Near-field Measurement System Research Articles

A Crane-Based Portable Antenna Measurement System—System Description and Validation

A portable near-field (NF) antenna measurement system for frequencies up to Ka -band is presented and evaluated in detail. The system follows the idea to collect measurement samples on arbitrary scan surfaces in the NF, where strong irregularities of the sample distribution may be tolerated as long as appropriate sampling criteria are fulfilled. The radio frequency (RF) equipment is integrated in a gondola, which is positioned by a standard overhead crane. During an NF scan, the exact position and orientation of the probe antenna are measured by a 6-D laser tracking system with high accuracy. The RF measurement system works with a phase-coherent measurement loop, where the signal transmission from the ground station to the RF equipment within the portable gondola is performed by an optical fiber transmission system with three optical fibers, realizing magnitude as well as phase compensation. The NF measurement samples are merged with the position and orientation data and, finally, transformed into the far-field by a flexible and highly efficient equivalent source algorithm. The complete setup of this measurement system is presented and discussed in detail, focusing on both hardware and software aspects. A series of validation and practical antenna measurement results is presented to demonstrate the feasibility of this approach.

A Wideband, Single-Layer Reflectarray Exploiting a Polarization Rotating Unit Cell

We present a new technique for designing wideband, single-layer reflectarray antennas. The proposed reflectarray exploits a wideband, polarization rotating unit cell that rotates the polarization of the reflected wave with respect to that of the incident wave by 90°. This unit cell and its mirror image were used as 1 bit spatial phase shifters capable of providing a 0°/180° phase shift over a wide bandwidth of 5.4–12.7 GHz. Using this, a reflectarray antenna with 1 bit phase quantization was designed to operate at ${X}$ -band with aperture dimensions of $28.8\,\,\text {cm}\times 28.8$ cm and a focal length of 30 cm. A prototype of the proposed reflectarray was fabricated and characterized using a spherical near-field measurement system. We determined the antenna’s 3 dB gain bandwidth to be approximately 37.4% with a maximum realized gain of 24.2 dBi. Over its entire band of operation, the polarization purity of the antenna remains better than 13 dB and sidelobe levels of better than 12 dB were achieved.

Performance analysis of a 3D unidirectional antenna opted for biomedical microwave imaging

AbstractIn this paper, a reflector type unidirectional 3D antenna for biomedical microwave imaging has been presented. A reflector wall perpendicular to the ground plane has been introduced to achieve higher gain and directive radiation pattern. Bending technique is utilized to reduce the overall antenna size and to get resonance at a lower frequency. The proposed antenna obtained measured operating band at 2.37 GHz to 3.70 GHz. The dimension of the 3D radiating structure is 30 × 10 × 17 mm3. The antenna has a peak realized gain of 4.52 dB. Unidirectional radiation pattern and gain within lower microwave frequency, make the proposed antenna a potential candidate to be used in microwave imaging for biomedical diagnosis. The design and simulation process are performed in the CST Microwave Studio software. The antenna is fabricated from 0.2 mm thick copper sheets. PNA Network Analyzer (N5227A) and Satimo Nearfield Measurement system has been used to measure the performance of the fabricated prototype.

Setup and Characterization of a Volumetric <inline-formula> <tex-math notation="LaTeX">$\boldsymbol{W}$ </tex-math> </inline-formula>-Band Near-Field Antenna Measurement System

A volumetric $W$ -band near-field (NF) antenna measurement system is presented and evaluated. The system supports measurements at arbitrary locations within the measurement volume with high positioning accuracy together with corresponding field transformations. The measurement performance of the system is carefully investigated with respect to accuracy and efficiency, e.g., by a comprehensive evaluation of room scattering and by laser scanner measurements. The fast irregular antenna field transformation algorithm (FIAFTA) is utilized to perform the necessary NF to far-field transformations. Due to the flexibility of FIAFTA, so-called nonredundant planar measurements become possible, which overcome the classical half-wavelength sampling requirement entailed by the fast Fourier transform-based transformation approaches. Thus, with a time-factor of about 35, accelerated planar measurement results are achieved by projecting angularly uniform sample grids on the minimum sphere around the antenna under test (AUT) onto the measurement plane, resulting in irregularly thinned planar measurement grids. The error levels between two completely independent measurements employing full and thinned grids are found at a level below −40 dB. Moreover, such measurements allow decreasing mutual interactions between the AUT and the probe by increasing the measurement distance, but without the need to collect more measurement samples.

