Large Earth Station Research Articles

The development of a model to estimate the bistatic transmission loss associated with intersystem interference

This paper presents a new method for evaluating transmission loss, which is a key factor used in determining the impact of interference between terrestrial radio relay systems and Earth-satellite systems operating at the same frequency. The current model used by the CCIR was developed in the early 1970's when system packing density was low and large earth station antennas allowed the consideration of narrow beam approximations, resulting in a small common volume of intersection of the two beams. The recent increase in microwave communications traffic and improvements in technology have meant that smaller earth station antennas, including very small aperture terminals (VSATs), can be employed and hence the model requires revision. Results from the new model proposed are compared with two experimental geometries and good agreement is found.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Twenty years of international satellite communication

This paper reviews the development of international satellite communications over the past two decades. To date over 100 satellites have been launched to provide both domestic and overseas commercial (i.e., non‐military) communications services and this paper largely confines itself to describing the technical developments involved in creating the INTELSAT system which are representative of the field as a whole. INTELSAT, is an international organization established in 1964 to provide overseas communications. It has developed a global system designed to provide (1) a high degree of connectivity and (2) a large communications capacity. Connectivity has been achieved using relatively broad (albeit “shaped”) satellite antenna patterns permitting earth stations in many countries that are illuminated by the same beam to be interconnected. This desirable attribute has, however, required the use of large earth stations and one future technical direction is likely to entail using satellites that generate narrow pencil beams permitting the use of smaller earth stations; on‐board switching will then be required to restore connectivity between beams. A large capacity has been achieved through the use of “frequency reuse,” i.e., techniques to utilize the C‐band frequencies assigned for satellite communications several‐fold. This has been accomplished through satellite designs that employ isolated antenna beams to illuminate different parts of the earth and/or beams that view overlapping parts but employ opposite senses of (circular) polarization. Associated with this approach have been efforts to use the assigned bands as efficiently as possible through “channelization,” i.e., subdividing them into frequency intervals, each of which is served by a transponder amplifier designed to yield minimum interference with its neighbors. The paper concludes with a brief discussion of the likely trends in the design of satellite systems as these evolve in competition with fiber‐optic cables.

Scattering induced microwave scintillations from clear air and rain on earth space paths and the influence of antenna aperture

The variance and spectrum of amplitude scintillations due to scattering in both turbulent clear air and rain, are investigated. Included are the important aspect of antenna aperture smoothing with special emphasis on earth-space paths and the equations derived are applicable to system design and remote sensing. A detailed comparison with published experimental results is carried out and the agreement found is good. Two approaches are described in detail: 1) the point receiver classical wave scattering results are modified to include aperture effects, 2) a scalar scattering cross-section approach is combined with the radar equation and the results derived are similar to those of 1). In addition, approach 2) includes the case of rain. Among the results found it is shown that because the scintillation intensity depends on the ratio between the antenna diameter and the diameter of the Fresnel zone in the turbulent region, low elevation paths counteract the tendency to smoothing by large earth station antennas and the scintillations observed remain large. Also pure scattering induced rain scintillations, even in the millimeter region, are in general reduced to an almost negligible level due to aperture smoothing even though for a theoretical point receiver they would be very intense. The time variability of rain attenuation and its polarization dependence as a source of apparent scintillations are also discussed.

Efficient space segment utilization in satellite data networks

A generalized approach to the efficient utilization of the space segment in multicarrier per transponder applications is presented. Based on the concept of normalized satellite link densities, the conditions required to fully utilize the available transponder resources (power and bandwidth) are derived. These conditions are applied to the design of satellite data networks comprising a large number of stations of various sizes. The design approach is based on the idea of determining the ground segment configuration that ensures that the satellite links to small earth stations (power-limited links) and those to large earth stations (bandwidth-limited links) are balanced in such a way, that both the transponder power and the bandwidth are fully utilized. An example of the design of a simple data network using this technique is shown.

Maintenance-Free Cryogenic Noise Standard for Continuous Antenna Operation Independent of Elevation Angle

Current stringent demands for high-accuracy measurements in low-noise technology have created a need for cryogenic noise standards, usually of liquid refrigerant type. However, implementation of this type of standard in large earth stations imposes problems where measurements must be performed for arbitrary antenna inclination angle and during active communication phase between a satellite and an earth station. A cryogenic noise standard utilizing helium gas refrigerant has been developed, installed, and made operative for continuous operation with minimal maintenance service without the aforementioned constraints.