Showing papers on "Ka band published in 1979"

The Ka-Band Communication Systems of the Lincoln Experimental Satellites LES-8 and LES-9

Abstract: Introduction L INCOLN Experimental Satellites LES-8 and LES-9 are a pair of experimental communication satellites designed and built to operate in a synchronous ecliptic orbit and to communicate on a crosslink from satellite to satellite as well as with surface terminals. At synchronous-orbit altitude, each satellite has a groundvisibility area about 8000 miles in diameter. With crosslink communication between two satellites spaced thousands of miles apart, a single pair of satellites could provide communications among terminals anywhere in an area covering more than 3/4 of the surface of the Earth. Communication links are possible at both UHF and Ka-band at approximately 37 GHz. Figure 1 shows a cutaway drawing of LES-9. The side facing the Earth is the forward platform, which is used for mounting and precision alignment of the Ka-band antennas and the Earth sensors. The Ka-band receiver diplexer filters and front ends are mounted as close as possible to the diplexer polarizer mounted on each antenna. The Ka-band transmitter power amplifiers are mounted on sections of the internal decagon adjacent to the forward platform to minimize the length of the waveguide runs to the antennas. LES-8 and LES-9 each utilize two independent Ka-band communication systems (see Fig. 2). The Ka-dish system uses a fixed paraboloidal reflector in conjunction with a steerable flat reflector to provide a narrow beam, tracking antenna for crosslink or uplink/downlink communications. The Ka-horn system includes a fixed horn to provide a wide-beam antenna coverage. Local oscillator requirements for both systems are provided by a single Ka-band local oscillator. Each receiver subsystem features a broadband low-noise mixer utilizing Schottky-barrier diodes to achieve a typical system noise figure of less than 8 dB. Each transmitter includes an array of solid-state amplifiers which utilize IMPATT diodes, and delivers 0.5 W of power to the antenna. The transmitter signal is modulated at a lower frequency and is upconverted to Kaband using a mixer similar to that used in the low-noise receiver. This paper will discuss the Ka-band systems carried on LES8 and LES-9, which were built to demonstrate component and

Simultaneous Observations ofCloudandPrecipitation Particles withVertically Pointing X-Bandand Ka-Band Radars

Abstract: The backscattered energy received ataradar fromacloud isproportional toseveral parameters whichinclude peakpower, an- tenna constants, andA-4, whereXistheradar wavelength. Thewave- lengths ofweather radars varyfromcentimeters tomillimeters. In theory, allsuchradars should beable todetect bothcloud andprecipi- tation particles but, because ofpractical limitation onantenna size and poweroutput, onlytheshortest wavelength weather radars aresensitive tothefuli range ofsizes covered bythese particles (0.01 mm toover 5mm indimensions) whichcanproduce echoes ranging over160dB. Simultaneous observations ofcloud andprecipitation systems withX- band(3-cm wavelength) andKa-band (0.86-cm wavelength) radars pro- vide theneeded realizable dynamic range. Simultaneous measurements ofthis typearedescribed andareshowntoreveal thelocations within clouds whereprecipitation isdeveloping andthegrowth ofprecipitation withfall distance, aswelasproviding continuous measurements of cloud topheights. Theinadequacy ofX-band radars tomeasure cloud topheights isdemonstrated.

Simultaneous Observations of Cloud and Precipitation Particles with Vertically Pointing X-Band and Ka-Band Radars

Abstract: The backscattered energy received at a radar from a cloud is proportional to several parameters which include peak power, antenna constants, and ?-4, where ? is the radar wavelength. The wavelengths of weather radars vary from centimeters to millimeters. In theory, all such radars should be able to detect both cloud and precipitation particles but, because of practical limitation on antenna size and power output, only the shortest wavelength weather radars are sensitive to the full range of sizes covered by these particles (0.01 mm to over 5 mm in dimensions) which can produce echoes ranging over 160 dB. Simultaneous observations of cloud and precipitation systems with X-band (3-cm wavelength) and Ka-band (0.86-cm wavelength) radars provide the needed realizable dynamic range. Simultaneous measurements of this type are described and are shown to reveal the locations within clouds where precipitation is developing and the growth of precipitation with fall distance, as well as providing continuous measurements of cloud top heights. The inadequacy of X-band radars to measure cloud top heights is demonstrated.