Exposure Evaluation of an Actual Wireless Power Transfer System for an Electric Vehicle With Near-Field Measurement

In this paper, we propose an experimental approach for determining the internal electric field for exposure evaluation of wireless power transfer (WPT) systems by using measured magnetic near-field data. Two WPT systems are fabricated and used in the measurements: one without ferrite tiles, and the other with ferrite tiles and a metal plate. The amplitude and phase of the magnetic near field in the vicinity of the WPT systems are then measured by using in-house magnetic-field probes and a near-field measurement system. Numerical dosimetry of human exposure is performed using the measured near field as an incident field in the impedance method to derive the internal electric field strength inside numerical human models. Validation of the proposed approach has been demonstrated by comparing measurement results with those obtained from numerical simulations. Additionally, the coupling factor, which represents the relationship between the incident magnetic field and the induced electric field in the human body, at different distances is derived for realistic exposure scenarios.

A Capstone Design Project on the Development of a Prototype Near-Field Antenna Measurement System [Education Corner

This article presents the capstone design project of four final-year electrical and computer engineering undergraduate students, which focused on the development of a nearfield antenna measurement system from the ground up. The aim of this article is 1) to demonstrate that a prototype near-field antenna measurement system can be developed as a final-year capstone design project and 2) to show that the development of such a prototype can engage students with a multidisciplinary engineering design. To this end, this article discusses all the subsystems designed by the students to achieve full functionality for this prototype near-field antenna measurement system. Finally, the experimental validation of the system is presented, along with discussions on how to use this system for educational and research activities.

Study on Magnetic Probe Calibration in Near-field Measurement System for EMI Application

Near-field measurement, as an efficient method for studying the electromagnetic interference (EMI) problem, is becoming increasingly important. The calibration of the near-field probe is a critical part in the measurement procedure. This paper presents a fast and effective calibration method of magnetic probe. The factors that influence the calibration method is analyzed and discussed. Two kinds of calibration structures are designed and fabricated to determine the probe factor (PF) of two magnetic probes, which are horizontal magnetic field probe and vertical magnetic field probe, respectively. Moreover, PF is obtained through comparing the measurement data with the simulation data of the same calibration structure. Another sample is designed and fabricated to verify the obtained PF and the calibration method. The measurement results match simulation results well with the relative errors at the “large signal region” less than 20%, which indicates a good accuracy of the calibration method.

Probe Characterization in Terahertz Near-Field Beam Measurement Systems

The characterization of radiation patterns in the terahertz frequency range is usually performed with near-field beam measurement systems. In order to measure accurate patterns, the effects of the measurement probe must be compensated, especially at terahertz frequencies, because aperture sizes are very small and prone to fabrication errors. This paper presents detailed steps on how to characterize probe antennas at terahertz frequencies and confirms the possibility to extend probe compensation methods to this frequency range. This method has been applied to characterize the radiation patterns of probes for the 900 and 1400 GHz bands.

Reconfigurable Near-Field Beam Pattern Measurement System From 0.03 to 1.6 THz

With the discovery and utilization of great observation sites, on-ground radio astronomical observations have been extended from the millimeter-wave (mm-wave) range to around 1.6 THz. The radiation collected by the telescope reflector antenna is coupled to the receiver by means of the receiver optics. These optics must be designed to match the in-coming fields from the telescope and properly characterized by amplitude and phase measurements. This paper presents a reconfigurable near-field beam pattern measurement system which can characterize magnitude and phase patterns of antennas and optics from the mm-wave to the THz region. Measurements at 900 GHz and 1.37 THz are presented for two different configurations, using different phase-lock components, and measured under cryogenic and room-temperature conditions, respectively.

Broadband Sounding Rocket Antenna for Dual-Band Telemetric and Payload Data Transmission

This letter presents and investigates a broadband sounding rocket antenna developed for dual-band data transmission of telemetric and payload systems. This single-element antenna permits the use of both the well-established 869.4-869.65 MHz and 2.4-2.4835 GHz frequency bands available in Europe to implement a redundant transmission of telemetric and tracking data desired for reliability. Furthermore, the available spectrum in the upper band offers a high-speed wireless link for transmitting payload data. To preserve the mechanical integrity and aerodynamics of rocket, the antenna is integrated in its nose cone. The proposed low-cost and low-weight structure is based on printed circuit board (PCB) pieces assembled in a LEGO-like manner to form a broadband three-dimensional (3-D) biconical antenna, which is fed by a diplexer integrated in its base. A prototype has been fabricated and validated using a reduced-length fuselage in a near-field measurement system.

