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A good understanding of the nonlinearity mechanism in SAW devices is a crucial aspect in the filter stage. Nonlinear intermodulation distortion (IMD) may lead to spurious signals falling into the receiver band and limiting its sensitivity. Identify the dominant source of nonlinearity specially at high-power is important for a good prediction of the filter nonlinear response. In this work, third-order intermodulation (IMD3) products in TC-SAW (Temperature Compensated-SAW) devices are presented. Within this work we apply the previously developed Input-Output Equivalent Sources (IOES) method to compute nonlinearities of more complex structures such as ladder-type and CRF (Coupled Resonator Filter) filter structures. This work was supported in part by the Spanish Government through grant PID2020-118410RB-C21. Research was also supported by the Secretary of Universities and Research of the Generalitat de Catalunya and the European Social Fund through grant FI_B-00136.

Improving power handling and lifetime are key assets to ensure device performance and reliability. SAW resonators composed by very thin cross-section inter-digital transducer (IDT) structures make difficult to control the current density and thus acoustomigration plays and important role since degradation of the metallization is one of the main failure modes. The motivation of this work is to monitor and characterize the resonator behavior even at high powers levels that can damage the device. The method is based on a feed-forward-based technique to measure the reflection coefficient of SAW resonators under a fixed-frequency high power heating (HPH) signal. This work was supported in part by the Spanish Government through grants TEC2017-84817-C2-2-R, TEC2017-88343-C4-2-R and 2017 SGR-813. Research was also supported by the Secretary of Universities and Research of the Generalitat de Catalunya and the European Social Fund through grant FI_B-00136.

Understanding the mechanism of nonlinearity in SAW/BAW devices is growing up in importance because these, even being weak, can cause desensitization of the receivers and limiting their performance. Proper nonlinear distributed models have been extensively used, usually running Harmonic Balance (HB) simulations being in some cases very time consuming. The motivation of this work is to apply a new method of analysis for the simulation of harmonics (H) and intermodulation products (IMD) generation in SAW devices. The method is called the Input-Output Equivalent Sources (IOES) and it allows extremely fast and robust simulations of large distributed weak nonlinear circuits. This work was supported in part by the Spanish Gov. through grants TEC2017-84817-C2-2-R, TEC2017-88343-C4-2-R and 2017 SGR-813. Research wasalso supported by the Secretary of Universities and Research of the Generalitatde Catalunya and the European Social Fund through grant FI_B-00136.

This is the pre-peer reviewed version of the following article: González‐Rodríguez, M., Collado, C., González‐Arbesú, J. M., Mateu, J., Montoro, G., & Gilabert, P. L. (2021). Tone injection‐based cancellation technique for nonlinear distortion reduction of modulated signals in BAW resonators. Microwave and Optical Technology Letters, 63(3), 781-786, which has been published in final form at https://onlinelibrary.wiley.com/doi/10.1002/mop.32670. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. A technique for the reduction of third-order intermodulation distortion (IMD3) occurring in bulk acoustic wave (BAW) filters and multiplexers is presented. The method consists of using the intrinsic second-order intermodulation distortion generated by BAW filters and multiplexers themselves by injecting an externally controlled amplitude and phase modulated signal at low frequency to compensate for the IMD3. The proposed technique has been experimentally verified by performing IMD3 measurements in a single BAW resonator subject to several modulated signals under a nonlinear scenario. Secretary of Universities and Research of the Generalitat de Catalunya and the European Social Fund, Grant/Award Number: FI_B-00136; Spanish Government, Grant/Award Numbers: 2017 SGR-813,TEC2017-84817-C2-2-R, TEC2017-88343-C4-2-R

This paper performs a comprehensive nonlinear modeling of a Bulk Acoustic Wave (BAW) duplexer operating at the band 7 of the LTE wireless communication standard. The modeling starts by an accurate characterization of the resonators forming the filters by performing measurements of the second harmonic (H2). The modeling of individual resonators has then been used to predict second order nonlinear manifestations occurring in a real duplexer. These are H2, second order intermodulation products (IMD2), for the case where a jamming signal is set to low frequencies (IMD2-Low) and when the jamming signal is set to high frequencies (IMD2-High). Predicted results are then validated with real measurements. The authors would like to thank Qorvo Inc. for providing the on-wafer measurements that appear in this article. Work supported in part through grants TEC2017-84817-C2-2-R, TEC2017-88343-C4-2-R and 2017 SGR 813

