Radar and Electronic Peacekeeping
Scientists and engineers are constantly working on stealth technology. Using facets and Radar Absorbing Materials (RAMs) such as iron ball paint, Jaumann layers, and foam absorbers; their mission is to make military aircraft, ships, submarines, and missiles virtually invisible to radar detection systems.
Military and major aerospace companies maintain radar cross section (RCS) facilities as part of Radar and Electronic Peacekeeping. Tests are conducted at these labs to verify that stealth designs are successful in reducing RCS to a level that can protect our forces.
Peacekeeping organizations maintain communications systems that can be deployed anywhere and are capable of voice, video and data transmission to aid in peacekeeping operations (PKOs). Technology is being used to help monitor conflicts and arms embargoes, carry out early warnings, and maintain situational awareness necessary to identify threats and support humanitarian efforts.
RADAR is an acronym which stands for Radio Detection and Ranging. The basic concept is that a pulsed electromagnetic wave of known power and frequency is transmitted in a specific direction where it encounters a target that reflects some portion of the signal back, which is measured by a receiving device. Radars can use CW signals, basic pulses and a wide variety of other signal waveforms.
In addition to range, other information about the target can be detected, such as speed and direction, by varying parameters of the radar system. For example, scanning an area with a highly directive antenna can provide the direction of the target in azimuth and elevation, while measuring the frequency shift of the received signal can provide the target’s speed.
Target range is a fundamental use for most radar systems. Radar systems have evolved significantly in how they are constructed, the signals used, the information that can be captured, and how this information can be used in different applications. Radar is used in a wide array of both military and civilian applications, including:
- Surveillance (threat identification, motion detection, or proximity fuses)
- Detection and tracking (target identification and pursuit or maritime rescue)
- Navigation (automotive collision avoidance or air traffic control)
- High resolution imaging (terrain mapping or landing guidance)
- Weather tracking (storm avoidance or wind profiling)
Ground Penetrating Radar
Ground-penetrating radar (GPR) aids in finding buried arms caches, while ground surveillance radars (GSR) detect illegal movements. Peacekeepers detect airspace violations common in war-torn areas using air surveillance radars. Synthetic aperture radar and commercial satellites are used to locate and confirm large refugee movements.
Doppler Pulsed Radar
This is a coherent radar system in which the received pulse-to-pulse phase variations enable the element of speed to be added to the distance and direction of the target. They typically utilize high pulse repetition rates (PRRs), which enables more accurate radial velocity measurements, but have less range accuracy. Doppler pulsed radar systems are used to detect moving targets while rejecting static clutter, which can be very helpful in weather monitoring applications.
Moving Target Indicator (MTI) Radar
MTI radar also uses Doppler frequencies to differentiate echoes of a moving target from stationary objects and clutter. Its waveform is a train of pulses with a low PRR to avoid range ambiguities, at the expense of velocity accuracy. These types of radar systems are often used in ground-based aircraft search and surveillance applications.
Pulse Compression Radar
Short pulse width signals provide better range resolution, but have limited range. Long pulse width signals contain more energy and provide a longer detection range, but sacrifice resolution. Pulse compression combines the power related benefits of long pulse widths with the resolution benefits of short pulse widths. By either modulating the frequency (e.g., linearly for an FM chirp) or the phase (e.g. with a Barker code) of the transmitted signal, the long pulse can be compressed in the receiver by an amount equal to the reciprocal of the modulating signal bandwidth. Many weather monitoring systems have moved to pulse compression radar.
Signal Amplitude and Target Movement
When a target is moving, the amplitude of the pulse signal will also vary with respect to the distance from the receiver. Adding AM to the pulse provides a simple means by which you can vary the amplitude of the pulse over time. The rate is the time in which the variation in amplitude occurs. The depth defines how much the amplitude varies. 1 kHz is selected to line up with the period of the pulse (1/1 ms = 1 kHz). The modulation wave is set to ramp down to simulate the decreasing power of the radar return of a target moving away (which corresponds to the increasing delay we set). Using AM in this way is only a conceptual simulation because the amplitude reduction of an actual radar return would not be linear.
