This article presents a historical review of the research carried out on dielectric resonator antennas (DRAs) over the last three decades. Major research activities in each decade are highlighted. The current state of the art of dielectric-resonator-antenna technology is then reviewed. The achievable performance of dielectric resonator antennas designed for compactness, wide impedance bandwidth, low profiles, circular polarization, or high gain are illustrated. The latest developments in dielectric-resonator-antenna arrays and fabrication techniques are also examined.

Dielectric Resonator Antennas: A Historical Review and the Current State of the Art

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

........................................................................................................................ iv ACKNOWLEDGEMENT ........................................................................................................ v LIST OF FIGURES .............................................................................................................. viii LIST OF SYMBOLS .............................................................................................................. xv CHAPTER 1 ......................................................................................................................................................... 1 INTROUDUCTION .............................................................................................................................................. 1 CHAPTER 2 ......................................................................................................................................................... 3 OVERVIEW ......................................................................................................................................................... 3 2.1 History of Dielectric Resonator Antennas ................................................................................................... 3 2.2 Characteristics of the Dielectric Resonator Antennas ................................................................................. 4 2.3 Materials for dielectric resonators .............................................................................................................. 5 2.3.1 Losses and quality factor ................................................................................................................................... 6 2.3.2 Barium‐titanates ................................................................................................................................................ 7 2.3.3 Zirconium – titanates ......................................................................................................................................... 7 2.3.4 Pseudo‐tungsten bronze‐type ........................................................................................................................... 7 2.3.5 Low Temperature Cofired Ceramics .................................................................................................................. 7 2.3.6 Alumina .............................................................................................................................................................. 8 2.3.7 Titania ................................................................................................................................................................ 8 2.3.8 Cerium Oxide ..................................................................................................................................................... 8 2.3.9 Silicates .............................................................................................................................................................. 9 2.3.10 Bismuth based low‐firing ceramics ..................................................................................................................... 9 2.3.11 Antenna applications .......................................................................................................................................... 9 2.4 Types of modes ......................................................................................................................................... 11 2.5 Shapes of Dielectric Resonator Antennas .................................................................................................. 14 2.5.1 The Cylindrical Dielectric Resonator ................................................................................................................. 15 2.5.1.1 Field Distribution .................................................................................................................................... 15 2.5.1.2 Resonant Frequencies ...................................................................................................................................... 19 2.5.2 The Hemispherical Dielectric Resonator ........................................................................................................... 25 2.5.3 The Rectangular Parallel Epiped Dielectric Resonator ...................................................................................... 27 2.5.4 Other Shapes for Dielectric Resonator Antennas ............................................................................................. 28 2.5.4.1 Split‐Cylinder Dielectric Resonator ......................................................................................................... 28 2.5.4.2 Cylindrical‐Ring Dielectric Resonator ..................................................................................................... 29 2.5.4.3 Cross‐Shaped Dielectric Resonator ........................................................................................................ 29 2.5.4.4 Perforated Dielectric Resonator ............................................................................................................. 29 2.5.4.5 Cone‐Shaped Dielectric Resonator ......................................................................................................... 30 2.5.4.6 Stepped‐Stair Structured Dielectric Resonator ...................................................................................... 31 2.6 Wideband Techniques ............................................................................................................................... 31 2.7 Excitation Techniques ................................................................................................................................ 32 2.8 Polarization ............................................................................................................................................... 34 2.9 Input Impedance ....................................................................................................................................... 35 CHAPTER 3 ....................................................................................................................................................... 40 METHODOLOGY ............................................................................................................................................. 40 vii 3.1 Decision of Shape ...................................................................................................................................... 40 3.2 Omni‐directional Dielectric Resonator Antenna Design ............................................................................ 42 3.2.1 Excitation techniques ....................................................................................................................................... 42 3.2.2 Choosing parameters ........................................................................................................................................ 44 3.2.3 Matching ........................................................................................................................................................... 55 3.2.3.1 Coaxial Cable Coupling ........................................................................................................................... 56 3.2.3.2 Microstrip Feeding ................................................................................................................................. 57 3.2.4 Outcome ........................................................................................................................................................... 60 3.3 Broadside Array Antenna Design .............................................................................................................. 61 3.3.1 Excitation Technique ........................................................................................................................................ 62 3.3.2 Choosing Parameters ........................................................................................................................................ 63 3.3.3 Matching ........................................................................................................................................................... 64 3.3.4 Outcome ........................................................................................................................................................... 65 3.4 Fabrication ................................................................................................................................................ 66 3.5 Measurement Methodology ..................................................................................................................... 68 3.5.1 Measurements of Scattering Parameters ......................................................................................................... 68 3.5.2 Measurements of Radiation Pattern ................................................................................................................ 69 3.5.3 Measurement of Efficiency ............................................................................................................................... 71 CHAPTER 4 ....................................................................................................................................................... 72 RESULTS ........................................................................................................................................................... 72 4.1 Scattering Parameters .............................................................................................................................. 72 4.1.1 Omni‐directional Antenna ..

