BENT 4343 RADIO NAVIGATION SYSTEM Dr. Ho Yih Hwa Room: A3/37 Tel:

Learning Outcomes At the end of this subject, students should be able to : Explain basic principles of radar radio navigation system in technical and application Analyze structures, characteristics and working principle of radar system. Analyze structures, characteristics and working principle of GPS. Design basic radio navigation system that use in flights and ships communication. Report and explain their given assignment clearly.

Radio navigation application of radio frequencies to determine a position on the Earth. The basic principles are measurements from/to electric beacons, especially – directions, by bearing, radio phases or interferometry – distances, ranging by measurement of travel times – velocity, by means of radio Doppler shit

Radio direction finding By tuning in a radio station and then using a directional antenna to find the direction to the broadcasting antenna/radio sources By using triangulation, two such measurements can be plotted on a map where their intersection is the position. Early systems used a loop antenna that was rotated by hand to find the angle to the signal, while modern systems use a much more directional solenoid that is rotated rapidly by a motor, with electronics calculating the angle. These later systems were also called Automatic Direction Finders, or ADF. A more sophisticated approach to ADF was to use two loop antennas, set up at a right angle to each other, and measure the ratio of the signals from each antenna to get the angle to the beacon.

BRITISH NAVIGATION SYSTEMS: GEE (GRID) It was the first hyperbolic navigation system to be used operationally and allowed an aircraft or ship to locate its position by timing the delays between two sets of signals. three transmitters were used (1 Master & 2 Slave A & B) that were sited about 80 to 160 kilometers (50 to 100 miles) from each other and transmitted on wavelengths in the range of 15 to 3.5 meters (20 to 85 MHz). The three transmitters sent out periodic radio signals in a four-part cycle, with each step of the cycle a millisecond apart: – START: Master emits a pulse. – 1 ms: Slave A emits a pulse. – 2 ms: Master emits a distinctive double synchronizing pulse. – 3 ms: Slave B emits a pulse. The cycle repeats every 4 milliseconds, 250 times a second. line-of-sight system, with poor accuracy. At a distance of 400 kilometers (250 miles), Gee could target a site within an ellipse about 1.6 kilometers long and 9.6 kilometers wide

BRITISH NAVIGATION SYSTEMS: GEE

LORAN (LOng RAnge Navigation designed to provide longer range than Gee at the expense of accuracy, primarily for naval navigation. The most recent version of LORAN in use is LORAN-C, which operates in the low frequency (LF) portion of the radio spectrum from 90 to 110 kHz.

RADAR & How It works Antenna Transmitted Pulse Target Cross Section Propagation Reflected Pulse (“echo”)

Advantages of Radar Long range detection and tracking of targets– 1000’s of miles All weather and day/night operation Wide area search capability Coherent operation enables– Simultaneous reliable target detection and rejection of unwanted “clutter” objects –Target imaging (fixed and moving) –Very fast beam movement with electronic scanning of antennas ( microseconds) –Ability to adaptively shape antenna beam to mitigate interference and jamming “Relatively lossless, straight line propagation at microwave frequencies

Disadvantages of Radar Long range detection requires– Large and heavy antennas –High power transmitters –Significant power usage –$$$$ Radar beams not propagate well –through the Earth, water, or heavy foliage –around obstacles Vulnerable to jamming, and anti-radiation missiles Target can detect that it is being illuminated Target can locate the radar in angle-space The echo from some targets is becoming very small –Low observable technology

What Radar Measure? Surveillance

What Radar Measure? Civil Radars

What Radar Measure? Airborne Radars

What Radar Measure? Instrumentation Radars

Pulsed Radar Terminology and Concepts

Example

Radar Observables Transmitted Signal: Received Signal: AmplitudeAngleTime DelayDoppler Frequency Depends on Radar Cross Section (RCS), range, etc. Azimuth & Elevation

Doppler Shift This peak leaves antenna at time t = 0, when aircraft at R 0 The peak A arrives at target at time Δt Aircraft moving with radial velocity V The period of the transmit pulse is T, and f 0 = 1/T and c = λ/T = λf 0 Note: c  t = R 0  V  t or Time when A arrives back at radar Time when B arrives back at radar

Doppler Shift The period of the transmitted signal is T and the received echo is T R = T B -T A or For V< < c then + Approaching targets  Receding targets

Block Diagram of Radar System

Radar Frequency Bands 21

Standard Radar Bands & Typical Usage HF 3 – 30 MHz VHF 30 – 300 MHz UHF 300 MHz – 1 GHz L-Band 1 – 2 GHz S-Band 2 – 4 GHz C-Band 4 – 8 GHz X-Band 8 – 12 GHz Ku-Band 12 – 18 GHz K-Band 18 – 27 GHz Ka-Band 27 – 40 GHz W-Band 40 – 100+ GHz Search Radar Tracking Radar Search & Track Radar Missile Seekers Range Instrumentation Radar

Propagation Effects on Radar Performance Atmospheric attenuation Reflection off of earth’s surface Over-the-horizon diffraction Atmospheric refraction

Radar Cross Section (RCS)

Antennas – Fundamentals and Mechanical Scanning Techniques

Problems 1.A radar sends a short pulse of microwave electromagnetic energy directed towards the moon. Some of the energy scatters off of the moon’s surface and returns to the radar. What is the round trip time? Given that distance between Earth and Moon is km. If the target was an aircraft 278 km, what is the round trip time? 2.A radar transmits a pulse of width of 2 microseconds. What is the closest 2 targets can be and still be resolved? 3.You are traveling 220 km/s in your new pereduo Viva. A nearby policeman, using his hand held X-Band (frequency = 9,200 MHz) speed radar, transmits a CW signal from his radar, which then detects the Doppler shift of the echo from your car. Assuming that you are speeding directly towards his speed trap, how many Hz is the frequency of the received signal shifted by the Doppler effect? Is the Doppler shift positive or negative?