Planar Near-field Antenna Measurements Research Articles

Planar Near-Field Antenna Measurements with a Uniform Step Larger than Half-Wavelength

Planar Near-Field Antenna Measurements with a Uniform Step Larger than Half-Wavelength

High-Speed Antenna Measurement System Using Multi-Probe Array Technique for 5G Applications

In this article, a high-speed antenna measurement system using multi-probe array technique for 5G application is suggested. The spherical near-field scan measurement system for millimeter wave frequency band (3 GHz–40 GHz) and the multi-probe array rotation method is adopted to improve the antenna measurement speed. The proposed measurement RF system consists of the 14 multi-probe array (28 channel with dual-polarization), switch matrix, downconverters, amplifiers/attenuators, digitizers, and signal generators, and is compared to the conventional planar near-field scan antenna measurement system. The measurement speed performance can be improved significantly and the 3D beam pattern of the AUT can be achieved. The designed system was verified through comparison with a verified far-field measurement system. In addition, to increase the measurement efficiency, an effective sampling technique was proposed and verified.

Reduction of Truncation Errors in Planar Near-Field Antenna Measurements Using Improved Gerchberg–Papoulis Algorithm

This article introduces an improved Gerchberg-Papoulis algorithm (IGPA) to resolve truncation errors in planar near-field (NF) antenna measurement and seeks to define the most accurate means of recovering patterns. The truncation errors in planar NF measurements can be reduced by considering the evanescent modes and introducing a new convergence criterion and a window function in the IGPA. A detailed design procedure is presented, and its effect on the field distribution of key parameters is discussed, which can be found in the Appendix at https://web.xidian.edu.cn/xli/files/Appendix.pdf. The results of a simulation and physical measurement are used to assess the validity and applicability of the proposed approach.

Valid angle criterion and radiation pattern estimation via singular value decomposition for planar scanning

Planar near-field antenna measurement techniques are addressed with particular reference to the error in the radiation pattern estimation due to the finiteness of the observation aperture. The valid angle (VA) concept is a commonly used rule-of-thumb for predicting the region of validity of the calculated far-field pattern according to observation domain, the aperture antenna size and the distance between the two. However, it is based on simple asymptotic arguments which often lead to erroneous estimations. In this contribution, a new VA criterion and related radiation pattern representation are derived by exploiting the singular value decomposition of the radiation operator. Numerical examples show the goodness of the new VA criterion and the greatest stability of the proposed radiation pattern estimation compared to the classical Fourier transform.

Multiplicatively Regularized Source Reconstruction Method for Phaseless Planar Near-Field Antenna Measurements

This paper approaches the source reconstruction method (SRM) for phaseless planar near-field (NF) antenna measurements by optimizing a multiplicatively regularized cost functional over the equivalent current distribution of the antenna under test (AUT). The utilized multiplicative regularization scheme, originally developed for image deblurring and inverse scattering problems, is adapted to phaseless NF antenna measurements performed over two parallel planes in front of the AUT. Current phaseless NF to far-field (FF) transformation techniques are highly dependent on the accuracy of the initial phase guess and the pattern features of the AUT. The proposed multiplicatively regularized SRM (MR-SRM) provides a robust and automated framework that can reconstruct the FF pattern of the AUT based on a nonsophisticated initial phase guess. In addition, advantages of the SRM are inherently incorporated into the MR-SRM, such as the capability for antenna diagnostics and allowing for extension to arbitrary measurement domains without the need for data interpolation. The cost functional associated with the MR-SRM is minimized with the conjugate gradient algorithm using closed-form expressions for gradient operators. The developed algorithm is presented in detail along with the synthetic and experimental examples demonstrating the method’s performance in different measurement scenarios along with a comparison to alternative methods.

