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     

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     

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     

Performance of a modified feedback loop adaptive array with TVROsatellite signals

Performance of an experimental adaptive antenna array system is evaluated using television receive-only (TVRO) satellite signals. The experimental system is a sidelobe canceller with two auxiliary channels. Modified feedback loops are used to enhance the suppression of weak interfering signals. The modified feedback loops used two spatially separated antennas, each with an individual amplifier for each auxiliary channel. Thus, the experimental system uses five antenna elements. Instead of using five separate antennas, a reflector antenna with multiple feeds is used to receive signals from various TVRO satellites. The details of the earth station are given. It is shown that the experimental system can null up to two signals originating from interfering TVRO satellites while receiving the signals from a desired TVRO satellite     

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     

TOPEX ionospheric height correction precision estimated fromprelaunch test results

Free electrons in the ionosphere will lengthen the electromagnetic path between the TOPEX/Poseidon altimeters and the ocean surface. The path delay is proportional to the total electron content of the ionosphere along the line of sight between the altimeter and the surface. Since these ionosphere delays are also inversely proportional to frequency squared, the nearly simultaneous use of both Ku-band (13.6-GHz) and C-band (5.3-GHz) TOPEX altimeters permits a first-order correction for ionospheric delays. Using results from prelaunch ground testing of the TOPEX satellite altimeters, the authors present the residual height tracking noise after application of the ionosphere correction algorithm. Results are presented as function of ocean significant wave height and for both the 320-MHz and 100-MHz bandwidth of the C-band altimeter     

Code division multiple access versus frequency division multipleaccess channel capacity in mobile satellite communication

A comparison between frequency-division multiple access (FDMA) and code-division multiple access (CDMA) when both methods operate in the mobile satellite communication environment is presented. The mobile satellites under consideration use multiple beams or scan beam antennas and employ frequency reuse of the allocated L-band frequency spectrum. Because CDMA can better absorb Doppler and multipath effects and permits higher rate coding, it appears in general, with practical considerations set aside, to be the more capable system     

Evolution of the large Deep Space Network antennas

The evolution of the largest antenna of the US NASA Deep Space Network (DSN) is described. The design, performance analysis, and measurement techniques, beginning with its initial 64-m operation at S-band (2295 MHz) in 1966 and continuing through the present Ka-band (32-GHz) operation at 70 m, is described. Although their diameters and mountings differ, these parabolic antennas all employ a Cassegrainian feed system, and each antenna dish surface is constructed of precision-shaped perforated-aluminum panels that are secured to an open steel framework     

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     

Offset Cassegrain Earth Station Antenna for the Japanese Domestic Satellite Communication System

Offset reflector antennas have advantages for communication systems because they are not severely subject to blocking. Difficulties mainly arising from structual asymmetries have inhibited the realization of an offset reflector antenna with a large aperture for commercial use. This paper describes the design of an offset Cassegrain earth station antenna for the Japanese domestic satellite communication system. Antenna measurements showed 76 and 69 percent aperture efficiencies at 20 and 30 GHz, respectively, less than -20 dBi wide angle directivity and an 18 K noise temperature in operating conditions. Performances are far superior to conventional axisymmetrical earth station antennas. The antenna was reassembled on a telephone office building after the measurements. The antenna gain was reconfirmed there, using the sun as a radio frequency source. Experiments show that the earth station antenna and a terrestrial antenna can be placed on the same building without serious interference.     

The transmission capacity of multibeam communication satellites

The transmission capacity which can be provided by a geosynchronous multiple-beam satellite employing frequency reuse is studied. Like all communication channels, satellite capacity is limited by available power, transmission bandwidth, and noise. In addition, factors peculiar to satellite links include cochannel interference among neighboring beams, channel nonlinearity, nonuniformly distributed traffic, and for satellites operating at frequencies above 10-GHz, rain attenuation. The effects of these factors upon the capacity of a satellite system are examined in detail. Results for a 12/14-GHz system with assumed satellite parameters compatible with a space shuttle launch and small 5 m earth station antennas show that a capacity of about 30 Gbit/s can be provided if the unavailability due to rain outage is no greater than 0.1 percent, and that about 10 Gbit/s can be provided for an unavailability no greater than 0.01 percent. Efficient utilization of the geosynchronous arc is also explored, and current trends in communication satellites are discussed.     

