The advent of multi-standard and multi-band software defined radio (SDR) applications has necessitated the design and deployment of dual-band RF components and circuits considering the numerous advantages of such designs over the traditional narrow band circuits and components. For example, a dual-band power amplifier (PA) not only simplifies the hardware complexity but also provides higher reconfigurability [1] and hence makes it a front runner for deployment in SDR architectures [2][3]. Furthermore, the evolution of communication technologies demands the use of dualband/ multi-band RF circuits so as to acc ommodate many standards simultaneously for facilitating and guaranteeing the backward compatibility of future standards (such as 4 G) based system for smooth network migration and upgrades. These technological requirements have also led to commercial introduction of dual-band base stations and repeaters [4][6]. Furthermore, the advancement in CMOS and other MMIC technologies, although, is challenging the transmission line based passive circuit techniques but the high power handling ability of transmission line based circuits are potentially very useful in applications such as the design of high power/high efficiency PAs and transmitters. This article elaborates on the techniques employed in the design of transmission line based dual-band RF components in the context of multi-band/multi-mode SDR architecture, highlighting the problems which need to be addressed during the design process.

Design of two novel orientation independent slot resonator based chipless RFID tags is proposed in this paper. These tags make use of multiple L-shaped slots of different lengths on a lossy substrate and are appropriate for item tracking and identifications. The data is encoded in the backscattered signal from the tag after its illumination. The first tag configuration includes multiple L-shaped slot resonators cascaded with each other. It exhibits wideband features and enables addition of extra resonators for encoding of additional data without increase in the tag size. The second configuration has alternate resonators on one side of the substrate while the remaining resonators, are inverted, and are on the other half of the substrate. It leads to reduced mutual coupling between the resonators, and hence an improved performance, and improved printing flexibility. The proof of concept is demonstrated through the design of tags in CST Microwave Studio and prototype development on Rogers 5880 substrate. Both the tags are compact, printed on 20 mm x 20 mm substrate, encode 8-bits in a bandwidth of 3 GHz and thus advance the state of the art significantly. An interesting feature of the proposed tags is the orientation independence and this is a very useful feature for applications such as tracking of items in a smart retail scenario where the products need to be read by the readers from any orientation.

This paper presents an extensive study and demonstration of efficient electrothermal large-signal GaN HEMT modeling approaches based on combined techniques of Genetic Algorithm (GA) with Artificial Neural Networks (ANN), and Particle Swarm optimization (PSO) with Support Vector Regression (SVR). Another promising Gaussian Process Regression (GPR) based large-signal modeling approach is also explored and presented. The GA-ANN addresses the typical problem of local minima associated with the backpropagation (BP) based ANN. The GA successfully aids in the determination of optimal initial values for BP-ANN and enables it to find a unique optimal solution after subsequent of iterations with higher rate of convergence. This is also achieved using PSO-SVR with lower optimization variables. The developed modeling techniques are demonstrated and used to simulate the gate and drain currents of a 2-mm GaN device. All the models are relatively simple, practical, and easy to implement. The gate and drain currents models are embedded in an equivalent large-signal circuit’s model and built in Advanced Design System (ADS) software. The implemented model is validated by large-signal measurements and very good fitting results have been obtained. The model also showed an accurate simulation for a nonlinear power amplifier with very good computational speed and convergence.

The development of a reliable Wireless Body Area Network (WBAN) relies significantly on the quality of wearable antennas. Therefore, this paper proposes a low-profile four-element Multi-Input-Multi-Output (MIMO) antenna for wearable millimeter-wave (mm-wave) WBAN applications. The MIMO antenna structure incorporates a standard Vivaldi antenna and a frequency-selective surface that encompasses the 28 GHz and 30 GHz of the mm-wave band with a 36.44% fractional bandwidth. It offers inter-element isolation of less than −20 dB in a compact space of $16\times 20$ mm2. Conformability analysis, along with testing on Gustav’s model chest, hand, and leg, was evaluated in terms of the antenna impedance bandwidth, gain, efficiency, and radiation pattern. The simulated characteristics of the MIMO antenna were tested through measurements in free space and on the human body using a prototype of the antenna. Furthermore, the MIMO antenna exhibits a low envelope correlation coefficient of less than 0.24, high diversity gain of greater than 9.95 dB, and an acceptable total active reflection coefficient of less than −10 dB. To ensure safety, the Specific Absorption Rate (SAR) analysis revealed acceptable levels of 0.397 and 0.267 (W/kg) at 28 GHz and 30 GHz, respectively. The proposed MIMO design is suitable for wearable WBAN applications owing to its small size, consistent gain, and compatibility with the human body in terms of a constant impedance bandwidth and end-fire radiation pattern.

This brief presents a novel design of a dual-band equal split Wilkinson power divider. It is based around a single coupled line section as core and uses stub-based port matching networks at each of the ports. It then incorporates only one isolation resistor, which is independent of frequency-ratio, for achieving perfect isolation. Closed form design equations are developed for the general analysis of the power divider and design case studies are provided to evaluate the proposed design. The developed prototypes for frequency-ratios of 2 and 7 show a good agreement between the electromagnetic simulated and measured results and thus validate the reported theory.