2022 Technical Papers

A Trade Study on Quasi Far-Field Accuracies and Measurements

Author: Marion Baggett
Publication: AMTA 2022
Copyright Owner: NSI-MI Technologies

Abstract— Recent papers have addressed making far-field measurements at much less than the traditional far-field distance, particularly for 5G MIMO test articles. These papers have focused on main beam measurements only, such as Total Radiated Power (TRP) and have stated that other normal antenna pattern metrics, such side lobe level measurements are not appropriate for this shortened distance. These papers have addressed fixed error levels acceptable for this quasi far-field technique. This paper will present main beam error from two other perspectives, looking at agreement with the previous efforts. In addition, the paper will present a trade study in terms of chamber size, measurement durations and measurement methods between the quasi far-field, compact range, and spherical near-field approaches. This trade study will cover five representative test articles in the C, Ka, and V frequency bands for 5G applications.

Further Exploration of the Holographic PNF Filter

Author: Scott T. McBride
Publication: AMTA 2022
Copyright Owner: NSI-MI Technologies

Abstract — A 2021 AMTA paper introduced a 3D holographic filtering algorithm optimized for the planar near-field (PNF) geometry. This filter has been shown to have an excellent combination of AUT-signal preservation, stray-signal rejection, and processing speed. It requires only the sampling of a conventional PNF measurement, along with a specified 3D boundary surrounding all the AUT’s possible radiating sources.

The 2021 paper suggested some topics for further investigation, specifically the optimal Z spacing through the 3D hologram and the X- and Y-widths of the blanking window’s tapered extension, and those are investigated here. This paper also explores the combination of filtering and probe correction, since the measured convolution of probe and AUT spatial distributions will be wider than that of the AUT by itself. Finally, filter effectiveness is evaluated for different stray-signal locations with respect to the AUT volume.

Measure Electromagnetic Fields with the Vector Field Analyzer

Author: Bruce Williams
Publication: Microwave Journal
Copyright Owner: NSI-MI Technologies

As wireless technology has evolved, the industry has integrated more “domains of control” to make useful measurements. The power meter can be triggered to measure at will; time is a controlled parameter. The spectrum analyzer integrates both time and frequency control. The SNA incorporates time and frequency control for both source and receiver, but also includes the added dimension of multiple measurement channels. Finally, the VNA includes all these as well as the ability to make coherent (amplitude/phase) measurements. There is one common factor among these measurement devices: They all center on measurement of microwave signals at ports, fixed connection points on the test article.

In keeping with the evolution of wireless technology, AMETEK NSI-MI has recently introduced a new instrument type, the Vector Field Analyzer (VFA). Like the other instruments, the VFA can measure signals at fixed ports, but its unique strength is its ability to make accurate electromagnetic (EM) field measurements. The VFA seamlessly blends multi-channel vector (amplitude/phase) electrical measurements with wide-band agile frequency control, 10-nanosecond precise timing, and convenient integration of complex device control schemes within the measurement flow. More importantly, the VFA precisely coordinates electrical measurements with spatial (position) measurements for complete understanding of three-dimensional EM fields.

MM-Wave S-Parameter Measurements with a Vector Field Analyzer in Antenna Measurement Systems

Authors: Niyati Sanandiya, Bruce Williams, Steve Nichols
Publication: AMTA 2022
Copyright Owner: NSI-MI Technologies

Abstract — Accurate antenna characterization is important in any wireless communication system. Traditionally, electrically large antenna ranges are not equipped to perform return loss measurements and thus a separate benchtop vector network analyzer (VNA) setup is required for measuring reflection coefficient or VSWR of an antenna under test (AUT).

In this paper, we demonstrate the two-port S-parameter measurement capability of the NSI-MI Vector Field Analyzer™ (VFA) and how it can be used to integrate return loss measurements in an antenna range. We selected three known millimeter-wave components as devices-under-test (DUT) and measured the S-parameter matrix for each. These WR-10 band measurements were made using the VFA with Virginia Diodes VNAX frequency extension modules. Results are compared with Keysight’s N5225A PNA network analyzer using the same set of extension modules for verification.

S-parameter measurements taken on VFA and PNA setups are compared based on three factors: Repeatability, reproducibility, and measurement comparison. The variations between successive measurements are presented in graphical form to compare repeatability of both instrument setups. Error distribution comparison is presented for reproducibility test data to show the difference between independent repeat measurements taken on both instrument setups. Measurement comparison result shows the total difference between independent VFA and PNA measurements taken for each DUT.

Testing Alternatives for Base Station OTA Standards Metrics

Author: Marion Baggett
Publication: Microwaves & RF
Copyright Owner: NSI-MI Technologies

Abstract — Several methods for measuring over-the-air metrics for communication base stations are being used. One is a recent development in measuring at less than the traditional far-field distance. This method, together with compact antenna range and spherical near-field approaches, are discussed in a trade study. Each approach has its advantages and disadvantages, which are also presented here.

Using a Higher-Order Basis Function based Method of Moments Analysis for Designing Compact Antenna Test Ranges

Authors: Vince Rodriguez, Anil Tellakula, Daniël Janse van Rensburg, Branko Mrdakovic
Publication: AMTA 2022
Copyright Owner: NSI-MI Technologies, WIPL-D

Abstract — Full wave electromagnetic simulation of a Compact Antenna Test Range (CATR) is not trivial given its electrical size. Typically, the reflector geometry is simulated using asymptotic methods using an assumed feed pattern, while RF absorber and its effects are ignored. A boundary element method of moments (MoM) implementation, using higher-order basis functions (HOBFs) is a good numerical technique for analyzing these ranges since the equations are only solved at the interfaces between different homogeneous regions. There is therefore no need to discretize and solve equations for the fields in the large empty volume portion of the CATR, unlike when using Finite-Difference Time-Domain (FDTD) or Finite Element Methods (FEM). Using HOBFs allows for the mesh size of the discretized CATR geometry to be as large as two wavelengths, reducing the number of unknowns while enabling fast, efficient solutions.

In this paper, a commercial software package that incorporates MoM with HOBFs is used to model a CATR that consists of a blended rolled edge reflector. The results for the reflector and feed model are compared with asymptotic analysis results to show agreement. A realistic feed horn, support structure, and RF absorber is then introduced to the model and its performance is also included to predict field distribution in the CATR test zone. Using this field solution, the Poynting vector is calculated to visualize the flow of energy in the range and from these results proper RF absorber layout can be designed to ensure optimum test zone performance. It is also shown how feed structure absorber treatment impacts CATR test zone performance.