RF Engineers Research Articles

Glass Devices for Next-Generation Packaging and RF Signal Conditioning

The push for higher communications frequencies, greater system integration, and smaller space imparts many unique challenges on RF and packaging engineers in the development of next generation cellular products for 5G, WiFi 6, Military, and other applications. Traditional materials, such as LTCC, organic laminates, and silicon face major limitations to dramatically improve system size, weight, and performance (SWAP). Photosensitive Glass-Ceramics (PSG) have gained a lot of attention as a next generation RF and RF packaging substrate for their ability to simultaneously solve these two important challenges. In this paper the authors will present on our work using PSG for RF and RF packaging solutions. We will share (1) the advantages of using PSG for advanced RF packages, and (2) our work demonstrating glass as an RF substrate integrating discrete components and embedded die for passive RF filters, and (3) our work towards building vertically stacked glass packages for advanced RF systems-in-package (SiP). The described work presents a manufacturing platform for the production of vertically stacked glass substrates with integrated high Quality Factor passive devices, such as inductors and capacitors, and heterogeneously integrated surface mount devices for advanced RF systems-in-package. The presented material demonstrates a production and assembly process for the manufacturing of advanced systems. In this paper, we present design, production, assembly considerations that impact size, weight, and performance (SWAP) metrics for a variety of product definitions and multiple simulation vs. product testing to demonstrate a reliable design to product flow.

CSRR DGS-Based Bandpass Negative Group Delay Circuit Design

The unfamiliar negative group delay (NGD) circuit is the less familiar function for most of RF and microwave design engineers. Among the existing types, the bandpass (BP) NGD type circuits are the most convenient for the wireless communication microwave technology. Therefore, it is particularly important to explore different microwave circuit topologies operating as BP-NGD function. An innovative design of BP-NGD topology constituted by defected ground structure (DGS) with complementary split ring resonator (CSRR) is developed in the present paper. The DGS-based BP-NGD structure design method is introduced in function of the CSRR geometrical elements followed by S-parameter parametric analyses. As proof-of concept (POC), the design method of the proposed BP-NGD passive fully distributed circuit is described. The effectiveness of the BP-NGD structure and the test feasibility are investigated by implementing two different prototypes represented by single- and double-wing DGS passive circuits. It is observed that significant BP-NGD function performances were validated by well-correlated simulations and measurements showing -1.9 ns NGD value around the center frequency, 2.46 GHz over 31 MHz NGD bandwidth. In addition, the tested BP-NGD prototypes present insertion loss better than 4 dB and reflection loss better than 16.7 dB. Because of its potential integration, the investigated BP-NGD circuit is potentially useful for the communication system performance improvement for example via delay effect reduction in the RF and microwave devices.

Penetration Depth Analysis of UMTS Networks Using Received Signal Code Power

This paper examines the coverage of three UMTS networks in Calabar, using the received signal code power (RSCP). A drive test conducted with the aid of a TEMS investigation software, collected log files of RSCP which were analyzed as coverage plots by a TEMS discovery software and further put through statistical measures using excel. The low values of calculated standard error depicts that the data used in this study is accurate and not manipulated. The data distribution in MTN and 9mobile network were slightly leptokurtic but slightly mesokurtic for Airtel network. Again, the data distribution for the three networks were approximately symmetric. Finally, 81.5%, 96.36% and 92.1% of the drive test routes for 9 mobile, Airtel and MTN network met with the NCC performance threshold. The result of this study will assist RF engineers in the optimization of UMTS networks and also in designing propagation models for accurate transmission of UMTS network signals in the study area.

Fast Unveiling of T max in GaN HEMT Devices via the Electrical Measurement-Assisted Two-Heat Source Model

Gallium nitride (GaN) high-electron-mobility transistor (HEMT) devices, which have wide application potential from power amplifiers to satellite, need to be thoroughly examined in terms of reliability in order to benefit the superior intrinsic properties of the device. The most critical parameter in the device reliability is the hotspot, or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {max}}$ </tex-math></inline-formula> , which occurs somewhere on the subsurface and along the channel of the GaN HEMT, which is optically inaccessible due to optical path disability. Therefore, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {max}}$ </tex-math></inline-formula> value is underestimated in optical measurements, such as the thermographic IR and Raman methods. With 3-D electrothermal simulations, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {max}}$ </tex-math></inline-formula> is obtained close to reality, but it requires a huge computation load and the complex modeling of semiconductor device physics. In 2-D or 3-D thermal simulations that do not use electrothermal simulations, since the self-heating is mostly modeled with a single heat source, neither the correct <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {max}}$ </tex-math></inline-formula> value is obtained nor the effect of bias conditions is considered. To address the aforementioned shortcomings, a hybrid method is demonstrated, which exploits the electrical measurements of GaN HEMT, which RF and reliability engineers often and easily do. It is demonstrated that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {max}}$ </tex-math></inline-formula> can be determined quickly and close to the electrothermal simulations in a GaN HEMT device with a two-heat source method and finite element analysis (FEA) hybrid interaction with respect to various bias conditions. Moreover, the impact of the knee voltage is investigated with different knee-detection techniques. The proposed method provides GaN HEMT reliability engineers with an easy-to-implement alternative to reveal the hotspot location and the value.