Millimeter-Wave Phaseless Antenna Measurement Based on a Modified Off-Axis Holography Setup

A novel scheme for planar near-field phaseless antenna measurement based on off-axis holography is presented. Separation of the image terms of the hologram is artificially increased by multiplexing the measurements of two sub-sampled holograms generated with two 180° phase-shifted reference waves. Combination of both sub-sampled holograms produces replicas of the image terms at half a period distance of the originals in the spectral domain, while the amplitude of the original image terms is highly reduced, easing the filtering process of the desired replica. The higher separation of the image terms reduces overlapping making the method suitable also for the characterization of medium and low gain antennas in the near-field. As the separation is artificially increased, the reference antenna can be placed close to the antenna under test allowing to reduce the scan distance and the sensitivity to scan axis errors. Nevertheless, spatial multiplexing requires the retrieved data to be spatially low-pass filtered to remove the effect of the aliasing. Mirror reflection is used for illuminating the acquisition plane with the reference wave, being the phase shift achieved by means of a mechanical displacement of the mirror. The effect of the location of the reference antenna on the position and shape of the image terms and their replicas has been studied through numerical simulations for a setup in the W-band. Experimental validation of the method is presented for the characterization of three different antennas at 94 GHz.

Phaseless planar near‐field antenna measurements: some aspects of aperture's mask and alignment error

A quick review of the planar phaseless near-field antenna measurement technique is presented and some interesting aspects related to the size of the mask used at the aperture of the antenna under test (AUT) are pointed out. It is shown simulatively and experimentally that due to the edge fields the AUT aperture's mask needs to be larger than the physical aperture of the AUT to achieve better accuracy. In addition, the misalignment of the setup has a big impact on the achieved far-field accuracy. This is emphasised experimentally.

Near-Field Antenna Measurements Using Photonic Sensor of Mach-Zehnder Interferometer

We have been developing a photonic sensor system to measure the electric near-field distribution at a distance shorter than one wavelength from the aperture of an antenna. The photonic sensor is a type of Mach-Zehnder interferometer and consists of an array antenna of 2.4 mm height and 2 mm width on a LiNbO3 substrate (0.5 mm thickness, 8 mm length, and 3 mm width) supported by a glass pipe. The photonic sensor can be considered to be a receiving infinitesimal dipole antenna that is a tiny metallic part printed on a small dielectric plate at microwave frequency. Those physical and electrical features make the photonic sensor attractive when used as a probe for near-field antenna measurements. We have demonstrated that the system can be applied to planar, spherical, and cylindrical near-field antenna measurements without any probe compensation approximately below 10 GHz. We show the theories and the measurements using the photonic sensor in the three near-field antenna measurement methods.

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.

Errors analysis of planar near-field antenna measurement

Errors analysis of planar near-field antenna measurement

Reduction of Truncation Errors in Planar Near-Field Aperture Antenna Measurements Using the Gerchberg-Papoulis Algorithm

A simple and effective procedure for the reduction of truncation errors in planar near-field measurements of aperture antennas is presented. The procedure relies on the consideration that, due to the scan plane truncation, the calculated plane wave spectrum of the field radiated by the antenna is reliable only within a certain portion of the visible region. Accordingly, the truncation error is reduced by extrapolating the remaining portion of the visible region by the Gerchberg-Papoulis iterative algorithm, exploiting a condition of spatial concentration of the fields on the antenna aperture plane. The proposed procedure is simple and computationally efficient; it does not require any modification of the measurement procedure and it allows for the usual probe correction. Far-field patterns reconstructed from both simulated and measured truncated near-field data demonstrate its effectiveness and stability against measurement inaccuracies.

A Modified Holographic Technique for Planar Near-Field Antenna Measurements

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A modification of the synthetic-plane-wave-based holographic technique for determining radiation patterns and aperture fields of medium-gain horn antennas is proposed. The modification is based on using both the sum and difference of the near field and reference signals to form the hologram via simple low-cost amplitude-only near field measurements. This approach when compared to the previous version, where only the sum signal is used, allows increased sample spacing, and also provides an improvement in quality of the final results. The effectiveness of the modified technique is confirmed by both calculated and measured results obtained for pyramidal and conical horn antennas at 10 GHz frequency. </para>

Prediction of far-field from uniform and non-uniform under-sampled near-field data in planar near-field antenna measurements

In near-field antenna measurements various forms of uniform and non-uniform sampling techniques have been widely deployed. Considering the fact that the near-field pattern of any antenna is a spatially quasi-band-width-limited function of space coordinates, Shannon's theorem simply defines the sampling frequency. Based on the sampling theorem, in order to precisely reconstruct a band-limited signal from its samples, the sampling frequency must be at least twice as much as the signal's bandwidth. Through the simulations and theoretical evaluations this research shows that if the near-field pattern is either uniformly or non-uniformly under-sampled due to any practical reasons, yet a good estimation of far-field pattern can be obtained especially if the antenna under test (AUT) is a directive high-gain or super high-gain antenna. Also the time efficiency of far-field prediction from under-sampled near-field data is discussed and the advantages and disadvantages are highlighted.

