Near-field Resonant Parasitic Antennas Research Articles

Flexible, Bandwidth-Enhanced, Electrically Small, Electric Near-Field Resonant Parasitic Antenna With Filtering Performance Characteristics

In this communication, a flexible, bandwidth-enhanced, electrically small, electric near-field resonant parasitic (NFRP) filtering antenna is presented. The inherent radiation null of the dipole-driven NFRP antenna is first presented. In addition, by properly adjusting the relative position of the NFRP element and the driven dipole, this radiation null can be placed at either the lower or upper operational band edge. Then, by implementing multiple NFRP elements and properly allocating their relative positions, excellent bandpass-filtering response together with the enhanced bandwidth of the electrically small NFRP filtenna is accomplished. A prototype of the optimized design operating centered at 1.9 GHz was fabricated and measured. The simulation and experimental results are in good agreement, indicating that the antenna exhibits a wide ~11.3% impedance bandwidth with good out-of-band rejection, while maintaining its electrically small size: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ka</i> ~ 0.924. The flexibility of this antenna is experimentally analyzed under different bending conditions and the results confirm that its performance characteristics are substantially maintained.

Efficient and Compact Near-Field Coupled Hybrid Antenna Using a Single Radiating Subwavelength Split-Ring Resonator

Modern applications in the realms of wireless communication and mobile broadband Internet increase the demand for compact antennas with well defined directivity. Here, we present an approach for the design and implementation of hybrid antennas consisting of a classic feeding antenna that is near-field-coupled to a subwavelength resonator. In such a combined structure, the composite antenna always radiates at the resonance frequency of the subwavelength oscillator as well as at the resonance frequency of the feeding antenna. While the classic antenna serves as impedance-matched feeding element, the subwavelength resonator induces an additional resonance to the composite antenna. In general, these near-field coupled structures are known for decades and are lately published as near-field resonant parasitic antennas. We describe an antenna design consisting of a high-frequency electric dipole antenna at f d = 25 GHz that couples to a low-frequency subwavelength split-ring resonator, which emits electromagnetic waves at f SRR = 10.41 GHz. The radiating part of the antenna has a size of approximately 3.2 mm × 8 mm × 1 mm and thus is electrically small at this frequency with a product k · a = 0.5 . The input return loss of the antenna was moderate at − 18 dB and it radiated at a spectral bandwidth of 120 MHz. The measured main lobe of the antenna was observed at 60 ∘ with a − 3 dB angular width of 65 ∘ in the E-plane and at 130 ∘ with a − 3 dB angular width of 145 ∘ in the H-plane.

Pattern Reconfigurable, Vertically Polarized, Low-Profile, Compact, Near-Field Resonant Parasitic Antenna

A vertically polarized, low-profile, compact, near-field resonant parasitic antenna with pattern reconfigurability is demonstrated. The antenna has three dynamic end-fire states facilitated with only three p-i-n diodes. The radiation pattern in each state covers more than 120° in its azimuth plane and, hence, it achieves beam scanning that covers the entire azimuth plane. The antenna height and transverse size are, respectively, only $0.048\lambda _{0}$ and $0.1\lambda _{0}^{2}$ . Measured results, in good agreement with their simulated values, demonstrate that the antenna exhibits a ~11% fractional impedance bandwidth, and a ~6.6 dBi peak realized gain in all three of its pattern-reconfigurable states. Stable and high peak realized gain values are realized over its entire operational band surrounding 2.22 GHz.

