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An edge-coupled meandered three-coupled-line Marchand balun with a partial ground plane implemented in 0.13 $\mu \text{m}$ SiGe Bi-CMOS technology is presented in this brief. The balance performance of the designed balun is significantly improved by creating a ‘no ground plane’ beneath the coupled-line structure, which is demonstrated by simulating two baluns: one with a partial ground and the other with a solid ground underneath. The measured amplitude and phase imbalances are less than 0.4 dB and 2.5°, across the 3-dB bandwidth from 21.5 to 95 GHz, surpassing previously reported results of edge-coupled Marchand baluns. The balun occupies 230 $\mu \text{m}\,\,\times370\,\,\mu \text{m}$ .

Measurement results performed on a GaN high-electron-mobility transistor that show the presence of a double-energy-level (DEL) trap center in the device are presented. A novel, yet simple, circuit implementation of a DEL trap center in an FET is presented that is immediately extendableto a trap centerwithmore than two energy levels. The model is based on the Shockley–Read–Hall statistics of the trapping process. The implementation is suitable for both time-domain and harmonic-balance simulations. Simulation results validate the proposed model.

The temperature response of field-effect transistors (FETs) to instantaneous power dissipation has been shown to be significant at high frequencies, even though the self-heating process has a very slow time constant. This affects intermodulation at high frequencies. A major difficulty in characterizing the self-heating process in microwave FETs is to differentiate between the self-heating and charge-trapping rates. An iso-trapping measurement technique is proposed by which it becomes possible to characterize the self-heating process in an FET in isolation from the effect of the charge-trapping process in the FET. The results of iso-trapping measurements performed on a GaN high-electron-mobility transistor are presented, and used to successfully characterize the self-heating process.

The results of measurements performed on a GaN high electron-mobility transistor (HEMT) by two different pulse-measurement techniques are presented. By performing two-stage pulse measurements, two distinct current-injection mechanisms responsible for triggering the trapping process are identified. By performing three-stage pulse measurements, the trap center at which the trapping process occurs is identified to be a double-energy-level trap center, which is a trap center with two distinct energy levels between which there is an interaction. This result has a significant impact on the design of more accurate large signal models for GaN HEMTs.

International audience; —The strongest-cell criterion has been extensively used for handover algorithms during the last cellular-network generations. When network topologies become multi-layered, it results in abrupt behaviors such as the ping-pong effect as a consequence of the power gap between tiers and their irregular deployment. This effect not only affects users' quality of experience but also introduces a significant network overhead. Therefore, we propose an original handover algorithm based on predicted incomplete channel states from a Radio Environment Map to reduce this effect. The proposed algorithm is user triggered, network assisted, and fully backward compatible with LTE-A. Moreover, we evaluate the performance of our proposed algorithm against LTE-A in a two-tier cellular network for different user speeds following the guidelines outlined by the 3GPP on diverse matters (channel, mobility, wrapping, etc.). When applying realistic timing, our results reveal a highly substantial improvement in the number of ping-pong handovers regardless of the handover policy adopted in comparison to LTE-A without sacrificing users' experience; for instance, we obtain at least an order of magnitude decrease in the ping-pong rate at the expense of losing less than 9 percent in spectral efficiency.

A 3D printed dual-ridged horn antenna (DRHA) is presented. The antenna design is optimized for additive manufacturing and is 3D printed using acrylonitrile butadiene styrene (ABS) and then painted with nickel based aerosol spray. The coaxial transition is also included in the 3D printed prototype. The antenna was manufactured with the intention of improving learning and education of electromagnetism and antennas for undergraduate students using a low-cost personal desktop 3D printer. The painted DRHA has a 10 dB return-loss bandwidth of 6621 MHz (1905 MHz–8526 MHz) with a peak gain of 11 dBi. This prototype is the first known ABS-based horn antenna with the coaxial transition embedded into it.

