The application of phased-array antennas for LEO constellation satellites is increasing dramatically. To meet the time-to-market demand of this NewSpace sector, the testing, calibration and verification of these antennas must be efficient. Addressing this need, MVG has introduced the SG Evo, a multi-probe spherical near-field antenna measurement solution capable of testing phased-array antennas on high-throughput satellites from 10x to 100x faster than previous near-field test methodologies.
SINGLE- VS. MULTI-PROBE NEAR-FIELD TESTING
When measuring antennas with a single probe near-field system, the probe is positioned in front of each radiating element while the RF is modulated according to the antenna’s operating parameters. The accuracy of the probe’s position relative to the element is not critical if the probe spacing matches the element spacing and meets the Nyquist sampling criteria. However, probe movement can introduce phase errors caused by RF cable movement, increasing measurement uncertainty. This measurement process is time consuming, since the probe mechanically moves between stop and go, point by point. For phased-array antennas with many embedded antenna elements, the process may require thousands of measurements and many hours—even days—to complete, with long measurements susceptible to additional errors from temperature fluctuations.
A multi-probe near-field measurement system can perform an electronic 2D scan of a probe array within a few milliseconds and a full 3D spherical radiation pattern in minutes. This saves a tremendous amount of time throughout the cycle of antenna system test and calibration, reducing overall satellite development time.
Like other antennas, phased-array radiation patterns are affected by their environment, so it is important to test the performance when the array is integrated into the final satellite assembly. Measurements of integrated phased-array antennas can interact with the surrounding structure and neighboring antennas. Full system-level testing of the antennas validates their operational connectivity and performance prior to deployment. Testing and calibration of the final payload assembly is a significant step to determine whether a satellite is ready for launch, lowering the risk of a failure in orbit and avoiding the significant costs associated with such a failure (see Figure 1).
THE SG EVO
To meet the time and accuracy demands of fast-moving LEO satellite development and increased production volumes, MVG developed the SG Evo (see Figure 2). The SG Evo is a multi-probe, spherical, near-field antenna measurement and over-the-air (OTA) test system covering 400 MHz to 30 GHz and measuring between 10x and 100x faster than traditional near-field measurement systems. Designed to provide configuration flexibility, wider frequency range and advanced oversampling capabilities while minimizing the movement of the device under test (DUT), the SG Evo accommodates various device types and sizes. This single antenna measurement system can be used during every stage of system development, from antenna subsystem characterization to system testing with the antennas integrated.
Evolved from MVG’s legacy multi-probe antenna measurement systems, the SG Evo delivers fast spherical near-field measurements with increased measurement accuracy. Using an efficient near-field to far-field transformation and other post-processing capabilities, antennas can be characterized within minutes. Standard measured antenna parameters produced by the SG Evo include gain, directivity, efficiency, radiation patterns, sidelobe levels, beam peak, beamwidth, front-to-back ratio and cross-polarization discrimination (see Figure 3).
Comprised of a mechanical arch of multiple wideband, dual linear-polarized probes, the SG Evo performs measurements over a wide frequency range with fast electronic switching of its integrated probe array. An azimuth stage enables easy mounting of DUTs and provides 180-degree rotation, enabling complete 3D spherical pattern characterization. The mechanical arch is designed to provide oversampling, if needed to accommodate measurements at higher frequencies, without repositioning the DUT. This capability increases measurement stability and accuracy by minimizing DUT and cable motion.
The SG Evo also has the capability to perform OTA measurements of subsystems and full system-level DUTs using complex signal modulation. Optimum signal transmission can be measured through total radiated power, total isotropic sensitivity, effective isotropic radiated power and effective isotropic sensitivity testing of coordinating satellite antennas in the SG Evo.
As dictated by the Nyquist sampling criteria, measurement sampling density increases with frequency. For phased-array antenna measurements involving thousands of beam states, hundreds of thousands of samples may be required, and the measurement time can be an issue. These high gain, high frequency space-borne antennas are often sensitive to both movement and temperature, which degrades measurement accuracy. The reduced measurement time and DUT movement afforded by the SG Evo help ensure measurement accuracy.
The SG Evo uses patented technology to perform oversampling and reference measurements. Oversampling is achieved using precision mechanical movement of the probe array. As a result, full 3D device characterization at higher frequencies requires only stepped azimuth rotation of the DUT, which minimizes gravitational deflections and cable motion. The very fast scan speed of the probe array reduces measurement errors caused by temperature change. Incorporating a reference channel into the probe array further compensates for temperature change during 3D measurements. These capabilities of the SG Evo work together to ensure fast and accurate measurements.
An additional time-saving feature of the SG Evo, advancing the legacy of the MVG SG series multi-probe systems, is a configurable system architecture supporting parallel receivers. Measurement time can be dramatically reduced by making simultaneous measurements using multiple receivers, an advantage for measurements at many frequencies or antenna beam states.
The modular design of the SG Evo accommodates customized builds to address a variety of requirements and test article sizes: the diameter of the probe array arch and the azimuth positioner model are selected based on the size and weight of the DUT; probes are selected based on the measurement frequencies and support 400 MHz to 30 GHz.
The capacity of the SG Evo is not limited to the measurement of phased-array antennas for satellite payloads. It is useful for other applications, such as base station antennas, and is suitable for initial prototype tests in research and development to the final validation of fully integrated antenna systems during production.