Figure 6. Generalized array configuration.
The final, and most important, array component is the radiating element itself. The element determines the ultimate bandwidth, polarization, weight, and cost of the entire radiating system in addition to fundamental architectural issues like integration with the transmission medium and the choice of distributed solid-state power modules or central tube source. Practical radiating elements range from open-ended waveguides to dipoles or monopoles and a variety of printed elements coupled to the transmission medium. Figure 5(a-c) shows elements used for tile fabrication, while Fig. 5(d-e) shows elements for brick construction. The microstrip patch-fed tile element of Fig. 5(a) is simple to fabricate and can be fed on-line or by using probe feeds, or aperture coupled from a lower-layer circuit, but has only a few percent signal bandwidth in the array environment. The proximity coupled patch element of Fig. 5(b) can have bandwidth exceeding 10%. Strip-line — fed cavity-backed slots as shown in Fig. 5(c), can be much wider bandwidth, but they are difficult to fabricate because of the need to define the cavities using plated holes. The elements for brick construction are typically wider band but do protrude from the aperture. Over modest scan sectors, stripline dipoles [Fig. 5(d)] can have up to 40% bandwidth, while flared notch elements [Fig. 5(e)] can have up to 4:1 bandwidth.