The current distribution and AC resistance of a microstrip structure

• Published in: IEEE transactions on microwave theory and techniques 1990-09, Vol.38 (9), p.1268-1277
• Main Authors: Faraji-Dana, R., Chow, Y.L.
• Format: Article
• Language: English
• Subjects: Applied sciences; Circuit properties; Conductors; Current distribution; Dielectric losses; Electric, optical and optoelectronic circuits; Electronics; Exact sciences and technology; Frequency; Inductance; Metallization; Microstrip; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; Skin; Strips; Surface resistance
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/22.58653

The AC resistance of the strip in a microstrip structure is compared with that of an isolated strip for better understanding of the conductor loss mechanism. An analysis is presented of the AC resistance in a microstrip structure for any metallization thickness by deriving the current distribution over the strip cross section. The analysis uses the separation of variables technique and the Green's function method. It shows that the skin current of the strip is concentrated toward the ground plane in a microstrip structure. In the extreme case, the AC resistance of the strip can be twice as high as the AC resistance of the same isolated strip. The imperfect ground plane also adds to the total conductor loss of a microstrip line. For a wide strip over a lossy ground plane at high frequency, the ground plane surface current distribution is concentrated directly under the strip, and the ground plane AC resistance can be as large as the strip AC resistance. Therefore, the total AC resistance at the microstrip line can be four times as high as that of an isolated strip conductor.< >