A higher frequency, over 2 GHz, is suggested for current 4G or 5G wideband applications. By adopting a unique gain control method, an analog-controlled variable-gain amplifier (VGA) with an accurate dB-linear characteristic is presented. The designed VGA not only features large bandwidth, but also has accurate gain adjustment with a relatively wide control voltage range. The VGA has a measured gain range of 24 dB, of which 17.3 dB is dB-linear with less than $\pm$ 0.3-dB gain error. The $-$ 3-dB bandwidth is relatively constant from 2 to 2.2 GHz for the entire dB-linear range. An output 1-dB compression point of 1.8 dBm and a noise figure of 24 dB are measured. Due to the simple structure, the current consumption of the VGA core is only 2.9 mA from a 1.2-V supply, and the size is only ${\hbox{225}}\ \mu{\hbox{m}}\times {\hbox{45}}\ \mu{\hbox{m}}$ , excluding pads. Moreover, the robustness of the designed VGA is verified by means of Monte Carlo simulation.

The temperature-dependent thermal conductivities of a GaAs pseudomorphic high-electron mobility transistor’s (pHEMT) substrate and epilayer regions are extracted to develop a 3-D finite-element-method thermal model. The thermal characterization is based on electrical gate-metal-finger temperature measurements of a customized GaAs pHEMT test structure. Heat flow from an integrated thin-film resistor is shown to be sensitive to the device’s substrate thermal conductivity, while heat flow from the device’s channel is most significantly affected by the epilayer region thermal conductivity. These observations are used in the formulation of the thermal parameter extraction technique, which serves as a useful and convenient device modeling tool that can be integrated into an engineering design flow. Specific knowledge about the semiconductor material fabrication process, which may be unavailable to the design engineer, is not required for accurate thermal characterization; this is the overriding advantage of the technique presented.

International audience; The advent of 5G networks, where a plethora of spectrum-sharing schemes are expected to be adopted as an answer to the ever-growing users' need for data traffic, will require addressing mobility ubiquitously. The trend initiated with the deployment of heterogeneous networks and past standards will give way to a multi-tiered network where different services will coexist, such as device-to-device, vehicle-to-vehicle or massive-machine communications. Because of the high variability in the cell sizes given the different transmit powers, the classical handover process, which relies solely on measurements, will lead to an unbearable network overhead as a consequence of the high number of handovers. The use of spatial databases, also known as radio environment maps (REM), was first introduced as a tool to detect opportunistic spectrum access opportunities in cognitive radio applications. Since then, REM usage has been widely expanded to cover deployment optimization, interference management or resource allocation to name a few. In this paper, we introduce a handover algorithm that can predict the best network connection for the current user's trajectory from a radio environment map. We consider a geometric approach to derive the handover and handover-failure regions and compare the current handover algorithm used in Long-Term Evolution with our proposed one. Results show a drastic reduction in the number of handovers while maintaining a trade-off between the ping-pong handover and the handover-failure probabilities.

The thermal impact of device bias-state and structures (such as source connected field plates, gate-pitch, back-vias, and number of gate fingers) in AlGaN/GaN-on-Si high electron mobility transistors (HEMTs) are measured using gate metal resistance thermometry (GMRT). The technique characterizes the thermal response of device gate metallization to determine the gate-epilayer junction temperature (Tj), which is directly influenced by the channel heat source due to its close proximity. It is found that low gate leakage levels in GaN HEMTs make them favorable candidates for GMRT. Bias-dependent self-heating, independent of power dissipation, is observed in the devices. Therefore, Tj of different device configurations are compared at constant bias state, as well as constant power density (3.75 W/mm) to improve accuracy. Tj reduction is observed at high drain bias due to the migration of the channel heat source toward the gate field plate edge. This provides independent experimental validation for a reported electrothermal model [7]. A 3-D thermal finite element method model is presented, which simulates measured Tj rise to within ~6% across a range of device configurations and operating conditions. This is ultimately made possible upon implementation of a thermal boundary resistance layer and extraction of its temperature response using GMRT data.

Gate junction temperature is presented as the crucial parameter for modeling thermal degradation in GaAs device reliability studies, and sufficient for modeling the impact of temperature on device terminal characteristics. Gate metal resistance thermometry (GMRT) is applied to a GaAs pseudomorphic high-electron mobility transistor to measure its gate junction temperature. It is found that gate leakage current due to impact ionization can interfere with dc GMRT measurements. To the best of our knowledge, for the first time it is demonstrated that this can be largely avoided by instead applying an ac version of GMRT. However, the dynamic resistance of the gate leakage current path can interfere with ac GMRT. Measurements and thermal finite element method simulations of devices at constant power dissipation conclude that the bias dependence of the channel heat source profile affects the gate junction temperature. A parameter extraction technique is presented and used in device lifetime calculations to demonstrate MTTF variations of more than an order of magnitude (despite fixed power) due to bias-dependent self-heating.

