Mu-zero Resonance Research Articles

Bandwidth enhancement of the omni‐directional and circularly‐polarized EZR‐MZR antenna

As electric and magnetic dipoles with inherent 90° phase difference (PD) can be easily realized by forming a circular array of the epsilon-zero resonance and mu-zero resonance (EZR-MZR) resonators, high design efficiency can be expected for low-profile, omni-directional and circularly polarized (CP) antenna designing. However, high Q factor of the EZR-MZR resonator makes narrow bandwidth. This research is dedicated to enhance the bandwidth. Low Q factor and multi-resonances techniques are utilized to enhance the impedance bandwidth. While polarization compensation technique is applied to improve the axial ratio (AR) bandwidth by tuning the amplitudes and PD of the orthogonal vectors. The proposed antenna obtains a − 10 dB impedance band of 1.370 to 1.690 GHz (20.91% at 1.530 GHz) and a 3 dB axial ratio (AR) band of 1.260 to 1.580 GHz (22.53% at 1.42 GHz). The diameter and profile of the proposed antenna are 0.402 λ and 0.082 λ, respectively.

Compact Controlled Reception Pattern Antenna (CRPA) Array Based on Mu-Zero Resonance (MZR) Antenna

Compact Controlled Reception Pattern Antenna (CRPA) Array Based on Mu-Zero Resonance (MZR) Antenna

Miniaturization of Planar Yagi Antennas Using Mu-Negative Metamaterial-Loaded Reflector

A technique to reduce the size and enhance the operating bandwidth (BW) of planar Yagi antennas, while maintaining their unidirectional radiation characteristics, is proposed in this paper. In this technique, the reflector element is loaded with mu-negative (MNG) metamaterial unit cells to excite a mu-zero resonance (MZR), which is independent of the size of the antenna. Thus, the antenna can operate at lower frequencies without the need to increase its physical size. To implement the proposed idea, the reflector, which acts as the host transmission line, is positioned at a close distance to the driven element, which is typically a dipole antenna. To validate the proposed technique, two design concepts based on coplanar and broadside-coupled strip configurations are presented, and a wideband Yagi antenna is presented. The antenna achieves a wide operating BW of 70% (0.72–1.48 GHz) with a peak front-to-back ratio (FBR) of 14 dB and peak gain of 4.1 dBi with a compact size of $0.24\lambda \times 0.24\lambda $ , where $\lambda $ is the wavelength at the lowest operating frequency. The proposed antenna achieves a 45% wider operating BW compared to similar structures, while being miniaturized by more than 60% compared to available structures that have over 50% fractional BWs.

EZR-MZR Resonators for Compact Low-Profile Omnidirectional Circular-Polarized Antenna Design

New zeroth-order resonator (ZOR): the curved EZR-MZR resonator [epsilon-zero resonance (EZR) and mu-zero resonance (MZR)] was proposed for circular-polarized (CP) antenna design with low-profile and omnidirectional characteristics. The proposed curved EZR-MZR resonator has two orthogonal polarizations with 90° phase difference (PD). By forming four resonators in a circular ring array, the MZR can be characterized as a magnetic dipole. Then, the unidirectional pattern of the horizontal polarization was transformed to be omnidirectional while the EZR with vertical polarization can be characterized as an electric dipole and it radiates omnidirectional pattern. As the PD of the vertical and the horizontal polarizations is inherently 90°, the allying of the two orthogonal polarizations leads to a CP radiation with an omnidirectional pattern. To feed the resonators with uniform amplitude and phase, a feeding network with four equal radial arms is used. The proposed omnidirectional CP antenna has the advantages of low profile from ZOR characteristics and high design efficiency from the inherent 90° PD between the orthogonal polarizations. A prototype with resonant frequency of 1.544 GHz was designed with a diameter of 57 mm (0.29 $\lambda _{r}$ , $\lambda _{r}$ is the free space wavelength of the resonant frequency) and a height of 4 mm (0.02 $\lambda _{r}$ ).

