Electrically small metamaterial-inspired antennas with active near field resonant parasitic elements: From theory to practice

© 2017 Euraap. By augmenting several classes of metamaterial-inspired near-field resonant parasitic (NFRP) electrically small antennas (ESAs) with active (non-Foster) circuits, we have achieved performance characteristics surpassing their fundamental passive bounds. The designs not only have high radiation efficiencies, but they also exhibit large frequency bandwidths, large beam widths, large front-to-back ratios, and high directivities. Furthermore, the various initially theoretical and simulated designs have led to practical realizations. These active NFRP ESAs will be reviewed and recently reported designs will be introduced and discussed

Metamaterial-inspired configurations to enhance the directivity of electrically small antennas

© 2016 European Association of Antennas and Propagation. It has been demonstrated that metamaterial-inspired electrically small antennas (ESAs) can be designed to have high radiation efficiencies and even large bandwidths with non-Foster circuit augmentations. However, being electrically small, it still remains a challenge to obtain directivities over interesting bandwidths which exceed those of simple dipoles, especially with only passive constructs. Different classes of metamaterial-inspired ESAs that have successfully produced higher directivities will be reviewed and new configurations will be introduced and discussed

Broadband Electrically Small Circularly Polarized Directive Antenna

© 2013 IEEE. A broadband electrically small antenna with directive circularly polarized radiation is presented. It is composed of a compact single-feed crossed dipole driver, which is backed by a near-field resonant parasitic (NFRP) reflector to achieve the directive radiation pattern. The NFRP reflector is designed to generate extra resonances and minimum axial ratio (AR) points in the antenna system. These features are combined with those resulting from the driver to broaden the operational bandwidth. The proposed antenna was fabricated and measured. The antenna prototype, with a low profile (0.066 λo at 1.45 GHz) and an electrically small size (ka = 0.71 at 1.45 GHz), has a measured S11<-10 dB bandwidth of 25.66% (1.362-1.763 GHz) and a 3-dB AR bandwidth of 10.56% (1.390-1.545 GHz). Additionally, the measurements resulted in a broadside gain of 2.31 ± 0.4 dBic and an average radiation efficiency of 80% within the operational bandwidth

Low profile, broadside radiating, electrically small huygens source antennas

© 2015 IEEE. It is demonstrated numerically that a metamaterial-inspired, low profile (height approximately A/80), electrically small (ka = 0.45) Huygens source antenna can be designed to radiate at 300 MHz in its broadside direction with a high radiation efficiency and a large front-to-back ratio. Two electrically small, near-field resonant parasitic (NFRP) antennas are first designed. Both are based on a coax-fed dipole antenna. An electric dipole response is obtained by combining it with a tunable Egyptian axe dipole (EAD) NFRP element. A magnetic dipole response is obtained by spatially loading the driven dipole with tunable, extruded capacitively loaded loop (CLL) NFRP elements. The driven dipole and the EAD and CLL NFRP elements are combined together and retuned to achieve a broadside radiating Huygens source antenna. Two different designs, one with two CLL elements and one with four, are obtained, and their performance characteristics are compared

Overcoming traditional electrically small antenna tradeoffs with meta-structures

© 2017 Euraap. Metamaterial-inspired near-field resonant parasitic (NFRP) electrically small antennas (ESAs) have been designed and experimentally validated to have not only high radiation efficiencies, but also multi-functionality, large bandwidths, high directivities and reconfigurability. These expanded capabilities have been attained by introducing more complex meta-structures, i.e., multiple NFRP elements loaded with fixed and tunable lumped elements, as well as active circuits. Different classes of passive and active NFRP ESAs that have successfully produced these effects will be reviewed, and several recently reported ESA systems will be introduced and discussed

Design and Testing of Simple, Electrically Small, Low-Profile, Huygens Source Antennas with Broadside Radiation Performance

