This paper explains the basic characteristics of dielectric resonator antennas (DRAs), with emphasis on the effect of the form factor on their resonance (operating) frequencies. It is followed by discussions on their recent developments in higher order mode, circularly polarized, dual function, and transparent designs over the last few years. The idea of using glass DRAs as decoration antennas is proposed and demonstrated for the first time.

Dielectric Resonator Antennas: From the Basic to the Aesthetic

In accordance with one or more embodiments, a communication device includes a dielectric antenna having a feed point and an aperture. A cable comprising a conductorless core is coupled to the feed point of the dielectric antenna. A transmitter is coupled to the cable and facilitates a transmission of first electromagnetic waves to the feed point of the dielectric antenna. The first electromagnetic waves are guided by the conductorless core and propagate along the conductorless core without requiring an electrical return path, and the first electromagnetic waves generate free-space wireless signals from the aperture of the antenna in accordance with a circularly polarized antenna beam pattern.

Antenna structure with circularly polarized antenna beam

In this letter, a broadband bent triangular omnidirectional antenna is presented for RF energy harvesting. The antenna has a bandwidth for ${\hbox {VSWR}}\leq2$ from 850 MHz to 1.94 GHz. The antenna is designed to receive both horizontal and vertical polarized waves and has a stable radiation pattern over the entire bandwidth. Antenna has also been optimized for energy harvesting application and it is designed for $100~\Omega $ input impedance to provide a passive voltage amplification and impedance matching to the rectifier. A peak efficiency of 60% and 17% is obtained for a load of $500~\Omega $ at 980 and 1800 MHz, respectively. At a cell site while harvesting all bands simultaneously a voltage of 3.76 V for open circuit and 1.38 V across a load of $4.3~\hbox{k} \Omega $ is obtained at a distance of 25 m using an array of two elements of the rectenna.

Broadband Bent Triangular Omnidirectional Antenna for RF Energy Harvesting

A new compact omnidirectional circularly polarized (CP) cylindrical dielectric resonator antenna (DRA) with a top-loaded modified Alford loop is investigated. Fed by an axial probe, the DRA is excited in its TM01δ-mode, which radiates like a vertically polarized electric monopole. The modified Alford loop comprises a central circular patch and four curved branches. It is placed on the top of the DRA and provides an equivalent horizontally polarized magnetic dipole mode. Omnidirectional CP fields can be obtained when the two orthogonally polarized fields are equal in amplitude but different in phase by 90°. This CP DRA is applied to the design of a two-port CP diversity DRA which provides omnidirectional and broadside radiation patterns. The broadside radiation pattern is obtained by making use of the broadside HEM12δ+ 1-mode of the DRA, which is excited by a balanced slot serially fed by a microstrip line. For demonstration, both the omnidirectional CP DRA and the diversity CP DRA were designed at ~ 2.4 GHz for WLAN applications. Their S-parameters, axial ratios, radiation patterns, antenna gains, and antenna efficiencies are studied. The envelope correlation is also found for the diversity design. Reasonable agreement between the simulated and measured results is observed.

Omnidirectional Circularly Polarized Dielectric Resonator Antenna With Top-Loaded Alford Loop for Pattern Diversity Design

The quasi-isotropic dielectric resonator antenna (DRA) is investigated for the first time. It uses a small ground plane which also serves as an electric dipole. The electric dipole combines with the equivalent magnetic dipole of the DRA to generate quasi-isotropic fields. A choke (balun) is connected to the outer conductor of the coaxial cable to suppress stray radiation. ANSYS HFSS was used to simulate the antenna, and a prototype operating at 2.4-GHz WLAN band was fabricated to verify the simulation. Results show that the difference between the measured maximum and minimum radiation power densities is 5.6 dB over the entire pseudo spherical radiating surface. By using a narrower ground plane and a higher dielectric constant, the gain difference can be reduced to 3.4 dB, approaching the theoretical limit of 3 dB.

