Hybrid-Frequency Cutoffs in Gyrotropic Waveguides (Short Papers)

The behavior of the Brillouin diagram /spl omega/ versus /spl beta//sub z/ is analyzed for axially magnetized gyrotropic waveguides in the vicinity of the hybrid frequencies /spl omega//sub k/ and /spl omega//sub i/. Starting from the exact dispersion relation for the modes in the waveguides under consideration it is shown that 1) the dispersion curves terminate at discrete cutoff points located along the /spl omega/ = spl omega//sub k/, /spl omega//sub i/ line and 2) the group velocity at these points is zero. These results modify the behavior of the dispersion curves existing in the literature.     

On The General Relation Between /spl alpha/ and Q (Correspondence)

The relation between the quality factor Q and the attenuation constant /spl alpha/ of a transmission line has been known as follows: /spl alpha/ = /spl beta/ / /2Q where /spl beta/ is the phase constant. Recently from the following relation of propagation constant at resonance /spl Gamma/(/spl omega//sub 0/) + /spl part//spl Gamma/ / /spl part//spl omega/ /spl Delta//spl omega//spl cong/ i/spl beta/(/spl omega//sub 0/), where /spl Gamma/(/spl omega//sub 0/) = /spl alpha/(/spl omega//sub 0/) + i/spl beta/(/spl omega//sub 0/). Yeh derived a general relation between Q and /spl alpha/, namely, /spl alpha/ = /spl upsi//sub p/ / /spl upsi//sub g/ /spl beta/ / /2Q where /spl upsi//sub p/, and /spl upsi//sub g/ are the phase velocity and group velocity of the wave respectively. This general relation can be derived very simply from the generally accepted definition of /spl alpha/ and Q.     

Dissipative Parameters in Ferrites and Insertion Losses in Waveguide Y-Circulators Below Resonance

Extensive microwave loss measurements have been performed at frequencies from 1.3 to 11 GHz on below-resonance waveguide Y circulators loaded with a wide variety of ferrite and garnet compositions. Dissipative internal and external magnetic parameters have been measured on the same compositions. Also, dielectric loss measurements have been carried out. Two classes have been distinguished, defined by the following conditions: /spl omega//sub M/ / /spl omega/ /spl les/0.8 and 0.85 /spl les//spl omega//sub M/ / /spl omega/ /spl les/1.05. It is inferred that the (insertion loss) IL of such devices is independent of /spl Delta/H and mainly depends on the internal dissipative susceptibility x/sub i/" and on the dielectric loss tan /spl delta/. The relation of the IL versus x/sub i/" and tan /spl delta/ in the case /spl omega//sub M/ / /spl omega/ /spl les/0.8 is independent of frequency and given by the semiempirical equation IL= 10 log/sub 10/ (1-2.85 x/sub i/" - 1.60 tan /spl delta/ - 0.017)/sup -1/.     

Sommerfeld Pre- and Postcursors in the Context of Waveguide Transients

For propagation in lossless waveguide, the rigorous impulse response function is given. It is shown that its instantaneous frequency is that which has reached the output at that time by propagating at the group velocity. For a square envelope pulse with a carrier frequency /spl omega/ above the cutoff frequency /spl omega//sub c/, the propagation of the envelope and of the phase are essentially described by the group and phase velocity, respectively. In addition, however, the bulk of the pulse is preceded by the so-called Sommerfeld precursors having an increasing amplitude and a frequency which decreases from a high value to /spl omega/. Similarly the bulk of the pulse k followed by the Sommerfeld postcursors in which both amplitude and frequency decrease, the latter from /spl omega/ to /spl omega//sub c/. The analytic results are illustrated by computed examples of waveguide transients.     

