By John G. Webster (Editor)

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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.

5(b) can have bandwidth exceeding 10%. Strip-linefed 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. Figure 5. Array elements. (a) Microstrip patch element.

The shift is with respect to ‘‘reference’’ (the line without the component) and ‘‘test’’ (the line and the component) lengths. Therefore it is always understood as the phase difference between the two. The shift may be fixed or variable. The variable phase shift uses mechanical or electronic techniques to change the phase dynamically. The main uses of these devices are as testing systems, measurement systems, modulation devices, and phased array antennas. The use of phase shifters in antenna systems provides controllable steering of the main beam of the radiation pattern without moving the antenna.

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02.Antennas and Propagation by John G. Webster (Editor)

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