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Reflectarray Antennas by Payam Nayeri download in ePub, pdf, iPad

There are cases

Consider two dipole antennas placed in a line end-to-end, or collinear. Another option for steering the beam is mounting the entire array structure on a rotating bearing and rotating it mechanically. Antennas that use this technique are called phased arrays and are being intensively developed, particularly for use in radar systems. This greatly improves the front-to-back ratio of the antenna, making it more directional.

This causes the wavefronts created by the superposition of the individual elements to be at an angle to the plane of the antenna. However, there are a number of factors that can change this distance, and actual reflector positioning varies.

The more elements used the narrower

Since the s, versions for use at microwave frequencies have been made with patch antenna elements mounted in front of a metal surface. This makes the array more sensitive horizontally, while stacking the dipoles in parallel narrows the pattern vertically.

There are cases when this is not desirable, and although reflectors are commonly seen in array antennas, they are not universal. The more elements used, the narrower the main lobe and the less power is radiated in the sidelobes. In theory there is no limit to this process. Ultimately, the rising inherent losses in the feed network become greater than the additional gain achieved with more elements, limiting the maximum gain that can be achieved.