Radar and Electronic Peacekeeping
Anritsu provides various test and measurement solutions for Radar related measurement. Some of the popular instruments from Anritsu are
- VNA Master (Handheld Vector Network Analyzer)
- Spectrum Master
- Site Master (Cable and Antenna Analyzer)
- Vector Star (Benchtop High performance VNA)
- Signal Generator
- Power meter & Power Sensors
- Signal Analzyer.
These instruments are used in R&D, production and maintenance of various communication network which use a lot of electronics inside. This article cover some basic terms used in A&D industry and measurement methods.
Radio-navigation aids such as Instrument Landing Systems (ILS) and VHF Omnidirectional Range (VOR) systems help aircraft successfully take off and land by providing exact vertical and horizontal navigation guidance. These ILS, VOR consist of electronics components and system inside to perform desired task.
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.
Instrumentation for A&D:
Vector Network Analyzer (VNA) is very popular T&M instrument used by many aerospace scientist/ engineers for design of RADAR and other communication network elements such as cable, connectors, cable assembly, antenna system transmitters etc, Radar Cross Section (RCS) measurement is very popular measurement in A&D segment and VNA is perfect candidate for this applicaiton. Radar cross section RCS is the measure of an object’s ability to reflect radar signal in the direction of the radar receiver i.e. it is the measure of the ratio of backscatter per steradian (unit solid angle) in the direction of the radar (from the target) to the power density that is intercepted by the target.
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.
Making Phase Cable Measurements in the Field:
When equipped with the Vector Voltmeter Option 15, the Anritsu VNA Master is a convenient and accurate vector network analyzer for measuring absolute insertion-phase characteristics or comparing phase match between multiple RF cables. It is an especially useful tool in field test configurations, where access to AC power is typically limited. The VNA Master’s Vector Voltmeter mode effectively replaces the functional ratio measurements of now obsolete vector voltmeters and the signal generator. However, it cannot be used to measure RF voltages, which of course, are not needed for determining phase shift. When configured with VVM Option 15, the VNA Master provides detailed software routines and data displays for making phase-cable measurements. It contains its own built-in vector insertion loss and phase receiver, a wideband signal source and directional bridges/couplers—all configured internally—for conducting both 1-port and 2-port measurements at selected CW frequencies . Unlike VVMs with their 1000-MHz limit, the VNA Master with Option 15 measures cable characteristics to 4 GHz, 6 GHz, or 20 GHz (depending on model), making it a suitable replacement for the most used VVM ratio function—measuring component parameters.
The two techniques used by the VNA Master to obtain cable-phase measurements are:
- Insertion technique: This technique utilizes the VNA Master’s 2-port setup to make cable-phase measurements and is generally considered the preferred technique. It characterizes the insertion phase delay of a signal by measuring S21 through the cable. This allows the operator to determine the phase shift of the component or cable from input connector to output connector. Measured S21 data is displayed as insertion loss in dB, while insertion phase is displayed in degrees.
- Reflection technique: This technique measures the S11 reflected signal on a component or cable, and is dependent on the far end of the cable being deliberately mismatched—either shorted or left as an open circuit. With the mismatch, virtually 100 percent of the input signal is reflected and as a result, the phase delay of the measured reflected signal is equal to twice the one-way phase of the cable. Likewise, the cable measured return loss is twice the one-way loss. The reflection technique is especially useful for situations where the operator must manually create multiple phase-matched cables using the “measure-and-snip” operation. This operation requires the engineer or technician to carefully snip small amounts of cable with a diagonal cutter, perhaps 1/8th inch at a time, and re-measure the effect on the 2-way phase.
VNA Master plays an important role in Aerospace and Defence communication network maintenance and deployment.