Antenna Design For Mobile Devices

Chapter 2

Antenna Matching

The most important thing one must always remember when designing a matching circuit for antenna is that only inductors or capacitors can be used. In active microwave circuit designs, such as amplifier designs, resistors are frequently used to improve the port matching and circuit stability [1]. But in antenna designs, one should NEVER use resistors or other lossy components. The whole purpose of an antenna in a cellular device is to transmit or receive power, so the efficiency of the antenna is the most critical parameter. Whenever a resistor is added to a matching circuit, the efficiency always drops and that is not our goal. This mistake is repeatedly made by amateur antenna designers, so it is better to set the record straight before we start this chapter.

In this chapter, familiarity with basic electromagnetic concepts, such as characteristic impedance, return loss, reflection coefficient, voltage standing wave ratio (VSWR), and transmission line is assumed. If not, then the following textbooks are recommended before continuing [2–5]. An understanding of the Smith Chart, which is the essential tool used in any antenna matching, is also recommended.

For those who want to have an in-depth report of matching techniques used in microwave circuit matching, the book by Professor Gonzalez, Microwave Transistor Amplifiers: Analysis and Design, [1] is a good reference. A paper by Professor Cripps [6] also provides some good discussions on the matching issue ...