RF HBT oscillators with low-phase noise and high-power performance utilizing a (/spl lambda//4/spl plusmn//spl delta/) open-stubs resonator

This paper presents a new type of transmission-line resonator and its application to RF (microwave and millimeter-wave) heterojunction bipolar transistor (HBT) oscillators. The resonator is a parallel combination of two open stubs having length of /spl lambda//4/spl plusmn//spl delta/(/spl delta//spl Lt//spl lambda/), where /spl lambda/ is a wavelength at a resonant frequency. The most important feature of this resonator is that the coupling coefficient (/spl beta//sub C/) can be controlled by changing /spl delta/ while maintaining unloaded Q-factor (Q/sub u/) constant. Choosing a small value of /spl delta/ allows us to reduce /spl beta//sub C/ or equivalently to increase loaded Q-factor (Q/sub L/). Since coupling elements such as capacitors or electromagnetic gaps are not needed, /spl beta//sub C/ and Q/sub L/ can be precisely controlled based on mature lithography technology. This feature of the resonator proves useful in reducing phase noise and also in enhancing output power of microwave oscillators. The proposed resonator is applied to 18-GHz and 38-GHz HBT oscillators, leading to the phase noise of -96-dBc/Hz at 100-kHz offset with 10.3-dBm output power (18-GHz oscillator) and -104-dBc/Hz at 1-MHz offset with 11.9 dBm (38-GHz oscillator). These performances are comparable to or better than state-of-the-art values for GaAs- or InP-based planar-circuit fundamental-frequency oscillators at the same frequency bands.     

Mode Propagation in a Nonuniform Cylindrical Medium (Correspondence)

A simplified form of the coupling coefficient C(/spl beta//sub p/, /spl beta//sub q/) resulting from a coupled mode theory analysis of wave propagation in a nonuniform medium is derived. It is found for most situations of interest that C(/spl beta//sub p/, /spl beta//sub q/) is proportional to 1/(/spl beta//sub p/-/spl beta//sub q/) and the power transfer between two modes is proportional to 1/(/spl beta//sub p/ - /spl beta//sub q/)/sup 4/. /spl beta//sub p/ and /spl beta//sub q/ are the two different modal propagation constants. For a dielectric rod C(/spl beta//sub p/, /spl beta//sub q/) is a simple line integral around the rod boundary. Approximate forms are presented for optical waveguides.     

Analysis of Four-Frequency Nonlinear Reactance Circuits

Several advantages of multiple-frequency nonlinear reactance circuits are described in this paper. In particular, a circuit is considered in which a nonlinear reactance couples four basic frequencies: /spl omega//sub 0/, /spl omega//sub 1/,/spl omega//sub 2/, and /spl omega//sub 3/; these are so related that /spl omega//sub 2/ = /spl omega//sub 0/ + /spl omega//sub 1/ and /spl omega//sub 3/ = /spl omega//sub 0/ - /spl omega//sub 1/. Here, /spl omega//sub 0/ is taken to be the power source or pump. It is found to be desirable to allow for the possible presence of the pump harmonic, 2/spl omega//sub 0/, and individual cases are characterized by whether 2/spl omega//sub 0/, is present or not. The major results are as follows: 1) Unlimited amplification gain is theoretically possible at frequencies higher than the pump, by reflecting negative input resistance at /spl omega//sub 2/, but without relying on any effects due to pump harmonics. 2) Unlimited up- or down-conversion gains between /spl omega//sub 1/ and /spl omega//sub 2/ are theoretically possible in the additional presence of the first pump harmonic, but without reflecting negative input or output resistance. 3) Unlimited amplification gain is theoretically possible at frequencies both lower and higher than the pump fundamental, without reflecting negative input resistance.     

On the theory of 1/f noise of semi-insulating materials

The 1/f noise phenomena associated with devices involving semi-insulating materials, for instance GaAs MESFET's on semi-insulating GaAs, has long been a perplexing problem. In this particular case the 1/f noise corner frequency can be up to 100 MHz before the mean square noise current at the drain is dominated by the Nyquist noise associated with the channel conductance. No reasonable explanation has ever been given, although there are many different theories. 1/f noise is a common phenomena in nature and other devices involving semi-insulating materials. We propose here that this 1/f noise is a bulk phenomena associated with localized high frequency variations and long range low frequency fluctuations, the lowest frequency being limited only by the volume of the material. Specifically the proposal here is that injection of a current I into a semi-insulating material will result in a mean square noise voltage at the point of injection given by v/sub n//sup 2/~=2(kT/q)q/spl Delta/fR(/spl omega//sub c///spl omega/) Volts/sup 2/ where /spl omega//sub c/=1/t/sub t/, for the radian frequencies, /spl omega/, larger than /spl omega//sub c/ which is the reciprocal of the transit time of the carriers. For a long sample and long transit times then this 1/f noise voltage due to current injection will be larger than the Nyquist mean square noise of the sample alone as long as the DC voltage developed across the semi-insulating sample exceeds ((2kT/q)l/sup 2/(/spl omega///spl mu/))/sup 1/2/. This theory then gives the 1/f or 1//spl omega/ frequency dependence. The dc current I might be injected for instance by the substrate current in a GaAs MESFET being injected into the semi-insulating substrate, or gate current in an IGET being injected into the gate insulator.<>     

