A protective cover configured for use with an electronic device having antenna regions. The protective cover comprises a protective shell configured to receive the electronic device when the electronic device is installed in the protective cover. The protective shell is configured to contact and cover at least portions of the back and sides of the electronic device when the electronic device is installed in the protective shell. The protective shell includes a first material and a second material where the second material has a dielectric constant that is different than a dielectric constant of the first material in at least one operating frequency range of the electronic device. The second material is present in regions of the protective shell that are in proximity to the antenna regions of the installed electronic device.