A Microstrip Line with Two Side Grounded Rectangular and Rounded Conductors with Different Thicknesses

The article investigates a microstrip line (MSL) with two side grounded conductors having rectangular and rounded shapes of conductors. Each shape of conductors was simulated in the TALGAT system, and the values of the per-unit-Iength capacitance of the line
$(C)$
and the per-unit-Iength capacitance of the line in vacuum
$(C_{0})$
were calculated. The results demonstrated good convergence when the thicknesses of conductors were
$t=18,35,70$
, and
$105\mu\mathrm{m}$
for two shapes of conductors. The results obtained did not confirm the lower computational costs with rounded conductors, compared with rectangular ones, and important causes of this were revealed. In the meantime, it was found that the rounding has a considerable influence on secondary characteristics. For example, when thickness increases, the difference of per-unit-length delays rises from 1.58% to 2.56%, while the difference of wave impedance rises from 2.14% to 4.67%. Moreover, we also considered an important case of grounding the side conductors at the ends rather than along the central conductor. This case allows this MSL to be used as a modal filter (MF) for protection against ultrashort pulses based on their modal decomposition into two lower amplitude pulses. In this case, with rounded conductors, the difference of per-unit-length modal delays decreases up to 8.25%. It decreases the duration of USPs that will be completely decomposed in MF and, therefore, deteriorates the protection. Thus, accurate modelling of the conductor shape can be critical for simulating such protective devices.