Eng Hock Lim

Dielectric Resonator Antennas: From the Basic to the Aesthetic

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.

Use of the Dielectric Resonator Antenna as a Filter Element

For the first time, the dielectric resonator antenna (DRA) is simultaneously used as a filtering device, named as the DRA filter (DRAF). The theory and design methodology of the DRAF are elucidated using the cylindrical DR. It was found that the operating frequency of the filter part can be made equal to, or different from, that of the antenna part. The return loss, input impedance, radiation patterns, and insertion loss of the DRAF are studied. To improve the insertion loss of the filter part, the DR is top-loaded by a metallic disk without significantly affecting the radiation efficiency of the antenna part. The disk, in addition, can be used to tune the frequency of the filter. It was found that the antenna and filter parts of the DRAF can be designed and tuned almost independently. A second-order DRAF is also designed in this paper. As the dual function DRAF is compact and cost effective, it should find applications in modern wireless communication systems.

Novel application of the hollow dielectric resonator antenna as a packaging cover

The dual functions of the rectangular hollow dielectric resonator antenna (DRA) as an antenna and a packaging cover are investigated. The design methodology is discussed, and the return loss, impedance, and radiation patterns for the fundamental mode are presented at 2.4 GHz, a popular frequency band for the WLAN and wireless communications. A low-noise amplifier is integrated successfully into the embedded cavity to form an active DRA, and the amplified radiation patterns are analyzed. The proposed DRA provides a possible solution to the size minimization of transceivers.

Transparent Dielectric Resonator Antennas for Optical Applications

The transparent dielectric resonator antenna (DRA) for optical applications is proposed for the first time. For demonstration, a dual function transparent hemispherical DRA made of Borosilicate Crown glass (Pyrex) is investigated. The dual function DRA simultaneously works as an antenna and a focusing lens for an underlaid solar cell. The system is very compact because no extra footprint is needed for the solar cell. A conformal strip is used to excite the hemispherical DRA in its fundamental broadside TE111 mode. Due to the focusing effect of the DRA, higher voltage and current outputs of the solar cell can be obtained. In this paper, the transparent rectangular DRA was also studied, and it was found that the rectangular DRA does not provide the focusing function. It was also found that the proposed transparent DRAs can provide a higher gain ( ~ 4 dBi) than for the state-of-the-art transparent microstrip antennas ( ~ -5 dBi to 0 dBi). The reflection coefficients, input impedances, antenna gains, and radiation patterns of the two transparent DRAs are studied, and reasonable agreement between the simulated and measured results was observed. The proposed configurations can potentially be used for applications that need a self-sustaining power.

The Compact Circularly-Polarized Hollow Rectangular Dielectric Resonator Antenna With an Underlaid Quadrature Coupler

The wideband circularly polarized (CP) dielectric resonator antenna (DRA) is investigated with an underlaid quadrature coupler. The idea is used to realize a CP hollow rectangular DRA. Since the coupler is located beneath the DRA, it does not increase the footprint of the antenna, making the system very compact. The underlaid coupler is placed entirely inside the hollow region of the DRA and, thus, it can be designed easily as if there is no overlaid DRA. Two configurations are considered in this paper. In the first configuration, an external 50-Ω load is used for the matching port of the coupler. For the second one, a strip loaded by the DRA is used to provide a load and, thus, no lumped elements are required in this configuration. In this paper, a network model is also given to aid engineers in designing the proposed integrated DRA. The reflection coefficient, axial ratio, antenna gain, and radiation pattern for each configuration are studied. It was found that wide impedance and axial-ratio bandwidths can be obtained with the proposed CP DRAs. Measurements were carried out to verify the simulations, and reasonable agreement between them was obtained.

Singly-Fed Dual-Band Circularly Polarized Dielectric Resonator Antenna

This letter presents a new dual-band circularly polarized (CP) dielectric resonator antenna (DRA). The dual-band design utilizes the quasi- TE111 and -TE113 modes of the rectangular DRA, which is coupled by a simple underneath rectangular aperture. Two opposite corners of the DRA are removed at 45° to obtain CP fields. A diagonal groove is introduced at the top face of the DRA to facilitate tuning of the DRA. A design guideline of the dual-band CP DRA is given. The reflection coefficient, radiation pattern, axial ratio, and antenna gain of the DRA are simulated and measured, with good agreement between them.

Novel Utilization of the Dielectric Resonator Antenna as an Oscillator Load

For the first time, the idea of using the dielectric resonator antenna (DRA) as an oscillator load, named as DRAO, is presented in this paper. Unlike the conventional dielectric resonator oscillator (DRO), where the DR was merely used as a resonator, the DR here serves as both the radiating and oscillating loads. In addition, a compact tri-function hollow DR that incorporates the packaging function to the above dual function is demonstrated. The design procedures of the dual- and tri-function DRAOs are discussed. For demonstration, the DRAOs are designed at 1.85 GHz, which is used in the popular personal communications system (PCS). The return losses, input impedances, antenna gains, signal spectrums, phase noise, and radiation patterns of the two DRAOs are presented. It is shown that the loaded QL factor of the DRA can be increased by internally embedding a compact metallic cavity to the DR. It is found that with a higher loaded QL factor, the phase noise of the antenna oscillator using the hollow DRA (tri-function DRAO) is better than that using a solid DRA (dual-function DRAO).

Compact Differential Rectangular Dielectric Resonator Antenna

In this letter, a compact differential hollow dielectric resonator antenna (DRA) is investigated. The hollow DRA is fed by two identical conducting strips connected to the outputs of an underlaid 180° hybrid coupler (rat-race). With this compact configuration, loss of the feed network can be minimized and, thus, the differential gain can be made about the same as for the single-ended case. By using the differential feed, the DRA can be integrated with differential integrated circuits directly. Also, its cross-polarized fields are generally weaker than those of the single-ended version. The reflection coefficient, radiation pattern, and antenna gain of the proposed differential DRA are simulated, and the result agrees reasonably with our measurement.

New Single-/Dual-Mode Design Formulas of the Rectangular Dielectric Resonator Antenna Using Covariance Matrix Adaptation Evolutionary Strategy

New single-/dual-mode design formulas of the rectangular dielectric resonator antennas (DRAs) are obtained using the covariance matrix adaptation evolutionary strategy (CMA-ES). The new dual-mode formula has an advantage over the previous one in that it allows an input of a specified dimension ratio of the DRA. Also, it is simpler but more accurate than the previous one. To validate our formulas, four dual-band rectangular DRAs of different dimension ratios were designed and fabricated, and the measured resonance frequencies agree very well with the design frequencies. The reflection coefficients, radiation patterns, and antenna gains of one of the dual-band DRAs were also simulated and measured.

Dual-Function Radiating Glass for Antennas and Light Covers—Part II: Dual-Band Glass Dielectric Resonator Antennas

This paper is the second part of our study that investigates using glass dielectric resonator antennas (DRAs) as light covers. To begin, designs of dual-band hemispherical DRAs are investigated for the first time. Both broadside and omnidirectional dual-band DRAs are included in the study. The former makes use of the broadside TE111 and TE112 modes of a hollow hemispherical DRA, whereas the latter utilizes the endfire TM101 and TM103 modes of a solid hemispherical DRA. New design formulas that determine the radii of the two dual-band hemispherical DRAs are found. To demonstrate the usefulness of the formulas, two dual-band hemispherical DRAs for WLAN/WiMAX applications were designed and fabricated using K9 glass. ANSYS HFSS was used to simulate the DRAs, and the results agree reasonably well with our measurements. Results of using the DRAs as light covers are reported.