This is because most transmission lines use one of their two conductors as a local datum e.g., the ground plane of a printed circuit board for microstrip line is tied to ground, and the outer conductor (“shield”) of a coaxial cable is usually tied to ground. Although a series reactance scheme is also possible in principle, it is usually not as convenient. This scheme is usually implemented using the parallel reactance approach, as depicted in the figure. Figure 3.23.2: Single-stub matching.įigure 3.23.2 shows the scheme. Figure 3.23.1: A practical implementation of a singlestub impedance match using microstrip transmission line. This section explains the theory, and we’ll return to this implementation at the end of the section. Figure 3.23.1 shows a practical implementation of this idea implemented in microstrip. Section 3.16 explains how a stub can replace a discrete reactance. Whatever the reason, a possible solution is to replace the discrete reactance with a transmission line “stub” – that is, a transmission line which has been open- or short-circuited. In many problems, the required discrete reactance is not practical because it is not a standard value, or because of non-ideal behavior at the desired frequency (see Section 3.21 for more about this), or because one might simply wish to avoid the cost and logistical issues associated with an additional component. In Section 3.22, we considered impedance matching schemes consisting of a transmission line combined with a reactance which is placed either in series or in parallel with the transmission line.

Smith chart series shunt