Frequently Asked Questions

NSI-MI Technologies designs and manufactures advanced RF (radio frequency) measurement systems used to characterize antennas, radar cross section (RCS), phased arrays, radar systems, radomes, and more. We provide complete turnkey test systems, individual precision components, target-simulation systems, precision motion equipment, and antenna test services for the aerospace, defense, satellite, and wireless industries.

Solutions range from fully customized, site-built ranges to commercial-off-the-shelf (COTS) configurations, and are backed by in-house design, manufacturing, installation, and long-term support.

NSI-MI Technologies is an antenna and RF measurement company formed from the combination of two long-established industry pioneers (Nearfield Systems and MI Technologies) and is part of AMETEK, Inc. It is recognized as the oldest company in the antenna measurement industry, having installed the world's first commercial compact range in 1973 and delivered its first commercial spherical near-field system in 1980.

NSI-MI is a long-term, value-added supplier — not only delivering accurate, reliable test equipment but committing to support the full lifecycle of each system.

NSI-MI Technologies is headquartered in the Atlanta, Georgia (USA) area, with an additional U.S. facility in the Los Angeles, California region and an office in the United Kingdom. Compact range systems are manufactured in the USA at the Atlanta, GA facility and shipped to customers worldwide.

Regional contact numbers:
Atlanta +1 678 475 8300
Los Angeles +1 310 525 7000
UK +44 1246 581500.

The company also supports customers through a global network of sales teams and partners

NSI-MI serves aerospace, defense, satellite/SATCOM, and wireless (including 5G and mmWave) markets, plus automotive and research & development. Typical applications include antenna pattern and gain characterization, phased-array and AESA testing, radar cross section (RCS) measurement, radome evaluation, satellite antenna testing, automotive antenna testing, and precision positioning.

NSI-MI has more than 50 years of experience in RF and antenna measurement. It has been setting the standard in near-field testing for over 45 years, delivered its first commercial near-field systems more than 45 years ago, and installed the world's first commercial compact range in 1973.

Near-field testing measures an antenna's radiated fields close to the antenna over a defined surface (planar, cylindrical, or spherical) and then mathematically transforms that data to predict the far-field pattern; data collection is not real-time because it uses synthetic-aperture scanning. Far-field testing measures the antenna pattern directly at a distance where the wavefront is effectively a plane wave, capturing each pattern cut in real time.

Near-field ranges are compact, controlled, and highly repeatable, making them ideal where space is limited or full-pattern accuracy is required. Far-field and compact range methods are faster per pattern cut and well suited to high-throughput production testing.

The far-field (Fraunhofer) distance is the range at which an antenna's radiated wavefront becomes approximately a plane wave, commonly estimated as 2D²/λ, where D is the largest antenna aperture dimension and λ is the wavelength. It matters because traditional direct far-field measurements must be taken at or beyond this distance to be accurate.

For large or high-frequency antennas this distance can become impractically long, which is why near-field scanning and compact antenna test ranges (CATR) exist: both deliver far-field results without requiring the full physical separation.

A quiet zone is the volume within a test range where the test signal closely approximates an ideal plane wave, with amplitude and phase variations held to tight tolerances so that the antenna or target under test is illuminated uniformly. The size of the quiet zone determines the largest device that can be tested accurately.

NSI-MI compact ranges offer quiet zones from roughly 0.5 m up to elliptical or cylindrical zones exceeding 10 m (including a 7.3 m × 10.7 m elliptical quiet zone for the largest systems). Near-field ranges don’t typically specify a quiet zone – we instead refer to the maximum antenna under test (AUT) size possible based on the dimensions of the system and facility.

Near-field to far-field transformation is the mathematical process that converts field data measured close to an antenna into its equivalent far-field radiation pattern. Because near-field scanning captures amplitude and phase over a surface, the transformation can reconstruct the full far-field pattern provided the majority of radiated energy is collected by the probe.

Accurate transformation depends on adequate sampling, probe correction, and ensuring minimal energy escapes the measurement surface. NSI-MI's Advanced Antenna Acquisition and Analysis (A4) software performs planar, cylindrical, and spherical transformations

AUT stands for “antenna under test” and DUT stands for “device under test.” Both refer to the antenna, array, sensor, or radome being measured on the range. The terms are used interchangeably in most antenna measurement contexts, with AUT being specific to antennas.

EIRP (Effective Isotropic Radiated Power) is the power an antenna system appears to radiate in its direction of maximum gain, equal to the transmit power multiplied by the antenna gain relative to an isotropic radiator. It is a key performance metric for active antennas, phased arrays, and 5G mmWave devices.

