Dielectric resonatorantennas (DRAs) have received much attention due to several attractive characteristics, such as light weight, low proﬁle and high radiation eﬃciency [1–7]. Even though DRAs were originally devised for millimeter-wave applications, they are also extensively studied at microwave frequency. Resonant frequencies, Q factors, ﬁeld distributions and radiation properties of resonant modes of the isotropic DRA have been extensively analysed by various methods. Basic characteristics of DRA resonant modes are treated in [1, 2]. The much of the literature investigates isotropic cases. Crystals (such as calcite and sapphire) are examples of natural anisotropic materials. The single crystal rutile has a dielectric anisotropy at GHz frequencies, but its high cost prevents practical use. Recently, the investigation and characterization of anisotropic materials have been intensively carried out, owing to the recent advances in material science and technology. They have also been applied in microwave engineering and electromagnetic scattering . Dielectric resonators (DRs) made of crystal materials, such as sapphire, have received substantial attention due to their very low loss nature for fabricating high-stability and low-noise microwave oscillators [9–11]. In addition to the extensively used sapphire material, other materials for building very low loss DRs are also reported . Approximate and rigorous solutions have been used to obtain the resonant frequency and ﬁeld distribution of a cylindrical anisotropic DR [13–15].
There has been increasing interest in investigations of the dielectric resonatorantennas (DRAs) [1–4]. DRAs are known for the inherent merits of small size, ease of excitation, low dissipation loss and high radiation efficiency . However, the typical bandwidth of the regular- shaped DRAs is about 10%.
Dielectric ResonatorAntennas (DRAs) offer many appealing features such as larger impedance bandwidth and higher radiation efficiency due to the lack of conductor and surface wave losses . Nevertheless, compared to their metallic counterparts, fabrication of DRAs is challenging since they have traditionally been made of high permittivity ceramics, which are naturally hard and extremely difficult to machine. The fabrication of these three dimensional structures is even more difficult at millimetre-wave frequencies where the size of the antenna is reduced to the millimetre or sub-millimetre range, and tolerances to common manufacturing imperfections are even smaller requiring a wideband antenna to compensate the possible inaccuracies. Several methods have been considered in the literature to increase the bandwidth of DRAs. Exotic shapes [2–4], parasitic metal strips [5– 7], and stacking parasitic DRAs [8–10], are among the most common ways, all of which are less suitable for millimetre-wave fabrication due to their complicated structures and use of metallic parts.
Abstract—Novel compact ultra-wideband (UWB) rectangular stacked dielectric resonatorantennas (DRAs) with band-notched characteristics are proposed. The DRAs are designed to cover the FCC band (3.1–10.6 GHz) and have very compact sizes, due to the shorting conductor. Printed dipoles that are placed on one side of the dielectric resonator will resonate and generate band notches within the ultra-wide operating band. Simulations and measurements conﬁrm the validation of the design principle.
In this paper, reconfigurability is added to dielectric resonatorantennas, and two types of reconfigurable dielectric resonatorantennas are presented. The first is an ultra wideband DRA with a reconfigurable band rejection or notch to help limit interference to different narrowband services operating inside the 3.2–5.1 GHz frequency range. The second is a DRA with reconfigurable resonance frequency suitable for different microwave applications and WiMAX applications. The reconfigurability of the notch and the resonance is achieved by rotation the Dielectric Resonator (DR) placed on the patch of the antenna, using a DC stepper motor connected to the DR. The characteristics of the designed antennas are investigated via HFSS and experimentally verified.
In the last decade, a considerable attention has been focused on dielectric resonatorantennas (DRAs) as an alternative to microstrip ones [6–11]. DRAs represent a relatively novel application of dielectric resonators (DRs). These resonators are unshielded and rely, for field confinement within their boundaries, on a very high difference between their own permittivity and the permittivity of the outer medium. The low-loss, high permittivity dielectrics used for DRs (10 ≤ ² r ≤ 100),
Dielectric Resonators (DRs) are widely used in microwave circuits including oscillators, ﬁlters and cavity resonators [1, 2]. Also, Dielectric ResonatorAntennas (DRAs) are attractive as electromagnetic wave radiators due to high radiation eﬃciency, ease of excitation, simple geometry, compactness and ability to obtain diﬀerent radiation characteristics using diﬀerent modes of operation [3–8]. These advantages of DRs make them as practical elements for antenna applications  at microwave frequencies.
Abstract—A comparative study using numerical models on the mutual coupling (MC) between two diﬀerent heterogeneous beam steering dielectric resonatorantennas (DRAs) and an omni-directional dielectric resonator antenna (DRA) is presented in this paper. The mutual coupling was investigated by varying the separation between the antennas and manipulating the far ﬁeld radiation pattern of each antenna. Several arrangements with element separation ranging from 0.1 to 0.5 free space wave length were investigated at the design frequency of 10 GHz. Diﬀerent conﬁgurations contributed to diﬀerent isolation levels. It was found that a signiﬁcant isolation ( < − 15 dB) between an array of heterogeneous DRAs can be obtained even with antennas placed in close proximity (0.1 free space wavelength separation). It was also shown that the resonant frequency and return loss are most aﬀected at settings where the direction of the main lobe of antenna A overlaps with the direction of the main lobe of antenna B. The expected inverse proportionality between ‘ d ’ (the separation between two antennas) and the level of MC was also demonstrated.