Enhancing Laboratory Experience Using 3D-Printing Technology in Microwave and Antenna Education [Educator's Corner

The development of modern wireless techniques has resulted in a need for more trained RF engineers. For college students majoring in microwaves and antennas, practical training is essential to understanding abstract electromagnetic theories and to cultivating their engineering skills <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> . However, the traditional fabrication methods for microwave devices used in university labs aren’t appropriate for undergraduate students because of their inflexibility, high cost, and use of harmful chemicals.

Guaging of key performance indicators for 2G mobile networks in Calabar, Nigeria

The increase in the number of mobile subscribers, coupled with the increase in mobile services is enough reason to monitor the QoS of mobile network operators frequently. This work looks into the QoS of network operators in Calabar, Nigeria, taking into consideration some KPIs ((CSSR, DCR, CST, HOSR, and network quality and network coverage). Analysis of data obtained after a benchmarking drive test shows that Globacom network was within NCC performance threshold for all network KPIs monitored. Also, MTN network performed poorly in HOSR but met the minimum benchmark in other network KPIs. Airtel network failed in the required DCR benchmark but was within the minimum benchmark for other KPIs while 9mobile failed in CSSR and DCR performance threshold but met the performance threshold for other KPIs. This result will be useful to the regulatory body, NCC, those in academic, RF engineers, network subscribers and especially, the network operators which we expect, will optimize their networks immediately.

Development of Educational Materials for Practical RF Engineers in College

Development of Educational Materials for Practical RF Engineers in College

Cryogenic Noise-Parameter Measurements: Recent Research and a Fully Automated Measurement Application

Since the conception of radio astronomy [1], researchers have been striving to develop a "zero-noise" broadband receiver. Although this goal has remained elusive, the pursuit of it has led to numerous low-noise circuit innovations [2], [3]. Perhaps the most notable of these innovations are cryogenic low-noise amplifiers (cryo-LNAs) [3]-[6] as this technology has been able to achieve the lowest noise levels to date. While references to cryogenic amplifiers in the literature date back to the early 1950s [7], they are still a subject of much interest among researchers. Cryo-LNAs were initially conceived of to address challenges in the fields of space exploration [8], [9] and radio astronomy [10]. More recently, researchers in other fields have become interested in "zero-noise" receivers, making this a topic of widespread interest among RF and microwave engineers.

The Fairy Tale of Simple All-Digital Radars: How to Deal With 100 Gbit/s of a Digital Millimeter-Wave MIMO Radar on an FPGA [Application Notes

The advantages of digital radars are frequently highlighted, leading to the impression that the realization of such a sensor is simple. However, when it comes to applications that require a large bandwidth, not only is the absence of high-speed data converters a problem, but it is also challenging to deal with data rates that easily exceed 100 Gb/s. With recently available RFSoC modules, it is now possible to realize research and development platforms for digital radars. For the first time, this allows designers to characterize and optimize all components involved in such systems. This includes evaluating suitable transceiver MMICs, baseband processing architectures, and modulation formats, just to mention the aspects that have been addressed. The article also emphasizes that sophisticated digital designs are required to realize the radar processing in there is still great potential in digital realizations; it simply needs to be exploited. We expect radar design to change: where mostly sophisticated RF engineers were required in the past, an interdisciplinary team working closely together will be needed to handle the challenges presented by digital radars.

MTT-20 on HF/VHF/UHF Technology [MTT Society News

The IEEE Microwave Theory and Techniques Society (MTT-S) Technical Committee MTT-20 (originally MTT-17) was formed in 1997 to address the needs of some 25,000 RF engineers whose work was primarily at frequencies below 1 GHz. Fritz Raab and Clark Bell presented the idea to the MTT-S Administrative Committee and served as the first chairmen. Prior to the formation of MTT-20, no IEEE Society served the high-, very high-, and ultrahigh-frequency (HF/ VHF/UHF) community. Publications were scattered among many trade conferences and trade journals as there was no place within IEEE to publish on these topics.