NSI-MI provides dedicated near-field and far-field EIRP analysis modules within its acquisition and processing software to measure radiated power performance of active and integrated antenna systems.

An anechoic chamber is a shielded room lined with RF-absorbing material that suppresses reflections and external interference, creating a controlled electromagnetic environment for accurate, repeatable antenna measurements. It allows testing of sensitive or classified devices in a secure, weather-independent space.

Most NSI-MI near-field and compact range systems are designed to operate inside an anechoic chamber, though some configurations can be installed in open facilities.

A planar near-field (PNF) system measures an antenna's fields over a flat (planar) surface in front of the aperture and transforms them to the far field. It is ideally suited to characterizing medium- and high-gain antennas accurately and efficiently, and is the industry standard for calibrating Active Electronically Scanned Arrays (AESAs) using the “park and probe” technique.

A key advantage is that the device under test remains stationary during the measurement, which is important for complex modern antennas. NSI-MI recommends PNF for antennas with gain of about 15 dBi or higher, with data collection limited to roughly ±80° from boresight. PNF systems are available in vertical and horizontal configurations.

A spherical near-field (SNF) system measures an antenna's fields over a sphere surrounding it, making it among the most accurate methods available for full-sphere radiation pattern characterization. The SNF method was pioneered by the Technical University of Denmark, and NSI-MI delivered its first commercial SNF system in 1980.

SNF is used to measure virtually all antenna types, including complex defense and space antennas. Available configurations include roll-over-azimuth (the most common, supporting full-sphere measurement of antennas up to about 3 m in diameter), overhead theta-axis, and stationary SNF solutions.

A cylindrical near-field (CNF) system acquires data over a vertical cylinder surrounding the device under test. It provides wider angular coverage than a planar system but not the full-sphere coverage of a spherical system, and is well suited to testing fan-beam antennas and measuring antenna backlobes.

Because a vertical PNF scanner already includes the linear axis a CNF needs, adding CNF capability to a vertical planar system is a common and cost-effective upgrade. Care must be taken to keep radiation away from the open top and bottom of the cylinder.

Choose planar (PNF) for medium- to high-gain directional antennas (about 15 dBi or higher) where a stationary device and high throughput matter; choose cylindrical (CNF) for fan-beam antennas or when backlobe coverage is needed; and choose spherical (SNF) when you need the most accurate full-sphere pattern, including for low-gain, omnidirectional, or complex antennas.

Combination systems are available: some PNF systems can be upgraded with cylindrical or spherical add-ons, and the 8-axis robotic system supports all three geometries. NSI-MI's applications engineers help match the geometry to your antenna type, frequency, and throughput requirements.

The Robotic Antenna Measurement System (RAMS) is NSI-MI's 8-axis system that uses a 6-axis robotic arm combined with precision positioners to perform planar, cylindrical, and spherical near-field measurements in a single platform. It is designed for antennas up to about 2.4 m × 1.2 m (8 ft × 4 ft) and supports high-, medium-, and low-gain antennas

Its multi-geometry flexibility makes it well suited to R&D environments and facilities that need to test a wide variety of antenna types without dedicating separate ranges to each

MARS (Mathematical Absorber Reflection Suppression) is an NSI-MI post-processing software technique that identifies and mathematically removes unwanted range reflections and scattering from near-field measurement data. It improves measurement accuracy and can reduce reliance on extensive physical absorber, enabling accurate results in less-than-ideal test environments.

MARS is available within the NSI-MI’s A4 software suite and is particularly valuable for smaller chambers, lower-frequency testing, or ranges where reflections would otherwise degrade pattern accuracy.

Yes. NSI-MI offers economical, pre-engineered (pre-configured) near-field systems for customers with accelerated delivery schedules or budget constraints. These turnkey solutions are designed for straightforward assembly in either an anechoic chamber or an open facility and support frequency ranges from about 0.4 to 110 GHz.

Both spherical and planar pre-configured systems are available, with options and accessories to maximize range throughput and flexibility.

A Compact Antenna Test Range (CATR) is an indoor far-field measurement system that uses a precision parabolic reflector to convert a spherical wave from a feed into a collimated plane wave, creating true far-field conditions within a compact, controlled space. This eliminates the need for very large indoor or outdoor ranges.

NSI-MI installed the world's first commercial compact range in 1973 and has led reflector design, manufacturing, installation, and characterization ever since. CATR systems capture data in real time and are widely used for antenna pattern measurement, RCS, and radome testing.

