bandwidth of a miniaturized patch antenna. Analytical and numerical approaches, based on the anisotropic effective medium theory (AEMT) and the finite-difference time-domain (FDTD) technique, are applied to carry out the analyzes and fully characterize the performance of finite and infinite periodic magneto-dielectric meta-materials integrated into the EBG and antenna designs.     

A photonic bandgap microstrip filter based on YBCO superconducting film

Photonic bandgap (PBG) structures can stop propagation of electromagnetic waves of certain frequencies and hence can be applied to construction of microstrip filters. In this paper, a novel PBG microstrip filter based on YBa/sub 2/Cu/sub 3/O/sub 7/ high-temperature superconductor films is presented. The PBG patterns forming the filters were etched on a 0.3- and a 0.7-/spl mu/m-thick film. Experimental results showed that the transmission coefficient S/sub 21/ of the filter is dependent on the thickness of the YBa/sub 2/Cu/sub 3/O/sub 7-x/ film. The thinner PBG filter exhibits an effective stopband of a center frequency of 20 GHz, a bandwidth of 4.7 GHz (at -40 dB), an attenuation of -55 dB, and a rolloff rate of 38 dB/GHz, while the thicker structure exhibits narrow notches only in the S/sub 21/ characteristics.     

An interconnected 2D-TM EBG structure for millimeter and submillimeter waves

Due to their unique properties, electromagnetic bandgap (EBG) materials are of high interest for applications in communication technology for many frequency bands from microwave up to optical frequencies. We have investigated in both simulation and experiment a two dimensionally periodic EBG structure made by reactive ion etching of silicon with a bandgap for transverse magnetic waves in the millimeter wave range around 100 GHz. The structure comprises both a large bandgap and a high mechanical stability due to interconnecting dielectric bridges.     

MOS transistors operated in the lateral bipolar mode and their application in CMOS technology

Operation of an MOS transistor as a lateral bipolar is described and analyzed qualitatively. It yields a good bipolar transistor that is fully compatible with any bulk CMOS technology. Experimental results show that high /spl beta/-gain can be achieved and that matching and 1/f noise properties are much better than in MOS operation. Examples of experimental circuits in CMOS technology illustrate the major advantages that this device offers. A multiple current mirror achieves higher accuracy, especially at low currents. An operational transconductance amplifier has an equivalent input noise density below 0.1 /spl mu/V//spl radic/Hz for frequencies as low as 1 Hz and a total current of 10 /spl mu/A. A bandgap reference yields a voltage stable within 3 mV from -40 to +80/spl deg/C after digital adjustment at ambient temperature. Other possible applications are suggested.     

Photonic bandgap dielectric waveguide filter

The application of photonic bandgap (PBG) structures as the sidewall of the printed circuit board (PCB) dielectric waveguide filter is investigated. The effect of different PBG parameters on the Q-value of PBG dielectric waveguide resonator is evaluated. A PBG dielectric waveguide three-pole Chebyshev bandpass filter is realized. The measured performance matched well with the calculated results. The newly proposed I/O coupling structure makes the filter much easier for mass production     

1 W fibre coupled power InGaAsP/InP 14xx pump laser for Raman amplification

A 1 W record singlemode fibre coupled output power using 1460 nm InGaAsP/InP non-tapered buried ridge lasers has been demonstrated. The impact of the bandgap of the passive quaternary waveguide on internal loss was investigated. Optimised design allows internal losses as low as 3.3 cm/sup -1/, external efficiency of 0.46 W/A for a 3 mm-long laser and symmetrical (12/spl deg//spl times/12/spl deg/) far-field pattern.     

High-temperature electronics - a role for wide bandgap semiconductors?

The fact that wide bandgap semiconductors are capable of electronic functionality at much higher temperatures than silicon has partially fueled their development, particularly in the case of SiC. It appears unlikely that wide bandgap semiconductor devices will find much use in low-power transistor applications until the ambient temperature exceeds approximately 300/spl deg/C, as commercially available silicon and silicon-on-insulator technologies are already satisfying requirements for digital and analog VLSI in this temperature range. However practical operation of silicon power devices at ambient temperatures above 200/spl deg/C appears problematic, as self-heating at higher power levels results in high internal junction temperatures and leakages. Thus, most electronic subsystems that simultaneously require high-temperature and high-power operation will necessarily be realized using wide bandgap devices, once they become widely available. Technological challenges impeding the realization of beneficial wide bandgap high ambient temperature electronics, including material growth, contacts, and packaging, are briefly discussed.     

Efficient modeling of 3-D photonic crystals for integrated optical devices

We propose a full-wave numerical model of a three-dimensional (3-D) photonic crystal with the absolute photonic bandgap (PBG) centered at /spl lambda//spl sim/1.6 /spl mu/m. The analyzed structure is widely used in integrated optical circuitry. The electromagnetic analysis is performed by using the finite-element method (FEM) and transmission line matrix-integral equation (TLMIE) method. We analyze the reflection properties and compare theoretical results to experimental data. Due to its exact boundary conditions, TLMIE shows much higher accuracy with respect to FEM in the PBG optical band. As a demonstration, we have realized and analyzed a holographic polymer dispersed liquid crystal grating.     

Improved 60/spl deg/ bend transmission of submicron-width waveguides defined in two-dimensional photonic crystals

We compare quantitatively the transmission properties of various 60/spl deg/ bends carved into a photonic crystal based on a two-dimensional triangular lattice of holes perforating a GaAs-based heterostructure. The bends are inserted into channel waveguides defined by three missing rows in the photonic crystal. Their design is inspired by some ideas from classical integrated optics. We show experimentally that in some cases the transmission of the bent waveguide is fairly high, up to 70%, within a bandwidth of 3%, e.g., 30 nm at 1 /spl mu/m, sufficient to contemplate wavelength-division-multiplexing applications. The observed performance opens the opportunity to implement a variety of optical functions in view of future photonic crystal integrated circuits for which low-loss bends constitute an essential building block.     

Roles of wave impedance and refractive index in photonic crystalswith magnetic and dielectric properties

We investigated the roles of wave impedance and refractive index in photonic crystals by means of analytical expressions for edges frequencies of a photonic bandgap (PBG) in a one-dimensional photonic crystal with magnetic and dielectric properties. The analytical expressions were derived when the optical thicknesses of layers are the same. The wave impedance governs the formation of PBG's and the intensity of defect modes. Meanwhile, the position of PBG's and the creation of defect modes are related to the refractive index