卫星固定站天线控制系统改造的探讨

卫星固定站是指在特定站点的卫星通信地球站,通常是通过同步轨道通信卫星进行卫星业务的通信。卫星固定站大多使用的是2.4 m-7.3 m静中通天线,早期的工程施工中大部分天线未安装自动控制系统,靠手动控制驱动电机进行对星。文章对Ku频段卫星固定站天线控制系统改造进行探讨,提出更好的改造方案。     

Dual-chip GaAs monolithic integration Ku-bandphase-locked-loop microwave synthesizer

Two novel multifunction monolithic chips, GaAs microwave monolithic integrated circuit (MMIC) and large-scale integration (LSI) chips, have been developed to realize an extremely small and lightweight microwave synthesizer. The MMIC includes a voltage-controlled oscillator, a dual-output buffer amplifier, a balun, and dynamic/static prescalers. To integrate these functions on a single chip, each circuit has been drastically reduced in size by utilizing a uniplanar MMIC configuration. The LSI includes a dual-modulus prescalar, programmable counters, and a phase/frequency comparator. By incorporating these two monolithic chips in the structure, a Ku-band microwave synthesizer has been fabricated in an 11-mm×23-mm flat package. The synthesizer to which these multifunction chips were applied had a tuning range broader than 1 GHz in the Ku-band with a flatness within 2 dB_pp. In spite of low-Q monolithic circuitry, single-sideband (SSB) phase noise was as low as -70 dBc/Hz     

Comparisons between a shaped and nonshaped small Cassegrain antenna

An X-band 8.5-ft brassboard antenna system was designed and developed which required a 70% total antenna efficiency and a 25 dB isolation between the circularly polarized transmit and receive ports. To maximize the aperture efficiency, a shaping technique was used to generate a specially contoured subreflector and main reflector. To reduce cost, a configuration was chosen such that the shaped main reflector could be matched with negligible phase error using a commercially available paraboloid. The antenna gain of this shaped system with an electrically small subreflector (10.7 λ) is 0.75 dB higher than that of a conventional system using the same paraboloid and a matching hyperbolic subreflector. Measured results demonstrated that even for a small system the antenna performance can be appreciably improved at low cost by using a shaped subreflector     

Antenna selection in a multisector packet radio system

To improve performance on the inbound (mobile-to-base-station) channel of a packet radio system consisting of a base station and a number of mobile users, the area around the base station is divided into M sectors. Signals originating from users in different sectors are received by different directional antennas at the base station. It is shown that, if the number of receivers at the base station is less than M, the selection of the antennas to be connected to the receivers becomes an issue. A number of antenna selection schemes are compared for three different channel models, assuming an ideal antenna pattern. It is found that the scheme that selects the antennas with the largest received signal powers is nearly optimum. The effects of a more practical nonideal antenna pattern are discussed     

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     

A personal communications network using a Ka-bandsatellite

The feasibility of a personal communications network using portable terminals that can provide 4.8 kb/s voice communications to a hub station via Ka-band geosynchronous satellite has been investigated. Tradeoffs are examined so that the combined system of hub and gateway earth stations, the satellite, and the personal terminals can provide a competitive service in terms of cost, availability, and quality. A baseline system that uses a spacecraft with approximately 140 spot beams to cover the contiguous US (CONUS) and 5 W power amplifiers in each beam is described. Satellite access in both the forward and return directions uses frequency-division multiple-access/code-division multiple-access (FDMA/CDMA) with a chip rate of 2.5 Mchip/s     

Prelaunch performance of the NASA altimeter for the TOPEX/Poseidonproject

The TOPEX/Poseidon radar altimeter satellite applies advances in remote sensing instrumentation to reduce long wavelength measurement errors to dramatically lower levels. The TOPEX altimeter measures the range to the ocean surface with 2-cm precision and accuracy through the use of both Ku- and C-band radars, a high pulse repetition frequency, an agile tracker, and absolute internal height calibration. Dual pulse bandwidths for both frequencies make it possible to quickly acquire the surface and begin tracking after crossing the land/ocean boundary. The altimeter requirements and the elements of the altimeter design that have resulted in meeting these requirements are presented. Prelaunch test data, based on the use of a radar altimeter system evaluator to simulate the backscatter from the ocean surface, are presented to demonstrate that the TOPEX altimeter will meet these requirements and provide the data necessary to the understanding of basin scale mean circulation