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THE STRIPLINE

I mentioned earlier in this book that filters for UHF and above are often too difficult
to make from standard capacitors and inductors. I mentioned that filters could be
made using transmission line principles. One type of filter and/or transmission line is
called stripline. At UHF and higher frequencies, transmission lines become so short
in terms of wavelength that half and quarter wavelength lines can easily be made of
copper printed circuit board track. These printed circuit board transmission line filters
are called stripline filters. They can be used to create an inductive or capacitive
reactance, and act as resonant tank circuits, or filters.

The stripline for Advanced Theory is examined only to the point that you need to
know stripline can be used for filters and transmission lines at UHF and above.
Microstrip is not in the Australian syllabus and there is often confusion between the
two, I will cover both.

Microstrip vs. Stripline

The importance of printed circuit board (PCB) interconnect techniques increases
with frequency of operation. At higher frequencies, transmission line wiring provides
superior performance by minimising crosstalk, signal distortion and radiation
(compared to ordinary point-to-point wiring). When implementing transmission lines
on a printed circuit board (PCB), there are two options: microstrip and stripline.

MICROSTRIP.

A microstrip transmission line consists of a copper trace separated from a ground.

Figure 38-14. Microstrip transmission line
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