Phased Array Radar Principles AN/SPY - 1 Phased Array Radar Principles

Objectives Understand the basic principles of electronic scanning radar Identify advantages and disadvantages of phased array Identify applications Discuss methods of beam steering Determine and calculate phase relationships between elements Review history and specifications of AN/SPY 1

Basic Principles Relies on constructive interference Point target at point P Maximum energy on target when in phase System may have thousands of elements

Basic Principle System can be used to direct beams Phase shifting between elements Various methods Active and passive Based on location of target and distance between radiating elements and target Off boresight in elevation (greater than or less than 0 degrees) or Azimuth ( clockwise from boresight (greater than 0 degrees) or counter clockwise (less than 0 degrees)) Time delay, phase scanning, frequency scanning Passive: Source of signal is the transmitter, Active: signal is generated at the antenna. Array of T/R modules on face of radar. Beam steering control unit (BSC) directs phase shift required to steer the beam

Electronic Scanning Pros and Cons Advantages Disadvantages Increased data rates and reduction of system reaction time High reliability and sidelobe control Stealthy, low profile, and great for aircraft Virtually instantaneous positioning of the radar beam anywhere with a set sector Elimination of mechanical errors and failures Increased flexibility allows for multimode operation i.e. search, track, and control in one system High cost in comparison to traditional radar sets Complexity Straddle loss results in lower gain Typically only support narrowband applications 1. Increased data rates: a. There is a reduction of system reaction times (i.e.. don’t have to wait for the antenna to come back around. 2. Reliability, Stealth a. Can reduce drag on aircraft due to low profile. 2. Virtually instantaneous radar beam positioning. a. Can change the beams and the beam axis almost instantaneously. Don’t have to mechanically move/tilt the antenna. b. Beam position can be changed in a matter of microseconds. 3. Elimination of mechanical errors and failures associated with mechanically scanned systems. 4. Increased flexibility: Can develop more complex radar systems including a. 3D Radar with only one radar b. Multi mode operations (Search, Tracking, and Fire Control!) Disadvantages: 5. Price driven even higher for AESA Straddle loss results from a. Deviating from the broadside of the antenna elemetns and results in gain degradation for both range and Doppler b. Most significant at large scan angles c. Can combat by increasing dwell time at off boresight axis i.e. 2T, 3T, 4T depending on angle d. Compare with squinting in peripheral. Effective apperature lowers, therefore beamwidth grows

Applications Defense Weather Broadcasting In flight entertainment AN/SPY 1 (D) Radar Part of Aegis system developed by KU alum Weather National Sever Storms Laboratory Norman, OK Broadcasting AM Radio In flight entertainment Provide internet access to airliners Multi function to handle search, track, and command functions simultaneously  Wayne E. Meyer known as the father of Aegis was an Electrical Engineering graduate from KU in 1946. Also recipient of Distinguished Engineering Service Award in 1981 Early warning system for tornados and other dangerous weather Simultaneously perform aircraft tracking, wind profiling, and weather surveillance with a single phased array weather radar AM radio in order to ensure signal quality to prime listening areas Transmitting high-speed Internet/voice data between airborne aircraft and ground stations via Ku-Band active phased array antenna or communication AESA, bringing broadband Internet access to in-flight passengers

Beam Steering Adjustments to the free space propagation from various elements Result positions interference at different locations Implemented by altering time, frequency, or phase Time Delay Scanning Frequency Scanning Phase Scanning

Frequency Scanning Based on frequency propagation through waveguide At different frequencies behavior changes Beam shifting away from boresight

Frequency Steering

Time Delay Scanning Independent of frequency Uses time delay networks and outputs identical waveforms from each element Periodic shifting of the waveforms producing a time delay in which the waveform generated by each element will reach the desired area

Phase Scanning Uses phase shifters Phase varies from 0 to 2π radians Frequency dependent Can calculate phase between elements

Phase between elements In order to steer beam appropriately the required phase shift is needed This can be calculated based on following equation: ΔΦ= 2𝜋∗sin⁡(𝜀) λ where ε is the angle off bore-sight (azimuth or elevation) Example Problem

AN/SPY 1 For Ticonderoga class Cruisers and Arleigh-Burke class Destroyers Capable air defense radar Can handle search, track, and fire control Recently implemented in Ballistic Missle Defense Various upgrades over its years of service SPY-1 is the primary air search radar the Aegis Combat System. The S-band multi-function phased array radar system is designed to meet the most demanding requirements and environments. SPY-1 can automatically track multiple targets simultaneously while maintaining continuous surveillance of the sky, from the wave tops to the stratospher

AN/SPY 1 S-band Radar Designation SPY (Water, Radar, Surveillance) Size: 12 ft octagon Weight above deck (lb): 13,030 per face Weight below deck (lb):131,584 Range (nm): 175, 45 against sea-skimming missiles Band: S band (3.1 – 3.5 GHz) Instantaneous bandwidth (MHz): 40 Beam (º): 1.7 x 1.7 Peak power (MW): 4 – 6 Average power (kW): 58 Gain (dB):42 Pulse compression ratio: 128:1 Sea skimming targets (reduced range mainly due to sea scatter (“clutter”)

Civilian conversion National Severe Storm Laboratory in Norman, OK

Multi-function Phased Array Radar 1970’s repurposed Navy radar Goal is to replace radars for Single focus aircraft tracking Single focus weather tracking Why not both?

MPAR System Benefits 4-5 min mechanical scan reduced to under a minute Estimated $4.8 billion in savings to the taxpayer: $1.8 billion with single radars having multi-function capability $3 billion in life-cycle costs projected over 30 years. Proven to function in presence of weather and clutter Provided a mean tornado lead-time of 20.1 minutes in real scenario Collaborative effort through multiple schools, agencies, and corporations In spring, 2014, engineers successfully tested aircraft detection and tracking algorithms that were robust in the presence of weather and ground clutter\ 13 minute national mean tornado lead-times using current NWS radars. (8 min improvement) NOAA NSSL and National Weather Service Radar Operations Center; the Federal Aviation Administration; Lockheed Martin, Raytheon, Northrup Grumman, Ball Aerospace, and Saab Sensis; the Department of Defense; University of Oklahoma’s School of Meteorology, School of Electrical and Computer Engineering, and Advanced Radar Research Center; Oklahoma State Regents for Higher Education; Basic Commerce and Industries; Massachusetts Institute of Technology/Lincoln Laboratory, Georgia Tech Research Institute, and the Office of the Federal Coordinator for Meteorology

References Payne, Craig M. Principles of Naval Weapon Systems. Annapolis, MD: Naval Institute, 2006. Print. Richards, Mark A., James A. Scheer, and William A. Holm. Principles of Modern Radar Basic Principles. Edison, NJ: SciTech, 2010. Print. "AN/SPY-1." Wikipedia. Wikimedia Foundation, 22 Feb. 2016. Web. 25 Apr. 2016. Fields, Glen. "Phased Array Radar At the Intersection of Military and Commercial Innovation." Microwave Journal. 14 Jan. 2014. Web. 27 Apr. 2016. Phased Array Radar." NOAA National Severe Storms Laboratory. Mar. 2016. Web. 27 Apr. 2016.