Optical time-shifters for microwave phased array antenna steering
In electronically steered phased array antennae, pointing is accomplished by controlling the relative microwave phase between successive antenna elements in the array. The phase of these radiation elements can be shifted by using lumped-element components typically less than a wavelength long. This approach suffers, however, from the drawback that the constructive interference condition is satisfied only over a narrow frequency band, giving rise to undesirable phenomena such as "beam-squinting." An alternative technique known as true-time-delay steering imposes differential delays between successive antenna elements in real time. This approach is inherently broadband, but is presently implemented by routing the RF signals through bulky coaxial cables or waveguides whose length can be as long as LsinΘm, where L and Θm are, respectively, the aperture size and maximum steering angle of the antenna.
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