Marco Rossi

In the last years, the increasing demand for ever higher data rates in wireless communication has exposed the limits of current sub-6 GHz communication systems and pushed the technology towards the exploration of the mmWave frequency spectrum. In particular, 3 frequency bands have been licensed at 26 GHz, 28 GHz and 39 GHz for the new generation of mobile communication (5G), each exhibiting as much as 3 GHz of operational bandwidth. However, systems operating at mmWave have to cope with much higher free space losses then in the sub-6 GHz frequency range. Moreover, the physical size of interconnects (chip-to-chip, chip-to-antenna) becomes comparable to the operating wavelength. Therefore, new packaging technologies are required, which allow implementing large antenna arrays for massive MIMO and short interconnects to minimize package losses. Within the funded project IPCEI “mmWave Modules” a scalable and reconfigurable module for mmWave 5G small cell base stations has been developed. In particular, the module measures and exhibits two dual-band patch antenna arrays for operation at 28 GHz and 39 GHz. Moreover, it may be easily upscaled for the deployment in base stations covering larger cells. Packaging technology is based on a double molded Fan-out Wafer Level Package (FOWLP) approach with integrated antenna-in-package (AiP) that has been adapted and evaluated. The Analog-Front-End-IC (AFE IC) has been packaged as a start in an RDLfirst FOWLP on 300 mm wafer size. Redistribution layers were built-up on a glass carrier consequently followed by plating of the through package vias [TPVs] for later front and backside package connection. The AFE IC is then assembled as a flip chip on the RDL and compression molding is used to underfill the flip chip ICs and overmold the wafer carrier in one step. A backgrinding step is applied to open the TPVs for further electrical connection. Direct metallization using seed layer sputtering, copper plating and subtractive etching is used to add a shielding layer on the mold cap. After debonding the wafer is overmolded a second time using compression molding again. The antenna is then directly metallized on the second mold cap connected by laser drilled and metallized vias to TPVs and shielding layer. Finally solder balls are attached and packages are separated by dicing. Focus of the development was the double mold process with the related warpage challenges, direct metallization on mold as well as antenna and via integration and alignment on the second mold layer. Besides the development of the entire package the AiP concept has been evaluated using a GHz/39 GHz dual-band antenna test structure considering the later double mold approach including an inner shielding layer, laser drilled through mold vias and direct metallized antenna on mold. Measured bandwidths of 1 GHz and 700 MHz and gains of 5.3 dBi and 6.2 dBi at 28 GHz and 39 GHz, respectively, prove the applicability of the proposed packaging technology for mmWave 5G applications. In summary the paper will describe the FOWLP package development for a mmWave 5G MIMO application with focus on a double mold approach with antenna-in-package application.

For the design and production of reliable devices applied in wearable components, characterization of the electromagnetic properties of materials is of paramount importance. Therefore, we propose a novel approach, based on a resonance-perturbation method, which compares simulations and performed measurements. An inset-fed patch antenna with a resonance frequency in the vicinity of the 2.45-GHz Industrial, Scientific, and Medical band enables us to quickly estimate the characteristics of a given material sample. In a first step, the two frequencies for which the simulated return loss of the fixture crosses a defined threshold are modeled as polynomial functions of the relative permittivity and loss tangent of the material under test. Then, the electromagnetic properties of the material are obtained by comparing the modeled and measured frequencies. The electromagnetic properties of several textile materials of interest are determined with this method. It is shown that the proposed technique is fast, precise, and nondestructive. Owing to this, it is suitable for integration into an assembly line, where substrate samples are straightforwardly characterized before being used for the manufacturing of actual antennas.

