From Practical Microstrip Design and Applications


Discontinuities and junctions denote any change in the cross-section of a straight waveguiding structure. Waves are scattered, and transmitted power is reduced due to reflection loss at a given obstacle. Higher-order modes are excited as local (evanescent) waves, storing electromagnetic energy, which can be described by reactive lumped networks. The microstrip circuitry is an open configuration, so that radiation loss additionally occurs in discontinuities and junctions. At moderately low frequencies, radiation loss is commonly small and is therefore frequently negligible.

In other respects, discontinuities and junctions are the real elementary building blocks of any microstrip integrated circuit. They are found, for example, in microstrip hybrid couplers, filters, matching networks, and transformers. Similarly, the insertion of lumped hybrid elements, such as capacitive and inductive chips or transistors, and electrical contacting of devices with the microstrip line by using wire-bonds as well, signify a discontinuity that influences the wave propagation of the fundamental mode. The frequency-dependent quantification of discontinuities and junctions is of great practical importance for a reliable circuit design.

Frequency-independent lumped elements of equivalent circuits (capacitances, inductances, and resistances) are calculated under the assumption of static electric or stationary magnetic fields. The derived circuit models are often described by simple analytical functions that are very convenient for computer aided design. On the other hand, it must be noted that these quasi-static equivalent circuits are only applicable within a limited lower frequency region.

It is known that the theoretical treatment of waveguide discontinuities is rather difficult. An exact analysis of...

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Topics of Interest

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