As the power requirements in BAW filters steadily increase, thermal behaviour emerges as a key asset to ensure device performance and reliability. Under these conditions, self-heating mechanisms drive to possible situations where the filters no longer meet the electrical specifications. In addition to that, the evaluation of the heat spreading might help to define the resonators and pillars distribution along with the overall performance of current BAW filters. In the past, numerical methods based on FEM have been used to study the temperature distribution under high-power (HP) signals, lacking efficiency in terms of computational time. The motivation of this work is to describe an analytical method that is able to simulate very fast, without the need of costly FEM simulation, the heat spreading in a filter according to the spatial distribution of the resonators. This work was supported in part by the Spanish Gov. through grants TEC2017-84817-C2-2-R, TEC2017-88343-C4- 2-R and 2017 SGR-813. Research was also supported by the Secretary of Universities and Research of the Generalitat de Catalunya and the European Social Fund through grant FI_B00136

This work presents a new technique to cancel third-order intermodulation distortion (IMD3) by using a low frequency injected tone to generate a second-order intermodulation product (IMD2) that fall exactly at the same frequency of the undesired IMD3. The phase and amplitude of the injected tone are controlled to cancel out the IMD3. A proper characterization and a good modeling are needed to demonstrate the concept. Narrow band characterization and modeling of second harmonic (H2) and IMD3 in a Bulk Acoustic Wave (BAW) resonator has been done to evaluate the nonlinear contribution of each material composing the resonator and to identify the dominant nonlinear terms. The concept of this technique will be demonstrated by doing measurements of an on-wafer resonator. The measurement system, including the cancellation procedure, will be described. The cancellation achieved with this technique is in good agreement with the simulations.

©2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. This paper describes a measurement setup to obtain the reflection coefficient response over the frequency of a given device when this is subjected to a single-tone high-power (HP) signal. The proposed system is based on a feed-forward technique to cancel the reflected HP signal before reaching the vector network analyzer. This allows measuring the effects of the HP interfering signal into the device's low-power frequency response. This technique does not require either power-calibrated standards or complex calibration techniques. Experiments in several devices are also reported to validate the suitability of this technique.

Linearity of RF filters is in the focus of system-architects as carrier aggregation (CA) schemes in down- and uplink emerge as a requirement. The nonlinear electro-thermal-acoustic constitutive equations of the piezoelectricity and the number of different materials involved in the manufacturing of BAW resonators make it difficult to discern between different sources of nonlinearity. It is hard to identify the root-cause of undesired effects, such as harmonics, intermodulation products and detuning effects. A systematic procedure must be defined to unambiguously determine the origin of nonlinearities, and all the nonlinear observations must be consistent with the stated hypothesis. Better understanding of the nonlinear mechanisms is crucial for designing more linear resonators, and consequently improved filters.

A metamaterial spacer composed of spiral resonators (SRs) and narrow metal strips has been tested to operate like a bidirectional artificial magnetic conductor (AMC) reflector at 2.45 GHz. The performance of the spacer has also been evaluated in a closely spaced multiple-antenna system applied to successfully increase the transmission capacity of a commercial wireless IEEE 802.11b router.

The use of a low profile, light weight and easy to fabricate transpolarising surface placed on one side of a trihedral corner reflector (TCR) as polarimetric calibrator is presented in this letter. The transpolarising-TCR (TTCR) presents a high backscattered cross-polar response contrary to standard TCRs. The performance of this device has been tested at X-band using the UPC GB-SAR., Comment: Accepted for publication in IEEE Geoscience and Remote Sensing Letters

A metamaterial spacer to decorrelate two closely spaced antennas has been designed and tested. The metamaterial spacer exhibits an artificial magnetic conductor (AMC) behavior around 2.6 GHz. Its performance has been checked against a simple metal spacer (PEC), providing a quasi orthogonal radiation pattern and good results in terms of decoupling and decorrelating a two-antenna system. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1414–1417, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23365

Metamaterial slabs made of magnetic resonators (artificial magnetic conductor, AMC surfaces) can provide unusual electromagnetic properties, such as the dual PMC/PEC behavior, when used as reflectors. This property has been assessed and tested with the design and fabrication of a one-layer spiral AMC slab. Moreover, two bidirectional AMC surfaces have also been designed and measured. These structures, composed of spiral (SR) or capacitive loaded loop (CLL) resonators printed on dielectric strips, can provide 0° reflection coefficient phase when the incident electric field wave impinges on any side. A very low electrical thickness is achieved. Compact antenna systems with two (or more) close isolated antennas can be designed with such structures. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1949–1953, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22567

Prefractal Hilbert curves are analyzed in terms of radiation efficiency, quality factor, and electrical size for their use as small self-resonant monopole antennas. The structures show better performance as loads of monopoles than as radiating structures. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 45–49, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11122

The performance of space-filling curves used as small antennas is evaluated in terms of quality factor and radiation efficiency. The influence of their topology is also considered. Although the potential use of these curves is for antenna miniaturization, their behavior is not exceptional when compared with other intuitively generated antennas.

A multi-objective genetic algorithm (GA) has been applied in conjunction with the numerical electromagnetic code (NEC) to the optimization of wire pre-fractal Koch-like antennas in terms of bandwidth, efficiency, and electrical size. Their performance is compared to that of other nonfractal designs.

