1.9: Summary

Today six billion individuals regularly transmit information wirelessly using transmitters and receivers that can be smaller than an infants hand, contain trillions of transistors, and provide connectivity in nearly any location.

The history of radio communications is remarkable and nearly every aspect of electrical engineering is involved. The most important factor of all is that consumers are prepared to part with a large portion of their income to have untethered connectivity. This overwhelming desire for ubiquitous communication surprised even the most optimistic proponents of personal wireless communications. Wireless communication is now a significant part of every country’s economy, and governments are very involved in setting standards and protecting the competitiveness of their own industries.

The history of radio communications has led to the current mode of operation, allocating a narrow slice of the EM spectrum to one or a few users. This choice dictated the need for very stable oscillators and high-rejection filters, for example. The stability of oscillators in consumer products is a few hertz around \(1\text{ GHz}\), a few parts in a billion, a level of precision that is unrivaled for any other physical quantity in a manufactured device.

The RF spectrum is used to support a tremendous range of applications, including voice and data communications, satellite-based navigation, radar, weather radar, mapping, environmental monitoring, air traffic control, police radar, perimeter surveillance, automobile collision avoidance, and many military applications. A big trend is the virtual disappearance of analog radio and now the almost complete use of digital radio. Digital radio is much more tolerant to interference and can use a much smaller slice of the EM spectrum. Another big trend is the tremendous demand for EM spectrum resulting in appreciable use of the spectrum up to \(100\text{ GHz}\) and soon beyond that. Currently large parts of the spectrum are allocated for exclusive military use and there is pressure to reduce the spectrum allocated for government use of all kinds.

In RF and microwave engineering there are always considerable approximations made in design, partly because of necessary simplifications that must be made in modeling, but also because many of the material properties required in a detailed design can only be approximately known. Most RF and microwave design deals with frequency-selective circuits often relying on line lengths that have a length that is a particular fraction of a wavelength. Many designs can require frequency tolerances of as little as \(0.1\%\), and filters can require even tighter tolerances. It is therefore impossible to design exactly. Measurements are required to validate and iterate designs. Conceptual understanding is essential; the designer must be able to relate measurements, which themselves have errors, with computer simulations. The ability to design circuits with good tolerance to manufacturing variations and perhaps circuits that can be tuned by automatic equipment are skills developed by experienced designers.

Chapter 2 describes modulation methods and the ideas that led to being able to transmit many bits of data per hertz of bandwidth. High orders of modulation send many bits of information and the higher the order of modulation the more sophisticated the modulation and demodulation schemes must be. Transmitters and receivers that implement the modulation and demodulation methods and up-convert and down-convert, respectively, between the low frequency baseband information and the high frequency radio signals are described in Chapter 3. Antennas reviewed in Chapter 4 are the interface between electronic circuits and freely propagating EM waves. Directional antennas are essential to supporting many users by enabling frequency reuse of the EM spectrum in the same cell. The 1G through to 5G cellular systems are described in Chapter 5. In addition other microwave systems such as radar and WiFi are briefly described and their development has closely followed or just preceded that of cellular radio. The tremendous advances are the result of the synergistic development of system concepts and of digital and microwave hardware.