Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

This paper describes a beamforming microphone array consisting of pressure microphones that are mounted on the surface of a rigid sphere. The beamformer is based on a spherical harmonic decomposition of the soundfield. We show that this allows a simple and computationally effective, yet flexible beamformer structure. The look-direction can be steered to any direction in 3-D space without changing the beampattern. In general the number of sensors and their location is quite arbitrary as long as they hold a certain orthogonality constraint that we derived. For a practical example we chose a spherical array with 32 elements. The microphones are located at the center of the faces of a truncated icosahedron. The radius of the sphere is 5 cm. With this setup we can achieve a Directivity Index of 12 dB and higher. The operating frequency range is from 100 Hz to 5 kHz.

A highly scalable spherical microphone array based on an orthonormal decomposition of the soundfield

A computationally efficient global optimization method, the differential evolution algorithm (DEA), is proposed for the synthesis of uniform amplitude arrays of two classes, i.e., unequally spaced arrays with equal phases and unequal phases. Phase-only synthesis and the synthesis of uniformly exited unequally spaced arrays (position only synthesis) are compared and it is seen that, by using the unequal spacing, the number of array elements can be significantly reduced for attaining reduced sidelobe levels. From the DEA-based synthesis of unequally spaced arrays with uniform amplitudes and unequal phases, it is found that a tradeoff exists between the size of the unequally spaced arrays and the range of phases for the same radiation characteristics. The proposed synthesis technique using uniform amplitudes, unequal spacing, and unequal phases (position-phase synthesis) not only decreases the size of the array for the same sidelobe level compared to both the phase-only synthesis and position-only synthesis but also retains their advantages.

Synthesis of uniform amplitude unequally spaced antenna arrays using the differential evolution algorithm

The proliferation of wireless services is driving innovative phased array solutions that are able to provide better cost/performance tradeoffs. In this context, the use of irregular array architectures provides a viable solution. This paper reviews and highlights some of the most recent advances in this field, including clustered, thinned, sparse, and time-modulated arrays, and their proposed design methodologies.

Unconventional Phased Array Architectures and Design Methodologies—A Review

This paper presents a 1-W, class-E power amplifier that is implemented in a 0.35-/spl mu/m CMOS technology and suitable for operations up to 2 GHz. The concept of mode locking is used in the design, in which the amplifier acts as an oscillator whose output is forced to run at the input frequency. A compact off-chip microstrip balun is also proposed for output differential-to-single-ended conversion. At 2-V supply and at 1.98 GHz, the power amplifier achieves 48% power-added efficiency (41% combined with the balun).

A 1.9-GHz, 1-W CMOS class-E power amplifier for wireless communications

Classical antenna array synthesis techniques such as Fourier, Dolph-Chebyshev and Taylor synthesis efficiently obtain array current distributions for equally spaced arrays that generate a desired far-field radiation pattern function or keep important parameters like beamwidth and sidelobe level within prescribed performance bounds. However, the concept of optimization of the field pattern (e.g., by decreasing sidelobes or beamwidth) of an given equally spaced array realization by altering its element spacings still represents a challenging problem having considerable practical advantages. These include reduction in size, weight, and number of elements of the array. This paper describes a new approach to synthesis of unequally spaced arrays utilizing a simple inversion algorithm to obtain the element spacings from prescribed far-zone electric field and current distribution, or current distributions from prescribed far-zone electric field and element spacings.

Design of unequally spaced arrays for performance improvement

An effective method for optimizing the performance of a fixed current distribution, uniformly spaced antenna array has been to adjust its element positions to provide performance improvement. In comparison with the default uniform structure, this approach yields performance improvements such as smaller sidelobe levels or beamwidth values. Additionally, it provides practical advantages such as reductions in size, weight and number of antenna elements. The objective of this paper is to describe a unified mathematical approach to nonlinear optimization of multidimensional array geometries. The approach utilizes a class of limiting properties of sinusoidal, Bessel or Legendre functions that are dictated by the array geometry addressed. The efficacy of the method is demonstrated by its generalized application to synthesis of rectangular, cylindrical and spherical arrays. The unified mathematical approach presented below is a synthesis technique founded on the mathematical transformation of the desired field pattern, followed by the application of limiting forms of the transformation, and resulting in the development of a closed form expression for the element positions. The method offers the following advantages over previous techniques such as direct nonlinear optimization or genetic algorithms. First, it is not an iterative, searching algorithm, and provides element spacing values directly in a single run of the algorithm, thereby saving valuable CPU time and memory storage. Second, It permits the array designer to place practical constraints on the array geometry, (e.g., the minimum/maximum spacing between adjacent elements)

Generalized analytical technique for the synthesis of unequally spaced arrays with linear, planar, cylindrical or spherical geometry

A complete empirical large-signal model for high-power AlGaN/GaN HEMTs (GaN HEMT) utilizing an improved drain current (Ids) formulation with self-heating and charge- trapping modifications is presented. The new drain current equation accurately models the asymmetric bell-shaped transconductance (gm) for high Ids over a large range of biases. A method of systematically employing dynamic IV behavior using pulsed-gate IV and pulsed-gate-pulsed-drain IV datasets over a wide variety of thermal and charge-trapping conditions is presented. The composite nonlinear model accurately predicts the dynamic IV behavior, S-parameters up to 10 GHz, and large-signal wideband harmonic behavior for a multitude of quiescent gate-source and drain-source biases as well as third-order intermodulation distortion (IM3).

A Wideband Multiharmonic Empirical Large-Signal Model for High-Power GaN HEMTs With Self-Heating and Charge-Trapping Effects

GaN will play a strong role in advanced RF and microwave applications including 5G and satellite communications. The specifications of these systems will push next-gen GaN devices towards mm-wave operation. The challenges and opportunities for commercial deployment of GaN are identified and a variety of circuit designs are presented. A 5G high-linearity power amplifier MMIC in 0.20um GaN with Pout=36dBm at 51.1% PAE and a Sat-com Ku-band mixer in 0.25um GaN with conversion loss < 10.5dB and IIP3=36.4dBm are demonstrated.

Future directions for GaN in 5G and satellite communications

A primary factor affecting optimum performance of microwave multipliers employing nonlinear devices is the proper termination of the fundamental and other harmonic frequency components. The objective of this paper is to present a quantitative analysis leading to the assessment of optimum terminating impedances in the design of active frequency multipliers with special attention given to harmonics other than those desired. The analysis includes computer modeled HEMT data and supporting measured data for corresponding circuit realizations. Circuit designs are presented utilizing HEMT transistors as the active element to verify modeled results. Based on available literature, the results demonstrate, for the first time, the quantitative effects of harmonic termination on active multiplier conversion gain and fundamental and higher harmonic suppression. An experimental design reveals an improvement in multiplier gain of 124% over the conventional approach and data is presented which quantitatively illustrates the advantages of impedance termination considerations under optimal bias conditions.

G.R. Branner

Papers

Design of unequally spaced arrays for performance improvement

Generalized analytical technique for the synthesis of unequally spaced arrays with linear, planar, cylindrical or spherical geometry

A Wideband Multiharmonic Empirical Large-Signal Model for High-Power GaN HEMTs With Self-Heating and Charge-Trapping Effects

Future directions for GaN in 5G and satellite communications

Optimization of active microwave frequency multiplier performance utilizing harmonic terminating impedances