A Universal Wall-Current Detector

A universal X-band waveguide detector has been developed which offers the possibilities of a broad-band untuned detector with a stable frequency characteristic. The wall-current detector is a reflectionless two-port with an insertion loss, less than 0.05 db, no extra phase-shift, a sensitivity of about 10 mv/mw and a frequency characteristic which repeats within /spl plusmn/0.1 db over the 8.2-12.4 Gc band for any 1N26. This performance made it possible to flatten the output of a Hewlett-Packard sweep oscillator (as seen by another wall-current detector) within /spl plusmn/0.15 db over the whole X band. As a result many frequency-dependent measurements can now be done automatically with reasonable precision. Plotters and reflectometers will be simplified, resulting in a higher precision. Circular and ridge waveguide types have also been made. The latter seems very promising for an ultra broad-band detector. A sum detector and a difference detector have been made. They can be used for phase-sensitive detection, zero measurements, etc. The wall-current detector can easily be scaled down to mm waves.     

A Waveguide Impedance Meter for the Automatic Display of Complex Reflection Coefficient

A waveguide impedance meter has been developed, comprising some specially designed components and some components previously designed for other applications. When this circuit is used in conjunction with the X-band rapid sweep oscillator and suitable display and control circuits, the impedance focus of a waveguide component is automatically and rapidly measured and oscilIographically displayed in the reflection coefficient plane. A waveguide component having a 11/4-inch X 5/8-inch (large X-band) waveguide input port can be continuously measured throughout the frequency range extending from 8.5 to 9.6 kmc (12 per cent X-band). The bandwidth of the system is limited by the design bandwidth of the waveguide components. The plane of the impedance measurement may be referred to a plane internal to or external to the input port of the component under test. An expanded portion of the reflection coefficient plane may be displayed on the crt when small reflections are measured. The measurements of several representative impedances by the waveguide circuit were compared with slotted line measurements of these same components. For measurements of large reflections, standard /spl infin/ db swr full scale display, the maximum observed errors of the magnitude and phase of the reflection coefficient as measured by the waveguide circuit were 10 per cent and 5 degrees respectively. These maximum errors occurred for measurements performed at the ends of the 12 per cent frequency band. The average errors of the magnitude and phase of the reflection coefficient were 2.5 per cent and 2 degrees respectively. For measurements of small reflections, with the crt display of the reflection coefficient plane expanded to 6 db swr full scale, the maximum observed deviation of the waveguide circuit measurements from slotted line measurements was 0.5 db swr, and the average deviation was 0.2 db swr. The maximum errors again occurred at the ends of the 12 per cent frequency band.     

General Synthesis of Asymmetric Multi-Element Coupled-Transmission-Line Directional Couplers

An exact synthesis procedure is derived for a class of asymmetric multielement coupled-transmission-line directional couplers with any number of elements. It is based on the equivalence between the theory of the directional coupler and that of a stepped quarter-wavelength filter. This can be treated using Richards' theorem for the synthesis of transmission-line distributed networks, as described previously by Riblet. The method is extended to give a general expression for the input reflection coefficient of the stepped filter, which corresponds to the voltage coupling of the directional coupler. Explicit formulas for the parameters of two, three, four and five couplers are derived and the extension to larger number of elements is straightforward. Two and three element couplers have been designed on this theoretical basis, and show excellent agreement with theory, for example a three element coupler of 20 db /spl plusmn/ 0.5 db over a 6:1 bandwidth, and a two element coupler of 3.2 db /spl plusmn/ 0.85 db over a 6.7:1 bandwidth. It is possible to design a 3-db /spl plusmn/ 0.43 db-coupler for decade bandwidths using only four elements. The 3 db-couplers may be used as 90/spl deg/ hybrids by careful choice of reference planes in the output parts.     

Techniques for the Measurement of Complex Microwave Conductivity and the Associated Errors

Complex microwave conductivity of 9 /spl Omega/ /spl dot/ cm p-type silicon samples has been measured using conventional reflection and transmission bridges to examine their relative advantages and disadvantages. An attempt has been made to improve the reflection results from an analysis of the parameters of a circle diagram for reflection coefficient obtained on using a variable reactive termination after the semiconductor-filled waveguide section. In conformity with the calculated accuracy attainable from different types of measurement under the actual experimental condition, using commercial standards, the dielectric constant for the sample was found to be scattered over a region of /spl plusmn/0.4. It has been concluded that because of lack of accuracy in commercial standards for attenuation and phase shift, the potential accuracy of the conventional microwave methods falls too short of its mark to make any detinite conclusion about the effective mass of carriers in semiconductors at room temperatures.     

Two-wire bridge-to-frequency converter

An integrated two-wire bridge-to-frequency converter is presented for use as a remote-signal conditioner for sensor bridges such as strain-gauge bridges of platinum-wire temperature-sensing bridges. The converter has a sensitivity on the order of 1 Hz per 1-/spl mu/V/V relative bridge output. A center frequency of 10 kHz allows the application of an untrimmed bridge with an imbalance up to /spl plusmn/10000 /spl mu/V/V. The instability is less than 10/SUP -4/ per Kelvin and per 1-V supply-voltage variation. The untrimmed transfer inaccuracy is lower than 1%. The linearity error is lower than 0.01%. Different bridge readout functions can be chosen by different circuit configurations. The converter can be connected to a single supply voltage. The frequency output is modulated on the supply current. The supply voltage is 12-24 V.     

