1

Fundamentals of Transmission channels

• Introduction to Microwave

• Introduction to Mobile Radio Channels

• Large-scale path loss

• Small-scale fading and multipath

2

Introduction to Microwave

• All electronic communications systems send information from one point to another by transmitting electromagnetic energy from the sender to the intended receiver.

• This electromagnetic energy can travel in various modes,

frequency

velocitywavelength

3

Velocity, Frequency, and Wavelength

• Velocity of an electromagnetic (EM) wave in free space (vacuum)

where μ0 is the permeability of free space and ε0 is the permittivity of free space. They are the distributed values of L and C of free space.

m/s 100.31 8

00

v

4

• Absolute permittivity of a medium is noted as ε and is given by ε= εr ε0

where εr is the relative permittivity (dielectric constant).

• Absolute permeability of a medium is noted as μ and is given by μ= μr μ0

where μr is the relative permeability, equaling to 1 for a vacuum and most nonmagnetic metals. Thus, μr equals 1 for most purposes.

• If the wave travels through a medium of εr, the new velocity is vr = C/ εr

1/2

where c = 3.0x108 m/s is the velocity of light in vacuum.

5

Frequency and Wavelength

• Frequency f is the number of cycles per second a signal contains.

• Signal (wave) period T is the time of one complete cycle, i.e. T= 1/f

• Wavelength λ of an EM wave is the physical distance the wave travels in one cycle,

i.e., λ = c/f (in free space)

Example 2: caculate the wavelength λ for an EM wave f=50GHz where εr=3.0.

6

The Electromagnetic Spectrum

The total span of frequencies and corresponding wavelengths used in communications systems is called the electromagnetic spectrum. The overall useful electromagnetic spectrum extends from about 10,000Hz to several billion hertz.

7

Microwaves

• Microwaves are electromagnetic radiation of frequencies from several hundred MHz to several hundred GHz.

8