Wideband average power handling capability of coupled microstrips on polyimide and polyimide/GaAs substrates

The wideband average power handling capabilities (APHC) of coupled microstrips on a single-layer polyimide substrate and also on a polyimide and GaAs double-layer substrate are studied. Since the thermal conductivity of polyimide materials is only about 0.2 W/m °C, the APHC of the coupled microstrips is severely limited by the polyimide thickness. As a first step to obtaining the APHC, the ohmic and dielectric losses of even and odd modes need to be calculated. The rise in temperature is determined using a proposed thermal model in which the lateral heat dissipation on the neighbouring microstrips is appropriately treated. Numerical results are presented to show the effects of microstrip conductivity and thickness, and polyimide thickness on the APHC for different coupled microstrip configurations. Several ways to effectively enhance the APHC are suggested, which could be useful in the design of coupled microstrips on, or embedded in, polyimides.