G. Almpanis

Comparison of the Radiation Efficiency for the Dielectric Resonator Antenna and the Microstrip Antenna at Ka Band

The radiation efficiency of a dielectric resonator antenna (DRA) and a microstrip antenna (MSA) at Ka band is investigated numerically and experimentally. For direct comparison, one cylindrical DRA and one circular disk MSA were designed with similar feeding networks for operation at around 35 GHz. The efficiency of both devices was measured using the directivity/gain (D/G) method and the Wheeler cap method, in both of which the losses in the test system and the feeding structure were taken into account for calibration purposes. A good agreement between measured and simulated results for both methods is found, when considering the effect of the sampling interval and cross-polarization in the D/G method and the effect of the metallic cap size in the Wheeler cap method. It is finally demonstrated that the radiation efficiency of the DRA is significantly higher than that of the MSA at millimeter wave frequencies.

Offset Cross-Slot-Coupled Dielectric Resonator Antenna for Circular Polarization

A cross-slot-coupled cylindrical dielectric resonator antenna (DRA) is studied theoretically and experimentally. In previous papers, a cross-slot of unequal slot lengths was centered under the dielectric resonator (DR), resulting in circular polarized operation of the antenna. In the present study, the design is enhanced by setting the centers of the two slots at different positions and taking into consideration the partial independence of the slot modes from the DRA mode. Thus, circular polarization (CP) bandwidth of up to 4.7% is attained experimentally in the broadside direction. It is also shown that a largely asymmetrical structure results in a very high bandwidth, but with the tradeoff of distorted CP operation off-broadside

The Trapezoidal Dielectric Resonator Antenna

The operational concepts of the trapezoidal dielectric resonator antennas (DRAs) are presented and their performance is studied theoretically and experimentally. The rectangular parallelepiped is a special case of the more general trapezoid and therefore a comparison between both is useful in order to highlight their similarities and differences. It is shown in this paper that the inverted trapezoidal DRA exhibits a significantly larger impedance bandwidth than the rectangular parallelepiped, while the rest of their properties remain similar. Based on that, two versions of a probe-fed wide-band linearly polarized (LP) DRA are designed by combing the resonances of the first two lower-order modes of the trapezoidal DRA. The resulting impedance bandwidth exceeds 55% (S11 < -10 dB) and the patterns are broadside with low cross-polarization. The antennas are simple to fabricate and they can be easily made to be mechanically stable. The numerical analysis was performed with a commercially available FEM solver and an in-house developed finite-volume-time-domain (FVTD) code. The measurements confirmed the results of the simulations.

A Truncated Conical Dielectric Resonator Antenna for Body-Area Network Applications

An inverted truncated annular conical dielectric resonator antenna (DRA) for potential use in body-area network (BAN) applications is introduced. The antenna is designed to operate within the lower European ultrawideband (UWB) frequency band (3.4-5.0 GHz). The selected DRA geometry in combination with a capacitively loaded monopole as the feeding mechanism results in a low-profile antenna with wide bandwidth and stable monopole-like patterns. In addition, the antenna exhibits good UWB properties, as characterized through the dispersion effect on the transmitted impulse voltage signal. The DRA has been numerically and experimentally examined for both free-space and on-body applications, demonstrating a good performance in the frequency- and time-domain.

Dual-Mode Bridge-Shaped Dielectric Resonator Antennas

Different configurations of bridge-shaped dielectric resonator antennas (b-DRAs) made of high-permittivity materials are presented in this letter. These DRA geometries can be seen as an evolution of the notched rectangular DRAs introduced by other authors, but their operational principle is different. The particularities and advantages of the proposed geometry will be investigated and demonstrated for a single bridge first. Afterward, the concept will be extended to two realizations of well-operating dual-mode b-DRAs with stable radiation patterns and low cross polarization. For the analysis of these structures, a full-wave analysis solver (HFSS) was used. Prototype fabrication and measurements confirm the results of the simulations.

Dual Mode Slot Coupled Cylindrical Dielectric Resonator Antenna

A simple slot-coupled cylindrical dielectric resonator antenna (DRA) with wideband characteristics is studied theoretically and experimentally. In previous studies, the slot has been designed to radiate at the same frequency as the fundamental HEM11delta mode. In this paper, the partial independence of the slot mode from the DRA mode is discussed and a simple design is described, in which the slot mode and the DRA mode are offset, allowing an impedance bandwidth of 27%

Simulation and experimental investigation of the radiation efficiency of a dielectric resonator antenna

In this paper, we attempt to get a deeper insight into the radiation efficiency of the DRA and the difference of accuracy between the D/G method and the Wheeler cap method by measuring a simple rectangular DRA at C band with both methods. It is, on one hand, confirmed that, the radiation efficiency of the DRA can be as high as 98% at C band. On the other hand, the comparison of the two efficiency measurement methods shows discrepancies that can be explained from simulations. The radiation efficiency obtained by the D/G method is generally lower than that by the Wheeler cap method. The paper demonstrates that this arises from the effect of cross-polarization and from the finite sampling of the radiation pattern used in the D/G technique, which are inherent defects of this method.

Comparison of various non-canonical rectangular dielectric resonator antennas for enhanced bandwidth

A probe-fed rectangular DRA is investigated and compared with two non-canonical structures, whose geometries can be seen as deviations from the parallelepiped. It is shown that these advanced geometries exhibit a larger impedance bandwidth than the canonical RDRA, while the rest of their properties are largely unchanged. In addition to that, the new structures do not require lengthy and complex fabrication procedures due to their relatively simple shape and feeding scheme. Finally, since these shapes are derivations from the rectangular geometry, similar modes are excited and hence their overall performance can be described and designed starting from the analytical expressions for the parallelepiped.

Semi-trapezoidal dielectric resonator antenna for wideband applications

A semi-trapezoidal probe-fed dielectric resonator antenna (DRA) of very wide bandwidth is studied theoretically and experimentally. The design is an evolution of the double-slab DRA that exploits the advanced antenna geometry and the position of the feeding probe in order to facilitate the excitation of multiple modes with similar radiation characteristics. As a result, an impedance bandwidth of 62 per cent is achieved, while the patterns remain broadside and the polarization purity is within acceptable limits for the entire frequency domain.