Bandwidth enhancement of capacitive fed monopole antenna using parasitic patches

This paper proposed a compact planar monopole antenna operating at 5 GHz (5.180–5.825 GHz) industrial, scientific and medical (ISM) radio band. The antenna constructed with 20 mm × 12 mm radiating element and 25 mm square of the ground plane in FR4 substrate provided −10 dB bandwidth of 1 GHz (5.4–6.4 GHz). To improve the bandwidth, parasitic elements are added with the monopole antenna. A capacitive feed is also incorporated in the design. It observed that the proposed antenna with parasitic elements provides a larger impedance bandwidth of about 3 GHz (5.1–8.1 GHz), which is three-fold improvements over the one without parasitic patches. The prototype of the antenna that operates at 5.8 GHz frequency range is fabricated and characterized using a near-field measurement system. A good agreement is found between the simulation and measured results.

A quasi-optical vector near-field measurement system at terahertz band.

This paper describes a vector near-field measurement system at terahertz band based on a high sensitivity superconducting receiver equipped with a quasi-optical probe for high resolution near-field sensing. A novel single-receiver rather than commonly used dual-receiver configuration is adopted for vector measurement. Performances of the measurement system including stability and dynamic range are studied. Vector near-field measurement of a diagonal feedhorn at 850 GHz is presented and shows good agreement with simulation and direct far-field measurement.

Phase-sensitive near field Investigation of Bloch surface wave propagation in curved waveguides

Bloch surface waves (BSWs) are electromagnetic surface waves excited in the band gap of a one dimensional dielectric photonic crystal. They are confined at the interface of two media. Due to the use of dielectric material, the losses are very low, which allows the propagation of BSWs over long distances. Another advantage is the possibility of operating within a broad range of wavelengths. In this paper, we study and demonstrate the propagation of light in ultra-thin curved polymer waveguides having different radii fabricated on a BSWs-sustaining multilayer. A phase-sensitive multi-parameter near-field optical measurement system (MH-SNOM), which combines heterodyne interferometry and SNOM, is used for the experimental characterization. Propagating properties, bending loss, mode conversion and admixture are investigated. We experimentally show that when light goes through the curved part of the waveguide, energy can be converted into different modes. The superposition and interference of different modes lead to a periodically alternating bright and dark beat phenomenon along the propagation direction. Experimental optical phase and amplitude distributions in the curved waveguide show a very good agreement with simulation results.

Electrooptic Inspection of Vector Leakage in Radiofrequency Multichip Modules

This paper demonstrates a new approach for the measurement of vector electromagnetic leakage within tightly integrated electronic subsystems. Specifically, the effect of shielding and encapsulation techniques commonly used in radiofrequency (RF) multichip modules is investigated using an electrooptic (EO) near-field measurement system. The test vehicle used for this study is a single-chip 50-W microwave power amplifier integrated into a multilayer low-temperature cofired ceramic module. The measured near-field data show power intensity at 2.5 GHz with up to 0.2-mm resolution for each of the three x-, y-, and z-directed electric field vectors. The resulting images illustrate 1) the polarization-dependent shortcomings of the ubiquitous “via-fence” shielding technique and 2) the formation of surface waves in microstrip substrates due to impedance mismatch. These results are evidence of the applicability of the EO technique to the diagnosis of electromagnetic compatibility issues within compact RF multichip modules.

Performance Limitations and Measurement Analysis of a Near-Field Microwave Microscope for Nondestructive and Subsurface Detection

Near-field microwave microscopy provides a means for nondestructive localized characterization of both surface and subsurface materials and devices. This paper details the design and implementation of a near-field microwave measurement system capable of achieving large scan areas (>; 1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) with micrometer spatial resolution, good signal-to-noise and long-term measurement stability. We discuss the measurement topology, system design, and qualification, as well as the design and optimization of the probe circuit and equivalent microwave circuit. The system noise floor is measured and noise-limiting elements are identified. A calibration method is discussed that allows for the quantitative extraction of the tip-sample impedance and enables tip-sample modeling. Several demonstration measurements are provided that show differentiation of not just metals and dielectrics, but compound targets. Additionally, resolution of 10-μm features at the surface are demonstrated with a factor of 4 degradation in spatial resolution at a depth approximately equal to the tip diameter.