The use of a transpolarizing surface placed on one side of a trihedral corner reflector (TCR) as polarimetric calibrator is presented in this paper. The transpolarizing-TCR presents a high back-scattered cross-polar response. This structure has been tested at 9.65 GHz (X-band) with the help of the UPC GB-SAR system.

The primary objective of many antenna measurement facilities is to provide a specified high accuracy of the measured data. The validation of an antenna measurement facility is the process of proving that such a specified accuracy can be achieved. Since this constitutes a very challenging task, antenna measurement accuracy has been the subject of much research over many years and a range of useful measures have been introduced. Facility comparisons, together with antenna standards, error budgets, facility accreditations, and measurement procedure standards, constitute an effective measure towards facility validations. This paper documents the results of a comparison between 8 European antenna measurement facilities with a specially designed reference antenna, the DTU-ESA 12 GHz validation standard antenna (VAST-12). The electrical and mechanical properties of the VAST-12 antenna are presented and its three different coordinate systems are defined. The primary objective of the comparison is to obtain experience and results that can serve to develop standards for validation of antenna measurement facilities. The paper focuses on the comparison of the radiation pattern and presents not only the measurement data obtained at the facilities, but also investigates several procedures for comparing these data. This includes various definitions of pattern difference and statistical measures as well as a reference pattern. The comparison took place in 2004-2005 as part of the European Union network of excellence called ACE-Antenna Centre of Excellence.

Conventional antenna radiation efficiency measurement techniques, such as the Wheeler cap, are generally narrow-band and, thus, well suited for resonant antennas. In this work, the Johnston-Geissler (J-G) method based on the Wheeler cap principle is used in a wide frequency range. First, a good agreement between measurement and simulation in an ultrawide frequency band is shown on a straight wire monopole antenna with different attenuators emulating antenna losses. Then, this technique is used to measure the radiation efficiency of several ultrawideband (UWB) antennas.

The broadside power radiation enhancement has been tested for the case of a magnetic dipole in presence of an MNZ metamaterial substrate. In order to assess the theoretical estimations, a slot antenna on a ground plane has been fabricated and an AMC composed of 1 layer square spiral resonators has been used as an MNZ metamaterial slab. The radiation patterns have been measured in the anechoic chamber, achieving a gain in directivity of more than 1 dB. However, it should be taken into account that the thickness of the fabricated metamaterial slab (6 mm) is much smaller than the theoretical optimum thickness (hundreds of mm). The directivity of the antenna might be improved when increasing the number of layers of the metamaterial slab; in fact, in such a case, the leaky waves responsible of directive radiation are expected to be more significantly excited giving rise to the sought broadside power enhancement.

Transpolarizing surfaces are characterized for their property of rotating by 90deg the reflected electric field with respect to the incident one. Several transpolarizing surface designs are presented, and their potential applications and limitations, mostly for oblique incidence, are discussed.

Artificial magnetic surfaces have interesting applications in antenna design where one wants to replace, over a limited frequency range, electric conducting surfaces with magnetic equivalents. One of the many challenges in constructing such a surface is that of miniaturizing the resonator elements making up the structure whilst at the same time maintaining a reasonable bandwidth and a tolerable level of dielectric and copper losses. In this paper we present some novel structures, fabricated using chemical etching techniques, which have only 6.5% of the area of a capacitive loaded loop (CLL) and less than 30% of the area of spiral resonators and have measured return losses of less than 1.5 dB.

Like many multi-dimensional problems, there is not always a single best solution but a set of solutions, known as Pareto front, representing all possible trade-offs that can be made for given problem and criteria. Once the front is identified, the designer can choose the best solution for the current application. In this paper, a particle swarm optimization (PSO) technique is used to determine the Pareto front of a set of possible parabolic resistive loading profiles carried out on a monopole antenna. This Pareto front is the result of an optimization in terms of spatially averaged fidelity (SAP) and mean radiation efficiency for a given bandwidth. The optimum loading profile is selected as a compromise between these two parameters. This Pareto front shows what we could expect from a continuously tapered, resistively loaded monopole for UWB applications.

Artificial Magnetic Conductors (AMCs) offer many reflecting applications. When non symmetrical elements (diagonal slots, offset vias) are used, a cross-polar reflected response is achieved given an incident copolar electric field. This electromagnetic property can be used for polarisation conversion or RCS reduction purposes. A cross-polarising surface composed of square patches and diagonal slots over a ground plane has been designed and measured, providing good results for normal incidence. (4 pages)

A novel transpolarizing or crosspolarizing surface has been proposed to be applied in polarimetric SAR calibrating systems, like trihedrals, since they can not provide initially a crosspolar response. So the trans-surface has been designed and measured in an anechoic chamber, providing good results for normal incidence.

