The AN/SPS-52C is a ship mounted, air search, three-dimensional radar system that provides target position data in range, bearing, and elevation. It produces three-dimensional coverage from a single antenna by using electronic scanning in elevation and mechanical rotation in azimuth. The 52C uses the AN/SPA-72B antenna as did the earlier AN/SPS-52 systems, but has completely different below-the-decks electronics. Because of this, the 52C has significant improvements over earlier versions of the 52 radar in the areas of detection, reliability, and maintenance.

The antenna assembly (fig. 2-1) is a planar array, tilted back at an angle of 25 degrees. This 25-degree tilt allows the antenna to provide high-elevation coverage. The array is a collection of rows of slotted waveguides and is fed RF from a feed system running the length of one side of the total array assembly. This antenna scans in the vertical plane by transmitting different frequencies, as selected by a digital computer.

The AN/SPS-52C radar has four modes of operation: high angle, long range, high data rate, and MTI (Moving Target Indicator). The operator selects the appropriate mode, depending on the threat type and environment. The primary mode is high angle. In this mode, the radar provides coverage to a range of approximately 180 miles and an elevation of approximately 45 degrees. In the long-range mode, the radar provides coverage to a range of approximately 300 miles and an elevation of approximately 13 degrees. The high data rate mode provides a range of approximately 110 miles and an elevation of approximately 45 degrees. This mode is used because of its unique ability to acquire pop-up and close-in targets quickly. The MTI mode is useful in a high-clutter environment (such as weather in extreme sea-state conditions) where targets are normally hard to locate. Coverage is about 70 miles and up to an elevation of 38 degrees.

The 52C radar is used with the SYS-1/SYS-2 radar system. The SYS-1/SYS-2 system coordinates all radar sensors on a ship into a single system. It does this by using a processor designed around integrated automatic detection-and-tracking (IADT). The advantage of using such a system is that the unique

Figure 2-I.-AN/SPS-52 radar antenna.

characteristics of the various ship's radars can be integrated, resulting in more accurate and quicker detection of threats. This is part of a program for non-AEGIS class ships called New Threat Upgrade (NTU).

The AN/SPS-52C radar is presently found on the WASP (LHD) class and the TARAWA (LHA) class amphibious assault ships. It will eventually be replaced by the AN/SPS-48E.

AN/SPS-48 RADAR

The AN/SPS-48 radar is a complete system upgrade of the AN/SPS-52C including all component elements - transmitter, receiver, computer (radar and automatic detection and tracking), frequency synthesizer and height display indicator. Figure 2-2 shows an antenna for the SPS-48 radar on the USS Boxer LHD-4 (see arrow).

The SPS-48 radar is a long-range, threedimensional, air-search radar system that provides contact range, bearing, and height information to be displayed on consoles and workstations. It does this by using a frequency-scanning antenna, which emits a range of different frequencies in the E/F band. The SPS-48 radar has three power modes: high, medium, and low.

An upgrade was needed because the 52C radar's single elevation beam could not dwell long enough in any particular direction. To solve this problem, the 48 series uses a process that stacks nine beams (a train of nine pulses at different frequencies) into a pulse-group. The nine beams simultaneously scan a 5-degree elevation area, allowing the stack to cover 45 degrees of elevation.

Two versions of the SPS-48 are currently in use: the 48C and the latest version, the 48E. Maximum elevation has increased somewhat, 65 degrees versus 45 degrees for the 52C. The "E" version has twice the radiated power of the "48C", developed by reducing the sidelobes and increasing the peak power. Receiver sensitivity is increased and the 48E has a four-stage solid state transmitter. The main operating modes are:

EAC (Equal Angle Coverage)-The radar's energy is concentrated at a low angle.

MEM (Maximum Energy Management)-Both high and medium power are regulated.

AEM (Adaptive Energy Management)-Allows the radar to be adapted to a priority target radar

Figure 2-2.-SPS-48 series radar on USS Boxer, a WASP class amphibious assault ship.

cross section and a potential jamming environment.

LOW-E (Low Elevation)-Gives priority to the lower beam groups and transmits them as a Doppler wave.

The radar can also transmit as a single steerable beam group or it can burn through jamming using a chirp pulse.

Radar video, converted to a digital format, is displayed on consoles to allow operators to perform manual radar search, detection and tracking functions. True bearing indications appear when the track position is displayed in relation to true north, rather than to ownship.

Variation in frequency tends to make this radar more resistant to jamming than if it were operated at a fixed frequency. This provides a solution to the blind speed problem ("blind speed" is the speed a target travels that is too fast for the radar to track it) in systems. Frequency scanning imposes some limitations because a large portion of the available frequency band is used for scanning rather than to increase the resolution of targets. It also requires that the receiver bandwidth be extremely wide or that the receiver be capable of shifting the bandwidth center with the transmitted frequency.

The radar provides accurate height data by factoring in the effects of pitch and roll of the ship and changing the transmitted frequency accordingly. The ship's gyro system provides the radar set with this pitch and roll data.

The AN/SPS-48 radar works with other onboard radar sensors through the SYS-1/SYS-2, as did the AN/SPS-52C. Search data from the AN/SPS-48 radar is sent to multiple weapon systems. These include the Mk 91 Fire Control System for the SEASPARROW missile system, the Mk 95 radar, the Mk 23 Target Acquisition System, the Close-In Weapon System, and the Rolling Airframe Missile (RAM) System.

The AN/SPS-48 search radar is found onboard NIMITZ (CVN-68) (figure 2-3), KITTY HAWK (CV-63), and ENTERPRISE (CVN-65) class carriers, BLUE RIDGE (LCC) class amphibious command ships, and WASP (LHD) and TARAWA (LHA) class amphibious assault ships.

Q1. What operational characteristic makes the AN/SPS-48 series radar resistant to jamming?