© 2016 IEEE. The efficacy of a simple, electrically small, low-profile, Huygens source antenna that radiates in its broadside direction is demonstrated numerically and experimentally. First, two types of electrically small, near-field resonant parasitic (NFRP) antennas are introduced and their individual radiation performance characteristics are discussed. The electric one is based on a modified Egyptian axe dipole NFRP element; the magnetic one is based on a capacitively loaded loop NFRP element. In both cases, the driven element is a simple coax-fed dipole antenna, and there is no ground plane. By organically combining these two elements, Huygens source antennas are obtained. A forward propagating demonstrator version was fabricated and tested. The experimental results are in good agreement with their analytical and simulated values. This low profile, ∼0.05λ0, and electrically small, ka = 0.645, prototype yielded a peak realized gain of 2.03 dBi in the broadside direction with a front-to-back ratio of 16.92 dB. A backward radiating version is also obtained; its simulated current distribution behavior is compared with that of the forward version to illustrate the design principles

Metamaterial-inspired Electrically Small Platforms: Enhanced Directivity Properties

© 2018 IEEE. A variety of near-field resonant parasitic (NFRP) antennas have been developed as electrically small platforms to realize high directivity. These include compact arrays and Huygens dipole and multipole radiating systems. A brief review of these developments and their scattering equivalents will be presented

Eletrically-Small Rectenna with Huygens Radiation Pattern for Wireless Power Transfer Applications

© 2018 IEEE. An electrically-small Huygens rectenna is reported that operates at 915 MHz in the ISM band for wireless power transfer (WPT) applications. The rectenna consists of an electrically-small Huygens linearly-polarized (HLP) antenna and a rectifier circuit. The HLP antenna is developed by systematically combining two near-field parasitic resonant (NFPR) elements: an Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL), together, with a small dipole antenna. The designed HLP antenna is electrically-small (ka < 0.89), low profile (0.0420), and produces cardioid-shaped directivity patterns with a very satisfactory peak realized gain value (4.4 dBi), wide half power beamwidth (136°), and high front-to-back ratio (26 dB). A rectifier circuit is designed and integrated with the HLP antenna to realize the rectenna. The rectifier consists of one HSMS286 Schottky diode and three lumped elements. The rectenna achieves a maximum RF to DC conversion efficiency: 86%, and a 2.4 V output DC voltage for a -5.0 dBm input power. Owing to its compact footprint and excellent radiation performance, this electrically-small rectenna is suitable for wirelessly powering sensors and unmanned aerial vehicles (UAVs)

Designs of Compact, Flexible, Directive, Near-Field Resonant Parasitic (NFRP) Antennas

© 2018 IEEE. The designs of compact, low-profile, planar, flexible, directive, quasi-Yagi antennas are presented. By placing near-field resonant parasitic (NFRP) elements around the basic driven dipoles, these NFRP antennas achieve compactness, high efficiency and high directivity. The NFRP elements act either as director or reflector elements, empowering the antenna with desirable quasi-Yagi performance characteristics. These NFRP antennas are fabricated using thin substrates which can be bent without enduring any structure damage. The flexibility of these antennas is investigated under two bending conditions by mounting them on different radii cylinders. These antennas can be used in many advanced applications such as intelligent transportation system (ITS) and wearable devices

Maximum Gain, Effective Area, and Directivity

Fundamental bounds on antenna gain are found via convex optimization of the current density in a prescribed region. Various constraints are considered, including self-resonance and only partial control of the current distribution. Derived formulas are valid for arbitrarily shaped radiators of a given conductivity. All the optimization tasks are reduced to eigenvalue problems, which are solved efficiently. The second part of the paper deals with superdirectivity and its associated minimal costs in efficiency and Q-factor. The paper is accompanied with a series of examples practically demonstrating the relevance of the theoretical framework and entirely spanning wide range of material parameters and electrical sizes used in antenna technology. Presented results are analyzed from a perspective of effectively radiating modes. In contrast to a common approach utilizing spherical modes, the radiating modes of a given body are directly evaluated and analyzed here. All crucial mathematical steps are reviewed in the appendices, including a series of important subroutines to be considered making it possible to reduce the computational burden associated with the evaluation of electrically large structures and structures of high conductivity.Comment: 12 pages, 15 figures, submitted to TA