C-band Microwave Research Articles

Inversive Technique of Surface Roughness Estimation Using Multi-incident Angular Data by Microwave Scatterometer

This paper explores the possibility of inversion technique of surface roughness estimation using multi-incident angular data by microwave scatterometer. We made field experiments to measure soil moisture, surface roughness and soil backscatter by C-band microwave scatterometer mounted on a car. Surface roughness observed 1 dimensionally is scattered widely even in a same land cover and we have to make more than eight observations to get the representative roughness. Algorithm of the inversion technique is developed based on the surface scattering model and surface roughnesses are estimated inversely. However the observed and estimated roughnesses are quite different each other and the latter one proves to be suitable for decision of relational curve for soil moisture-backscattering coefficients.

Thermal infra-red underflights compared to ERS-1 C-band synthetic aperture radar focusing soil moisture distribution

This paper is focused on the applicability of remotely sensed data of different platforms to determine spatial variability and distribution of soil mositure on a local scale. A plane agricultural test site of ≈ 2 km2 in Central Europe is the basis for a comparison of simultaneously recorded high resolution (<0.2 m) thermal infra-red data with C-band microwave data (<30 m). In situ measurements link the remote sensing data to ground truth. Heterogeneity in landform, soil and vegetative cover are accounted for in a resolution of less than a hectare. Results of this study show that there is no correlation between backscattering coefficients and brightness temperatures over vegetated fields, but brightness temperature indicates a distribution of plant available water in the root zone. Bare fields in dry conditions demand in-situ determination of soil moisture of the top few millimeters to compare remote sensing data to reliable ground truth.

Internal-node waveform analysis of MMIC power amplifiers

A novel internal-node waveform probing technique has been demonstrated on a C-band monolithic microwave integrated circuit (MMIC) power amplifier. The error of the measurement and its perturbance to circuit operation was estimated and verified to be within /spl plusmn/10%. Valuable insight was obtained from the variation of waveforms as a function of frequency, drive and location. The potential impact of this technique includes MMIC design verification, in-situ device model extraction, process diagnosis, and reliability assessment.

Seasonal changes in relative C-band backscatter of northern forest cover types

Reports the results of an experiment performed to investigate the changes of C-band microwave backscatter as a function of season in northern forests. The purpose was to determine whether seasonal changes can be used to increase the information content of single-polarization C-band SAR data. Data were acquired in four consecutive seasons along the same east-west line with a pixel spacing of 3.9 m (azimuth) by 4.7 m (range) with incidence angles ranging from 45 degrees to 75 degrees . Calibration was carried out within each scene, allowing seasonal changes in relative backscatter and absolute dynamic range to be studied. The investigation demonstrated that the entire dynamic range of mean C-HH backscatter values of forest stands was never more than about 6 dB. The range exhibited seasonal variations, from only 3.5 dB in February, to 6.0 dB in May. The seasonal changes in dynamic range of the nondeciduous softwoods are hypothesized to be dominated by changes in the dielectric constant of the woody and foliar parts of the trees. Seasonal changes of deciduous backscatter relative to the softwoods allows multitemporal SAR data to be used to distinguish between hardwood and softwood species. >

The use of a microwave backscatter model for retrieving soil moisture over bare soil

Abstract Most attempts at predicting soil moisture from C-band microwave backscattering coefficients for bare soil are made by fitting experimental calibration relations obtained for limited ranges of incidence angle and soil surface roughness. In this paper, a more general approach is discussed using an inversion procedure to extend the use of a single experimental calibration relation to a wider range of incidence angle and surface roughness. A correcting function is proposed to normalize the backscattering coefficients to the conditions (incidence angle and surface roughness) of the calibration relation. This correcting function was derived from simulated data using the physical optics or KirchhofTs scatter model using the scalar approximation. Before discussing the inversion procedure, the backscattering coefficients calculated by the model have been compared with experimental data measured in the C-band, HH polarization and three incidence angles (Θ= 15°, 23°, 50°) under a wide range of surface soil moisture conditions (0.02Hv  0.35cm3 cm-3) and for a single quite smooth soil surface roughness (0–011 s  OOI4/n)m. The model was found to be experimentally validated from 15° to 23° of incidence and for surface soil moistures higher than 0-I0cm3cm-3. For the inversion procedure, it is assumed to have a wider range of validity (15°  Θ 35° ) for ihc incidence angle. A sensitivity analysis of the model to errors on roughness parameter and incidence angle was performed in order to assess the feasability and suitability of the described inversion procedure.

