The Medium

Unguided Medium- This refers to transmission media that does not use physical media to facilitate
communication

Guided Medium- This refers to transmission media that requires physical media to facilitate communication
Transmission line

Is a metallic conductor system that is used to transfer electrical energy from one point to another.
Length of Transmission Line

Physical Length- This refers to the actual length of the transmission line, typically measured in
m/km/ft/miles.

Electrical Length- This refers to the length of the transmission line based on the fraction of its wavelength.
Types of Transmission Line

Balanced or Differential - This is a transmission line consisting of two conductors of the same type, each of
which have equal impedances along their lengths and equal impedances to ground.

Unbalanced or Single Ended - This is a transmission line whose conductors have unequal impedances to
ground. It usually consists of a conductor that is considered the signal line and another conductor that is
grounded or is ground itself.

Balun - This refers to a device used to connect a balanced transmission line to unbalanced load.

Parallel–Wire Transmission Line - A parallel-wire transmission line is composed of two conducting wires
separated by a dielectric.

Coaxial cable - Is composed of two concentric conductors and is used extensively for high frequency
applications to reduce losses and to isolate transmission paths. This also provides excellent shielding against
external interference.
Transmission Line Equivalent Circuit - Physical properties like diameter and conductor spacing and electrical
properties such as conductivity and relative permittivity (otherwise known as dielectric constants) determine what
we call the primary line constants.
Problem Solving
A parallel–wire transmission line is constructed of #6 AWG copper wire (d=0.162 in) with a 12-inch separation in air.
Determine the per-meter values of L,C and R assuming a frequency of 1MHz.
Problem Solving
The specifications for rigid Teflon-dielectric coaxial line used in a radar set operating at 3 GHz are: copper-material,
stub supported at intervals to maintain the Teflon dielectric; outside diameter, 7/8 inch; wall thickness, 0.032 inch;
inner conductor diameter, 0.375 inch. Determine the per meter values of L, C, and R.
Secondary Line Constants
Characteristic Impedance - This refers to the impedance looking at the input of an infinitely long transmission line.

For maximum power transfer from source to the load, a transmission line must be terminated in a purely
resistive load equal to the characteristic impedance of the line.

Also known as surge impedance.
Problem Solving
Given the following primary line constants: R=0.1 ohm/ft, L=76.8 nH/ft, G=0.05 S/ft, C= 31.4 pF/ft Determine the
characteristic impedance of the line at (a) 60 Hz; (b) 1 MHz; (c) 2.45 GHz
Problem Solving
Calculate the Z o for an air dielectric two -wire parallel transmission line. The ratio of the distance between the
centers of the two conductors and the radius of the conductors is 12.3
Problem Solving
From the propagation constant, determine the values of the attenuation and phase shift coefficients. The
distributed parameters are: R = 0.1 ohm/m , G= 0 s/m , L= 76.8 nH/m, and C = 22.2 pF/m. Assume an operating
frequency of 750 MHz.
Problem Solving
Attenuation is one of the major concerns in the application of transmission lines in communications engineering.
How much attenuation in dB, does a 100 m of air-dielectric parallel wire transmission line introduce? Assume that
R=0.1 ohm/m, and Zo= 300 ohms.
Seatwork
A lossy parallel-wire transmission line consists of No. 12 wire AWG (d = 81 mils). The distance between the wire
centers is 10 inches. If the lossy characteristic impedance is almost equal to the lossless characteristic impedance,
what is the attenuation coefficient in dB per 100 ft of the line at 400 MHz?