Use a compact range (CATR) when you need real-time far-field data and high throughput, especially for production testing of directional antennas, AESA radar, and 5G NR devices. Unlike near-field scanning, a CATR does not require scanning the entire aperture to produce a single far-field pattern cut, making evaluations faster and reducing operating costs

Compact ranges are also preferred for testing sensitive or classified antennas, radars, and AESAs because they operate in a shielded, secure, interference-free indoor environment. Near-field systems remain advantageous where full-sphere accuracy or a stationary device under test is the priority.

NSI-MI compact ranges are offered in small, medium, and large classes with quiet zones from about 0.5 m up to over 10 m, plus custom sizes. Small systems provide roughly 0.5–1.2 m quiet zones (about 2 GHz to 110 GHz and beyond), medium systems about 0.9–2 m (about 1.5–110 GHz and beyond), and large systems elliptical or cylindrical quiet zones from 3 m to over 10 m (about 0.5–40 GHz and beyond).

Portable compact range measurement systems are also available with quiet zones starting around 0.2 m, ideal for measuring medium- to high-gain antennas at higher frequencies. Each site-built system includes a reflector and support structure, feed and AUT positioners, a control system, a Windows workstation, and acquisition and processing software.

A compact range reflector is the precision-engineered parabolic (often rolled-edge) surface at the heart of every compact range, responsible for collimating the feed signal into the uniform plane wave required for accurate antenna, RCS, and radome measurements. Reflector accuracy directly determines quiet-zone quality.

NSI-MI has designed, manufactured, installed, and characterized compact range reflectors since 1973 and offers single-panel through large multi-panel reflector systems

.

Indoor far-field ranges place the antenna and source at the required far-field separation inside a shielded, anechoic environment, providing security, repeatability, and freedom from weather. Outdoor far-field ranges use long physical separations in the open air and are typically used for very large antennas or where the required far-field distance cannot be achieved indoors.

NSI-MI supplies both indoor and outdoor far-field systems, as well as compact ranges that deliver far-field conditions in a fraction of the space required by a traditional direct-illumination far-field range.

Yes. NSI-MI systems support 5G New Radio (NR) and millimeter-wave (mmWave) testing, including base-station antennas, wireless handsets, massive-MIMO arrays, and on-chip antennas. Compact ranges and near-field systems both support the high frequencies these technologies use, with configurations operating up to 110 GHz and beyond.

Relevant measurements include radiated pattern and gain, EIRP, and active antenna performance, supported by NSI-MI's Active Antenna Test Suite and EIRP analysis software.

Active Electronically Scanned Array (AESA) and phased-array antennas are commonly tested using planar near-field systems with the “park and probe” technique, in which the array beam is held in a fixed state while the probe scans the aperture. This characterizes element-level and beam-level performance with the array stationary, which suits complex active arrays.

Compact ranges are also used for AESA performance testing where real-time far-field measurement and a secure, shielded environment are required. NSI-MI's Active Antenna Test Suite supports specialized active-array measurements.

Radar cross section (RCS) measurement assesses how detectable a target is by radar by illuminating it with a plane wave across a defined frequency range and quiet-zone volume and measuring the reflected energy. Compact ranges are ideal for RCS testing because they replicate far-field plane-wave conditions indoors in a secure environment.

Accurate RCS testing requires RF instrumentation, specialized RCS feeds, and low-RCS target positioning hardware such as rotators and low-scatter pylons, all engineered to minimize stray scattered and diffracted energy that could corrupt the measurement.

Radome testing evaluates the electromagnetic performance of a radome — the protective cover over an antenna — to confirm it is transparent to the enclosed antenna's signal. Key measured parameters include transmission efficiency, beam deflection, and boresight error (BSE), which is the angular pointing error a radome introduces into the antenna beam.

Compact ranges are used to characterize both military and commercial aircraft radomes. NSI-MI supports test methods including electronically calibrated antenna and null-search BSE techniques, ensuring radomes meet safety and mission performance standards.

Satellite and SATCOM antennas are tested for pattern and gain, feed characterization, radome characterization, and the measurements required for terminal operations certification. Spherical near-field and compact range methods are both used, depending on antenna size, frequency, and the need for full-sphere coverage.

NSI-MI's long heritage in spherical near-field measurement makes it a frequent choice for complex space and satellite antennas, and it also provides gain calibration of customer antennas and near-field probe calibration as services.

Automotive antennas are tested for pattern and gain, integrated (in-situ) antenna performance, and behavior over a simulated vehicle ground plane. Because vehicle antennas are increasingly integrated into the body and serve connectivity, radar, and V2X functions, testing often characterizes the antenna as installed rather than in isolation.

