Microstrip and Printed Antenna Design
Written for practicing engineers new to the field, this book includes a succinct treatment of wireless designs with enough detail that CAD formulas may be implemented with relative ease.
TABLE OF CONTENTS Microstrip and Printed Antenna Design
Appendix D: Antenna Topics
D.1 Friis Transmission Formula
An equation which describes the path loss between two antennas was introduced by Friis. [1] The formula was introduced in terms of the effective area of the transmitting and receiving antenna.
Where:
P r is the power available at the output port of the receiving antenna.
P t is the power fed into the input port of the transmitting antenna.
A r is the effective area of the receiving antenna.
A r is the effective area of the transmitting antenna.
R is the distance between the antennas
? is the wavelength
The power delivered to the terminals of an antenna is defined as:
S is the power density of a plane wave incident on the antenna in W/m 2
A e is the effective area of the antenna m 2
The gain of an antenna in terms of effective area is:
The Friis equation may now be written in terms of antenna gain.
G t is the transmit antenna gain
G r is the receive antenna gain
The relationship between gain over an isotropic source ( G) and that gain in decibels with respect to an isotropic source is:
It is often useful to write the Friis equation using logarithms to determine path loss:
Where:
F is frequency in MHz
R is the distance between antennas in meters
The Friis Transmission Formula assumes the value of R is sufficiently large so...
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