Propagation Measurements and Pertinency of Models for Communications Systems in Oman

This article discusses the usefulness of Okumura-Hata model and Sakagami model in urban areas for 2G and 3G communication systems. At some places, applicability of the models (Okumura Hata and Extended Sakagami) is studied and extended to a much lower distance from the tower than the specified minimum distance indicated in the model. Authors did an extensive drive test in urban areas and post also processed data and proposed theoretical modified model which is presented and compared for different data sets at different locations in Oman. Higher order interpolating polynomial was also used which helps in reasonable prediction for RF engineers.

Multibias and temperature dependence of the current‐gain peak in GaN HEMT

Thermal and multibias behavior of the peak in the short-circuit current-gain (h21) has been investigated for a GaN HEMT, aiming to contribute to an extensive knowledge on it. To obtain a simple and complete insight of this phenomenon and its influence in device performance over operating conditions, high-frequency multibias scattering (S-) parameter measurements have been analyzed from low to high temperature. It has been observed that the current-gain peak might get to be more or less serious depending on the working circumstances. The peak affecting h21 has been successfully reproduced by using an equivalent-circuit model. Moreover, a novel procedure has been developed to interpret this kind of phenomenon by quantifying the area of the current-gain peak (ACGP), which is denoted as the area corresponding to h21 curves with and without the peak. It is found that the ACGP is strongly dependent on bias and less dependent on temperature. The relevance of a comprehensive evaluation of the peak in h21 lies in its usefulness for empowering RF engineers to efficiently consider it for both device modeling and circuit design.

Thermal influence on S22 kink behavior of a 0.15 μm gate length AlGaN/GaN/SiC HEMT for microwave applications

Thermal influence on S22 kink behavior has been carried out on a 0.15 μm gate length AlGaN/GaN/SiC high electron mobility transistor over a wide range of temperature. The size and the shape of the S22 kink effect (KE) in terms of biasing and temperature have been evaluated. The main finding is that S22 of the studied device is affected by two kinks: the first one appears at approximately 19 GHz and then the second one appears at about 43 GHz. The impact of the intrinsic circuit parameters on the S22 kink phenomena is inspected to assess their contribution. In addition, a new procedure is proposed to quantify this type of phenomenon by defining the kink area as the area between the two curves corresponding to S22 with and without the KE. The relevance of this study emerges from the fact that an exhaustive characterization of these anomalous phenomena can empower RF engineers to effectively take them into account for both modeling and design purposes.

Canary in the Gold Mine? [MicroBusiness

Our technologies, the ones RF and microwave engineers and researchers have been working on for decades, are having unprecedented commercial success. Companies are doing billions of dollars of business selling components, subsystems, systems, services, and tools. Our technologies touch virtually every person on the planet. We've enabled worldwide connectivity, location services, information acquisition, security, health care, and entertainment. Our technologies have never been more relevant or valuable than they are now, and there are prospects for even more success with advanced semiconductors, greater use of millimeter-wave and terahertz frequencies, advances in materials, and new concepts in design and integration.

Spectrum Modeling of Cross-Modulation for Concurrent Dual-Band RF Power Amplifiers in OFDM Modulation

In this paper, the nonlinear effects of amplified dual-band orthogonal frequency-division multiplexing (OFDM) signals are analyzed. Furthermore, a spectrum model of the intermodulation and cross-modulation for dual-band OFDM signals in terms of third-order intercept points ( ${IP}_{3}$ ) is derived. The experimental measurements match the analytical predictions, which is useful to the design and test of concurrent dual-band RF transmitters for RF engineers.

RF noise modeling of Black Phosphorus Junctionless Trench MOSFET in strong inversion region

In this paper, RF noise modeling of Black Phosphorus Junctionless Trench (BP-JL-T) MOSFET has been investigated in strong inversion region. The simulated and modeled results are simultaneously compared with Conventional Trench (CT) MOSFET at THz frequency range. By using analytical expressions from RF equivalent schematic, few RF figure-of-merits (FOMs) have been evaluated. It is found that RF noise parameters such as noise resistance (Rn), minimum noise figure (NFmin), optimum source susceptance (Bopt) and conductance (Gopt) are reduced to more than 200%. Modeled results reveal that BP-JL-T-MOSFET minimizes RF noise thus, providing the detailed insight to RF engineers for microwave applications/RFIC design.

