542 



ANTENNAS AND RF COMPONENTS 



100 



50 



20 



10 



0.5 



0.02 0.05 0.1 0.2 0.5 



VOLTAGE REFLECTION COEFFICIENT 



1.0 



Fig. 10-16 Plot of Power Reflected as a Function of the Voltage Reflection 

 Coefficient of a Mismatched Transmission Line. 



are affected in their operation by energy reflected back to them. Frequency 

 of oscillation, power output, and frequency stability are all functions of 

 the phase and amplitude of reflected waves. Long transmission lines and 

 the changing impedance of scanning antennas present particular problems 

 in this respect. The design of Automatic Frequency Controls (AFC) is 

 strongly affected by these problems, as was indicated in Paragraph 8-5. 



It is important to realize that standing waves can exist at the input of 

 a transmission line even though it is properly terminated at the far end. 

 Any irregularity or abrupt change in dimension of a transmission line can 

 be the source of undesirable reflected waves. Poorly brazed or soldered 

 waveguide joints, for example, are often the source of objectionable 

 reflections. 



A frequently encountered matching problem arises when two trans- 

 mission lines of different impedances must be connected together. Such a 

 transition is most readily accomplished by using a quarter-wave transformer 



