Far-field retarded potentials — formula, phase delay t−R/c, antenna radiation
Far-field retarded potentials: evaluate sources at delayed time t−R/c so radiated fields carry the correct phase — formulas for antenna / array radiation.
far field
Near-field – far-field : Where is the boundary ?
Antenna models — reading order Maxwell’s equations Retarded potentials Near-field / far-field boundary (this article) Far-field retarded potentials Array pattern multiplication Dipole power gain patterns Introduction Antenna fields change character with distance: reactive storage near the element, Fresnel diffraction at intermediate range, and spherical-wave radiation farther out. Link-budget and pattern formulas almost always assume that … Read more
Fresnel zones
An important consideration for propagation models are the existence of objects within what is called the first Fresnel zone. Fresnel zones, referenced in Figure 1 are ellipsoids with the foci at the transmitter and the receiver, where the path length between the direct path and the alternative paths are multiples of half-wavelength ($latex \lambda/2$). Rays … Read more
Modeling diffraction loss : Single knife-edge diffraction model
Modeling diffraction loss Propagation environments may have obstacles that hinder the radio transmission path between the transmitter and the receiver. Idealized models for estimating the signal loss associated with diffraction by such obstacles are available. The shape of the obstacles considered in these model are too idealized for real-life applications, nevertheless, these models can serve … Read more
Two-ray ground reflection model — path loss with LOS and ground bounce
Two-ray ground reflection: direct plus ground-reflected rays, breakpoint distance, and why path loss approaches 40 dB/decade at large range.
Hata Okumura model for outdoor propagation
Outdoor propagation models involve estimation of propagation loss over irregular terrains such as mountainous regions, simple curved earth profile, etc., with obstacles like trees and buildings. All such models predict the received signal strength at a particular distance or on a small sector. These models vary in approach, accuracy and complexity. Hata Okumura model is … Read more
Large scale propagation models – an introduction
Radio propagation models play an important role in designing a communication system for real world applications. Propagation models are instrumental in predicting the behavior of a communication system over different environments. This chapter is aimed at providing the ideas behind the simulation of some of the subtopics in large scale propagation models, such as, free … Read more
Friis free-space path loss — formula, assumptions, and dB form
Friis transmission equation and free-space path loss: $latex (4\pi d/\lambda)^2$, dB form, assumptions, and when to move to log-distance or two-ray models.