Stripline is often used as a generic term for any transmission line consisting of a thin planar conductor supported on a dielectric sheet parallel to an earthed metallic plane. Symmetrical stripline has the conductor in the region between two earthed metallic conductors, and is sometimes called triplate line. It has the advantage that the microwave field is enclosed and is symmetrical and can be analysed from electrostatic principles assuming a pure TEM-mode. It can be constructed with a printed conductor sandwiched between two dielectric plates and their ground planes. A good summary of stripline design theory is given by Gupta, Garg and Chadha,' who quote all the formulas needed to determine the characteristic impedance and loss of the line and the corresponding inverse design formulas. The most accurate empirical formulas have been given by Wheeler, who also publishes some curves which may be used for design. Some curves of characteristic impedance for some particular standard sizes of stripline substrate are given in the 'Microwave Engineers' Handbook'.