NSI-MI offers dedicated automotive antenna test solutions, ground-plane simulation and testing, gain calibration of customer antennas, and near-field probe calibration.

NSI-MI's RF instrumentation includes receivers (such as the Vector Field Analyzer and the Vector Digital Receiver), synthesized signal sources, RF accessories (multiplexers, multiplier-amplifier-couplers, and remote mixers), measurement controllers, and a range automation system. Together these acquire and control the RF measurement chain for antenna, RCS, and radome ranges.

NSI-MI offers a broad line of precision positioners, including rotary positioners (azimuth, azimuth-over-elevation, elevation-over-azimuth, polarization, turntables, arches, and high-power rotators), linear positioners (vertical and horizontal XY positioners, floor slides, offset slides, and vertical slides), pointing-and-tracking systems with gimbals, and low-RCS rotators and pylons.

Positioner motion is managed by NSI-MI position-control products such as precision axis controllers, motion controllers, and integrated position controllers. High-power rotators are built to handle heavy loads, high speeds, and harsh outdoor environments.

The Vector Digital Receiver is NSI-MI's latest receiver product, designed to act as the master timing controller for complex electronic measurement and data acquisition. By taking command of system timing, it enables faster, tightly synchronized measurements across the range.

It is part of NSI-MI's receiver product family alongside the Vector Field Analyzer, multi-channel extenders, and distributed frequency converters.

NSI-MI offers two primary software platforms: MI-3000 and NSI2000. Both provide acquisition, analysis, and near-field to far-field transformation for planar, cylindrical, and spherical measurements, along with specialized modules for radome analysis, RCS analysis, EIRP, antenna gain calibration, time-domain analysis, and test-zone analysis.

NSI2000 is available in Standard and Professional editions and includes MARS (Mathematical Absorber Reflection Suppression), a Motion Tracking Interferometer module, the Active Antenna Test Suite, and EIRP capability. The Advanced Antenna Acquisition and Analysis package supports demanding measurement workflows.

Yes. In addition to building systems, NSI-MI operates in-house test facilities and offers antenna, radome, and RCS testing as a service. Customers who do not have their own range — or who need overflow capacity, specialized capability, or independent verification — can have devices measured at NSI-MI's facilities.

NSI-MI's facilities include a compact antenna test range, a combination near-field range, multiple spherical near-field ranges (including a high-frequency range), and a dedicated calibration range.

NSI-MI's test services cover aerospace, defense, wireless, automotive, SATCOM, and R&D devices. Common measurements include pattern and gain, phased-array performance, radome testing, gain calibration of customer antennas, near-field probe calibration, 5G mmWave measurements, massive-MIMO antenna testing, on-chip antenna testing, and ground-plane simulation.

The company also supports maintenance, repair, and overhaul (MRO) operations and measurements required for SATCOM terminal operations certification.

Yes. NSI-MI's in-house test ranges are configured with NIST-traceable calibrated components, and the company operates a dedicated calibration range. This traceability supports defensible, repeatable results for commercial and military antenna, radome, and RCS measurements.

NSI-MI also provides gain calibration of customer antennas and near-field probe calibration as standalone services.

NSI-MI provides all three. Customers can purchase complete turnkey measurement systems, highly customized site-built ranges engineered to specific requirements, or individual precision components and software to upgrade an existing range. Pre-configured systems are available when delivery speed or budget is the priority.

Every system is backed by in-house design, construction, and system integration, plus a long-term support commitment across the system's lifecycle.

NSI-MI provides long-term, lifecycle support including technical support, maintenance, calibration, training, upgrades, and applications engineering. The company emphasizes being a “partner for life,” furnishing expert guidance and best-in-class tools for the full life of each system.

Support is delivered through a broad customer service network spanning the company's U.S. and UK locations and its global partners.

Yes. NSI-MI offers a Virtual Short Course covering antenna measurement theory and practice, drawing on the company's decades of measurement expertise. The short course material spans near-field and far-field techniques, transformations, error analysis, and best practices for accurate measurement.

Training complements NSI-MI's technical paper library, videos, and published books, which together form a deep knowledge base for antenna measurement engineers.

You can request information or a quote through the “Request for Info or Quote” form on the NSI-MI website, or contact a regional office directly:

Atlanta: +1 678 475 8300
Los Angeles: +1 310 525 7000
UK: +44 1246 581500. NSI-MI also maintains a sales team, global partners, and a technical support contact for existing customers.

For standard parts and accessories, NSI-MI operates an online store at store.nsi-mi.com.