A Simple Technique for Real-Time Measurement of Complex Reflection Coefficient (Correspondence)

A simple method for making real-time measurements of complex reflection coefficient p/sub x/ is described. The technique uses a hybrid tee and two crystal detectors to provide analog outputs from which the reflection coefficient is obtained. Sample measurements of p/sub x/ made at 34.3 GHz are presented which indicate a precision of greater than 0.02 units and 0.05 radians in magnitude and argument, respectively, for 0.1 /spl les/|p/sub x/|/spl les/ 1.0.     

The Comparison Reflectometer

The comparison reflectometer is an instrument designed to locate and measure the characteristics of reflections in waveguide and transmission-line systems: it is particularly suitable for measuring small reflections in precise microwave measuring instruments up to one meter in length. It consists of a reflectometer in which the returning waves are combined with an accurately known reference wave and a measure of the total reflection coefficient is recorded automatically on punched paper tape at a number of preset frequencies covering a particular waveband. From sets of readings taken without, and with, the test component connected, a computer calculates and plots the distribution of reflections as a function of distance and prints out their magnitudes and phases. The reflection coefficients of individual discontinuities are also plotted by the computer as a function of frequency on Smith charts. Under suitable conditions point reflections may be Iocated in X-band waveguide within a few tenths of a millimeter and measured with an accuracy of /spl plusmn/3 percent in magnitude and /spl plusmn/ 5/spl deg/ in phase angle. The method compensates for imperfections in the reflectometer and so reduces the background level of spurious reflections to less than 0.00006.     

Analysis and Exact Synthesis of Cascaded Commensurate Transmission-Line C-Section All-Pass Networks

An analysis of cascaded commensurate transmission-line C-section all-pass networks is presented. The analytical form of the transmission coefficient is found to have a very simple form, intimately related to the reflection coefficient of the stepped-impedance transformer prototype of the cascaded C-section. The phase function of cascaded commensurate transmission-line C-sections is investigated and found to be the arctangent of a reactance function in tan /spl theta/. Last, general, exact synthesis procedures for designing cascaded commensurate transmission-line C-section all-pass networks to have prescribed phase characteristics are presented, and two design examples are given. One of the examples is the exact design of a 3-section Schiffman 90/spl deg/ phase shifter, which has not been previously reported in the literature.     

An 8-bit, 5 ns monolithic D/A converter subsystem

Describes a 5 ns settling time digital-to-analog converter device, which has been designed for use in video speed successive approximation analog to digital converters. The chip includes a precision reference source with a 25 ppm per degree C average temperature coefficient and a high-speed comparator. The successive approximation approach, restricted to low-speed converters until now, has the advantages of low cost and straightforward drive requirements. The achievement of the operating speeds described is dependent both on the circuit techniques used and the process employed. The DAC circuit, unlike most other devices, uses a multiple-matched current source array technique, which leads to a very linear, low glitch output. Without any form of trimming, most functional devices meet a /spl plusmn//SUP 1///SUB 2/ LSB differential and integral linearity specification, and many are /spl plusmn//SUP 1///SUB 4/ LSB or better.     

Measurements of Intercavity Couplings (Short Papers)

This short paper describes the determination of couplings within a system of coupled cavities by measuring frequencies at which the phase of the input reflection coefficient is either 0/spl deg/ or 180/spl deg/. A high degree of accuracy may be achieved and corrections can be made for finite cavity Q.     

Compact planar multiband antenna for GPS, DCS, 2.4/5.8 GHz WLAN applications

A compact single-feed multiband planar antenna configuration suitable for GPS, DCS, 2.4/5.8 GHz WLAN applications is presented. The antenna has dimensions 38/spl times/3/spl times/1.6 mm and offers good radiation and reflection characteristics in the above frequency bands. The antenna has a simple geometry and can be easily fed using a 50 /spl Omega/ coaxial probe.     

An accurate integrated voltage-to-current converter

Presents a monolithic integrated differential voltage-to-current converter. The transconductance of the converter is determined accurately by one external resistor. A total error in the conversion factor as low as /spl plusmn/0.5 percent is obtained by using composite transistors and by using the mutual equality of integrated resistors. The transconductance has a nonlinearity of 0.02 percent and a temperature coefficient of 4/spl times/10/SUP -5///spl deg/C. The output impedance is 5 M/spl Omega/. The voltage-to-current converter is a versatile building block. It can be applied as an instrumentation amplifier, a universal current mirror or current follower, etc.     