Carbon nanotube (CNT) yarns are novel CNT-based materials that extend the advantages of CNT from the nanoscale to macroscale applications. In this study, we have modeled CNT yarns as potential data transmission lines. Test structures have been designed to measure electrical properties of CNT yarns, which are attached to these test structures using gold paste. DC testing and microwave S-parameter measurements have been conducted for characterization. The observed frequency independent resistive behavior of the CNT yarn is a very promising indicator that this material, with its added values of mechanical resilience and thermal conductivity, could be invaluable for a range of applications such as body area networks. A model is developed for the CNT yarn, which fits the measured data collected and agrees in general with similar data for non-yarn CNTs.

© 2016 IEEE. Personnel detection embedded in foliage is extremely important to border patrol, perimeter protection and search-and-rescue operations. In this paper, we explore the utility of radio-sensor network (RSN) to distinguish between humans and animals. We explore the phenomenon that signals are always affected by the presence of obstacles and identify human based on the received signals by transceivers, which leads to a potential low-cost way for personnel detection without specific sensors. In our study, the impulse radio ultra-wideband (IR-UWB) technology is selected for the RF transceiver due to the fact that it is not only energy efficient, but also robust against interferences. The principle component analysis (PCA) is applied to extract the feature vector, and a support vector machine is used as the target classifier. Experiment result with an average accuracy of 97.5% based on actual data collected in a cornfield indicates that this approach has a good capability to distinguish between human and animals in a foliage environment.

Different placement strategies for Field-Effect-Transistor (FET) active switching devices in an electromagnetic band gap (EBG) periodic structure are investigated. Two possible placements for the switches are considered: (a) switches on top of a substrate and (b) switches at the ground-plane level. Their advantages and drawbacks are analyzed and discussed in relation to fabrication, extension to 2-D and ground plane design. The transmission results and band gaps of the EBG structure are presented for both switch placements. When determining the transmission of the structure, the FET switches are modeled in two different ways, first as an ideal conductor and then using a more accurate model consisting of embedded scattering parameters. Significant differences have been observed between the results predicted using simple and accurate models. Experimental characterization of the switch reveals technological issues related to their biasing.

A digitally controlled half-width microstrip leaky-wave antenna (LWA) is presented for fixed-frequency beam scanning. The free edge of a half-width microstrip line is loaded with a number of periodic interdigital capacitors. Each capacitor is connected to the ground plane by a digital switch. By dynamically changing the reactance profile at the free edge of the microstrip the beam direction is changed at a fixed frequency. Full-wave numerical simulations show that the antenna has the ability to scan the main beam from 35° to 56 ° at 5.75 GHz. Refereed/Peer-reviewed

Carbon Nanotubes (CNTs) have emerged as potential candidates for replacement of conventional metals due to their significant mechanical, electrical, thermal properties and non-oxidizing abilities [1, 2]. The density of CNT composites is about five times lower than copper and around half that of aluminium. Moreover, their thermal conductivity is about ten times that of copper. With the above mentioned distinguishing features, CNTs have been of interest in medical, electronics and antenna applications [3]. CNTs are drawn into yarns by pulling and twisting them from CNT forests. Previously we have presented microwave characterization of CNT yarns [4]. Our results have shown that the CNT yarns exhibits frequency independent resistive behavior and is beneficial for wideband applications such as ultra-wideband (UWB) and wireless body area networks [4]. Electrical conductivity of a CNT yarn depends on the properties, loading and aspect ratio of the CNTs. It also depends upon the twist angle and the characteristics of the conductive network. By doping or adding materials, such as gold, silver or NiCr, electrical conductivity of CNTs can by varied. In [5], highly conductive carbon nanotube-graphene hybrid yarns are reported. They are obtained by drawing vertically aligned multi-walled carbon nanotubes (MWCNT) into long MWCNT sheets. Then graphene flakes are deposited onto the MWCNT sheet to form a composite hybrid structure that is transformed into yarns by twisting. The electrical conductivity of these composite MWCNT-graphene hybrid yarns is over 900 S/cm. In this work, we have modeled this hybrid material as a potential data transmission line and compared it with a transmission line made out of copper on the same substrate. The results are tabulated in Table-I. They show a good agreement between copper based and composite MWCNT-graphene hybrid material based transmission lines. The hybrid material is high conductive, flexible and stretchable. This makes it suitable to use as transmission lines and connecting wires in systems that require stretching and flexibility, such as wearable systems.