In2O5Sn based transparent gate recessed channel MOSFET: RF small-signal model for microwave applications

This paper discusses the small signal RF model of Transparent Gate Recessed Channel (TGRC) MOSFET using a 3D TCAD device simulator. Small signal model is studied in terms of microwave parameters such as S (scattering) parameters, Z (impedance) parameters, Y (admittance) parameters, and h (hybrid) parameters with an aim to analyze the behavior of TGRC MOSFET at microwave frequency. All the results of TGRC-MOSFET have been compared with Conventional Recessed Channel (CRC) MOSFET having aluminum as gate metal electrode. Modeled results have also been compared with simulation results and found good agreement with the 3D-simulation results. Moreover, it is perceived from the results that 99.4% enhancement in the input impedance of TGRC-MOSFET and input admittance is improved by 32.9% in the proposed device (TGRC-MOSFET) in comparison to CRC-MOSFET. It has also been observed that the transit (cut-off) frequency (fT) and maximum oscillator frequency (fMAX) enhances significantly by 42.85% and 123% respectively in TGRC MOSFET owing to the remarkable reduction in intrinsic capacitances. Results reveal that the proposed device design improves the small signal behavior thus, may provide detailed insight to RF engineers for microwave applications and testing of RF ports.

Signal Progress: Early Developments in U.S. Radar TR Switching

When Privates George Elliott and Jo s eph Lockard discovered a large fleet of airplanes approaching Pearl Harbor, Hawai'i, on the morning of 7 December 1941, they were operating a new U.S. Army Signal Corps radar that used the same antenna for transmitting and receiving RF energy [1]. RF engineers had to quickly develop a variety of new techniques to keep the multikilowatt transmitter signals from degrading or damaging the sensitive receivers in those early systems. This past December marked the 75th anniversary of that event. Tying in with the exhibit of related hardware at the IEEE Microwave Theory and Techniques Society's (MTT-S) 2017 International Microwave Symposium in Honolulu this June, the goal of this article is to highlight some of the components and circuits used for transmit?receive (T/R) switching in U.S. radars from the pre-World War II era through the following few decades.

Small Cell Transmit Power Assignment Based on Correlated Bandit Learning

Judiciously setting the base station transmit power that matches its deployment environment is a key problem in ultra dense networks and heterogeneous in-building cellular deployments. A unique characteristic of this problem is the tradeoff between sufficient indoor coverage and limited outdoor leakage, which has to be met without explicit knowledge of the environment. In this paper, we address the small base station (SBS) transmit power assignment problem based on stochastic bandit theory. Unlike existing solutions that rely on heavy involvement of RF engineers surveying the target area, we take advantage of the human user behavior with simple coverage feedback in the network, and thus significantly reduce the planned human measurement. In addition, the proposed power assignment algorithms follow the Bayesian principle to utilize the available prior knowledge from system self configuration. To guarantee good performance when the prior knowledge is insufficient, we incorporate the performance correlation among similar power values, and establish an algorithm that exploits the correlation structure to recover majority of the degraded performance. Furthermore, we explicitly consider power switching penalties in order to discourage frequent changes of the transmit power, which cause varying coverage and uneven user experience. Comprehensive system-level simulations are performed for both single and multiple SBS deployment scenarios, and the resulting power settings are compared to the state-of-the-art solutions. Significant performance gains of the proposed algorithms are observed. Particularly, the correlation structure enables the algorithm to converge much faster to the optimal long-term power than other methods.

Dependence of B1+ and B1- Field Patterns of Surface Coils on the Electrical Properties of the Sample and the MR Operating Frequency.

In high field MRI, the spatial distribution of the radiofrequency magnetic ( B1) field is usually affected by the presence of the sample. For hardware design and to aid interpretation of experimental results, it is important both to anticipate and to accurately simulate the behavior of these fields. Fields generated by a radiofrequency surface coil were simulated using dyadic Green's functions, or experimentally measured over a range of frequencies inside an object whose electrical properties were varied to illustrate a variety of transmit [Formula: see text] and receive [Formula: see text] field patterns. In this work, we examine how changes in polarization of the field and interference of propagating waves in an object can affect the B1 spatial distribution. Results are explained conceptually using Maxwell's equations and intuitive illustrations. We demonstrate that the electrical conductivity alters the spatial distribution of distinct polarized components of the field, causing "twisted" transmit and receive field patterns, and asymmetries between [Formula: see text] and [Formula: see text]. Additionally, interference patterns due to wavelength effects are observed at high field in samples with high relative permittivity and near-zero conductivity, but are not present in lossy samples due to the attenuation of propagating EM fields. This work provides a conceptual framework for understanding B1 spatial distributions for surface coils and can provide guidance for RF engineers.