Optimal filters provide minimum variance interpolation and smoothing of noisy data, but the form of the noise power spectrum must be known for their design. We analyse data from the Microwave Limb Sounder (MLS) experiment onboard the Upper Atmosphere Research Satellite (UARS) to quantify parameters describing the noise spectra. MLS views space as part of its calibration sequence providing regular samples of the radiometer output. From these samples we determine breakpoint frequencies at which the spectral power density of the low frequency l/f noise is equal to that of the white noise. Breakpoint frequencies were in the range from 0.005 to 0.02 Hz for the 90 filter channels of the MLS. A method was developed to distinguish between l/f noise and systematic disturbances caused by cyclic changes in the operating environment as the spacecraft traverses its orbit.

The Upper Atmosphere Research Satellite (UARS) microwave limb sounder (MLS) makes measurements of thermal emission at 183.3GHz which are used to infer the concentration of water vapor over a pressure range of 46 - 0.2hPa ( 20 to  60km). We provide a validation of MLS H20 by analyzing the integrity of the measurements, by providing an error characterization, by comparison with data from other instruments. It is estimated that version 3 MLS H20 retrievals are accurate to within 20-25 % in the lower stratosphere and to within 8-13 % in the upper stratosphere and lower mesosphere. The precision of a single profile is estimated to be  0.15 parts per million by volume (ppmv) in the midstratosphere and 0.2ppmv in the lower and upper stratosphere. In the lower mesosphere the estimate of a single profile precision is 0.25-0.45 ppmv. During polar winter conditions, H20 retrievals at 46 hPa can have a substantial contribution from climatology. The vertical resolution of MLS H20 retrievals is  5 km.

The Upper Atmosphere Research Satellite (UARS) microwave limb sounder (MLS) makes measurements of thermal emission at 183.3 GHz which are used to infer the concentration of water vapor over a pressure range of 46 – 0.2 hPa (∼20 to ∼60 km). We provide a validation of MLS H2O by analyzing the integrity of the measurements, by providing an error characterization, and by comparison with data from other instruments. It is estimated that version 3 MLS H2O retrievals are accurate to within 20–25% in the lower stratosphere and to within 8–13 % in the upper stratosphere and lower mesosphere. The precision of a single profile is estimated to be ∼0.15 parts per million by volume (ppmv) in the midstratosphere and 0.2 ppmv in the lower and upper stratosphere. In the lower mesosphere the estimate of a single profile precision is 0.25–0.45 ppmv. During polar winter conditions, H2O retrievals at 46 hPa can have a substantial contribution from climatology. The vertical resolution of MLS H2O retrievals is ∼5 km.

The Microwave Limb Sounder (MLS) has monitored the composition of the stratosphere and lower mesosphere for more than three years since its launch on the Upper Atmosphere Research Satellite in September 1991. The MLS measures thermal emission from the atmospheric limb at millimetre wavelengths and is the first limb sounder to operate at these wavelengths from space. The primary measurements are of the concentrations of O/sub 3/, ClO and water vapour and of atmospheric temperature. Secondary products which have been produced include SO/sub 2/ from volcanic injections, HNO/sub 3/, and upper tropospheric water vapour. Vertical profiles of atmospheric concentrations are retrieved from the measured radiances. Daily global maps at a number of levels in the atmosphere are produced from these profiles. Major results to date are summarised. The depletion of ozone in the Antarctic spring is illustrated with maps for 1991, 92 and 93. Maps for the Arctic are compared with corresponding maps for the Antarctic. Significant decrease in gaseous HNO/sub 3/ has been observed in the Antarctic vortex. Water vapour fields used as tracers illustrate dynamical features of the winter polar vortices and, in the tropics, show a clear semi-annual oscillation in the upper stratosphere and a modulation of the annual cycle by the quasi-biennial cycle in the lower stratosphere. At low latitudes increased SO/sub 2/ was observed following the 1991 Pinatubo volcanic eruption.

