Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 107

Figure (3.12) shows that the i^th port of a multiport network is terminated in a load equal to the characteristic impedance of the port. The power wave b_i coming out of the port is incident on the load Z_L, whereas the incident power wave a_i is the reflected wave from the load. If a port is terminated in its characteristic impedance, i.e. Z_L = Z₀, then the reflection from the load at the port is zero, i.e. a_i = 0. Thus, for the excitation a_j applied at the j^th port, while all other ports are terminated in their characteristic impedances, the ports have . However, the power b_j is reflected from the j^th port.

The reflection coefficient at the j^th port is obtained from equation (3.1.40):

Figure 3.12 At the i^th port, the load is terminated in port characteristic impedance.

(3.1.41)

Therefore, S_jj is the reflection coefficient (Γ_j) at the j^th port, provided all other ports are terminated in their characteristic impedances. However, if other ports are not terminated in their characteristic impedances, then S_jj is not a measure of the true reflection coefficient of the network or a device at the j^th port. The true reflection coefficient at the j^th port, under the unmatched load condition, is more than S_jj that is defined under the matched load condition.