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Electronic Warfare and Radar Systems Engineering Handbook
- Propagation Time / Resolution -

[Go to TOC]

 

PROPAGATION TIME /
RESOLUTION



1. ROUND TRIP RANGE: RF Cafe - Round trip range equation with t = time to reach target

                        Rules of Thumb

In one μsec round trip time, a wave travels to and from an object at a distance of: The time it takes to travel to and from an object at a distance of:
≈ 150 m
≈ 164 yd
≈ 500 ft
≈ 0.08 NM
≈ 0.15 km
≈ 1 m ≈ 0.0067 μsec
≈ 1 yd ≈ 0.006 μsec
≈ 1 ft ≈ 0.002 μsec
≈ 1 NM ≈ 12.35 μsec
≈ 1 km ≈ 6.7 μsec


2. ONE WAY RANGE: R = ct with t = time to reach target
 
Time Distance Traveled   Distance Time it Takes
1 milli sec (ms) 165 NM 1 NM 6.18 μsec
1 micro sec (μs) 1000 ft 1 km 3.3 μsec
1 nano sec (ns) 1 ft 1 ft 1 nsec


3. UNAMBIGUOUS RANGE
Radar range diagram - RF Cafe(DISTANCE BETWEEN PULSES):RF Cafe - Unambiguous range equeation
Normally a radar measures "distance" to the target by measuring time from the last transmitted pulse. If the interpulse period (T) is long enough that isn't a problem as shown in "A" to the right. When the period is shortened, the time to the last previous pulse is shorter than the actual time it took, giving a false (ambiguous) shorter range (figure "B").


       Rules of Thumb
       RNM ≈ 81Pms
       RKm ≈ 150Pms
    Where Pms is PRI in milliseconds


4. RANGE RESOLUTION

             Rules of Thumb
   500 ft per microsecond of pulse width
   500 MHz IF bandwidth provides 1 ft of resolution.

5. BEST CASE PERFORMANCE:

    The atmosphere limits the accuracy to 0.1 ft
    The natural limit for resolution is one RF cycle.



Table of Contents for Electronics Warfare and Radar Engineering Handbook
Introduction | Abbreviations | Decibel | Duty Cycle | Doppler Shift | Radar Horizon / Line of Sight | Propagation Time / Resolution | Modulation | Transforms / Wavelets | Antenna Introduction / Basics | Polarization | Radiation Patterns | Frequency / Phase Effects of Antennas | Antenna Near Field | Radiation Hazards | Power Density | One-Way Radar Equation / RF Propagation | Two-Way Radar Equation (Monostatic) | Alternate Two-Way Radar Equation | Two-Way Radar Equation (Bistatic) | Jamming to Signal (J/S) Ratio - Constant Power [Saturated] Jamming | Support Jamming | Radar Cross Section (RCS) | Emission Control (EMCON) | RF Atmospheric Absorption / Ducting | Receiver Sensitivity / Noise | Receiver Types and Characteristics | General Radar Display Types | IFF - Identification - Friend or Foe | Receiver Tests | Signal Sorting Methods and Direction Finding | Voltage Standing Wave Ratio (VSWR) / Reflection Coefficient / Return Loss / Mismatch Loss | Microwave Coaxial Connectors | Power Dividers/Combiner and Directional Couplers | Attenuators / Filters / DC Blocks | Terminations / Dummy Loads | Circulators and Diplexers | Mixers and Frequency Discriminators | Detectors | Microwave Measurements | Microwave Waveguides and Coaxial Cable | Electro-Optics | Laser Safety | Mach Number and Airspeed vs. Altitude Mach Number | EMP/  Aircraft Dimensions | Data Busses | RS-232 Interface | RS-422 Balanced Voltage Interface | RS-485 Interface | IEEE-488 Interface Bus (HP-IB/GP-IB) | MIL-STD-1553 & 1773 Data Bus |
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