Antennas, Transmission Lines, Matching Networks

Abstract

AbstractThis chapter on antennas starts with Maxwell’s equations that describe electromagnetic waves. Antenna is the key element that transmits or receives radio waves. With that introduction, the topic of transmission line is elaborated taking both coaxial cable and waveguide as examples. It describes the conditions necessary to allow the radio wave to move along this conducting medium and how the antenna must interface to it in order to radiate the wave.This is followed by key parameters of the antenna, what they mean and how they affect the quality of sending the waves over the air. A key understanding includes the physical motion of waves can be seen in a video—that dates back to Bell Labs explanation in 1950s on how waves of different types behave. Radiation pattern is perhaps the most vital characteristic of an antenna. How this is measured to create a 3D pattern, how the data sheets typically portray radiation in 2D with elevation and azimuth diagrams are described with examples. The video in reference [14] provides a view of how this complex measurement is done to generate radiation pattern.This is followed by types of antennas—by listing many popular types and elaborating on a some of them. The intent is to describe how the antenna design process works, how to control radiation patterns, how are they visualized during design. The direction of antenna feed (in line or orthogonal) makes considerable difference in radiation pattern—this is highlighted using helical antenna where the pattern becomes completely different depending on the type of feed. A unique antenna is the radiating cable that works as an antenna but is actually a coaxial cable with holes punched in its outer conductor—it is meant for propagation within tunnels or narrow passages.Since the late 1960s, Monolithic Microwave Integrated Circuit (MMIC) broght a great impact on the design of radio communication, particularly in the upper microwave bands. Design based on MMIC and strip line with antenna printed along with feed and balancing circuit is described to show how the technology progressed. This process of printing antennas lends itself to customized characteristics and radiation patterns, some examples are shown to illustrate this.Perhaps the biggest driver for antenna in recent times is the smart phone. Requiring multiple antennas within a small package, it forces RF engineers to provide solutions known as RFFE (RF Front End) that takes care of all antennas and their interconnections. Such solutions result in a better smart phone that works well without compromising quality of signal and performance.With integration of multiple technologies in compact packages, the issue of interference from nearby devices and how each wireless device could become an interferer, are reviewed. Millimeter wave band ushered a new role to antennas. To keep components small and accurate in terms of beam forming, antenna is closely integrated with active components in the form of matrix array behind the panel antenna. The modern panel antenna is a passive element on one side but acts as the base for multiple layers of integrated circuits to make up RFFE. Such antenna matrix stacked together as arrays are expected to offer 5G services in every neighborhood.