DETAILED DESCRIPTION I claim: 1. An array antenna connectable to an input/output port forming an aperture to transmit or receive radar signals, said array antenna being switchable between at least two modes, comprising: aperture means divided into four quadrants, two of said quadrants forming the upper portion of said aperture means, and two of said quadrants forming the lower portion of said aperture; a feed means connected between said input/output port and said aperture means, including a first power divider means connected to divide the energy of an illuminating radar signal between, or for combining the energy of a received radar signal from, two of said quadrants forming the left-half and the right-half of said aperture; azimuth monopulse difference port means connected to said first power divider; switch means connected between said first power divider means and the said quadrants forming each half of said aperture, said switch means having a first and second position; and whereby with each of said switch means in said first position, said input/output port is connected such that a radar signal is either presented to, or received from, all of the said quadrants equally, however, with said switch means in said second position, said input/output port is connected to only at least a portion of two quadrants forming one-half of said aperture means. 2. An array antenna according to claim 1, wherein there are two upper intermediate feed means and also two lower intermediate feed means, each of which is connected to a power combiner/divider. 3. An array antenna according to claim 1, further including a phase shift means positioned in the feed path to a waveguide stick at the lower end of each of said quadrants forming said upper portion of said aperture means, and wherein said phase shift means is transitioned between a first position and a second position simultaneously with said switch means such that in said first position said phase shift means causes no phase shift in the radar signal to, or from, the waveguide sticks at the lower end of said upper portion of said aperture means, and in the second position said phase shift means causes a phase shift in the radar signal to said waveguide sticks at the lower end of said upper portion of said aperture means
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