Microwave Communications

Wireless Communication

Communications through space (no physical wiring between the two points)

Examples: Garage door opener, cordless phone, remote control, radio, television, satellite communication, radar ,and so on.

Systems:

• Simplex: One way communication - Single frequency

• Half Duplex: Two way communication, One at a time - Single frequency

• Duplex (full): Simultaneous communications- Two separate frequencies

Communication protocol: From very simple systems to highly complicated systems with digital signal processing

Modulation techniques:

• Amplitude modulation,
• frequency and phase modulation and
• various digital modulation
  • Time Division Multiplexing
  • Frequency Division Multiplexing
  • Quadrature Modulation
  • Spread Spectrum Modulation

Frequency Spectrum used for communication purposes

Microwaves cover frequency range from 500 MHz upto Millimeter wavelengths (few hundred GHz).

We can ask the following questions.

• What applications are there that uses microwaves?
• What are the differences between the low frequency circuits and high frequency circuits?

Some Examples:

• Mobile Phone

• Satellite Communication

• Radar

Why Microwaves are different than low frequency circuits?

• Resonant Circuit

• Wavelength versus circuit dimensions
  • Wavelength longer than dimenions of the circuit element [Lumped parameter approximation] L's and C's are valid

  • Wavelength equal to or less than the dimesnions of the circuit element [Distributed circuit elements] L's and C's are not valid

For a phased array radar: Typical circuit.