Page:Electronics Technician - Volume 7 - Antennas and Wave Propagation - NAVEDTRA 14092.pdf/52

 The reflector is 24 feet wide and has a double-curved surface composed of a series of horizontal members that form a reflecting surface for the horizontally polarized C-band energy. The antenna has a 28-dB gain, with a beamwidth of 9 degrees minimum vertically and approximately 3.3 degrees horizontally. Antenna roll and pitch stabilization limits are plus or minus 25 degrees. Stabilization accuracy is plus or minus 1 degree with the horizontal plane.

The antenna is equipped with a safety switch located near the antenna pedestal area. The safety switch disables the azimuth and elevation functions in the antenna and the radiate function in the transmitter to provide protection for personnel working on the antenna.

OE-172/SPS-55

The OE-172/SPS-55 antenna group consists of the antenna and the antenna pedestal. The antenna group is mast-mounted by means of four bolt holes on the base of the pedestal.

The antenna consists of two waveguide slotted arrays mounted back-to-back. One array provides linear polarization, while the other provides circular polarization. The array used is selected by means of a remotely controlled waveguide switch located on the pedestal. Linear polarization is used for most conditions. Circular polarization is used to reduce return echoes from precipitation. Each antenna forms a fan beam that is narrow in the azimuth plane and moderately broad in the elevation plane.

Figure 2-49 shows a cross-section of the SPS-55 antenna. During transmission, the rf signal enters the antenna through a feed waveguide and then enters a feed manifold region of 80 periodic narrow-wall slots. The slots are skewed in angle and alternated in direction of skew. They are separated by approximately one-half wavelength, resulting in broadside radiation into the sectoral horn region of the antenna. The horizontally polarized radiation from the manifold travels in the horn region toward the aperture, where it encounters an array of vertical sheet metal slats.

Figure 2-49.—SPS-55 antenna cross section. 2-30