A ferroelectric layer is deposited or in close proximity to a ferromagnetic ferrite layer to make a microwave substrate on which conductors can be deposited or placed to make devices. The permittivity of the ferroelectric layer can be changed by applying a voltage and the permeability of the ferromagnetic layer can be changed with a magnetic field. This makes it possible to tune the device characteristics with two different effects taking best advantage of the capabilities of each. A material example is ferromagnetic yttrium-iron-garnet on which is deposited a thin film of ferroelectric barium strontium titanate. To minimize losses, the ferroelectric film should be high quality, but practical yttrium-iron-garnet substrates are polycrystalline so that the use of buffer layers is desirable. At least two methods can be used to deposit the ferroelectric film, pulsed laser deposition and metal-organic chemical liquid deposition. A variety of dual tunable microwave devices can be made with this substrate, including by way of example only, phase shifters, frequency filters, and resonators.