RF Circuit Design, 2nd Edition

Chapter 2: Reflection and Self-interference

2.1 Introduction

Generally speaking, there are internal and external sources of interference to the signal in RF, digital, or analog circuitry.

The internal interference sources include the following:

1. Reflection at every node in the circuitry, which is called self-interference;

2. Nonlinearity of the device;

3. Additional radiation or interference due to improper grounding, layout, and packaging of the circuitry;

4. Electromagnetic radiation from a part, a runner, or a current loop on a PCB (printed circuit board) since any of these acts as a small antenna.

The external interference sources include the following:

5. There are two types of the artificial electromagnetic interference sources: one is electromagnetic waves transmitted from broadcasting stations, stations for navigation, remote control, exploration, detection, and so on. The other is electromagnetic emission from industrial equipment, home facilities, traffic vehicles, and so on.

6. Environmental interference sources such as lightning, cosmic rays, and so on.

All the interferences mentioned above must be the objectives to be studied in an EMC (electromagnetic compatibility) course. Unfortunately, in most EMC courses, the main interferences 1 and 2 are excluded though 3 to 4 are covered. Consequently, many EMC problems remain unknown since many of these problems arise because of the interference sources 1 and 2.

The ideal case without voltage or power reflection never exists ...