Abstract: When an IFF system interrogates a target aircraft and receives IFF reply signals, monopulse processing of the reply signals can provide more accurate determination of target azimuth. However, when reply signals have amplitudes close to noise or jamming levels, azimuth processing by non-monopulse techniques such as beamsplitting or center of gravity analysis can provide better accuracy than monopulse azimuth processing. Methods are described to enable adaptive selection of the type of azimuth processing to be employed. Such selection is based on active comparison of received signal magnitudes against monopulse sum and difference signal threshold values and a noise threshold value. Monopulse azimuth processing can thus be used at all times, except when non-monopulse azimuth processing is chosen by such adaptive selection.

Abstract: A 90 degree azimuth beamwidth is achieved in a narrow cellular antenna, by inclusion of sidewalls. To improve front-to-back performance, slot radiating elements extending through the sidewalls re-radiate signals behind the antenna. Signals re-radiated from the slot elements are effective to partially cancel signals otherwise radiated behind the antenna as a result of diffraction. H-shaped slots are described for sidewall use and side-to-side slots are described for endwall use. Slots may be dielectrically loaded by contiguous portions of a radome.

Abstract: Performance of multibeam cellular antenna systems is improved by use of space diversity in antenna placement and angle diversity in antenna alignment. Space/angle diversity is achieved on a single tower structure (20) by placement of eight antennas (B1-B8) in pairs at four spaced locations (I, II, III, IV) at the tower corners. Antennas are placed with an orthogonally directed pair at each location. For each orthogonal pair (e.g., B1 and B2 at location I) there is an antenna located at a different corner which is pointed between the orthogonal directions (e.g., B5 at location II). Antenna placement and alignment for achieving space/angle diversity in triangular tower configurations are also described.