The effects of the break‐up of the antarctic vortex on the water vapour distribution are studied using MLS measurements of water vapour made during September 1991 and November 1991. In early November at 22 hPa a moist area is found within the polar vortex, consistent with an observed descent of order 10 km and strong radiative cooling. As the vortex erodes (beginning of November 1991), parcels of moist air become detached from the edge of the vortex and mix rapidly (within 2–3 days) with drier mid‐latitude air. When the vortex breaks up (mid‐November), larger parcels of moist air from both the edge arid the inner vortex migrate to mid‐latitudes. These parcels have a longer lifetime than those produced by vortex erosion, probably because they are correlated with higher potential vorticity gradients. The break‐up of the vortex is accompanied by a mean adiabatic equatorward transport resulting in a significant increase in mid‐stratospheric water vapour values at mid‐latitudes in late spring.

Ion-implanted In/sub (x)/Ga/sub (1-x)/ As MESFETs on GaAs substrate are very attractive devices for ultra-high-frequency and ultra-high-speed integrated circuit applications due to the simplicity of material structure and manufacturability of ion implantation technology. The advances in ion-implanted In/sub (x)/Ga/sub (1-x)/As/GaAs MESFET technology are reviewed, focusing on material structures, device fabrications, manufacturability, current gain cutoff frequency, and maximum power oscillation frequency performance, as well as low noise, power, and oscillator performance in the millimeter-wave frequency range. >

Both single and trilayer technologies have been evaluated for the production of sub-half micron gate-length devices on 3-in. diameter GaAs substrates using deep ultra-violet photolithography. The trilayer technique is capable of fabricating 0.4-mu-m gate-length devices with yields exceeding 86%. However, the single layer process has the advantages of fabricating 0.5-mu-m gate-length devices with greater simplicity, reduced cost, and east of rework. The improved gate resolution and yield of the trilayer process are attributed to the very thin top layer resist, planarized surface, and the reactive ion etching in process. The trilayer process also has the potential for fabricating 0.25-mu-m gate-length devices with good uniformity and high yield. We compare dc and microwave characteristics of devices fabricated with both single and trilayer techniques. These data indicate no device degradation resulting from the more complicated trilayer process.

Millimeter-wave power performance achieved by ion-implanted InGaAs-GaAs MESFETs with a gate length of 0.25 mu m is described. When a device with a gate width of 150 mu m was measured at 22 GHz, an output power of 95 mW, a power-added efficiency of 33%, and an associated gain of 7.3 dB were observed. At an output power of 93 mW, a power-added efficiency of 25% and an associated gain of 4 dB were obtained at 44 GHz. When a device with a gate width of 200 mu m was measured at 60 GHz, an output power of 121 mW with 3-dB associated gain and 13% power-added efficiency were observed.<>

A brief description is given of how the simple eigenmode approach can be utilized to develop a first-order model that yields explicit ready-to-use formulas for predicting the performance characteristics of a symmetrical six-port microstrip ring coupler. Prototype tests conducted over the 2-5 GHz frequency range show the agreement between the predicted and measured values of the coupler&#39;s scatterin...

Monolithic, two-stage amplifiers using 0.5 x 80-mu-m2 gate GaAs/AlGaAs heterojunction FETs have been developed for Ka-band operation. These monolithic two-stage amplifiers were fabricated using ion implantation for the active layer and optical lithography for the 0.5-mu-m gate length. MMIC two-stage amplifiers achieved average gains of 12.6 +/- 1.4 dB at 30 GHz and 8.8 +/- 2.0 dB at 40 GHz, respectively, for all 39 sites across a 3 inch diameter wafer. These are the first reported results the MMIC two-stage amplifiers using 0.5-mu-m gate length ion-implanted GaAs/AlGaAs heterojunction FETs achieved over 10 dB gain at Ka band.