C-band 10 W MMIC class-A amplifier manufactured using the refractory SAG process

The authors describe the design, fabrication, and test results of a C-band single-chip GaAs monolithic microwave integrated circuit (MMIC) class-A amplifier manufactured using a multifunctional self-aligned gate (MSAG) process. The amplifier demonstrates a 10-W power output (0.625 W/mm power density) at 5.5 GHz with an associated gain of 5 dB and a power-added efficiency of 36%. The average functional yield of the IC is above 70%. This excellent performance is attributed to an accurate model for 4-mm FETs, the IC design method used, simple circuit topology, and high-yield, high-performance MSAG processing. >

Salinity Effects on the Microwave Emission of Soils

Passive microwave remote sensing has been proposed as a method for measuring both surface soil moisture and soil salinity. Since both of these characteristics will vary over an area, it is important to know how information about one of them can be isolated from the remotely sensed data. Water in the soil changes the microwave dielectric constant, which in turn changes the emission. Several dielectric mixing models have been developed and evaluated to describe soil-water-air systems. However, the concentration of salts in water also affects its dielectric properties in a well-known manner. When saline water is mixed with soil, the dielectric properties of this mixture will be different from those of a pure water and soil mixture. Although there are a few theories available to describe this process, very little verification of these theories has been done. In this study, a series of controlled field experiments were conducted using truck-mounted L-and C-band microwave radiometers. Experiments were designed to develop a data set that isolated the effects of salinity and soil moisture. This data set was used to evaluate the importance of each variable and to test proposed dielectric mixing models. The mixing models explained the observed data trends and range of values; however, the observed effects of salinity were not as large as predicted by the models. These differences may be related to model structure or field sampling problems. Variation in profile properties near the surface may also introduce some error.

Direct fibre-optic transmission of entire microwave satellite antenna signals

The entire 500 MHz bandwidth multicarrier C-band microwave signal spectrum from a satellite antenna is transmitted over low-loss optical fibre. The optical system introduces 1dB or less of degradation for both low-spectral-density QPSK signals and high-spectral-density FM video signals present in typical satellite transmission systems. For the video signals, the signal/noise ratio after AM conversion was reduced from 56 dB to 55dB.

Long distance fiber-optic transmission of C-band microwave signals to and from a satellite antenna

We demonstrate here the use of high-speed semiconductor lasers and detectors with low loss optical fiber for the transmission of the 500-MHz C-band microwave signal spectrum to and from a satellite antenna. The optical system has low attenuation and large band, width, so the microwave signals can be transmitted directly at the microwave frequency (4 or 6 GHz) over 20 km of fiber without regeneration or qualization. The optical system introduces ≈ 1 dB or less of degradation for both low spectral density QPSK signals and high spectral density FM video signals present in typical satellite transmission systems. For the video signals, the signal to noise after AM conversion was reduced from 56 to 55 dB. The microwave drive level to the laser must be significantly larger (typically > -10 dBm) than the intensity noise of the laser, yet small enough (typically < 10 dBm) to reduce the intermodulation distortion signals to an acceptable level. The laser bias current must be several times threshold so that the resonance frequency is beyond the frequency band of interest (4-6 GHz in this case). A flat modulation response is then obtained, and the intensity noise and intermodulation levels are low.

Passive Microwave Spectral Emission from Saline Ice at C-Band During the Growth Phase

This paper focusses on microwave radiometer measurements of the emission from saline ice as a function of ice thickness. The instrument used is a C-band stepped-frequency microwave radiometer (SFMR) that can be tuned to operate at any center frequency from 4 to 8 GHz at a bandwidth of 100 MHz. The measurements were undertaken at a facility constructed by the U. S. Army Cold Regions Research and Engineering Laboratory, which was specifically designed to satisfy remote-sensing requirements. In addition to presenting the data, a simple theory is developed to explain the experimental results in terms of the relevant electromagnetic parameters; namely, the complex dielectric constant and thickness of the ice.

Aerospace: Landing aircraft under poor conditions: Time-reference scanning beams characterize the all-weather microwave landing system that will replace present systems

Describes the principle of the time-reference scanning-beam microwave landing system (TRSB MLS) which is a system approach to the landing-guidance problem, it can meet a wide variety of diverse-performance, economic, and safety requirements and still supply a universal airborne receiver-processor able to operate with all ground systems. MLS can achieve these objectives because of two major factors: the choice of an operating frequency in the microwave C-band (5 GHz), and the design of its signal format.

Memory-correlator cells employing acoustically induced charge hologram in piezoelectric semiconductors

Memory-correlator cells operated in the c-band microwave frequencies, employing the scheme of the acoustically induced charge hologram, are described. The cell structure is a quasi-TEM mode resonant circuit built on the piezoelectric crystal, such as CdS. The structure combines the circuit and the storage media together. The experimental device is able to store a 7-bit signal in a volume of 3.10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

Observation of Microwaves Mixing in Air Glow Plasma

An experiment on the generation of X-band heterodynes due to mixing of C-band microwave and S-band microwave in an air glow plasma is reported. The measured mixing coefficient agrees with the predictions based on the kinetic theory.

Hyperfine interactions in the gas-phase E.P.R. spectra of35ClO (2Π3/2) in theJ= 5/2 andJ= 3/2 levels

Gas-phase E.P.R. spectra of 35ClO have been measured accurately both in the J=5/2 and J=3/2 rotational levels, using C-band (4·4 GHz) and X-band (9·4 GHz) microwaves, respectively. Special attention has been paid to separate the spectral lines of 35ClO from those of 37ClO. Analysis of the spectra has resulted in the simultaneous determination of the hyperfine parameters h and b and, when combined with a-(b+c)/2 obtained by microwave spectroscopy, the hyperfine parameters a, b and c are all determined. Molecular constants which describe the distribution of the unpaired electron around the chlorine nucleus are derived from them. The molecular g values of the rotational levels indicate the mixing of the 2Π state both with the 2Σ+ and with the 2Δ electronic excited states.