Simple and Electrically Small EZR-MZR Resonator With Quasi-Isotropic Pattern

A new zeroth-order resonator that composites epsilon-zero resonance and mu-zero resonance characteristics (called EZR-MZR resonator) can be used to design quasi-isotropic antenna. Compared to the presented quasi-isotropic antenna, the EZR-MZR resonator has the advantages of simple structure for high efficiency design and electrically small size. The EZR-MZR resonator includes a patch, a ground plane, and a shorting pin. The single frequency EZR-MZR resonator with rectangular patch has a volume of 0.13 $ {\lambda _{r} \times } 0.20 {\lambda _{r} \times } 0.03 {\lambda _{r}}$ (where $ {\lambda _{r}}$ is the free space wavelength of the resonant frequency $ {f_{r} = 1.500}$ GHz). While the dual frequencies antenna ( $ {f_{r1} = 1.038}$ GHz and $ {f_{r2} = 1.443}$ GHz) with two curved EZR-MZR resonator has a volume of 0.078 $ {\lambda _{r1} \times } 0.214 {\lambda _{r1} \times } 0.024 {\lambda _{r1}}$ (where $ { \lambda _{r1}}$ is the free space wavelength of the resonant frequency $ {f_{r1}}$ ). The field distributions, patterns of different polarizations, Z/S -parameters and parametric studies were used to reveal the operational mechanism of the EZR-MZR resonator antenna. The resonant frequency of the EZR-MZR resonator can be easily tuned by adjusting the size parameters of the resonator, thus, the EZR-MZR resonator with quasi-isotropic pattern is a good candidate to design antenna that accommodates with different RFID frequency.

Design and Analysis of a New ZOR Antenna with Wide Half Power Beam Width (HPBW) Characteristic

Abstract Novel zeroth-order resonator (ZOR) composites epsilon-zero resonance (EZR) and mu-zero resonance (MZR) characteristics was proposed. The proposed resonator was constructed by moving via from centre of the conventional mushroom structure (CMS) to the edge, then, an edge-located via mushroom structure (ELV-MS) was formed. Thus, boundary conditions were transformed from all open-ended to half short-ended and half open-ended. Then, the new ZOR composites EZR and MZR characteristics (called EZR-MZR resonator). Owing to the unique characteristic of the composite EZR and MZR, the proposed ZOR antenna radiates both horizontal-polarized field (uni-directional) and vertical-polarized field (omni-directional). Then, wide half power beam width (HPBW) radiation patterns were realized for the antenna. The deduction and analysis of the proposed EZR-MZR resonator were conducted based on the composite right/left-handed transmission line (CRLH TL) and ZOR theories, and field distributions. The proposed ZOR antenna was investigated with two cases of coupling feeding.

Bandwidth and Directivity Enhancement of Loop Antenna by Nonperiodic Distribution of Mu-Negative Metamaterial Unit Cells

The theory, design, analysis, and verification of a wideband and unidirectional loop antenna loaded with mu-negative (MNG) metamaterial unit cells is presented. It is shown that by nonperiodic positioning of MNG unit cells on the loop structure, the amplitude of the surface current can be modified in a desired section of the loop, and hence, unidirectional radiation is achievable at the mu-zero resonance frequency. Moreover, it is demonstrated that as a result of the capacitive MNG loading, a 90° phase difference occurs between the vertical arms of the loop. Therefore, its radiation mechanism can be characterized as an array of two dipole antennas positioned a quarter wavelength apart, thus creating unidirectional radiation. To further improve the performance of the antennas, a quarter-wavelength strip is located in the vicinity of the loop to act as a resonator and director at higher frequencies. With the proposed structure, the final design is at least 50% smaller, in terms of the occupied area, than recent antenna designs of conventional loops, MNG loaded loops, and loop–dipole composite antennas. It also achieves a wide fractional bandwidth of 52% from 0.64 to 1.1 GHz, which is 50% wider than recent MNG metamaterial unit cell loaded loops, with a measured peak front-to-back-ratio and gain of 13 dB and 4.8 dBi, respectively.

Compact Wideband Loop Antenna Partially Loaded With Mu-Negative Metamaterial Unit Cells for Directivity Enhancement

A wideband and unidirectional loop antenna partially loaded with mu-negative (MNG) metamaterial unit cells is presented. To reduce the electrical size of the antenna, its first resonance is formed by capacitively loading a conventional one-wavelength loop antenna to excite the mu-zero resonance that is independent of the resonator's size. As a result of partial loop loading using properly designed and distributed slots, the amplitude of the surface current can be engineered to be higher in the feeding arm while achieving a zero phase shift along each arm of the loop structure. Consequently, unidirectional radiation with a moderate front-to-back ratio (FBR) is achieved without using any reflectors. Moreover, as a result of the capacitive loading, the loop antenna is divided into an array of dipoles that are excited with a 90° phase difference, enabling unidirectional radiation at the loop-mode resonance. To both enhance the impedance matching of the antenna at lower frequencies and excite an additional resonance, a strip patch is added in the vicinity of the loop. The proposed structure is smaller by 80% than similar MNG loaded loops and achieves a wide fractional bandwidth of 52% (0.64–1.1 GHz) with a peak FBR and gain values of 12 dB and 3.2 dBi, respectively.

