Читать книгу Antenna and EM Modeling with MATLAB Antenna Toolbox - Sergey N. Makarov - Страница 37

A quarter wave transmission line transformer is characterized by (from Eq. (1.27))

(1.28)

An antenna with Z_a = 200 Ω is to be perfectly matched to the generator with R_g = 50 Ω by a proper choice of line characteristic impedance Z₀.

Solution: The perfect match means that generator sees Z^* = 50 Ω in the reference plane. Then, from Eq. (1.28), one has

(1.29)

It is not difficult to construct such a transmission line using, for example, a somewhat narrower microstrip as compared to the 50 Ω microstrip line.

Emphasize that the quarter wave transformer is relatively narrowband; it cannot be used for antenna matching over a wide band. Also, some reflections and standing waves will occur along the quarter wave line.