A new look at phaseless planar near-field measurements: limitations, simulations, measurements, and a hybrid solution

In this paper, we have revisited the phase-retrieval problem for planar near-field antenna measurements. It will be shown that the complexity of retrieval procedures is a function not only of the independency of different sets of measurements, but also of the characteristics of the antenna under test (AUT). Antenna-pattern features, such as its beam direction, will have a profound effect on the success of phase-reconstruction algorithms. The failure of a well-known phase-retrieval method, the iterative Fourier technique, is investigated for a case where the antenna has a scanned beam. It is found that this is due to a less-than-optimum choice of the initial guess. To alleviate the deficiency of the iterative Fourier technique, a simple but effective initial guess is sought by the use of the differential evolutionary algorithm. This global search technique tries to find the best initial phase guess that minimizes an error criterion. Subsequently, this best guess is fed to the iterative Fourier phase-retrieval routine for further phase refinements. Having done this, the far-field can subsequently be constructed. The improvement in the phase-reconstruction algorithm is examined through a series of simulations and measurements.

A NEW INTERPOLATION TECHNIQUE FOR THE RECONSTRUCTION OF UNIFORMLY SPACED SAMPLES FROM NON-UNIFORMLY SPACED ONES IN PLANE-RECTANGULAR NEAR-FIELD ANTENNA MEASUREMENTS

A novel fast and accurate interpolation technique for recovering the uniformly distributed samples from the irregularly spaced samples, collected non-uniformly due to the probe position error in planar near-field antenna measurements, is presented. The technique employs Yen’s interpolator and tries to make it as practical as possible for the use in near-field antenna measurements. A comprehensive simulation capability is developed and through out the simulations the speed and precision of this accurate and timely efficient interpolation technique is compared with some other techniques which are also based on Yen’s interpolators. The results well demonstrate the advantages of our technique we termed “The Cross-Rail Technique”. 48 Dehghanian, Okhovvat, and Hakkak

Scan-plane reduction techniques for planar near-field antenna measurements [AMTA corner

In this work, two planar near-field scan-plane reduction techniques are considered and results are presented. It is shown how truncation based on field-intensity contours, instead of simple geometric truncation, can in some cases improve the efficiency of the truncation process. Both techniques are applied to measured data sets, and it is shown how these methods can be used to reduce data-acquisition times, while also assessing the impact of the total acquisition surface reduction on the far-field radiation-pattern integrity.

Strategy to avoid truncation error in planar and cylindrical near-field antenna measurement setups

A simple and effective method to avoid the truncation error in antenna near-field measurements is presented. The method can be applied to planar or cylindrical near-field setups, whenever it is possible to vary the distance between the antenna under test and the probe during the scanning procedure.

Probe-position error correction for time-domain planar near-field antenna measurements

In order to construct the far-field pattern of an antenna in the time domain from its near-field samples, uniform sampling techniques have been widely used. If a signal is unequally sampled due to ...

Spacecraft antenna measurement eliminating gravity effect by using planar near-field antenna measurement technique

Spacecraft antenna measurement eliminating gravity effect by using planar near-field antenna measurement technique

Phaseless bi-polar planar near-field measurements and diagnostics of array antennas

Antenna near-field measurements typically require very accurate measurement of the near-field phase. There are applications where an accurate phase measurement may not be practically achievable. Phaseless measurements are beginning to emerge as an alternative microwave antenna measurements technique when phase cannot be directly measured. There are many important aspects for successful implementation of a phaseless measurement algorithm. This paper presents appropriate phaseless measurement requirements and a phase retrieval algorithm tailored for the bi-polar planar near-field antenna measurement technique. Two amplitude measurements and a squared amplitude optimal sampling interpolation method are integrated with an iterative Fourier procedure to first retrieve the phase information and then construct both the far-field pattern and diagnostic characteristics of the antenna under test. In order to critically examine the methodologies developed in this paper, phaseless measurement results for two different array antennas are presented and compared to results obtained when the near-field amplitude and phase are directly measured.