Core technology: Spherical near-field testing (near- and far-field conversion)
+ tight-field fast calibration
Phased array antennas require amplitude-phase calibration during the development and production, and testing of the multiple wave position direction maps that are formed. The most common planar near-field needs to be calibrated one by one for each phased array unit in a high-precision two-dimensional plane, which is slow; and as the scanning frame range usually does not exceed 45° and the probe cross-polarisation deteriorates sharply at large angles, it is difficult to meet the testing requirements in terms of capability and accuracy of phased array far-wave position testing; in addition, the geometrically increasing amount of phased array multi-wavelength directional map testing also The problem is that
General Test Systems (GTS) has pioneered an integrated phased-array fast calibration test system that combines the advantages of tight-field and spherical near-field systems to compensate for the shortcomings of planar near-field systems. The tight-field configuration of planar wave radiation eliminates the need for slow mechanical scanning for amplitude-phase calibration and replaces it with microsecond channel switching, improving calibration efficiency by a factor of ten or more. The spherical scanning system overcomes the drawbacks of the planar scanning system with its narrow scanning range and poor cross-polarisation, enabling highly accurate testing of any type of phased array antenna. In addition, General Test (GTS) has creatively proposed a multi-wavelength fast test solution, which completely solves the problems of calibration and test speed and accuracy of phased arrays.
General Test (GTS) has introduced a highly advantageous and innovative total solution. Combining the advantages of a tight field and a spherical near field (patented technology), it solves the challenges of installation, calibration, and testing of active phased arrays.
The solution solves the problem of phased array calibration speed by using the compact field and the problem of test accuracy and long-wave testing by using the spherical near field. Combined with the phased array multi-wavelength testing method, it greatly improves the testing efficiency and completely solves the problems in all aspects of phased array calibration and testing.
Highly capable of testing at remote wavelengths
The spherical near-field test system is not limited by the scanning range and theoretically supports the scanning of any angle range on the global surface, therefore it is not limited by the type of component under test and can test any type of antenna with any beam pointing, and the test accuracy is not reduced by the far beam.
Large part sizes can be measured
For tight field systems, when testing in the directional map, it is generally required that the size of the part under test is smaller than the static zone to test accurately. However, when doing the amplitude-phase calibration, this restriction does not apply. When the size of the measured part is large, the measured part can be divided into several areas, and each area of the measured part can be gradually moved to the static area for calibration using a rotary table, relatively independent of each other. With this method, the calibration of larger DUTs can be achieved within the limited size of the reflective surface.
For the spherical near-field test system, we have specifically designed a wide beam low cross-polarisation corrugated horn probe for large DUT test scenarios, which can cover the directional map test of large DUTs. At the same time, the sampling density can be increased according to the sampling density = λ/D (D is the minimum measurable sphere diameter) to achieve directional mapping of large parts.
Easy installation and erection
The solution places the reflective surface on top of the darkroom and, with the rocker arm for scanning the sphere, the measured part is simply placed flat on the 1D orientation table, making it easy to operate. It also simplifies the test process by eliminating the need for precise positioning of the test piece as in a planar near-field, which greatly reduces the preparation time for mounting and positioning before the test.
The use of spherical near-field testing allows for speed improvements in two areas.
(1) Multi-frequency point, multi-channel and multi-wavelength fast testing
The system interacts with the phased-array wave controller in real-time through the test software, and combines multi-channel switching and instrument multi-frequency point sampling, ultimately realizing microsecond timing control automation testing for the entire test process. During testing, multiple frequency points, multiple beams, and up to thousands of wave positions can be tested simultaneously with just one 3D scan, which increases the testing efficiency by tens of times compared to traditional testing methods.
(2) Easy installation, no need for accurate alignment
The spherical near-field uses a swing-arm structure for spherical scanning, and the test piece only needs to be placed flat on the 1D azimuthal turntable, making it easy to set up. In addition, the spherical near-field scanning does not require precise alignment of the measured part, but simply places it roughly in the static zone, calculates the required sampling density using the equation λ/D (minimum spherical diameter D), and performs the near and far field transformation. The whole installation process saves several hours compared to a planar near-field.
The use of a tight field for calibration can increase speed in two ways.
(1) Electrical scanning instead of mechanical scanning, significantly increasing the speed of calibration
Unlike conventional planar near-field test systems where mechanical scanning leads to slow calibration, this solution uses the plane wave formed by the compacted field to cover the DUT in the static zone, eliminating the need to move the DUT and probe, and only requires switching the array element channels to collect amplitude phase data one by one to complete calibration. For a 6,000-element phased array, the switching time for each channel plus the instrument sampling time is approximately 1ms~2ms depending on the parameter settings, totaling approximately 6~12 minutes.
(2) Reduction in preparation time for installation and calibration before calibration
Before the planar near-field amplitude-phase calibration, a total station, photogrammetry, and other auxiliary means are needed to install and adjust the phased array antenna position to ensure alignment with the feed probe. This process usually takes 1 to 3 hours or even longer. With the use of a tight field for calibration, the measured object only needs to be placed in the static zone, no position adjustment is required and the installation can be completed in just a few minutes.
RayVerse® 2700 system cross-section
Comparison of planar near-field, tight-field and this solution
Wide angle low cross polarisation corrugated horn probe
Comparison of planar near-field, tight-field and this solution
High testing accuracy
(1) Sampling accuracy does not decrease as the scanning range increases
With a spherical near-field test system, the probe is always pointing towards the part under test when it is being scanned. Theoretically, the same accuracy can be guaranteed at any angle of sampling, unlike in planar near-field, where the probe cannot be pointed squarely at the test object as the scanning range is extended, and the directional map changes and cross-polarisation deteriorate, leading to a reduction in test accuracy.
(2) International top-level wide-angle low cross-polarisation corrugated horn probe
The test probe has a great impact on the test accuracy of the near-field scanning system. The cross-polarisation performance of ordinary dual-polarised horn antennas cannot meet the requirements of use, so corrugated horn antennas with better cross-polarisation suppression are usually used. However, the corrugated horn antenna is difficult to design and complex to process, and few domestic antennas can be designed and developed, and usually only at the apex of the corrugated horn antenna can get good cross-polarization performance, it is difficult to achieve good cross-polarisation in a wide range of angles.
In addition, with conventional corrugated horn, there is a difference between the E and H sides of the phase center, resulting in large differences in horizontal and vertical polarization.
GTS has developed and designed its corrugated horn feeders with low cross-polarisation over a wide angle range. The cross-polarisation performance of approximately -40dB can be maintained over a range of ±20°, and the phase fluctuation between the E- and H-plane is less than 5° over a range of ±50°, providing excellent symmetry. These two features are among the best in the world. The high phase stability over a wide frequency band ensures low phase fluctuations in the static region, the high edge irradiation level (wide beam) results in low amplitude fluctuations in the static region, and the integrated design with absorbing material (the outer side can be covered with absorbing material) results in an overall low RCS characteristic of the feed source.