Microstrip linear slot array antenna for X-band

The X-band microstrip slot antenna array is described as an attempt to achieve moderate bandwidth and overcome the problems of radiation from microstrip feed lines and surface waves in the dielectric. The discussion covers development of a mathematical simulation that computes the radiation pattern of a single microstrip slot and the feeding microstripline; construction of a uniform broadband microstrip slot antenna array; development of a mathematical simulation that computes the radiation pattern in the H- and E-planes; and investigation of the mutual coupling between the slots. A comparison is made between computed and measured results at X-band frequencies     

Interference effects on Space Station Freedom and Space Shuttleorbiter Ku-band downlinks

The Space Shuttle orbiter (SSO) Ku-band single access return (KSAR) link and the Space Station Freedom (SSF) KSAR link via the tracking and data relay satellite system (TDRSS) use the same carrier frequency. The interference between spacecraft is minimized by opposite antenna polarizations and by TDRSS antenna beam pointing, but if the SSF and SSO are in close proximity, it is expected that mutual interference will be significant. It is shown that a simplified analytical approach will yield adequate accuracy for the expected range of operating conditions. Relative degradation in bit-energy-to-thermal-noise power spectral density ratio to achieve a 10^-5 coded bit-error probability is determined to be 4 dB for the Ku-band SSO-to-TDRS I-channel return link with a 4.5-dB effective signal-to-interference total power ratio (S/I) when the Ku-band SSF-to-TDRS return link interferes. For the Ku -band SSF-to-TDRS return link, both analysis and simulation results yield a relative signal degradation of 0.4 dB at the effective S/I=21.6 dB     

An integrated mobile satellite broadcast, paging, communicationsand navigation system

The design of an integrated mobile satellite broadcast, paging, communications, and navigation system is described. Ku-band RadioSat ground stations will broadcast digital audio signals and data packets (including alphanumeric pages and group cells) to mobiles through a satellite to be launched in 1993. Each mobile radio will simultaneously receive L-band digital audio and data broadcasts from the satellite and L-band navigation broadcasts from the Global Positioning Systems (GPS) through a common omnidirectional mobile antenna and receiver front end. RadioSat mobile radios will use GPS broadcasts and differential corrections sent through the satellite to navigate with 2-m accuracy. With optional transmitters, RadioSat mobile radios can support two-way voice and data communications     

The SIR-C/X-SAR synthetic aperture radar system

The SIR-C/X-SAR synthetic aperture radar, a three-frequency radar to be flown on the Space Shuttle in September 1993, is described. The SIR-C system is a two-frequency radar operating at 1250 MHz (L-band) and 5300 MHz (C-band), and is designed to get four-polarization radar imagery at multiple surface angles. The X-band synthetic aperture radar (X-SAR) system is an X-band imaging radar operating at 9600 MHz. The discussion covers the mission concept; system design; hardware; RF electronics; digital electronics; command, timing, and telemetry, and testing     

Calibration of the CCRS airborne scatterometers

A series of experiments and associated analyses which were designed to lead to an end-to-end calibration of the Canada Centre for Remote Sensing (CCRS) fanbeam scatterometers are described. The method followed was originally introduced in 1984 by A. Yizhar et al. for the Ku-band scatterometer at one incidence angle. This work was extended to yield a full calibration for the Ku-band and C -band scatterometers over the complete range of incidence angles accessible to the instruments. An array of 12 trihedral corner reflectors was deployed in a grassy field near Ottawa. The CCRS CV-580, equipped with two scatterometers, repeatedly overflew the array collecting radar replicas of the targets proportional to the unknown two-dimensional antenna pattern. Data from inertial navigation systems and aerial photographs from a Wild RC-10 mapping camera were used to determine the exact track of the aircraft during the acquisition. This data, with a field survey, alloyed the reduction of the scatterometer data from the reflector array to yield the unknown antenna pattern of the instruments. The cross-polarized antenna patterns were then deduced from the like-polarized results. The results show consistency within 0.5 dB and overall calibration accuracy is estimated to be better than 1 dB     

A new method for obtaining antenna gain from backscattermeasurements

A method is presented for determining the gain of an antenna from analysis of backscatter data of the antenna. This approach is different from those which have been presented in the past because it accounts for the presence of resonances which can occur in the antenna during a backscatter measurement. In particular, this type of resonance appears in the backscatter measurement of symmetric reflector antennas. This technique is applied to determine the gain of a Ka-band Cassegrain antenna and an X-band prime focus-fed antenna     