Design of electrically small Hilbert fractal NFRP magnetic monopole antennas

ABSTRACTElectrically small, Hilbert fractal, near-field resonant parasitic (NFRP) antennas are reported and investigated in this paper. This type of electrically small antennas (ESAs) consists of Hilbert fractal curves as the NFRP resonators and small vertical monopoles as the driven elements. By offsetting the driven monopole off the centre position, good impedance matching can be easily realized. The current distributions on the fractal NFRP elements and the driven monopoles manifest that strong electric coupling could excite loop-mode currents along the Hilbert fractal NFRP structures, and thereby horizontal magnetic monopole patterns with broadside radiation property are realized. The results show that the 2nd-step evolution Hilbert fractal NFRP antenna witnesses an electrically size reduction of 25% compared to ka = 0.9622 of the square capacitively loaded loop (CLL) NFRP antenna, while maintaining its original broadside radiation. It is also demonstrated that there is a performance trade-off, i.e. higher fractal iteration orders leading to smaller resonant frequencies, narrower bandwidth and lower radiation efficiencies.

Bandwidth-Enhanced, Compact, Near-Field Resonant Parasitic Filtennas With Sharp Out-of-Band Suppression

The designs, simulations, and measurements of a class of compact, bandwidth-enhanced filtennas are reported. Our design strategy is illustrated by separately designing a monopole and a bandpass filter to operate primarily in their respective fundamental modes. By combining these elements and manipulating the mutual coupling between them, an enhanced impedance bandwidth filtenna is realized. This strategy is applied to augment metamaterial-inspired near-field resonant parasitic antennas with filters. Simulations of these filtenna systems demonstrate that one can maintain stable radiation performance characteristics no matter how one arranges their component configurations, i.e., their relative positions and orientations. A selected filtenna design prototype was fabricated and tested. The good agreement between the simulated and measured results validates these design principles.

A FULLY PLANAR NEAR-FIELD RESONANT PARASITIC ANTENNA

A near-field resonant parasitic (NFRP) antenna is presented. Unlike the conventional NFRP antenna, which is fed by coaxial cables, the topology is driven by a planar monopole. In this way, the antenna and the front end circuit can be designed in a single plane, which is crucial for system integration. The radiator is electrically small (λ0/19.3 × λ0/10.47 × λ0/76.4) while reaching a high efficiency (94%) and a good bandwidth (85 MHz). The operating frequency and input impedance are easily tailored. Measured results verify the working mechanism.

Compact planar near-field resonant parastic antenna for multiple-input multiple-output applications

A planar tri-band near-field resonant parasitic (NFRP) antenna for multiple-input multiple-output (MIMO) applications in the WLAN 2.4/5.2/5.8 GHz bands is presented. The tri-band functionality is obtained by introducing three different resonant parasitic elements near a simple driven element. Good impedance matching, radiation efficiency, and antenna patterns are realized at each of the desired resonant frequencies. Experimental confirmation of the simulated performance is presented. It is demonstrated that an array of these tri-band NFRP antennas obtains good isolation between elements even with small spacing between them. Calculated envelope correlation values are less than 0.12 within the bands of interest. The design methodologies of the tri-band NFRP antenna and the corresponding MIMO array are detailed. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:580–584, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26647

High-Directivity, Electrically Small, Low-Profile Near-Field Resonant Parasitic Antennas

A combination of metastructures is used to achieve high directivity, electrically small, low-profile, linear (LP) and circularly polarized (CP) near-field resonant parasitic (NFRP) antennas. A conformal metamaterial-inspired Egyptian axe dipole antenna is introduced, and its performance characteristics are presented. The electrically small, low-profile LP and CP high-directivity systems are achieved by amalgamating this NFRP antenna with an electromagnetic band-gap (EBG) structure, which acts as an artificial magnetic conductor (AMC) ground plane. As with all of the nonconformal metamaterial-inspired antennas, the designs of the driven and parasitic elements of these low-profile antennas are tailored to achieve nearly complete matching of the entire system to a 50- source without any matching network and to yield high radiation efficiencies.