Electromagnetic characterization of materials applied in wearable components is of paramount importance for the design and production of reliable devices. Therefore, we propose a novel approach that compares simulations and measurements performed by a resonance-perturbation method. An inset-fed patch antenna operating in the vicinity of the 2.45-GHz Industrial, Scientific, and Medical frequency band enables us to quickly estimate the properties of a given substrate sample. First, the two frequency values at which the simulated return loss peak of the fixture crosses a given threshold value are modeled as polynomial functions of the material's relative permittivity and loss tangent. Then, the comparison between modeled and measured frequencies yields the electromagnetic properties of the material. The approach is validated by characterizing the high-frequency laminate on which the antenna is implemented. Next, the method is applied to several textile materials of interest. It is shown that the proposed technique is fast, precise, and nondestructive. As such, it is suitable for integration into an assembly line, where substrate samples are first quickly characterized before being used in the production of the actual antennas.

A stochastic framework is presented to enhance the design of textile antennas, by addressing the impact of production uncertainties, substrate bending and compression on the performance of textile antennas. Each effect is considered separately and the probability density functions corresponding to the design parameters undergoing variations are experimentally estimated. In order to accurately quantify the statistical distribution of the antenna's figures of merit corresponding to these variations, we introduce a stochastic collocation method based on a generalized polynomial chaos technique or on Padé approximants.

The efficiency of a wireless power transfer (WPT) system in the radiative near-field is inevitably affected by the variability in the design parameters of the deployed antennas and by uncertainties in their mutual position. Therefore, we propose a stochastic analysis that combines the generalized polynomial chaos (gPC) theory with an efficient model for the interaction between devices in the radiative near-field. This framework enables us to investigate the impact of random effects on the power transfer efficiency (PTE) of a WPT system. More specifically, the WPT system under study consists of a transmitting horn antenna and a receiving textile antenna operating in the Industrial, Scientific and Medical (ISM) band at 2.45 GHz. First, we model the impact of the textile antenna’s variability on the WPT system. Next, we include the position uncertainties of the antennas in the analysis in order to quantify the overall variations in the PTE. The analysis is carried out by means of polynomial-chaos-based macromodels, whereas a Monte Carlo simulation validates the complete technique. It is shown that the proposed approach is very accurate, more flexible and more efficient than a straightforward Monte Carlo analysis, with demonstrated speedup factors up to 2500.

One of the many adverse effects modifying the performance of textile antennas in real operating conditions is substrate compression. Therefore, this communication presents a stochastic collocation method (SCM) that either relies on the generalized polynomial chaos (gPC) expansion or on a novel Hermite-Padé approximant. The method is introduced to rigorously quantify the effect of random variations in the height and the permittivity of the substrate on the figures of merit of a textile antenna. Next, the joint height and permittivity probability distribution of a compressible substrate are characterized by means of a new measurement setup based on a resonant-perturbation technique. Finally, the method is validated for a probe-fed GPS textile antenna. It is shown that Hermite-Padé approximants model the highly nonlinear relationship between these substrate random variables and the figures of merit of the antenna more efficiently than the gPC. Moreover, a Kolmogorov–Smirnoff test proves that the resulting distributions of the antenna’s figures of merit are as accurate as those obtained by means of a Monte-Carlo (MC) analysis, with demonstrated speedup factors up to 123.

A novel framework to accurately quantify the effect of stochastic variations of design parameters on the performance of textile antennas is developed and tested. First, a sensitivity analysis is applied to get a rough idea about the effect of these random variations on the textile antenna's performance. Next, a more detailed view is obtained by a generalized polynomial chaos technique that accurately quantifies the statistical distribution of the textile antenna's figures of merit, for a given range over which geometry and material parameters vary statistically according to a given distribution. The method is validated both for a simple inset-fed patch textile microstrip antenna and for a dual-polarized textile antenna. For the latter, the probability density function corresponding to its most sensitive design parameter, being the width, is experimentally estimated by means of measurements performed on 100 patches. A Kolmogorov-Smirnoff test proves that, for all considered examples, the results are as accurate as those obtained via Monte Carlo analysis, while the new technique is much more efficient. Indeed, speedups up to a factor 1667 are demonstrated.