Linearly and circularly polarized conformal strip-fed dielectric resonator antennas (DRAs) are studied in this article. In the latter case, a parasitic patch is used to excite a nearly degenerate mode. The hemispherical DRA, excited in its fundamental broadside TE111 mode, is used for the demonstration. In the analysis, the mode-matching method is used to obtain the Green's functions, whereas the method of moments is used to solve for the unknown strip currents. In order to solve the singularity problem of the Green's functions, a recurrence technique is used to evaluate the impedance integrals. This greatly increases the numerical efficiency. Measurements were carried out to verify the calculations, with good results.


Keywords:

circularly polarized antenna;
dielectric antennas;
mode-matching methods;
moment methods;
parasitic antennas;
resonance

Dielectric Resonator Antennas

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

Widely used medical imaging systems in clinics currently rely on X-rays, magnetic resonance imaging, ultrasound, computed tomography, and positron emission tomography. The aforementioned technologies provide clinical data with a variety of resolution, implementation cost, and use complexity, where some of them rely on ionizing radiation. Microwave sensing and imaging (MSI) is an alternative method based on nonionizing electromagnetic (EM) signals operating over the frequency range covering hundreds of megahertz to tens of gigahertz. The advantages of using EM signals are low health risk, low cost implementation, low operational cost, ease of use, and user friendliness. Advancements made in microelectronics, material science, and embedded systems make it possible for miniaturization and integration into portable, handheld, mobile devices with networking capability. MSI has been used for tumor detection, blood clot/stroke detection, heart imaging, bone imaging, cancer detection, and localization of in-body RF sources. The fundamental notion of MSI is that it exploits the tissue-dependent dielectric contrast to reconstruct signals and images using radar-based or tomographic imaging techniques. This paper presents a comprehensive overview of the active MSI for various medical applications, for which the motivation, challenges, possible solutions, and future directions are discussed.

On the Opportunities and Challenges in Microwave Medical Sensing and Imaging

Aspects of the subject disclosure may include an antenna having a feedline configured to receive a first signal and a second signal. A dielectric antenna body is configured to transmit the first signal as a first free space wireless signal and further configured to transmit the second signal as a first guided electromagnetic wave that is bound to a surface of a transmission medium, wherein the first guided electromagnetic wave propagates along the surface of the transmission medium without requiring an electrical return path. Other embodiments are disclosed.

Dual mode antenna systems and methods for use therewith

Breast cancer is a disease that occurs most often in female cancer patients. Early detection can significantly reduce the mortality rate. Microwave breast imaging, which is noninvasive and harmless to human, offers a promising alternative method to mammography. This paper presents a review of recent advances in microwave imaging for breast cancer detection. We conclude by introducing new research on a microwave imaging system with time-domain measurement that achieves short measurement time and low system cost. In the time-domain measurement system, scan time would take less than 1 sec, and it does not require very expensive equipment such as VNA.

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Recent Advances in Microwave Imaging for Breast Cancer Detection

The paper discusses the experimental analysis on a cylindrical dielectric resonator antenna (DRA) with a parasitic conducting strip, loaded coplanar with the 50Ω microstripline feed. The antenna offers an impedance bandwidth as high as 17.33% at a centre frequency of 2.77 GHz, as a result of the enhanced coupling produced by the coplanar strip. The return loss, impedance, polarization and radiation characteristics of the antenna are studied. The radiation patterns are broad and the low cross-polarisation levels confirm that the antenna is linearly polarised over the entire impedance bandwidth.

/pdf/microstripline-fed-cylindrical-dielectric-resonator-antenna-gj4mx90lys.pdf

Microstripline Fed Cylindrical Dielectric Resonator Antenna with a Coplanar Parasitic Strip

The letter proposes a novel cylindrical dielectric resonator antenna (DRA) geometry with low radiation Q-value facilitating wide band operation with conical radiation patterns. The DRA is fed by a microstrip transmission line with a vertical strip that is attached to the DRA surface. At optimum dimensions and position of the vertical strip on the horizontal microstrip, the DRA exhibits an impedance bandwidth ( $\vert {\rm S}_{11}\vert

A Wideband Conical Beam Cylindrical Dielectric Resonator Antenna

A dielectric resonator antenna (DRA) with hexagonal geometry for WLAN applications is proposed. The antenna is excited with a simple 50 Ω microstrip transmission line. The proposed antenna produces an impedance bandwidth of 105 MHz from 2.395 to 2.50 GHz, which covers the 2.4 GHz wireless local area networks band (WLAN: 2.4–2.485 GHz). The radiation patterns are measured and are found to be omnidirectional. An average gain of 5.4 dBi is measured in the operating band. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 162–164, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22095

Hexagonal dielectric resonator antenna for 2.4 GHz WLAN applications

A coaxial-fed hexagonal dielectric resonator antenna (HDRA) producing circular polarization is investigated experimentally. Circular polarization is achieved by exciting the orthogonal HE11δ modes of the HDRA in phase quadrature. The return-loss, impedance, and radiation characteristics are studied. The results show that the antenna produces circular polarization in the elevation plane with an axial ratio less than 3 dB over a bandwidth of 14.84% and a beam width of 66°. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 581–582 2006; Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.21413

Coaxial fed hexagonal dielectric resonator antenna for circular polarization

A simple metal-coated dielectric resonator antenna with a coaxial feed producing multiple frequencies with similar polarization is reported. The characteristics of the antenna at all these frequencies are measured. The experimental results show that, the antenna produces broad patterns at all the operating frequencies. This antenna finds applications in frequency-agile systems. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 573–575, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21233

Jaimon Yohannan

Papers

Microstripline Fed Cylindrical Dielectric Resonator Antenna with a Coplanar Parasitic Strip

A Wideband Conical Beam Cylindrical Dielectric Resonator Antenna

Hexagonal dielectric resonator antenna for 2.4 GHz WLAN applications

Coaxial fed hexagonal dielectric resonator antenna for circular polarization

A multifrequency coaxial-fed metal coated dielectric resonator antenna