The AMC behavior of a reflecting surface is mainly related to the frequency where the 0deg crossing in the phase of its reflection coefficient takes place. This frequency gives the resonant frequency that characterizes the AMC surface. Two different designs of AMC surfaces showing quite different properties are presented in this communication. A first design proves the AMC behavior using metallic tubes with slotted square profile instead of the typical periodic arrangement of strips printed on a dielectric substrate; and the latter, shows the AMC performance of an artificial material when the electromagnetic waves impinge on its opposite faces.

An artificial magnetic reflector is built based on squared spiral resonators. Numerical simulations using efficient MLMDA (multilevel matrix decomposition algorithm) techniques are used for designing the reflector and the antenna. Measurements of the reflection coefficient of the artificial screen are carried out in order to verify the viability of the proposal. The performance of the reflector in combination with a folded dipole as an active element is also evaluated.

Simulations and measurements have been carried out of a 1-layer metamaterial slab made of spiral resonators that shows an AMC behavior, with an equivalent electrical width of /spl lambda//12 for the thickness (z dimension) of the slab. This behavior has been experimentally verified through radiation pattern measurements. The results show that similar results are obtained by placing a PEC at a /spl lambda//4 distance and by placing the antenna close to the AMC. This latter solution is lower profile.

This paper proposes to characterize antennas for UWB applications, considering the transmitter-receiver system, using figures of merit that do not depend on direction. From the basic formulation for a single antenna we extend this concept to a system containing transmit and receive antennas. We use these parameters to optimize dipole design with respect to its conductivity.

A multiobjective genetic algorithm (GA) has been applied to the design of electrically small thin-wire antennas taking into account the resonance frequency, efficiency and Q factor of the different configurations. The performance of the resulting designs is compared to that of other prefractal antennas of similar size.

The fabrication of antennas with recycled materials but with good performance is possible by using the classical formulation from textbooks. Several antenna designs built with materials found at home are shown, and their performance is measured with professional equipment to assess an acceptable agreement between simulations and measurements. Practical design and fabrication of antennas made with used materials and operating at WiFi bands will surely stimulate students of basic topics of antennas to fabricate and test their own designs.

A method for decreasing the height of a fractal Sierpinski monopole is presented. The method is based on the construction of a wire Sierpinski monopole with a Koch island loop as initiator. This initiator changes the perimeter of the gasket while preserving the multiband behaviour and the radiation power pattern characteristics of the conventional Sierpinski gasket.

The design of self-complementary antennas with pre-fractal profiles is investigated in this paper for its potentiality in designing wideband antennas. This new family of antennas is expected to combine the performances of self-complementary antennas and pre-fractals, Two new antenna designs, the self-complementary Koch-tie dipole and the Gosper Island dipole, are fully described.

This work presents the nonlinear modeling of a real acoustic wave filter set at the cellular commercial receiver band B40. The paper outlines the synthesis procedure of the acoustic filter and presents the filter performance of the fabricated device in both, a narrow-band and a broadband range. Differences between synthesized and fabricated filters are modeled afterwards in order to account for all the out-of-band features. Measurements of the second harmonic have been performed over the bandwidth of the filter. Modeling of the nonlinear response has been developed by using nonlinear models of the acoustic wave resonators forming the filter.

In this letter,we present a concentric annular-ring microstrip antenna that covers the bands of Galileo (E5a, E5b, E1, E2, L1), GPS (L1, L2, L5), and GLONASS (L1, L3). This microstrip antenna is fed by four apertures that improve the coupling. Broadband phase shifters and Wilkinson power combiners are used to generate the required circular polarization.

We consider an UWB scatterer imaging technique for determining the most significant positions of scatterers and reflection coefficients, in order to characterize the channel in terms of impulse response. We use two focused orthogonally aligned arrays, where transmitter and receivers have known positions.

Efficient utilization of the radiansphere surrounding a small antenna could improve its bandwidth. The use of a fractal shape as antenna can be a potential solution to design efficient small antennas because its fractal dimension is greater than its topological, dimension. Besides, some fractal shapes are space-filling curves, a suitable property that helps miniaturization. However, we are limited to the use of prefractals. Although prefractals are considered to behave as fractals and retain its fractal dimension, the influence of the initiator and even the IFS that generates fractals with the same fractal dimension is important under the scope of radiation efficiency and quality factor. This relation is systematically investigated in this work.

After two years of basic research on fractal electrodynamics, the FractalComs consortium presents the conclusions of the FractalComs Project (http://www.tsc.upc.es/fractalcoms/). They state the performance limits (fundamental and technological) of pre-fractal shaped miniature devices compared with conventional ones. Many miniature antennas and devices have been designed, analyzed and/or measured, the most outstanding being the two-arm square spiral antennas and the Hilbert superconductor resonators for miniature filters.