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Dual polarized dielectric resonator antennas

This letter proposes an annular cylindrical dielectric resonator antenna (DRA) with two-port diversity realizing simultaneously omnidirectional horizontally and vertically polarized radiation patterns with low cross coupling. The horizontally and vertically polarized radiation patterns are achieved by exciting the orthogonal TE01δ and TM01δ modes in a single cylindrical dielectric resonator (DR). Due to the high Q-factor of the TE01δ mode, an air gap and multiple feeding lines are introduced to increase the impedance bandwidth. The proposed antenna provides an impedance bandwidth of 19.1% in the vertically polarized mode and an overlapping bandwidth of 7.4% in the horizontally polarized mode, with the overlapping band ranging from 3.78 to 4.07 GHz. Antenna diversity and multiple-input-multiple-output (MIMO) performance are examined in terms of envelope correlation coefficient and mean effective gain.

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Omnidirectional Cylindrical Dielectric Resonator Antenna With Dual Polarization

A novel multiple-input multiple-output (MIMO) dielectric resonator antenna (DRA) for long term evolution (LTE) femtocell base stations is described. The proposed antenna is able to transmit and receive information independently using TE and HE modes in the LTE bands 12 (698-716 MHz, 728-746 MHz) and 17 (704-716 MHz, 734-746 MHz). A systematic design method based on perturbation theory is proposed to induce mode degeneration for MIMO operation. Through perturbing the boundary of the DRA, the amount of energy stored by a specific mode is changed as well as the resonant frequency of that mode. Hence, by introducing an adequate boundary perturbation, the TE and HE modes of the DRA will resonate at the same frequency and share a common impedance bandwidth. The simulated mutual coupling between the modes was as low as - 40 dB . It was estimated that in a rich scattering environment with an Signal-to-Noise Ratio (SNR) of 20 dB per receiver branch, the proposed MIMO DRA was able to achieve a channel capacity of 11.1 b/s/Hz (as compared to theoretical maximum 2 × 2 capacity of 13.4 b/s/Hz). Our experimental measurements successfully demonstrated the design methodology proposed in this work.

Design of a MIMO Dielectric Resonator Antenna for LTE Femtocell Base Stations

A single dielectric resonator is used for a triple mode operation in filtering and dual band radiation purposes. A high unloaded quality factor over 2300 at 2.43 GHz is obtained simultaneously with both broadside and omni-directional radiation patterns of 7% and 8% bandwidths around 2.47 and 3.36 GHz, respectively. Series of parametric studies are developed to tune the filter's operating frequency range, to enhance its insertion loss and to obtain a sharp filtering skirt behavior. Finally, measurements of both filter insertion loss and antenna return loss, coupling coefficients and radiation patterns are illustrated for further verification.