Compact Quasi-Isotropic Dielectric Resonator Antenna With Small Ground Plane

The rectangular dielectric resonator antenna (DRA) centrally fed by a probe is investigated. Its operating mode is analogous to the TM011 mode of a cylindrical DRA. The DRA radiates like an electric monopole, generating omnidirectional linearly polarized (LP) fields. Based on this LP design, a novel omnidirectional circularly polarized (CP) DRA is studied for the first time. Slots are introduced to the sidewalls of the DRA, exciting a degenerate mode for the generation of CP fields. To demonstrate the idea, an omnidirectional CP DRA was designed for WLAN (2.4-2.48 GHz) applications. The reflection coefficient, axial ratio (AR), radiation pattern, and antenna gain are studied, and reasonable agreement between the measured and simulated results is observed.

Omnidirectional Linearly and Circularly Polarized Rectangular Dielectric Resonator Antennas

A new omnidirectional circularly polarized (CP) cylindrical dielectric resonator (DR) antenna (DRA) is excited by four open-ended logarithmic spiral slots in the ground plane. Radiated E
 θ
 and E
 φ
 components are obtained from the TM
 01δ
 mode of the DR and the slotted ground plane, respectively. Omnidirectional CP fields can be obtained when E
 θ
 and E
 φ
 are equal in magnitude but different in phase by 90°. This CP technique does not require any special shape or treatment of DR, greatly facilitating the design. To demonstrate the idea, a prototype using a glass DR was fabricated. It is a dual-function DRA that also serves as the cover of light sources. The prototype has a measured bandwidth of ~6.2%, covering the entire 2.4-GHz WLAN band.

Omnidirectional circularly polarized dielectric resonator antenna with logarithmic spiral slots in the ground

A three-dimensional (3-D)-printed wideband multi-ring dielectric resonator antenna (DRA) is investigated for the first time. It consists of four concentric dielectric rings with decreasing effective dielectric constants in the radial direction. To facilitate the 3-D-printed design, a basic unit cubic cell that can be easily adjusted to provide different effective dielectric constants is used. An axial coaxial probe is used to excite the DRA in three transverse magnetic (TM) modes (TM01δ, TM02δ, and TM03δ), which are merged to provide a wide impedance bandwidth. For demonstration, a prototype operating in C -band is designed and fabricated using a 3-D printer. Its reflection coefficient, radiation pattern, antenna gain, and antenna efficiency are measured, and reasonable agreement between the measured and simulated results is observed. The prototype has a wide measured 10-dB impedance bandwidth of 60.2% (4.3–8.0 GHz) with a low profile of 0.18 λ 0, where λ 0 is the wavelength in air at the center frequency (6.15 GHz). The prototype has an average measured antenna efficiency of 89%, with the peak efficiency given by 95%.

3-D-Printed Wideband Multi-Ring Dielectric Resonator Antenna

For the first time, the dielectric waveguide model (DWM) is used to calculate the resonance frequency of the hollow rectangular dielectric resonator antenna (DRA). In the analysis, the transverse transmission line technique is used along with the effective dielectric constant method to obtain characteristic equations of the hollow DRA. Good agreement between the calculation, measurement, and HFSS simulation is observed. The theory was used to facilitate the design of a strip-fed circularly polarized (CP) hollow DRA. It provides a wide 3-dB axial-ratio bandwidth of 12.4%, which is ~ 3 times of that of the solid CP DRA.

Kai Lu

Papers

Compact Quasi-Isotropic Dielectric Resonator Antenna With Small Ground Plane

Omnidirectional Linearly and Circularly Polarized Rectangular Dielectric Resonator Antennas

Omnidirectional circularly polarized dielectric resonator antenna with logarithmic spiral slots in the ground

3-D-Printed Wideband Multi-Ring Dielectric Resonator Antenna

Theory and Experiment of the Hollow Rectangular Dielectric Resonator Antenna