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This paper aims to introduce a phaseless near-field-far-field (NF-FF) transformation with planar wide-mesh scanning (PWMS) and to give a numerical validation of the technique. The here considered NF-FF transformation, based on a non-redundant sampling representation of the electromagnetic field developed by modeling the antenna under test (AUT) with a double bowl, allows to achieve a remarkable reduction (about 90%) of needed NF samples, as compared to standard λ/4 sampling. The reliability and stability of the phase retrieval problem is improved exploiting a proper representation of the unknowns and the a priori information on the AUT. Numerical results, assessing the proposed characterization technique, are shown.

Owing to the increasing interest in high frequencies, as the millimeter wave range, wherein accurate phase measurements are increasingly difficult and expensive, phaseless near-field techniques are prime candidates for antenna characterization. In this paper, an experimental validation of a phaseless near-field-far-field (NF -FF) transformation with plane-polar scanning for antenna characterization is presented. A proper representation of problem unknowns and data, using the available information on the antenna under test (AUT) and on the scanning geometry, is adopted in order to improve the reliability and the accuracy of the proposed characterization algorithm. By exploiting the nonredundant sampling representations of electromagnetic fields and by using an oblate spheroid to model the AUT, a remarkable reduction (about 90%) of the required NF samples is achieved. Experimental results on data acquired at the University of Salerno Antenna Characterization Lab are reported to validate experimentally the effectiveness of the proposed characterization technique.

Bi2Mo2O9-K2MoO4 (BMO-KMO) composite ceramics with >95% theoretical density were densified by cold sintering at 150 °C. XRD, Raman, back-scattered SEM and EDX spectroscopy indicated that the BMO and KMO phases coexisted in all composites without inter-diffusion and secondary phases. Temperature coefficient of resonant frequency with near-zero value ∼ -1 ppm/°C was acheived for BMO-10%KMO with pemittivity ∼ 31 and quality factor ∼ 3,000 GHz. Cold-sintered composite ceramics were directly pressed/integrated onto a printed circuit board (PCB) using the Cu metallisation as a ground plane for the design and fabrication of a circularly polarized microstrip patch antenna suitable for satellite navigation systems which achieved efficiencies 87% at 1561 MHz (BeiDou) and 88% at 1575 MHz (GPS/Galileo). The low cost, low energy integration of temperature stable, cold sintered ceramics directly onto a PCB represents a step change in substrate fabrication technology for RF devices.

CaTiO3-K2MoO4 (CTO-KMO) dielectric composites were successfully cold-sintered at 150 °C for 30 min with a uniaxial pressure of 200 MPa. X-ray diffraction, Raman spectroscopy, back-scattered SEM and energy dispersive x-ray mapping confirmed the coexistence of CTO and KMO with no evidence of interdiffusion and parasitic phases either between the two ceramic end-members or with Ag internal electrodes. As KMO concentration increased, the temperature coefficient of resonant frequency (TCF) and relative pemittivity (εr) decreased but the microwave quality factor (Q × f) increased. A near-zero TCF composition was obtained for CTO-0.92KMO composites which exhibited εr ∼ 8.5 and Q × f ∼ 11,000 GHz. A microstrip patch antenna was designed and fabricated using cold sintered CTO-0.92KMO as a substrate (40×40×1.4 mm), which gave a s11 of −14.2 dB and a radiation efficiency of 62.0 % at 2.51 GHz.

Ceramics-ceramic composites in series (1-x)Li2MoO4-xBaFe12O19 (LMO-BF12, 0.00 ≤ x ≤ 0.15) have been cold sintered at 120 °C and their structure and properties characterized. X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed that compositions were dual phase and had a dense microstructure. Composites in the xBF12-(1-x)LMO (0.0 ≤ x ≤ 0.15) series resonated at MW frequencies (∼6 GHz) with 5.6≤εr ≤ 5.8 and Qf = 16,000–22,000 GHz, despite the black colour of compositions with x > 0. The permeability of the composites was measured in the X band (∼8 GHz) and showed an increase from 0.94 (x = 0.05) to 1.02 (x = 0.15). Finite element modelling revealed that the volume fraction of BF12 dictates the conductivity of the material, with a percolation threshold at 10 vol% BF12 but changes in εr as a function of x were readily explained using a series mixing model. In summary, these composites are considered suitable for the fabrication of dual mode or enhanced bandwidth microstrip patch antennas.

© 2018 IEEE. Generalized continuous wave synthetic aperture radar (GCW-SAR) is a promising new imaging radar system since it applies the full-duplex (FD) transmission technique to achieve continuous signaling in order to overcome several fundamental limitations of the conventional pulsed SARs. As in any FD wireless communication system, self-interference (SI) is also a key problem which can impact on the GCW-SAR system. In this paper, the analog least mean square (ALMS) loop in the radio frequency domain is adopted to cancel the SI for a GCW-SAR system with periodic chirp signaling. The average residual SI power after the ALMS loop is analyzed theoretically by a stationary analysis. It is found that the ALMS loop not only works with random signals in general FD communication systems, but also works well with the periodic signal in GCW-SAR systems. Simulation results show that over 45 dB SI cancellation can be achieved by the ALMS loop which ensures the proper operation of the GCW-SAR system.

© 2017 American Chemical Society. A cold sintering process (150 °C, 30 min and 200 MPa) was employed to fabricate Na 0.5 Bi 0.5 MoO 4 -Li 2 MoO 4 (NBMO-LMO) composites with up to 96.4% relative density. X-ray diffraction traces, backscattered electron images and Raman spectra indicated the coexistence of NBMO and LMO phases in all composites with no detectable secondary phases. The pemittivity (ϵ r ) and temperature coefficient of resonant frequency (TCF) decreased, whereas microwave quality factor (Q × f) increased, with increasing weight % LMO. Near-zero TCF was obtained for NBMO-20 wt %LMO with ϵ r ∼ 17.4 and Q × f ∼ 7470 GHz. Functionally graded ceramics were also fabricated with 5 ≤ ϵ r ≤ 24. To illustrate the potential of these cold sintered composites to create new substrates and device architecture, a dielectric graded radial index lens was designed and simulated based on the range of ϵ r facilitated by the NBMO-LMO system, which suggested a 78% aperture efficiency at 34 GHz.

Reference EPFL-ARTICLE-225144doi:10.1049/iet-map.2016.0792View record in Web of Science Record created on 2017-01-24, modified on 2017-05-10

© 2016 IEICE. This paper presents a novel 3D-printed low-cost, light weight, broadband and high gain planar graded index (GRIN) lens. The GRIN lens was designed to transform spherical wavefronts into planar wavefronts which can be used for antenna gain enhancement. Fused deposition modelling 3D-printing was used to fabricate the lens in a single process with bespoke radially varying relative permittivity. Measured results showed that the lens had a realised gain of 16 to 24 dBi over the Ku-band frequency range from 12 to 18 GHz when fed by a conical horn.

“Nanoarchitectronics” (NTX) denotes a new interdisciplinary research area at the crossroad of Electromagnetics and Nanoelectronics. This new technology will develope reconfigurable, adaptive and cognitive structures with unique physical properties, and engineering applications in the whole electromagnetic spectrum. This FET project funded by the European Framework of Research “Horizon 2020”, gathers thirteen universities, research centers and high-tech industries, belonging to eight European countries, combining concepts of multidisciplinary systems in a huge frequency range.

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