A Compact Dual-Mode Metamaterial-Based Loop Antenna for Pattern Diversity

This letter presents a novel design of compact dual-port dual-mode metamaterial-based loop antenna for pattern diversity. The proposed metamaterial-based loop antenna consists of a loop based on periodically loaded capacitive arc strips and two independent ports with feeding networks. Similar to mu-zero resonance (MZR) antennas, the periodically loaded capacitive loop antenna proposed in this letter allows current along the loop to remain in phase and uniform. By making use of a hybrid feed network, the even and odd modes of the proposed metamaterial-based loop antenna are exploited so that its pattern diversity is achieved effectively. The theory of operation and performances of the proposed antenna are demonstrated in both a full-wave simulation and in the experiments.

Modified mu‐zero resonator for efficient wireless power transfer

A mu-zero resonator with an effective zero permeability is presented for efficient wireless power transfer (WPT) using resonant inductive coupling (RIC). An N-cell mu-zero resonator is modified to maintain a fixed size and resonance frequencies that are important design factors of WPT using RIC because they are related to the magnetic coupling coefficient and Q-factor. The resonator has many resonant modes with the extraordinary phenomena of metamaterials such as an infinite wavelength wave and backward-wave propagation. An analysis of the resonant modes and a design of the N-cell mu-zero resonator is performed by theory and full-wave simulation based on a dispersion diagram and magnetic field distribution. The power transfer efficiencies of one-cell and two-cell mu-zero resonators are simulated and measured. To optimise the transfer efficiency of the WPT system using the mu-zero resonance (MZR) mode, which supports stronger coupling than the other modes, an equivalent circuit of mu-zero resonator is analysed for a high Q-factor. The theoretical, simulated, and measured results of a one-cell resonator with optimum values confirm that an efficient WPT system can be successfully designed by the MZR mode.

Design of a Wideband Horizontally Polarized Omnidirectional Printed Loop Antenna

This letter presents the design of a novel wideband horizontally polarized omnidirectional printed loop antenna. The proposed antenna consists of a loop with periodical capacitive loading and a parallel stripline as an impedance transformer. Periodical capacitive loading is realized by adding interlaced coupling lines at the end of each section. Similarly to mu-zero resonance (MZR) antennas, the periodical capacitive loaded loop antenna proposed in this letter allows current along the loop to remain in phase and uniform. Therefore, it can achieve a horizontally polarized omnidirectional pattern in the far field, like a magnetic dipole antenna, even though the perimeter of the loop is comparable to the operating wavelength. Furthermore, the periodical capacitive loading is also useful to achieve a wide impedance bandwidth. A prototype of the proposed periodical capacitive loaded loop antenna is fabricated and measured. It can provide a wide impedance bandwidth of about 800 MHz (2170-2970 MHz, 31.2%) and a horizontally polarized omnidirectional pattern in the azimuth plane.

Mu-Zero Resonance Antenna

We present mu-zero resonance (MZR) antennas that use an artificial mu-negative (MNG) transmission line (TL). The equivalent circuit for verifying the peculiarity of the MNG TL is derived and analyzed. To operate the MZR antenna properly, the antenna is fed by magnetic coupling. The analysis and design of the MZR antenna are performed according to theory and simulation based on a dispersion diagram and field distribution. The surface current distribution shows that the radiation mechanism of the MZR antenna is essentially identical to that of a small-loop antenna. Applying the novel concept of the MZR antenna, a dual-band MZR antenna using two MZR antennas with different MZR frequencies is proposed. The radiation characteristics of the antenna are simulated and measured at two frequencies. The measured characteristics show agreement with the simulated results. It is confirmed that the characteristics of the MZR antenna, including the efficiency, gain, and fractional bandwidth, are suitable for a multiband antenna.