Aircraft radomes are traditionally considered to have only a mechanical function. However, consideration of dielectric-loaded slotted waveguide antennas suggests the possibility of incorporating such antennas directly into the radome. These antennas and the radomes commonly used in guided missiles are in fact highly compatible. For example, most of the dielectrics used in radomes are also used as substrates in flat, dielectric-loaded slot arrays. Moreover, the thickness of the material can be the same in both applications.
This article considers only low-loss plastic radomes. A conceptual radome-antenna incorporating several antennas is shown in Fig. 1. The array at the forward end has transverse slots; because of its position and end-fired radiation characteristics, its beam is directed along the longitudinal axis of the radome. The antenna located near the center section (four arrays, one in each quadrant) provides a complete conical beam around the body. A third antenna is a two-dimensional, planar, slotted array with a downward-looking beam normal to the radome axis. All antennas are flush-mounted and can be constructed as an integral part of the radome.
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Frequencies of the antennas described here are classified, but it can be stated that good results were obtained from L through C bands.
A composite radome-antenna (or radant) developed at Harry Diamond Laboratories is shown in Fig. 2. It is essentially a conical frustum made of silicone-fiberglass dielectric with dielectric-loaded slot antennas built into the surface of a 0.250-in.-thick radome. There are four antennas on the surface; each has five longitudinal shunt slots of varying length offset from the waveguide centerline. Each antenna is fed from a 50-ohm coaxial-to-waveguide transition. The top and bottom walls of the waveguide antennas are copper-plated. Waveguide edges are formed by plated-through holes closely spaced to minimize rf leakage.
The interior of the cone is completely copperplated, whereas the top slotted walls on the outside are plated in four places only. The plated interior minimizes rf energy within the radome. This model constitutes the basic, simplified version of an integrated radome-antenna system, a version that is relatively inexpensive to produce.