An electronically controlled half-width microstrip leaky-wave antenna (HW-MLWA) that can scan the main beam at a fixed frequency is presented. A technique is described to change the upper and lower limits of the beam direction without changing the scanning range itself. By varying the reactance profile at the free edge, the main beam of the proposed antenna can scan a range of 23° in discrete steps. There are 30 stubs positioned at the free edge of the antenna that gives the freedom to the designer to change the upper and lower scanning limits of the antenna without changing the scanning range itself Refereed/Peer-reviewed

A half-width microstrip leaky-wave antenna (HW-MLWA) is designed with forward (broadside-endfire) and backward (broadside-backfire) scanning capability. One feed and 50 ω load are connected at each end of the radiating element with a simple feed network and controlled switches that allow the antenna to scan in both forward and backward directions. The main beam is steered at any operating frequency by changing the admittance between the free edge of the radiating element and the ground. This is done by connecting 30 lumped capacitors (1 pF each) to the free edge of the radiating element with a total of 30 switches and vias. The antenna can scan a range of 34° in both forward and backward directions. © 2013 IEEE. Refereed/Peer-reviewed

This paper outlines the popular circuit tuning strategies reported for the implementation of reconfigurable low-noise amplifiers (LNAs). It presents a continuously-tuned LNA intended for multi-standard applications as well as enhancing the yield of conventional narrowband LNAs. The presented LNA is designed and implemented in a 0.25μm silicon-on-sapphire (SOS) CMOS process. It uses MOS-varactors at the output to continuously tune its load resonance frequency and input matching frequency without the need of a tunable input network, achieving optimized power consumption and noise figure (NF). The post-layout simulations show that the designed LNA can be continuously tuned from 2.6 GHz to 3.5 GHz. Over this frequency range, an input IP3 of of -12 dB, gain of 17 dB and a NF of less than 2 dB have been achieved with 3.4 mW of power consumption at 1.8V. © 2013 IEEE.

The effect of PIN diodes on the performance of a reconfigurable leaky-wave antenna (LWA) is studied. The PIN diode is modelled in three different ways. It is shown that the non-ideal behaviour of the PIN diodes changes the predicted return loss and radiation characteristics of the antenna compared to ideal switches. © 2013 IEEE. Refereed/Peer-reviewed

Changing the electromagnetic bandgaps (EBGs) and hence the stopbands in a multistate periodic microwave circuit is investigated experimentally. The state of the prototype circuit, consisting of 24 unit cells, is changed by closing or opening gaps in selected unit cells. This varies the periodic loading along the circuit and hence the EBG. In most states, the circuit behaves as a bandstop filter, and its stopband width and location are determined by the circuit state. Experimental results confirm that the first stopband width can be as large as 63% (at 4.92 GHz) or can be absent. The EBG leads to excellent isolation around 40 dB in the stopbands. Sharp roll-off between passbands and stopbands (upto 120 dB/octave) and small length compared to microstrip filters with similar cut-off and roll-off characteristics are other advantages of the proposed platform

Dispersion analysis of a unit cell in a one dimensional microstrip based periodic arrangement is studied. Topology of the unit cell allows it to reconfigure the internal design using active devices into two different states. Active devices are modeled using perfect electric conductors in this study, which take in to account the different state of the switches. The obtained dispersion diagram provides useful insight into bounded and unbounded modes inside the unit cell in both states. The modal analysis reveals the possible applications for this potentially reconfigurable unit cell based periodic arrangement in microwave filters and leaky wave antennas.