A microwave technique was used to determine the electron drift velocity in an ion-implanted GaAs MESFET with a 0.5*100- mu m gate. The characteristics of the velocity versus drain-to-source voltage for a GaAs MESFET exhibit a peak velocity of 4.0, 3.3, and 2.2*10/sup 7/ cm/s at 100%, 65%, and 31% of I/sub dss/, respectively. This work presents the first experimental determination of electron drift velocity at various gate biases and provides verification for velocity overshoot in ion-implanted GaAs MESFETs.<>

This work presents millimeter wave performance achieved by ion-implanted InGaAs/GaAs metal semiconductor field-effect transistor devices. A current gain cutoff frequency ft of 126 GHz and maximum frequency of oscillation fmax of 232 GHz have been measured for 0.20 μm gate length devices. The ft and low-field Hall mobility data, measured at 300 and 112 K, lead us to conclude that the average electron velocity under the gate is mainly due to the high-field velocity rather than low-field electron mobility.

Subhalf-micrometre gate length ion-implanted GaAs MESFETs have been fabricated on 3 inch diameter substrates using trilayer deep UV lithography. Implanted MESFETs with 0.3-mu-m gate lengths exhibit a maximum extrinsic transconductance of 205 mS/mm at a drain current of 600 mA/mm. From S-parameter measurements, a current gain cutoff frequency f(t) of 56 GHz and a maximum available gain cutoff frequency f(max) greater than 90 GHz are achieved. The gate-to-drain diode characteristics of the devices show a sharp breakdown voltage of 13-15 V. The high drain current-drain voltage and microwave characteristics indicate that ion-implanted technology with trilayer deep UV lithography has potential for the manufacture of power devices and amplifiers for Q-band communication applications. This is the first reported result using trilayer deep UV lithography to demonstrate both f(t) over 56 GHz and 13-15 V gate to-drain breakdown on 0.3-mu-m gate-length ion-implanted GaAs MESFETs.

Low-noise ion-implanted In(x)Ga(1-x)As MESFET's with 0.25-mu-m T-gates have been developed at 60 GHz. The device noise figure was 2.8 dB with an associated gain of 5.6 dB at 60 GHz. A hybrid two-stage amplifier using these ion-implanted In(x)Ga(1-x)As MESFET's achieved a noise figure of 4.6 dB with an associated gain of 10.1 dB at GHz. When this amplifier was biased at 100% I(dss), it achieved 11.5-dB gain at 60 GHz. These results, achieved using low-cost ion-implantation techniques, are the best reported noise figures for ion-implanted MESFET's.

A technique for determining the parasitic capacitance attributed to device layout geometry is described. This simple technique requires only on-wafer, cascade probe measurements on devices with varying gate widths. This technique will assist in the optimization of device layout design and in improving modeling performance for microwave and millimeter-wave applications.< >

A fundamental FET oscillator that operates at 92.3 GHz with an output power of 14 mW and with V/sub DS/=3.9 volts is reported. The efficiency is 11% at this point. The data are referenced to the waveguide output port with no corrections for the transition or fixture loss. By tuning the input waveguide short, the device oscillation frequency could be tuned from approximately 91-93 GHz. Maximum power was attained at 92.3 GHz. The output spectrum of this oscillator shows the sideband noise to be approximately -70 dBc/Hz for all offset frequency of 15 kHz. This is comparable to commercial W-band Gunn oscillators.< >

FETs fabricated by ion implantation into inverted GaAs-AlGaAs heterostructures grown by MOCVD are discussed. The AlAs fraction in the AlGaAs layer is graded from 0% at the substrate to 30% at the heterointerface. 0.5- mu m gate devices fabricated with the graded heterojunction show two transconductance peaks that are both greater than 420 mS/mm. These devices also exhibit enhanced power gain, espe...

Hybrid low-noise amplifiers using ion-implanted In/sub x/Ga/sub 1-x/As MESFETs with 0.25- mu m T-gates have been developed at 44 GHz. The hybrid two-stage amplifier using these ion-implanted In/sub x/Ga/sub 1-x/As MESFETs achieved a noise figure of 3.6 dB with an associated gain of 14.4 dB at 44 GHz. When two of these amplifiers were cascaded, the four-stage amplifier demonstrated a gain of 30.5 dB at 44 GHz and 37 dB at 40 GHz. These results, achieved using low cost ion-implantation techniques, rival the best high-electron-mobility transistor (HEMT) results.<>