Chapter 2

Microwave Technology

This chapter introduces the transmission line theory in microwave technology [2–4] which is closely related to EMC research. In particular, this chapter covers the concept of single-conductor transmission line and double-conductor transmission line in transmission line theory which is the basis to understand the mechanism and design method of electromagnetic shielding. Through this chapter, our readers will get knowledge of the effect of distributed variables and the cross talk problem in cable layout. We also make clear in this chapter that the characteristics of electronic circuit in DC are fundamentally different from that when the circuit’s linearity is comparable to wavelength.

Microwave usually refers to the wave in the frequency band from 300 MHz to 3000 GHz, that is, from decimeter wave to submillimeter wave. Microwaves have special properties that low-frequency radio waves do not have. Since its frequency is several orders of magnitude higher than the low-frequency radio wave, some effects which are not obvious at low frequency are very significant in the microwave band. The most significant effect is that it takes time for electromagnetic waves to travel from one end of the circuit to the other end, because the propagation velocity of the electromagnetic waves is finite (the velocity of electromagnetic waves in free space is the speed of light). This effect is called the delay effect, which makes each point in the circuit exhibit a different phase. The wavelength corresponding to the microwave is very short, so that the size of a general object is much larger than or comparable to the wavelength. Therefore, the general object exhibits a very strong distributed parameter effect, which means that the electromagnetic energy is dispersed over the entire object. This distributed parameter effect is fundamentally different from the lumped parameter effect of traditional low-frequency circuits (the energy is concentrated in the lumped elements). In addition, the skin effect and radiation effect of the high-frequency current in the microwave frequency band are more obvious; the quantum effect also appears in the high frequency range of the microwave frequency band [3].

The basic theory of microwave technology is the classical electromagnetic theory, based on Maxwell’s equation [5]. The basic research method is the “field solution” method, which involves the solution of partial differential equations. Since it is often

D. Su et al., Theory and Methods of Quantification Design on System-Level Electromagnetic Compatibility, https://doi.org/10.1007/978-981-13-3690-4_2