Fabrication and EMI shielding effectiveness of Ag-decorated highly porous poly(vinyl alcohol)/Fe2O3 nanofibrous composites

The Ag-decorated poly(vinyl alcohol) (PVA) composite nanofibrous webs incorporating Fe2O3 nanoparticles were fabricated by electrospinning and metal-deposition methods for electromagnetic interference (EMI) shielding applications. The Ag-decorated PVA/Fe2O3 composite nanofiber webs with various Ag thicknesses and different amounts of Fe2O3 nanoparticles were prepared and used for EMI shielding measurement. For the EMI SE measurement, a near-field antenna measurement system was used. The measurement of EMI SE was carried out at the frequency range from 0.5 to 18 GHz, and the electromagnetic parameters were measured. The morphologies and microstructures of the resultant PVA/Fe2O3 composite nanofiber webs were characterized using field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), respectively. The effects of surface morphologies and Fe2O3 nanoparticles on the EMI shielding effectiveness of Ag-decorated PVA/Fe2O3 composite nanofiber webs were investigated.

Lightweight nanofibrous EMI shielding nanowebs prepared by electrospinning and metallization

The metal-deposited poly(vinyl alcohol) (PVA) composite nanofibrous mats were fabricated by electrospinning and metal-deposition methods for electromagnetic interference (EMI) shielding applications. The metal-deposited nanofiber mats prepared with various metals (Cu, Ni, Ag), their different thicknesses, and different metal deposition systems composed of Cu and Ni were used for EMI shielding measurement. For the EMI SE measurement, a near-field antenna measurement system was used. The measurement of EMI SE was carried out at the frequency range from 0.5 to 18GHz, and the electromagnetic parameters were measured. The experimental results showed that absorption was the major shielding mechanism and reflection was the secondary shielding mechanism. The effect of unique porous structure of the metal-deposited composite nanofibrous mats was also discussed.

Examination of Far-Field Mathematical Absorber Reflection Suppression through Computational Electromagnetic Simulation

The mathematical absorber reflection suppression (MARS) technique has been used to identify and then suppress the effects of spurious scattering within spherical, cylindrical, and planar near-field antenna measurement systems, compact antenna test ranges (CATRs), and far-field measurement facilities for some time now. The recent development of a general-purpose three-dimensional computational electromagnetic model of a spherical antenna test system has enabled the MARS measurement and postprocessing technique to be further investigated. This paper provides an overview of the far-field MARS technique and presents an introduction to the computational electromagnetic range model. Preliminary results of computational electromagnetic range simulations that replicate typical MARS measurement configurations are presented and discussed which, for the first time, confirm through simulation many of the observations that have previously been noted using purely empirical techniques.

Reconfigurable Slot-Array Antenna With RF-MEMS

Cylindrical near-field measurement systems are being widely demanded, especially for imaging applications at millimeter-wave frequencies. One of their most important drawbacks is the long time required to perform a full measurement of an antenna. To avoid multiple receivers, the probe is mechanically moved to the points where the field must be measured. The mechanical movement increases the time required to take a full measurement. The process may be sped up in several ways. This letter proposes the use of a pattern reconfigurable slot-array antenna as a probe. The switching among the different patterns is carried out electronically by RF-MEMS, which are placed over the different slots. Simulations and measurements of a model in the X-band are shown in this letter.

Time-Domain Spherical Near-Field Antenna Measurement System Employing a Switched Continuous-Wave Hardware Gating Technique

A time-domain spherical near-field antenna measurement system capable of gating out erroneous signal components, which arise due to multipath propagation in nonideal anechoic chambers, is presented. The developed hardware (HW) gating technique evaluates a switched sinusoidal signal, which is synthesized by an application-specific pulse generator and acquired by either a commercial real-time digitizing oscilloscope or an application-specific equivalent-time sampling receiver developed for this particular purpose. The low-cost measurement system has been optimized for acquisition speed, dynamic range, and resolution. Its operating frequency range covers 1.5-8 GHz, and it is applicable to antennas exhibiting a typical 3-dB bandwidth in excess of 400 MHz. Test measurements of an omnidirectional and a directional antenna, respectively, have been carried out to demonstrate the performance of the novel HW gating technique. It is shown that the HW gating technique can significantly improve the absolute average deviation of the erroneous 3-D far-field pattern.