Define the following terms: Intra-Pulse modulation.
In pulse modulation
Modulation on or within individual pulses.
Define the following terms: Inter-Pulse modulation.
between pulse modulation
The changing or variation of the interval between
successive radar pulses.
Describe the methods of intra-pulse modulation.
- The three basic methods of achieving Intra-Pulse Modulation are:
- Amplitude Modulation on Pulse (AMOP),
- Frequency Modulation on Pulse (FMOP), and
- Phase Modulation on Pulse (PMOP).
- Pulse Compression is achieved by transmitting pulses with some form of internal modulation of sufficient width to provide the necessary power requirements for long
detection ranges.
Describe the methods of inter-pulse modulation.
Inter-Pulse Modulation techniques are described by the
following types:
* Constant PRI
* Staggered PRI
* Jittered PRI
* Dwell/Switch PRI
* Sliding PRI
* Periodic PRI
* Scheduled PRI
* Multi-Pulse
Explain the uses of intra and inter-pulse modulation techniques
as adopted by modern radar systems.
Intra-Pulse Modulation techniques may be used by a radar to:
* Improve range resolution while maintaining average power.
* Encode pulses for data transmission.
* Improve performance against electronic jamming.
Inter-Pulse modulation techniques may be used by a radar to:
* Reduce range ambiguity.
* Eliminate blind speeds.
* Overcome mainbeam eclipsing (Blind Ranges).
* Improve performance against electronic jamming.
* Reduce interaction between adjacent radars using similar PRI’s
Explain radar pulse modulation.
Describe AMOP
Amplitude Modulation on Pulse (AMOP) is achieved by:
* A modulating waveform causing variations in individual pulse
amplitude.
* The modulation may be used to apply a binary number to the
transmitted pulse for identification purposes in the receiver.
Describe FMOP
Frequency Modulation on Pulse (FMOP) is achieved by:
* Varying the frequency of the transmitted pulse within its
Pulse Width.
*Two methods of FMOP are:
* Linear FMOP
* Discrete FMOP
What is discrete FMOP
- The frequency “Steps up”
- Discrete FMOP is a method of coding pulses.
- Requires the modulating waveform to step through
discrete frequencies. - Can be used for pulse compression.
- Can be used for pulse encoding.
What is Linear FMOP
- FMOP is a pulse compression technique used in radar systems.
- the transmission pulse is linearly frequency modulated
- Linear FMOP is often used in chirp radar systems.
Describe PMOP
- Phase Modulation on Pulse (PMOP) is caused by the
carrier phase angle departing from its reference value due
to a modulating signal. - There are three basic types of PMOP:
- Quadrature (90° Phase Shift)
- Binary Phase (180° Phase Shift)
- Polyphase (0, 120 and 240° Phase Shifts)
Describe UMOP
A fourth intra-pulse modulation effect can occur
unintentionally. UMOP is caused by modulation
sensitivity problems in high power transmit tubes.
Common causes of UMOP are:
* Temperature
* Equipment Aging
* Poor Maintenance
Describe constant PRI
A PRI where the peak variations in PRI are less than 1% of the mean PRI.
- reduce the detectability of radar signals by adversaries.
Describe Staggered PRI
- Introduces controlled variations in the PRI timing
A pulse train with two or more Pulse Repetition Intervals (PRIs) that are alternated in a fixed sequence.
- Simple Staggered PRI
- Complex Staggered PRI
Describe Jittered PRI
- Introduces random or semi-random variations in the PRI timing
- A PRI displaying random or pseudo-random variation in the PRI.
- This differs from staggered PRI in that staggered PRIs follow a repetitive pattern.
Describe Dwell and Switch PRI
- In dwell mode, the radar system transmits pulses at a consistent PRI for a certain period of time.
- After the dwell period ends, the radar system switches to a different PRI value.
A PRI capable of being changed between a discrete set of values and dwelling for a fixed or variable intervals at each PRI.
Describe Sliding PRI
- A PRI system where the PRI is increased or decreased in a linear fashion followed by a switch upon reaching one extreme limit.
- continuously adjusting PRI intervals based on real-time conditions and operational requirements
- The time to complete one sweep of the Sliding PRI is called the
Sweep Time.
Describe Periodic PRI
- PRI values have intervals that vary periodically,
- PRI cannot be described as constant, staggered, jittered, dwell and switch or sliding.
- The modulating waveform is commonly a square, triangular or sinusoidal waveform.
Describe Scheduled PRI
- a structured radar technique that introduces periodic changes in PRI intervals based on predefined schedules or event triggers
*PRI variation that includes some features of all of the other types as determined by a controlling program.
Describe Multi-pulse
Multi Pulse systems use Pulse Groups to perform normal radar functions or to define frame and sub-frames in telemetry or data link systems.
The time interval from the leading edge of the first pulse in one group to the first pulse in the next group is called the Pulse Group Repetition Interval or PGRI.
what are the three basic types of PMOP?
- Quadrature (90° Phase Shift)
- Binary Phase (180° Phase Shift)
- Polyphase (0, 120 and 240° Phase Shifts)