Triple Mode Use of a Single Dielectric Resonator

The concept of achieving a dual-band antenna with two different radiation patterns using a single cylindrical dielectric resonator is presented. Both simulated and experimental measured results are conducted to prove the validity of the proposed concept. A broadside circularly-polarized pattern with 7% bandwidth and a vertically polarized omnidirectional pattern with 17.3% bandwidth are obtained, simultaneously. The minimum measured axial ratio is found to be 1.3 dB. The front-to-back ratio is measured to be 15 dB. A design suitable for both Global Positioning System and wireless local area network applications is proposed.

Dual-Band Compact DRA With Circular and Monopole-Like Linear Polarizations as a Concept for GPS and WLAN Applications

The asymptotic strip boundary condition (ASBC) is applied to analyze the solution of the electromagnetic scattering from a conducting cylinder coated with a homogeneous linear material layer and loaded with conducting helical strips. Such homogeneous material layer can be implemented by a conventional dielectric material, a single negative (SNG) or double negative (DNG) meta-material layer. A study of different materials’ constitutive parameters is presented with accordance to Drude and Lorentz material modeling. The boundary condition assumes that the strips are rounded around the coated cylinder in a helical form and both the strip’s period and the spacing between the helix turns are very small and mathematically approaching the zero. Scattering due to normal and oblique incident plane waves (θi, φi) of arbitrary polarization using the series solution is also computed. A number of parametric studies were investigated to illustrate the advantages of using metamaterials compared with conventional coating materials in terms of strip’s rounding pitch angle and coating layer electrical thickness variations. It is also shown that for SNG materials, modified Bessel functions are used to accept negative arguments. Coating with metamaterials proves to achieve higher forward scattering compared with conventional materials for the same electrical coating thickness.

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Electromagnetic scattering from conducting circular cylinder coated by meta-materials and loaded with helical strips under oblique incidence

A new concept of dual mode operation for oscillation and radiation characteristics using single dielectric resonator enclosed by modified rectangular cavity has been developed. High unloaded quality factor of 2700 at 2.54 GHz and omni-directional radiation patterns with radiation bandwidth of 5.13% around 3.31 GHz were achieved simultaneously. The high-Q mode is coupled to a microstrip line and the low-Q mode is coupled to a coaxial probe with capacitive plate. Reaction-type measurement of the unloaded Q factor with the help of a network analyzer is described in details. Measurements of the scattering parameters and of the radiation patterns were carried out to verify the simulation results.

Dielectric Resonator Antenna in a Polarization Filtering Cavity for Dual Function Applications

The use of whispering-gallery mode dielectric resonator (WGMDR) in the design of X -band five-way power divider is presented. Different excitation techniques are proposed to excite the higher order whispering-gallery H-polarized resonating mode such as probe excitation and C-slot type of coupling integrated with microstrip feeding technology. The cylindrical dielectric resonator is enclosed within a cylindrical shielding cavity to prevent radiation losses. Due to the natural behavior of the performed resonating mode, an out of phase equal power distribution can be observed. To obtain an in-phase power distribution, the adjacent C-slots are rotated with respect to each other for phase compensation. Both input matching and equal power distribution are experimentally maintained within several hundreds of megahertz frequency band around the resonance. Measured scattering parameters magnitude and phase of the proposed six-port structure are carried out to verify the expected simulation results for the different proposed excitation techniques.

L.K. Hady

Papers

Triple Mode Use of a Single Dielectric Resonator

Dual-Band Compact DRA With Circular and Monopole-Like Linear Polarizations as a Concept for GPS and WLAN Applications

Electromagnetic scattering from conducting circular cylinder coated by meta-materials and loaded with helical strips under oblique incidence

Dielectric Resonator Antenna in a Polarization Filtering Cavity for Dual Function Applications

Power Dividers Based on Dielectric Resonator Whispering-Gallery Modes Fed by Probe or Slot Type of Coupling