High-Speed Digitizer Method
A number of methods are currently being used to make pulse measurements, including narrowband or band-limited methods, triggered methods and wideband methods. Unfortunately, they all come with limitations and trade-offs. The high-speed digitizer measurement method represents major technology advancement over all prior pulse measurement test methods. While similar to the “historic” wideband method, this method is based on direct acquisition – but at a much higher data rate than was previously available.
By using a high-speed digitizer and performing the alignment with pulse data in a post-processing sense, one avoids the triggering latency issues associated with triggered measurements and potential jitter/inconsistency problems with that triggering. The resolution is set mainly by the acquisition rate instead.
The point-in-pulse measurement quantifies S-parameter data at any point in time within a pulse. The measurements are made with swept frequency or power and plotted accordingly. This measurement mode is useful when trying to avoid possible edge effects of the pulse. For example, amplifiers often have settling effects at the beginning of the pulse. Point-in-pulse measurements are useful when you need to measure the pulse as a whole, but the structure within the pulse is not of great interest nor is the variation from pulse to pulse.
Pulse Profile Measurements
The pulse profiling measurement focuses on the structure of data within the pulse. The measurements are made in the time domain, while the frequency and power are kept constant. This measurement mode is useful for determining pulse characteristics such as overshoot/undershoot, droop, and edge response (e.g., rise/fall time).
The pulse-to-pulse measurement quantifies variations between pulses in a pulse stream. The measurements are also made in the time domain, while the frequency and power are kept constant. This measurement mode is useful when trying to determine whether the pulse characteristics are varying over time. For example, high power amplifiers may have thermal effects which can cause variances in the gain or phase.
Airport Surveillance Radar
In 1998 the United States Federal Aviation Administration (FAA) introduced a new airport surveillance radar called ASR-11 that tracks aircraft movement and additionally provides some weather information. There are now over 400 of these radars deployed across the USA. The high peak power from these radars makes them very easy to detect miles from their location.
Another common application of radar is to monitor weather conditions, including rainfall, storms, and snow. Weather radars can be ground based for actively tracking rainfall and storms or satellite based for wider area monitoring. In the USA a network of over 150 ground based weather radars is operated by the national weather center. Known as the Next Generation Weather Radar (NEXRAD) system, the first radars were deployed and operated in the 1990’s and the system is under continual enhancement. The weather radar characteristics are similar to the airport surveillance radars. Both use the same frequency band and high power pulses. Frequency planning is important to ensure there is no interference between the technologies.
Vector Network Analyzers are perfect elements of an RCS measurement system. They have the measurement speed and accuracy – as well as Time Domain capability – to provide the overall S-parameter critical performance information to help ensure successful stealth designs.
The VNA Master and Site Master families are easy-to-use tools to help make these humanitarian efforts successful. Specifically designed for rugged field environments, they are lightweight and have field-replaceable Li-Ion batteries. Their wide operating temperature range means they will work wherever humanitarian operations are needed.
They also employ the Frequency Domain Reflectometry (FDR) measurement technique for distance-to-fault (DTF) measurements. This allows our instruments to locate slight signal path degradation that is missed by other instruments that use Time Domain Reflectometry (TDR) techniques. Such detection capability helps insure the safety and security of peacekeepers, as well as the effectiveness of their missions.
The Anritsu signal generator product line is ideal for radar or peace keeping applications, whether it’s the MG37020A Fast Switching Microwave Signal Generator with 100 µsec typical switching speed or the MG3690C family of microwave signal generators with the most comprehensive emulation and test of high performance narrow pulse radars.
The Field Master Pro MS2090A pulse analyzer option provides a powerful test solution to measurement pulsed radar signals in the field. The wide measurement bandwidth supports rise time measurements as fast as 30 ns. Coupled with IEEE compliant pulse measurements, routine testing of radars for maintenance or troubleshooting applications is possible in a way that was previously restricted to the lab and can be accomplished in the field.