Analysis of Passive Microstrip Circuits
As a physical element, a transmission line can transmit, dissipate, and store energy. Thus, for instance, a two-wire line, which is a typical lossy transmission line, has a lumped element equivalent circuit given by a ladder network composed of repeated L, T, or Π sections of resistive, inductive, capacitive, and conductive elements. Although this circuit implies many simplifications, it can model a wide range of possible two-conductor line geometries and hence is a valid and general physical representation. The circuit is segmented by several reference planes coinciding with the coaxial to microstrip transitions and the microstrip impedance steps. In order to accomplish an analytical study of several microstrip passive circuits, this chapter gives an introduction to some basic concepts. It gives a small review of the transmission line theory. The chapter also examines one simple transmission line section (as a building block), two impedance transformers, one low-pass filter, and one combiner/divider device.