
706 Microwave Engineering
temperatures and work at much higher voltages than GaAs transistors.
These transistors make ideal power ampliers at microwave frequencies.
16.4 Materials Used
The materials required for MMICs include substrates, conductors, dielectrics
and resistors.
16.4.1 Substrates
The selection of the substrate material depends on dissipation, function and
type of circuit used. The properties to be possessed by these materials include
(i) high dielectric constant usually greater than or equal to 9, (ii) low dissipa-
tion factor or loss tangent, (iii) constancy of
ε
and constancy of temperature,
both over frequency range of interes