This article introduces a low-cost time-domain near-field measurement system based on softwaredefined radio (SDR). The method is based on using a low-cost receiver to retrieve by Fourier techniques the amplitude and phase of the signal radiated by antennas. The uncertainties introduced by the receiver are modeled and compared with empirical data. Moreover, a setup based on a reference antenna is explored as a possible solution to fix the phase reference of the measurement. The limitations and optimization of the setup are analyzed for different geometries. Some postprocessing techniques are demonstrated to be suitable to overcome the inherent errors introduced by the setup. Once the amplitude and phase are recovered, diagnostic techniques or near-field to far-field transformation can be applied. The results demonstrate the potential and good accuracy of the method for fast and lowcost characterization of antennas when the reference is not accessible.

This paper introduces a near-field measurement system concept for the fast testing of linear arrays suited for mass production scenarios where a high number of nominally identical antennas needs to be measured. The proposed system can compute the radiation pattern, directivity and gain on the array plane, as well as the array complex feeding coefficients in a matter of seconds. The concept is based on a multi-probe antenna array arranged in a line which measures the near field of the antenna under test in its array plane. This linear measurement is postprocessed with state-of-the-art single-cut transformation techniques. To compensate the lack of full 3D information, a previous complete characterization of a “Gold Antenna” is performed. This antenna is nominally identical to the many ones that will be measured with the proposed system. Therefore, the data extracted from this full characterization can be used to complement the postprocessing steps of the single-cut measurements. An X-band 16-probe demonstrator of the proposed system is implemented and introduced in this paper, explaining all the details of its architecture and operation steps. Finally, some measurement results are given to compare the developed demonstrator with traditional anechoic measurements, and show the potential capabilities of the proposed concept to perform fast and reliable measurements.

Phase reconstruction is in general a non-trivial problem when it comes to devices where the reference is not accessible. A non-convex iterative optimization algorithm is proposed in this paper in order to reconstruct the phase in reference-less spherical multiprobe measurement systems based on a rotating arch of probes. The algorithm is based on the reconstruction of the phases of self-transmitting devices in multiprobe systems by taking advantage of the on-axis top probe of the arch. One of the limitations of the top probe solution is that when rotating the measurement system arch, the relative phase between probes is lost. This paper proposes a solution to this problem by developing an optimization iterative algorithm that uses partial knowledge of relative phase between probes. The iterative algorithm is based on linear combinations of signals when the relative phase is known. Phase substitution and modal filtering are implemented in order to avoid local minima and make the algorithm converge. Several noise-free examples are presented and the results of the iterative algorithm analyzed. The number of linear combinations used is far below the square of the degrees of freedom of the non-linear problem, which is compensated by a proper initial guess. With respect to noisy measurements, the top probe method will introduce uncertainties for different azimuth and elevation positions of the arch. This is modelled by considering the real noise model of a low-cost receiver and the results demonstrate the good accuracy of the method. Numerical results on antenna measurements are also presented. Due to the numerical complexity of the algorithm, it is limited to electrically small- or medium-size problems.

This paper presents a time domain antenna measurement technique that aims to measure antennas in referenceless scenarios. The technique resolves measurement challenges derived from antennas where the reference signal is not accessible, for intance in EMC or active antennas. The algorithm implemented in this work is based on the the Fast Fourier Transform of the time domain signal to estimate the power spectrum and the relative phase between measurement points. In order to do that a reference antenna is used to retrieve the phase, providing a full characterization in amplitude and phase of the electric field and allowing source reconstruction. The results demonstrate the potential of this technique for new antenna measurement systems and reveal some of the limitations of the technique to be optimized, like the undesired reflections due to the interactions between the probe and the reference antenna.

Inspec keywords: planar antennas; test facilities; waveguide transitions; reflector antenna feeds; three-dimensional printing; rectangular waveguides; melting; millimetre wave antennas; antenna radiation patterns; antenna testing; horn antennas Subjects: Antenna accessories; Communications equipment manufacturing; Production facilities and engineering; Other manufacturing processes; Waveguide and microwave transmission line components; Single antennas