On the Mode and Square Correspondence Between Circular Multimode Tapered Waveguides

In an axially straight multimode circular waveguide taper excited with a pure TE/sup /spl circle// /sub 11/ dominant mode, the first and only converted mode at and near cutoff is the TM/sup/spl circle// /sub 11/ mode. It is shown that in an axially straight multimode square waveguide taper excited with a pure TE/sup/spl square// /sub 10/ dominant mode, the TM/sup/spl square// /sub 12/ mode corresponding to the TM/sup/spl circle// /sub 11/ mode in circular case is not the only first converted mode at and near cutoff. The overall behavior or coupling mechanism of waveguides is similar whether the waveguide is rectangular, square, circular, or elliptical: i.e., the overall coupling coefficient at cutoff of a converted mode or modes approaches an ininfinity of the order 0/sup -1/4/.     

Time-frequency localisation of Shannon wavelet packets

It is well known that the 2/spl pi/ minimally supported frequency scaling function /spl phi//sup /spl alpha//(x) satisfying /spl phi//spl circ//sup /spl alpha//(/spl omega/)=/spl chi//sub (-/spl alpha/,2/spl pi/-/spl alpha/)/(/spl omega/), 0相似文献   

SOI technology for radio-frequency integrated-circuit applications

This paper presents a silicon-on-insulator (SOI) integration technology, including structures and processes of OFF-gate power nMOSFETs, conventional lightly doped drain (LDD) nMOSFETs, and spiral inductors for radio frequency integrated circuit (RFIC) applications. In order to improve the performance of these integrated devices, body contact under the source (to suppress floating-body effects) and salicide (to reduce series resistance) techniques were developed for transistors; additionally, locally thickened oxide (to suppress substrate coupling) and ultra-thick aluminum up to 6 /spl mu/m (to reduce spiral resistance) were also implemented for spiral inductors on high-resistivity SOI substrate. All these approaches are fully compatible with the conventional CMOS processes, demonstrating devices with excellent performance in this paper: 0.25-/spl mu/m gate-length offset-gate power nMOSFET with breakdown voltage (BV/sub DS/) /spl sim/ 22.0 V, cutoff frequency (f/sub T/)/spl sim/15.2 GHz, and maximal oscillation frequency (f/sub max/)/spl sim/8.7 GHz; 0.25-/spl mu/m gate-length LDD nMOSFET with saturation current (I/sub DS/)/spl sim/390 /spl mu/A//spl mu/m, saturation transconductance (g/sub m/)/spl sim/197 /spl mu/S//spl mu/m, cutoff frequency /spl sim/ 25.6 GHz, and maximal oscillation frequency /spl sim/ 31.4 GHz; 2/5/9/10-nH inductors with maximal quality factors (Q/sub max/) 16.3/13.1/8.95/8.59 and self-resonance frequencies (f/sub sr/) 17.2/17.7/6.5/5.8 GHz, respectively. These devices are potentially feasible for RFIC applications.     

Theory of Direct-Coupled-Cavity Filters

A new theory is presented for the design of direct-coupled-cavity filters in transmission line or waveguide. It is shown that for a specified range of parameters the insertion-loss characteristic of these filters in the case of Chebyshev equal-ripple characteristic is given very accurately by the formula P/sub 0/ / /P/sub L/ = 1+h/sup 2/T/sub n//sup 2/[/spl omega//sub 0/ / /spl omega/ sin(/spl pi/ /spl omega/ / /spl omega//sub 0/) / sin/spl theta//sub 0/'] where h defines the ripple level, T/sub n/ is the first-kind Chebyshev polynomial of degree n, /spl omega/ / /spl omega//sub 0/ is normalized frequency, and /spl theta//sub 0/' is an angle proportional to the bandwidth of a distributed lowpass prototype filter. The element values of the direct-coupled filter are related directly to the step impedances of the prototype whose values have been tabulated. The theory gives close agreement with computed data over a range of parameters as specified by a very simple formula. The design technique is convenient for practical applications.     

