The dome or window on a sensor suite seems, at first glance, to be a relatively low tech item. In reality, it can be one of the most costly items in the system. The choice of materials is highly dependent on the sensor, the anticipated operating conditions, and other requirements such as electromagnetic interference or radar cross section issues. The situation is further complicated when multiple sensor bands are used. Some dome materials are suitable for visible or near infrared applications, some for midwave infrared applications, and others for long wave infrared applications. Materials are also available which can be used for dual band sensors such as visible and midwave sensors.
The Army is currently developing a tri-mode seeker containing semi-active laser, midwave infrared, and millimeter sensors all using a common aperture. This added complexity is nowhere more apparent than in the missile dome. Optically transparent infrared optical materials tend to have relatively high dielectric constants. Millimeter wave radomes typically have low dielectric constants. Electromagnetic shielding for an optical seeker frequently consists of some type of grid that serves as a wideband filter. Electromagnetic shielding for millimeter wave missiles may use complicated frequency selective surfaces that block all but the frequency of interest. Unfortunately, those frequency selective surfaces tend to be predominantly metal and are opaque in the optical regime.
This paper will discuss the unique requirements that are placed on a tri-mode seeker as well as efforts to meet those requirements.