FETs and HEMTs at cryogenic temperatures-their properties and usein low-noise amplifiers

Typical DC characteristics and X-band noise parameters are presented and qualitatively correlated wherever possible with other technological or experimental data. While certain general trends can be identified, further work is needed to explain a number of observed phenomena. A design technique for cryogenically cooled amplifiers is briefly discussed, and examples of realization of L-band, C -band, X-band, and K-band amplifiers are described. The noise temperature of amplifiers with HEMTs in input stages is usually less than half of that for all-FET realizations, setting new records of performance for cryogenically cooled, multistage amplifiers     

Wet antenna effect on VSAT rain margin

The contribution of wet antennas to the antenna signal path losses in a VSAT environment is treated theoretically. The current commercial VSAT systems operating in either C-band or Ku-band generally have their remote terminal antenna reflectors and the antenna feed horn radomes coated with hydrophobic materials. The aim is to prevent the antenna and radome surfaces from becoming wet during a rainfall. This precaution relieves the burden of added rain margin necessary on the link budget. The magnitude of the propagation loss when the antenna reflector and the antenna feed horn radome surfaces are wet is determined. The results can indicate whether the expense of applying and maintaining the hydrophobic materials on the VSAT remote antennas and radomes is justified under specific loss conditions     

Combating sun outage in satellite television distribution systems

Two methods of sun outage avoidance in satellite television transmission are discussed. Each method requires two satellites and dual-beam antennas. The two C-band satellites transmit identical programs at the time when the sun outage period occurs. The separation of the spacecraft is dependent on the dual-feed earth station antenna size. For large television receive-only antennas, the separation must be small; for small antennas, or antennas with large beamwidths, the satellite separation can be large. If the separation is larger than 8° on the geosynchronous arc, only one transmit station is required to transmit program information. Scaling this system for Ku-band use is then considered. It is concluded that in a Ku-band direct-broadcasting system with earth station antenna diameters of 1-m and below, the rise in noise temperature due to sun outage is not significant and can be overcome by a modest amount of system margin, equivalent to that normally provided against rain fades     

Effects of solar transit in Ku-band VSAT systems

Behavior of networks of very small aperture satellite terminals (VSATs) operating at Ku band during the solar transit period, is compared to more traditional C or Ku-band satellite networks. Based on analyses and experiments, it is explained why solar transit outages are rarer in Ku-band VSAT systems than conventional satellite communications systems. In many cases, Ku-band VSAT systems will operate through periods of Sun transits without any significant increase in transmission error rates or incidences of link outages     

Microwave systems design for high-performance moving targetindicators in radars

Clutter cancellation of 65 dB and better is directly proportional to good radar stability, and since many hardware areas produce instabilities at various levels, the architecture of a radar requires special design considerations to support this high stability. The noise character and generation methods of these instabilities in the various hardware areas are described, and design solutions are given to eliminate them. Microwave delay line, a reliable, accurate method of measuring radar stability in L- and S-band radars, is described. The longest microwave delay line available for use at L -band and S-band frequencies is a 15-μs sapphire bulk acoustic wave (BAW) delay line. For higher-frequency radars, smaller delays must be used to keep the insertion loss down to a usable level. The question is raised as to the adequacy of this delay time to provide sufficient visibility for stability measurements of the stable noise. For transmitter measurements, it is adequate for the more common pulse widths, which are less than 15 μs. For LO measurements, the analysis shows that this delay does provide sufficient decorrelation for accurate LO noise measurements     

Ultralow-noise W-band pseudomorphic InGaAs HEMT's

Low-noise planar doped pseudomorphic (PM) InGaAs high-electron-mobility transistors (HEMTs) with a gate length of 0.1 μm for W-band operation are discussed. These devices feature a multiple-finger layout with air bridges interconnecting the sources to reduce gate resistance. The device exhibits a minimum noise figure of 2.5 dB with an associated gain of 4.7 dB at 92.5 GHz. This result demonstrates the feasibility of using PM InGaAs HEMTs for W-band low-noise receivers without the need for using lattice-matched InP HEMTs     

High-speed, 100+W RF switches using GaAs MMICs

A low-loss, inductive gate bias network structure which allows a very high stacking level of FET devices for high-power RF switching applications is reported. The design, implementation, and performance of S- and C-band SPDT switches based on this structure are described. Multiple GaAs MMIC chips integrated into a suspended-substrate hybrid circuit are used. At S-band, switch risetimes/falltimes of less than 40 ns and an RF power handling capability of 300 W CW have been demonstrated. This input signal level could be maintained during the switch state transitions (hot-switching), while being switched between the two output ports at rates of up to 500 kHz     

