# 1.1: Introduction

- Page ID
- 40999

The universe has a speed limit, the finite speed of causality or \(c\), the speed of light, which is embodied in Maxwell’s equations and in the special theory of relativity. The result of this is that a cause, say a voltage, in one part of a circuit produces an effect, say a current, in another part of the circuit after a delay. When using circuits at low frequencies the impact of this delay is insignificant as the effect occurs long before there is even the slightest discernible change in the cause. However the delay is important at microwave and higher frequencies. Electromagnetic (EM) radiation travels \(30\text{ cm}\) in a nanosecond in free space. Thus a circuit operating at \(1\text{ GHz}\) that is \(1\text{ cm}\) across will just see an appreciable affect due to the finite speed of the EM signal which, of course, is how the voltage and current “communicate.” The impact will be more significant at higher frequencies and if the EM signal travels in a dielectric as a dielectric reduces the speed of light.

A microwave engineer must design circuits to manage this finite delay, but what is particularly interesting is that the effect gives rise to an enormous number of useful circuit elements that have no analog at lower frequencies. Whole circuits, and quite complex circuits at that, can be designed by exploiting distributed effects. This book explores the design of circuits with transmission lines and introduces effects, such as coupling from one transmission line to another, that can be exploited to build novel circuits.

This book is the second volume in a series on microwave and RF design. The first volume in the series addresses radio systems [1] mainly following the evolution of cellular radio. The third volume [2] covers microwave network theory which is the theory that describe power flow and can be used to describe transmission line effects. Topics covered in this volume include scattering parameters, Smith charts, and matching networks that enable maximum power transfer. The fourth volume [3] focuses on designing microwave circuits and systems using modules introducing a large number of different modules. Modules is just another term for a network but the implication is that is packaged and often available off-the-shelf. Other topics in this chapter that are important in system design using modules are considered including noise, distortion, and dynamic range. Most microwave and RF designers construct systems using modules developed by other engineers who specialize in developing the modules. Examples are filter and amplifier chip modules which once designed can be used in many different systems. Much of microwave design is about maximizing dynamic range, minimizing noise, and minimizing DC power consumption. The fifth volume in this series [4] considers amplifier and oscillator design and develops the skills required to develop modules.

The books in the Microwave and RF Design series are:

- Microwave and RF Design: Radio Systems
- Microwave and RF Design: Transmission Lines
- Microwave and RF Design: Networks
- Microwave and RF Design: Modules
- Microwave and RF Design: Amplifiers and Oscillators