Microwave Integrated Circuit Components Design Through MATLAB® by Raghavan S.;

Author:Raghavan, S.;
Language: eng
Format: epub
Publisher: Taylor & Francis Group
Published: 2020-06-15T00:00:00+00:00

2.15.2 Introduction

From the expression of skin depth and field expressions, it is possible to show that the conducting wires are of no use at microwave frequencies, and waveguides become transmission media. From the dominant mode definition, one can see that waveguides also are of no use beyond certain frequencies and under certain conditions. Here comes the MIC where planar transmission lines (transmission lines that consist of conducting strips printed on surfaces of the transmission lines’ substrates) form the backbones of it. The progress of MICs would not have been possible but for the advances of planar transmission lines. To completely characterize the behavior of transmission lines for RF and microwave designs, it is enough if few necessary properties of them are known. To know the properties of each transmission line, it is sufficient to know which mode is supported by each transmission line, which will then facilitate expanding the characteristic properties. A planar configuration implies that the characteristics of the element can be determined by the dimensions in a single plane. From the equation for the sending end impedance, Zs = Zo(ZR coshγl + Zo sinhγl)/(Zo coshγl + ZR sinhγl), it is possible to show the miracles of “transmission line.” Length in lambda makes all the differences in obtaining various microwave components and systems. A shorted small (less than quarter wave length) transmission line acts as an inductor, while that of an open line acts as a capacitor. Using the stepped impedance method, Inductor and Capacitor can also be realized. This concept felicitates all MIC filter elements, amplifiers (input and output matching networks), and oscillators (matching networks) design. While the design relations remain constant, the effective dielectric constant alone varies with various transmission lines. It is a relative dielectric constant for stripline, and for all other planar transmission lines, it is an effective dielectric constant. This makes the design easier. Low cost, small size and weight, conformability, improved reliability and reproducibility, multi-octave performance and circuit design flexibility, and multifunction performance on a chip are the major features of planar transmission lines (Figure 2.23).

FIGURE 2.23

Concept map for passive microwave circuits.

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