Calibrated imaging radar polarimetry: technique, examples, andapplications

The authors developed a calibration procedure for imaging radar polarimeters and applied it to a set of images acquired by the NASA DC-8 multifrequency radar system. The technique requires the use of ground reflectors of known cross-section for absolute calibration, that is, solution for σ⁰; however, the image data themselves can usually provide all information necessary for phase calibration and for antenna crosstalk correction. The accuracy of the approach, as measured by calculating the cross-section residuals of known targets in each calibrated scene, is on the order of ±1-2 dB at the P- and C-band, but improves to ±0.5 dB at the L-band. The authors present the results of applying this technique to radar scenes of lava flows of varying roughness, temperate and tropical rain forests, and ocean water surfaces. They also present several example applications which are feasible with calibrated data but which would be difficult to implement with uncalibrated data     

Estimation of surface roughness parameters from dual-frequencymeasurements of radar backscattering coefficients

A simple model was developed for estimating the surface roughness parameters of a bare soil field. The model uses a set of dual-frequency measurements of the field's radar backscattering coefficients, which can be matched to calculated results obtained with assumed values for the surface roughness parameters, as represented by the surface height standard deviation σ and its correlation lengths. Scatter plots of measured and calculated radar backscattering coefficients at the C -band (4.25-GHz) frequency versus those at L-band (1.5 GHz) show that it is feasible to estimate the surface roughness parameters using this technique. The estimated values for σ are in excellent agreement with those of measurements. However, there are discrepancies between the estimated and measured values for the correlation length L. For a very rough field, the geometrical optics model could be more appropriate for modeling the C-band data     

Circular polarization for remote sensing of precipitation:polarization diversity work at the National Research Council of Canada

The precipitation radar work carried out at Ottawa, Ontario, by the National Research Council of Canada (NRC), using dual-channel circularly-polarized radars, is described. This work, and concurrent work by NRC on weather clutter suppression for centimeter-wavelength military radars, included both theory and equipment developments. The discussion covers the early years (1956-66), the NRC Ku-band precipitation radar (1966-80), apparatus built and operated by NRC for scattering-matrix measurements, the NRC X-band precipitation radar (1981-6), and polarization switching and rotation studies     

X-band 0.5, 1, and 2 watt power amplifiers with markedimprovement in power-added efficiency

Very efficient X-band MESFET power amplifiers, showing greater power-added efficiency over a wider bandwidth than any X-band amplifiers of comparable output reported to date, are discussed. The amplifiers were designed with attention given to optimum bias, proper harmonic termination, and efficient power combining. These device and design issues are discussed, and a straightforward design method which achieved the increased levels of efficiency is described     

An X-band spacecraft transponder for deep spaceapplications-design concepts and breadboard performance

The design concepts and measured performance characteristics of an X-band breadboard deep-space transponder (DST) for future spacecraft applications are summarized. The DST consists of a double-conversion, superheterodyne, automatic phase tracking receiver, and an X-band exciter to drive redundant downlink power amplifiers. The receiver acquires and coherently phase tracks the modulated or unmodulated X-band uplink carrier signal. The exciter phase modulates the X-band downlink signal with composite telemetry and ranging signals. The measured tracking threshold, automatic gain control (AGC), static phase error, and phase jitter characteristics of the breadboard DST are in good agreement with the expected performance. The measured results show a receiver tracking threshold of -158 dBm and a dynamic signal range of 88 dB     

Dependence of radar backscatter on coniferous forest biomass

Two independent experimental efforts have examined the dependence of radar backscatter on above-ground biomass of monospecie conifer forests using polarimetric airborne SAR data at P-, L- and C-bands. Plantations of maritime pines near Landes, France, range in age from 8 to 46 years with above-ground biomass between 5 and 105 tons/ha. Loblolly pine stands established on abandoned agricultural fields near Duke, NC, range in age from 4 to 90 years and extend the range of above-ground biomass to 560 tons/ha for the older stands. These two experimental forests are largely complementary with respect to biomass. Radar backscatter is found to increase approximately linearly with increasing biomass until it saturates at a biomass level that depends on the radar frequency. The biomass saturation level is about 200 tons/ha at P-band and 100 tons/ha at L-band, and the C-band backscattering coefficient shows much less sensitivity to total above-ground biomass