6 research outputs found
Electromagnetic Modeling of the Propagation Characteristics of Satellite Communications Through Composite Precipitation Layers, Part II: Results of Computer Simulations
A versatile Propagation Simulation Program (PSP) is developed to assess the degrading effects caused by the concurrent occurrences of an arbitrary mixture of ice plates and needles, melting snow and raindrops which may impede the reliability of dual-polarized satellite communications systems carrying independent channels on a single radio path. Specifically, results are presented for the Cross Polarization Discrimination (XPD) due to ice and rain, differential attenuation, Da, and differential phase shift, Df, due to rain and average specific attenuation, a, and phase shift, f , due to the melting layer at hitherto unconsidered frequencies. The inclusion of an ice-cloud medium is found to possess significant effects on rain-induced XPD even for low ice concentrations, particularly at low fade levels. The relative contribution of the melting layer on rain-induced attenuation is extensively studied for frequencies from 1 to 100 GHz and rain rates below 20 mm/h
Antenna polarisation adjustment for microstrip patch antennas using parasitic elements
A novel and simple approach to adjust the polarisation properties of a microstrip patch antenna in the entire axial ratio (AR) range is proposed. The proposed antenna consists of a radiating patch and a parasitic strip separated into two parts, and the separated strip is placed at the outer perimeter of the patch for capacitive coupling. This structure enables the antenna to induce opposite-direction currents on the strip, which allows flexible polarisation adjustment by moving the separated positions of the strip. For evaluation, two antennas with linear and circular polarisations are fabricated, and their performance is measured in a full anechoic chamber. The results prove that the proposed approach is suitable for flexible AR adjustment without a significant degradation of the matching characteristics and the design complexity
Electromagnetic Modeling of the Propagation Characteristics of Satellite Communications Through Composite Precipitation Layers, Part1: Mathematical Formulation
A systematic and general formulation of a Propagation Simulation Program (PSP) is developed for the coherent field of microwave and millimeter wave carrier signals traversing intermediate layered precipitation media, taking into account the random behavior of particle size, orientation, shape and concentration distributions. Based on a rigorous solution of the volumetric multiple-scattering integral equations, the formalism offers the capability of treating the potential transmission impairments on satellite-earth links and radar remote sensing generated by composite atmospheric layers of precipitation in conjunction with the finite polarization isolation of dual-polarized transmitting and receiving antennas. A multi-layered formulation is employed which encompasses an ensemble of discrete particles comprising an arbitrary mixture of ice crystals, melting snow and raindrops that may exist simultaneously along satellite-earth communication paths
Antennas
The basic purpose of a global navigation satellite
system (GNSS) user antenna is the reception of
navigation signals from all visible GNSS satellites.
Transmit antennas onboard the GNSS satellites,
on the other hand, are quite different and employ
large antenna arrays to create high-gain
global beams illuminating the entire surface of
the Earth.
This chapter presents different design options
for GNSS antennas operating in the L-band of the
radio frequency spectrum. It starts with a brief discussion
of key requirements for the GNSS receiving
antenna, where several design parameters are introduced
and explained. Thereafter, antennas of
different design technologies suitable to GNSS are
explored and discussed in detail. Following the
introduction of major antenna candidates, different
variants for specialized requirements, such
as the small form factor or multipath mitigation
are presented. Complementary to receiving antennas,
the design of antenna arrays for signal
transmission on the GNSS satellites is presented
next, along with a discussion on specific antennas
employed on the Global Positioning System
(GPS), Galileo, Global’naya Navigatsionnaya Sputnikova
Sistema (GLONASS) and BeiDou satellites.
Finally, a comprehensive discussion on antenna
measurements and the performance evaluation is
provided