Multifunctional, Electrically Small, Planar Near-Field Resonant Parasitic Antennas

Planar analogs of previously reported electrically small, electric metamaterial-inspired, near-field resonant parasitic (NFRP) antennas are reported. As with the nonplanar designs, the driven and parasitic elements in each presented case are designed to achieve nearly complete matching of the entire system to a 50-Ω source without any matching network and to yield a high radiation efficiency. By introducing multiple NFRP elements, linearly polarized (LP) dual-band and circularly polarized (CP) planar NFRP antennas are realized. These low-profile designs are validated with experimental results.

A metamaterial-inspired, electrically small rectenna for high-efficiency, low power harvesting and scavenging at the global positioning system L1 frequency

An electrically small rectenna was designed and tested at the global positioning system (GPS) L1 frequency (1.5754 GHz). The metamaterial-inspired near-field resonant parasitic antenna size (ka ∼ 0.467) and its direct match to the input impedance of the rectifying circuit decreased the whole size of the rectenna (ka ∼ 0.611). The simulated and measured rectifying efficiencies were, respectively, 75.7% and 79.6% when the input power to the rectifying circuit was 0.0 dBm (1 mW). The highest rectifying efficiency, 84.7%, was achieved at the GPS L1 frequency for a 3.0 dBm input power. The simulated and measured results are in good agreement.

Multi-Frequency, Linear and Circular Polarized, Metamaterial-Inspired, Near-Field Resonant Parasitic Antennas

Several metamaterial-inspired, electrically small, near-field resonant parasitic antennas are presented. Both electric and magnetic couplings to the parasitic are compared and contrasted. The electric-coupled versions are shown to be more efficient and to have more bandwidth. The evolution of circular polarized designs from their linear counterparts by introducing multiple parasitics having different resonant frequencies is demonstrated. Single L1 and dual band L1/L2 GPS systems are emphasized for practical illustrations of the resulting performance characteristics. Preliminary experimental results for a dual band, circularly polarized GPS L1/L2 antenna are provided and underscore several practical aspects of these designs.

Electrically Small GPS L1 Rectennas

An electrically small, metamaterial-inspired near field resonant parasitic (NFRP) planar protractor antenna is designed for operation, as a proof-of-concept choice, at the GPS L1 frequency (1.5754 GHz). It is based on electric coupling between a capacitively loaded loop (CLL) NFRP element and a driven monopole. Modified versions are then integrated with simplified rectifying circuits to realize two electrically small GPS L1 rectenna systems. The complex impedance matching capabilities of an NFRP antenna allow matching it directly to a rectifying circuit, reducing the overall rectenna size. Simulation results of the | S11 | values, radiation efficiencies and patterns, and Q-ratios are provided. For the low, 0-dBm input power level, the measured rectifying efficiencies of the larger (ka = 0.808) and 25% smaller (ka = 0.604) version are, respectively, 78.0% at 1.5754 GHz and 67.9% at 1.55 GHz.

Metamaterial-Inspired, Electrically Small Huygens Sources

Electrically small electric and magnetic dipole antennas are introduced that are based on electric and magnetic near-field resonant parasitic (NFRP) elements that are electrically coupled to the driven element. By properly combining these two NFRP antenna types, electrically small Huygens sources are realized. The proposed Huygens sources have one feed point, are well matched to 50 Ω, and have high radiation efficiencies. Their predicted directivity patterns approach the known Huygens source theoretical limit.

Design and Experimental Verification of a 3D Magnetic EZ Antenna at 300 MHz

Several variations of a 300-MHz version of the electrically small coax-fed three-dimensional (3D) magnetic EZ antenna were designed and tested. The final version of this low-profile antenna had an electrical size that was ka ~ 0.437 at 300.96 MHz. Nearly complete matching to the 50-Omega source and high overall efficiency (nearly 100%) were achieved. The measured fractional bandwidth was approximately 1.66%. The numerically predicted and the measured results were in good agreement. Comparisons to similar-sized loop antennas that were matched to the source with both custom-made and commercially available, general purpose external matching networks confirm the performance enhancements achieved with this metamaterial-inspired, near-field resonant parasitic antenna.