Spectral FDTD: a novel technique for the analysis of oblique incident plane wave on periodic structures

This paper introduces a new technique which calculates the reflection coefficient for the plane wave incident on planar periodic structures. The method referred to as spectral finite-difference time-domain (SFDTD) replaces the conventional single-angle incident wave, with a constant transverse wavenumber (CTW) wave. Because the transverse wavenumbers are constant, the fields have no delay in the transverse plane (x-y plane), and PBC (periodic boundary condition) can be directly implemented in the time domain for both oblique and normal incident waves. The stability criterion for this new FDTD technique is angle-independent and therefore this method works well for incident angles close to grazing (/spl theta/=90/spl deg/) as well as normal incident (/spl theta/=0/spl deg/). This shows the efficiency of the method compared to other available FDTD techniques for the same purpose that force a more restricted stability criterion as angles turns to grazing. The validity of this method is verified by comparing the reflection coefficient calculated by this method with the analytical results of a grounded slab. The results of this technique are also compared with method of moments for a periodic array of metallic patches and a good agreement is observed. A periodic array of metallic patches above a PEC plate is analyzed and the reflection coefficient is calculated over a wide frequency band for angles varying from 0/spl deg/ to close to 90/spl deg/.     

A capacitor-free CMOS low-dropout regulator with damping-factor-control frequency compensation

A 1.5-V 100-mA capacitor-free CMOS low-dropout regulator (LDO) for system-on-chip applications to reduce board space and external pins is presented. By utilizing damping-factor-control frequency compensation on the advanced LDO structure, the proposed LDO provides high stability, as well as fast line and load transient responses, even in capacitor-free operation. The proposed LDO has been implemented in a commercial 0.6-/spl mu/m CMOS technology, and the active chip area is 568 /spl mu/m/spl times/541 /spl mu/m. The total error of the output voltage due to line and load variations is less than /spl plusmn/0.25%, and the temperature coefficient is 38 ppm//spl deg/C. Moreover, the output voltage can recover within 2 /spl mu/s for full load-current changes. The power-supply rejection ratio at 1 MHz is -30 dB, and the output noise spectral densities at 100 Hz and 100 kHz are 1.8 and 0.38 /spl mu/V//spl radic/Hz, respectively.     

Piezoelectric transducer controlled multiple beam phased array using microstrip Rotman lens

A simple and low-cost multiple beam phased array is designed using a microstrip Rotman lens and multi-line phase shifter controlled by a piezoelectric transducer (PET) at Ka-band. A microstrip Rotman lens with five beam ports and nine array ports is used as a feed for a multiple beam antenna array to generate five beams centered at the angles of 0/spl deg/, /spl plusmn/15/spl deg/, and /spl plusmn/30/spl deg/. The lens fed nine-element patch array shows the antenna gain of 10 dBi and sidelobe suppression of 10 dB. Each beam is steered over /spl plusmn/8/spl deg/ using two PET-controlled phase shifters, and the five beams cover /spl plusmn/38/spl deg/ from the broadside.     

Integrated folding 4/spl times/4 optical matrix switch with total internal reflection mirrors on SOI by anisotropic chemical etching

A folding rearrangeable nonblocking 4/spl times/4 optical matrix switch was designed and fabricated on silicon-on-insulator wafer. To compress chip size, switch elements (SEs) were interconnected by total internal reflection (TIR) mirrors instead of conventional S-bends. For obtaining smooth interfaces, potassium hydroxide anisotropic chemical etching of silicon was utilized to make the matrix switch for the first time. The device has a compact size of 20/spl times/1.6 mm/sup 2/ and a fast response of 7.5 /spl mu/s. The power consumption of each 2/spl times/2 SE and the average excess loss per mirror were 145 mW and -1.1 dB, respectively. Low path dependence of /spl plusmn/0.7 dB in total excess loss was obtained because of the symmetry of propagation paths in this novel matrix switch.     

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.     

A Highly Stabilized MIC Gunn Oscillator Using a Dielectric Resonator

An X-band frequency-stabilized MIC Gunn oscillator of a very simple structure using a dielectric resonator is developed. It is studied how the oscillating characteristics can be controlled by circuit parameters, with special attention to the factors affecting the frequency stability with temperature. By optimizing these factors and by selecting the proper temperature coefficient of a newly developed dielectric resonator, the high frequency stability of less than /spl plusmn/100 MHz over the temperature range from -20 to 60/spl deg/C (2x10 /sup -7/ / /spl deg/C) was obtained.     

Propagation modeling of MIMO multipolarized fixed wireless channels

This paper addresses the extension of a stochastic geometry-based scattering model to multipolarized transmissions. The initial approach is based on a geometrical distribution of obstacles derived from known power-delay profiles. Each scattering process is statistically described by a matrix reflection coefficient corresponding to dual-polarization states. Ultimately, the model allows us to simulate the effects of the range on K-factor, delay-spread, Doppler spectrum, channel correlations and capacity, branch power ratio, and cross-polar discrimination. Simulation results are compared with existing measurements at 2.5 GHz. The proposed model is then used to investigate various dual-polarization 2 /spl times/ 2 multiple-input-multiple-output (MIMO) schemes such as 0/spl deg//90/spl deg/ or /spl plusmn/45/spl deg/, as well as to optimize the design of multipolarized MIMO schemes.