CHAPTER 9Antennas and Transmission Lines1.A transmission line is a two-wire cable used to carry RF energy between two different pieces of communications equipment or between an antenna and a receiver or transmitter.2. The two most common types of transmission lines are balanced and coaxial.3. The primary feature of a transmission line is its characteristic or surge impedance Zo which is afunction of the distributed inductance L and the capacitance C per unit length(Zo = L / C).

4. The characteristic impedance of a balanced line is determined by its physical dimensions. [ Zo =276 log(2 S I D) where S is the center-to-center spacing of the conductors and D is the diameter of theconductors.]

5. The characteristic impedance of coax also depends on its physical dimensions.[ Zo= 138 log(D I d) where D is the inside diameter of the shield and d is the diameter of the inner conductor.]

6. The proper use of a transmission line is to terminate it in a load impedance equal to its surgeimpedance. All the power applied to the line will be absorbed by the load.