Influence of photon reabsorption on the transfer efficiency of output intensity in semiconductor microcavities

Photon reabsorption effect on the transfer efficiency /spl beta//sub t/ of half-wavelength semiconductor microcavities was investigated by examining the excitation intensity dependence of the output light intensity. It is shown that /spl beta//sub t/ increases under intense excitation, and approaches to over-all spontaneous emission coupling coefficient /spl beta//sub 0/, as a result of the elimination of photon reabsorption. The results clearly demonstrate that the photon reabsorption is the predominant mechanism of the suppression of /spl beta//sub t/ at weak excitation, especially in the case of half-wavelength high-Q cavities.     

Radiation on Losses Due to Variations of Radius Dielectric or Optical Fibers

The total loss of the HE/sub 11/ mode to the radiation field of a finite dielectric rod with small amplitude surface irregularities is considered, and a simple approximate analytic expression for radiation due to sinusoidal roughness is presented. It is shown that radiation occurs only when the frequency of surface roughness /spl Omega/ is in the range /spl beta/-k/sub 2/相似文献   

Order statistics from a logistic distribution and applications to survival and reliability analysis

Joint moments involving arbitrary powers of order statistics are the main concern. Consider order statistics u/sub 1/ /spl les/ u/sub 2/ /spl les/ /spl middot//spl middot//spl middot/ /spl les/ u/sub k/ coming from a simple random sample of size n from a real continuous population where u/sub 1/ = x/sub r(1):n/ is order-statistic #r/sub 1/, u/sub 2/ = x/sub r(1)+r(2):n/ is order statistic #(r/sub 1/ + r/sub 2/), et al., and u/sub k/ = x/sub r(1)+/spl middot//spl middot//spl middot/+r(k):n/ is order statistic #(r/sub 1/ +/spl middot//spl middot//spl middot/+ r/sub k/). Product moments are examined of the type E[u/sub 1//sup /spl alpha/(1)/ /spl middot/ u/sub 2//sup /spl alpha/(2)//sub /spl middot/ /spl middot//spl middot//spl middot//spl middot//u/sub k//sup /spl alpha/(k)/] where /spl alpha//sub 1/, ..., /spl alpha//sub k/ are arbitrary quantities that might be complex numbers, and E[/spl middot/] denotes the s-expected value. Some explicit evaluations are considered for a logistic population. Detailed evaluations of all integer moments of u/sub 1/ and recurrence relations, recurring only on the order of the moments, are given. Connections to survival functions in survival analysis, hazard functions in reliability situations, real type-1, type-2 /spl beta/ and Dirichlet distributions are also examined. Arbitrary product moments for the survival functions are evaluated. Very general results are obtained which can be used in many problems in various areas.     

High bandwidth and low-leakage current InP-In/sub 0.53/Ga/sub 0.47/As-InP DBHTs on GaAs substrates

InP-In/sub 0.53/Ga/sub 0.47/As-InP double heterojunction bipolar transistors (DHBTs) were grown on GaAs substrates. A 284-GHz power-gain cutoff frequency f/sub max/ and a 216-GHz current-gain cutoff frequency f/sub /spl tau// were obtained, presently the highest reported values for metamorphic HBTs. The breakdown voltage BV/sub CEO/ was >5 V while the dc current gain /spl beta/ was 21. High thermal conductivity InP metamorphic buffer layers were employed in order to minimize the device thermal resistance.     