A recently proposed tunable microwave periodic structure requires many switches to dynamically change its microwave propagation and radiation characteristics. The performance of a discrete Field Effect Transistor (FET) switch package, suitable for the structure, is investigated in two potential configurations. In one configuration, the switch is co-planar with the ground plane and in the other it is on a different surface. Measurements made on two test boards confirm that when the switches are turned “on” the switch insertion losses are not significantly different between the two configurations. However when the switches are turned “off”, locating the switches on the ground plane provide better isolation between RF ports.

Wide-band matching of a tunable 1D periodic microwave structure, designed for fabrication in GaAs technology, is investigated. The two-layer unit cell of the periodic structure consists of a microstrip line loaded by multiple rectangular patches, which can be selectively short-circuited. The wide variation of the position of the bandgap, obtained by electrically controlled switches, induces a large variation of the effective dielectric constant in the considered wide frequency range. This effect is further reflected as a significant variation of the characteristic impedance, and hence a potentially high mismatch loss. A method for wide-band minimization of the mismatch (with respect to a 50Ω reference impedance), without compromising the performance of the device, is presented.

Effect on the electromagnetic bandgap (EBG) of an active, tunable, EBG structure, due to the insertion loss and other scattering parameters of active switching devices, is investigated. Active FET switches are modeled two ways, first as perfect conductors with the switch packaging and secondly as a black box with embedded scattering parameters provided by the switch manufacturer. The results obtained from the simulations for the transmission characteristics of the EBG structure shows a significant downshift in the resultant electromagnetic bandgap due to the additional transmission line effects introduced by the switches.

A planar, metamaterial-based, one-dimensional periodic structure that can be switched between multiple states is numerically investigated. It can be fabricated at low cost in gallium-arsenide (GaAs) technology for antenna-on-chip and system-on-chip millimeterwave applications. The device radiates in the leaky wave region and its radiation pattern can be changed by switching between states in addition to changing the frequency, over a wide bandwidth. It can also be employed to obtain nearly identical radiation patterns at different frequencies due to its reconfigurability. This digitally programmable device presents dynamic shifting of the band-gap by as much as 80 GHz. Tunability is obtained by externally controlled FET switches, directly integrated into the device in the GaAs substrate. The switches dynamically change reactive loads imposed by N rectangular patches in each unit cell, positioned below a microstrip line, allowing the device to switch between 2 N states. A representative CAD model is presen...

Numerical analysis of the dispersion characteristics of a 2D tunable periodic structure in microstrip technology is presented. The high relative dielectric constant gallium-arsenide (GaAs) substrate hosts the embedded active FET switches, allowing dynamic changes in the propagation conditions of the electromagnetic wave. The position, the aperture of band-gaps and hence the value of the effective dielectric constant can be controlled. These effects will be monitored through the change of the scattering parameters for different numbers of repetition of the unit cell in the transverse direction.

The effect of substrate thickness on the broadband (15–150 GHz) radiation characteristics of exponentially-tapered coplanar-strip antennas is explored using picosecond photoconductive pulse generation and sampling.

© 2015 The Institute of Electronics, Information and Comm. A simple leaky-wave antenna (LWA) array is presented here radiates in the boresight direction. It is based on uniform half-width (HW) microstrip leaky-wave antennas (MLWAs). Uniform HW-MLWAs usually radiate a fan-shaped beam with a beam direction near boresight at lower frequencies and near endfire at higher frequencies. One of the main challenges of uniform LWAs is to make them radiate toward the boresight. Six uniform HW-MLWAs are used in this array to overcome this limitation. The whole array is on a single substrate and is fed at the centre by a single probe. The peak gain of the array is 10.9 dBi and its 3dB gain bandwidth for boresight radiation is 270 MHz.

A new technique to implement fixed-frequency beam scanning using a half-width microstrip leaky-wave antenna (HW-MLWA) is presented. The main beam direction is electronically controlled by changing the reactance between the one edge of a microstrip and the ground. This is achieved through a set of patches periodically placed along the free radiating edge of the microstrip line, with the second edge of the microstrip line is grounded. The patches can be connected to or isolated from the ground using PIN diodes thus facilitating a sub-nanosecond means of controlling the reactance. The full-wave numerical simulations show the ability to control the main beam direction from 21°to 37°at 6.5 GHz within the first quadrant. © 2013 EurAAP.