Metal Space Frame Radomes

Transmission loss performance of Metal Space Frame (MSF) and Dielectric Space Frame (DSF) radomes is defined by two factors:

1. The metal beams of the MSF radome and the composite dielectric beams of the DSF radome
2. The MSF radome membrane or DSF radome wall

MSF Radome Frame

The MSF radome frame transmission loss is smooth as a decreasing function of frequency. Metal frame transmission losses are higher at low frequencies, typically below 1.0 GHz, where losses approach infinity and frequency approaches zero. Above 1.0 GHz these loses decrease dramatically as the frame approaches its pure optical blockage limit between 2.0 GHz and 20 GHz. when frequency approaches infinity. These loses will increase or decrease depending on the metal beam cross-section as a result of wind speed requirements. The MSF radome panel membrane transmission loss is smooth, increasing slightly as a function of frequency from 50 GHz to 200 GHz depending on membrane thickness. Within the frequency range of 1.0 GHz to 12 GHz, the steady drop in metal frame transmission loss combined with slow growth of membrane transmission loss creates a flat region along the transmission loss vs. frequency line. Above 12 GHz, due to the pure optical blockage of the frame where losses remain practically unchanged, the slow increase in total transmission loss is the result of the additional contribution to loss from the radome membrane. 

DSF Radome Frame

The DSF radome uses a structural frame of fiberglass beams that have to be a third larger in cross section area than the corresponding MSF beams to provide the equivalent structural stiffness and strength. Thus, the losses associated with the dielectric beams is a function of both scattering and significantly higher blockage that results in an oscillating pattern of losses starting at 0.5 GHz and increasing in occurrence as frequency increases. The DSF radome panel membrane transmission losses also result in increased scattering as a function of frequency because the DSF radome wall is typically thicker than MSF membrane. As a result, the combination of both the DSF beam and wall transmission losses combine together to cause the increasing and oscillating character of DSF radome transmission loss vs. frequency.

To improve DSF RF performance, “beam tuning” techniques have been developed, whereby the inclusion of tuning wires or grids in the beams can reduce the blockage and scattering levels. It should be noted, however, that the degree to which the RF performance can be improved by this technique is limited by the fact that predominantly just one polarization is effected by it, and that the tuning bandwidth is very limited. Additionally, the technique is only viable in the lower frequency bands—however—due to the increased size of the beams required in a DSF radome, the performance of the DSF radome will never be as good as the MSF radome above 1.0 GHz.

The graph below shows performance of both the MSF and DSF radomes from 0 GHz to 100 GHz and demonstrates the phenomena described above.