Efficiencies of Microwave 2-Ports from Reflection Coefficient Measurements (Short papers)

It is well-known that one can determine the efficiency of a microwave 2-port by measuring the reflection coefficient /splGamma//sub 1/ at the input port when the output port is terminated by a sliding short circuit. The locus of /spl Gamma//sub 1/ is a circle whose radius equals the efficiency /spl eta//sub 2m/ for energy entering port 2 when port 1 is terminated in a nonreflecting load. Similarly /spl eta//sub 1m/ is the radius of the circle when port is terminated in a sliding short circuit. This note describes a procedure for obtaining, from the same measured data, new reflection coefficients /spl Gamma//sub 1N/ and /spl Gamma//sub 2N/, whose circular loci have radii R/sub 1N/ and R/sub 2N/ which give the efficiencies of the 2-port when connected to an arbitrary load of reflection coefficient /spl Gamma//sub L/. Thus the /spl Gamma//sub 1/ or /spl Gamma//sub 2/ data may be used to obtain the efficiency of the 2-port when terminated in any arbitrary load. The method is potentially more accurate than the 3-point method since errors can be reduced by drawing a circle through many measured points.     

High-temperature thermal stability performance in /spl delta/-doped In/sub 0.425/Al/sub 0.575/As--In/sub 0.65/Ga/sub 0.35/As metamorphic HEMT

We report, to our knowledge, the best high-temperature characteristics and thermal stability of a novel /spl delta/-doped In/sub 0.425/Al/sub 0.575/As--In/sub 0.65/Ga/sub 0.35/As--GaAs metamorphic high-electron mobility transistor. High-temperature device characteristics, including extrinsic transconductance (g/sub m/), drain saturation current density (I/sub DSS/), on/off-state breakdown voltages (BV/sub on//BV/sub GD/), turn-on voltage (V/sub on/), and the gate-voltage swing have been extensively investigated for the gate dimensions of 0.65/spl times/200 /spl mu/m/sup 2/. The cutoff frequency (f/sub T/) and maximum oscillation frequency (f/sub max/), at 300 K, are 55.4 and 77.5 GHz at V/sub DS/=2 V, respectively. Moreover, the distinguished positive thermal threshold coefficient (/spl part/V/sub th///spl part/T) is superiorly as low as to 0.45 mV/K.     

Transients on multiconductor transmission lines above dissipative earth-numerical simulation and measurement

A finite-difference time-domain (FDTD) analysis is presented to simulate, up to the high-frequency regime, transients on multiconductor transmission lines above dissipative earth. Excitation is in the high-frequency regime if the pulse has significant spectral content up to /spl omega//spl ap//spl omega//sub c/, with /spl omega//sub c/ the frequency where the conduction and displacement current densities have equal magnitude. Thus, /spl omega//sub c/=/spl sigma//sub g///spl epsi//sub 0//spl epsi//sub rg/ with /spl sigma//sub g/ and /spl epsi//sub rg/ the ground conductance and relative permittivity. The FDTD algorithm extends the formulation of Agrawal et al. (1980), by incorporating the theory of D'Amore and Sarto for the interaction of wide-band transients with the earth. Careful experimental testing of the new algorithm is presented. The measurement configuration consists of two parallel wires; first suspended above an aluminum sheet to test the code in the low-frequency regime; then above a block of absorbing material for experiments in the high-frequency regime. The end of one of the conductors is driven with a 2-ns synthesized impulse by a stepped-frequency, automatic network analyzer. Reflected and cross-talk signals are presented in the time domain. These show good agreement with the numerically predicted common mode, differential mode and mode-converted pulses.     

Frequency domain characterization of LoS nonfading indoor wireless LAN channel employing frequency and polarization diversity in the 63.4-65.4 GHz band

This paper presents results of frequency domain measurements conducted to characterize the distortionless transmission bandwidth (DTB) of indoor nonfading channels employing vertically and horizontally polarized antennas in the frequency band 63.4-65.4 GHz. The mean delay spread (/spl tau//sub mean/), root mean square (rms) delay spread (/spl tau//sub rms/), and the DTB of the channel are also presented as functions of distance between terminals and are compared for both polarizations. The dependence of DTB on the separation between terminals d is modeled as DTB=kd/sup -n/ where k is a constant. /spl tau//sub mean/ increases linearly with d, and its relationship with DTB is characterized as DTB=(1//spl alpha//spl tau//sub mean//sup n/)+c, where /spl alpha/ and c are constants. The effectiveness of frequency and polarization diversity in mitigating the effects of multipath fading in indoor channels has also been evaluated. The performance of both diversity techniques when modulated signals with high data rates for multimedia applications are utilized is presented for maximum selection combining. The performance of frequency diversity is also shown as a function of frequency separation between diversity branch signals to determine whether an optimal frequency separation exists.