The Hughes Atlas radar for the P-530 is aimed at a compact installation to fit the Cobra nose and easy access to line replaceable units to facilitate maintenance.
The X-band radar occupies 3.9 cu. ft., weighs about 200lb., and uses a vertically polarized 23-in.-dia. flat plate antenna with 33 db. gain. The antenna can scan a full 90 deg. in azimuth to either side of the aircraft center-line and 165 deg. in elevation. It has a low pulse repetition frequency of 0.8 to 4 kc. and a medium PRF of 8 to 17 kc. Average power output is 260 w. while prime power requirement is 3.56 kw. Peak power output is 4.5 kw. at 20% duty cycle. Like its two competitors, the Hughes radar also boasts of an MTBF (mean-time-before-failure) of at least 150 hr. Per unit radar price in quantities of about 400 will be less than $200,000, according to the company.
The multimode radar will provide ground-map and navigation functions as well as air-to-ground ranging and air-to-air intercept modes. In normal wide-angle search patterns, the Atlas radar can detect a 5-sq.-meter airborne target at 30 mi. in the look-up mode. In the narrow search mode the detection range will be 39 mi. In looking down at targets against ground clutter, it can detect in medium PRF the same target at 16 mi. The radar can acquire and track a target in the lookdown mode, Hughes says, regardless of the aircraft’s attitude, altitude or speed.
In air-to-ground ranging, the pilot can designate a ground target by putting his headup-displayed radar cursor over a selected target. The radar will track the target automatically and supply range and angle data to the aircraft’s weapon delivery computer. For dogfighting, the antenna scans about the boresight and the headup display comes on after the pilot depresses a single switch. The radar then searches and acquires targets automatically.
The radar proposed by Rockwell’s Missile Systems Div. for the P-530 will radiate 4 kw. peak power and 160 w. average. The 212 lb. sensor requires 1.75 kw. of prime power. It takes less than 12 minutes mean-time-to-repair. The Rockwell radar has a planar array antenna with a multiple pillbox feed. Antenna field of View is +-90 deg. in azimuth and +-60 deg. in elevation. Beam width is 2.8 deg. in azimuth, 3.3 deg. in elevation. In the air-to-air mode, the radar has a 20 naut. mi. look-up range using coherent Doppler, 10 mi. when operating on a frequency agility feature. In clutter conditions, coherent Doppler range is reduced to 16 naut. mi. In air-to-ground mode, the radar provides ground-map, ground range and moving-target detection and tracking. Range for ground ranging at 70 to 10 deg. depression angles is 10 naut. mi. Moving target range is 10 naut. mi., assuming a 20-sq.-meter target traveling at speeds in excess of 5 naut. mi./hr.
Westinghouse’s entry in the P-530 derby is a 225 lb. version of its WX family of airborne radars (AW&ST Aug. 28, 1972, p. 54). The pulse Doppler radar occupies 4.23 cu. ft. It has an average power output of 200 w. The radar detection range on a 2-sq. meter target with 85% probability is 20 mi. in pulse Doppler. Conventional pulse ranging permits the figure to be stretched for targets not in clutter. The radar has frequency agility on a pulse-to-pulse basis in the conventional pulse mode.
Westinghouse uses a Cassegrain antenna with a subreflector located in the aircraft’s nose. The subreflector reflects radiated energy back against the radar’s
flat plate antenna so that energy will be reflected at twice the angle of the flat plate. Switching the polarization of the subreflector permits it to become transparent to the re-radiated energy.