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[Go to TOC] PROPAGATION TIME /
RESOLUTION
1. ROUND TRIP RANGE:  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
 (DISTANCE BETWEEN PULSES):
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 |
This HTML version may be printed but not reproduced on websites.
| 
Kirt