Dielectric resonator (DR) is a ceramic puck characterised by a definite volume, shape, high dielectric constant and low loss. Radiation from open DRs was realized by Richtmyer in 1939 . But the first theoretical and experimental analysis of a cylindrical DR antenna was carried out by Long et.al. in 1983 . Since then, DRAs transformed into a fast growing focus among the antenna researchers so that new DR geometries like rectangle, hemispherical, triangular, ring etc. were evolved and studied extensively [4-8]
Abstract—An ultra-wideband (UWB) planar monopole antenna integrated with a narrow-band (NB) cylindrical dielectric resonator antenna (DRA) is presented. The proposed antenna consists of a UWB monopole excited by a coplanar waveguide (CPW) transmission line, acting as a ground for a DRA excited by a slot. The mode HEM 11δ is excited in the NB DRA. To validate the concept of integration, an antenna is fabricated and measured. The measured results demonstrate that the UWB antenna provides a 2 : 1 voltage standing wave ratio (VSWR) bandwidth for 3.05–11 GHz, integrated with a dual-band NB antenna. Moreover, the two ports have the same polarization and a reasonable isolation (less than −10 dB) between each other. This is a promising candidate for applications in cognitive radio, where the UWB antenna can be used for spectrum sensing and the NB antenna for communication operation.
Dielectric Resonators (DRs) have been widely used in shielded microwave circuits such as cavity resonators, filters and oscillators. As the frequency range goes upward gradually to millimeter and sub- millimeter region (100 GHz–300 GHz), conductor loss limits the use of metallic antennas. On the other hand, Dielectric Resonator Antenna (DRA) made up of low loss dielectric material is a potential candidate for high frequency application. In recent years, application of DRAs in microwave and millimeter band has been extensively studied [1– 5], as they provide efficient radiation due to extremely low loss in the dielectric material. Its inherent wide band nature, compactness in size, light weight, low cost, ease of fabrication etc. make DRA very attractive. Theoretical and experimental investigations have been reported on cylindrical, spherical, rectangular, triangular, hexagonal and/or trapezoidal DRAs in literature.
Abstract—A single-layer partially reﬂective surface (PRS) structure is presented to design single-feed Fabry-Perot resonatorantennas (FPRA) with a large gain bandwidth and compact size. The design of the PRS structure applied in this antenna is based on the theory of tightly coupled antenna arrays. Owing to strong mutual coupling between the overlapped patches, the proposed antenna obtains a wider bandwidth and more compact size. Experimental results show that the antenna obtains a 32% 3-dB gain bandwidth from 8.8 GHz to 12.2 GHz, with a peak gain of 13.5 dBi. Moreover, the relative impendence bandwidth is 40.9% for the voltage standing wave ratio (VSWR) less than 2 from 8.45 GHz to 12.8 GHz.
The slot and DRA both radiates as a magnetic dipole and preserve the radiation patterns and polarization over the entire bandwidth. The method of fig. 8 combines a slot and DRA resonance and bandwidth of about 25 % has been achieved . The dual resonance is very useful to design compact and wide band dielectric resonatorantennas. The obtained width is not sufficient to use DRA for broadband operation in mobile communication and satellite communication. So band width can be further improved by multiple resonance technique and DRA arrays that can enable a DRA to be practically used for broadband applications [Amelia Buerkle et al.(2005)].
In the last two decades, Dielectric ResonatorAntennas (DRA) have received lots of attention due to the attractive characteristics such as high radiation efficiency, considerable bandwidth, low temperature coefficient and low profile. Since dielectric resonators (DRs) have very low loss, higher efficiency without any conductor loss is ensued. Thus, DRAs own much lower loss and also are a very good candidate to design the antenna for microwave bands .
The dielectric resonatorantennas (DRAs) have become attractive to antenna engineers due to its several beneficial features, such as its small size, light weight, low loss, high radiation efficiency, and easy of excitation. The need of the high-data rate, in the recent communication devices, has forced the researchers to enhance the small antenna bandwidth. In the literature, several studies have been reported to achieve wide-bandwidth enhancement of DRAs suitable for wideband applications, as using stacked segment dielectric resonators (DRs) , stacked-embedded DRs , hybrid DRA , and special geometries of DR, such as conical , tetrahedral , elliptical , stair , H-shaped , and P-shaped . Using these techniques, an impedance bandwidth range of 30–70% has been achieved.
Since its inception, wireless technology has undergone many stages of development. There has been revolutionary growth in the world of wireless communications systems. Antennas form the most integral part of any wireless communication systems. In order to keep pace with fast changing requirements of the wireless communication market, fast and eﬃcient antennas are in great demand. Besides, it is desired that antennas should be of that type which can be scaled up in frequency. There are two types of antennas which have been able to match up these needs namely microstrip antenna and dielectric resonator antenna. Initially, microstrip patch antennas were best suited, but from last few decades dielectric resonatorantennas have totally replaced them [1–3], since dielectric resonatorantennas (DRAs) have an edge over microstrip antennas because of its many attributes namely ease of fabrication, ﬂexibility infeed mechanism, low proﬁle, high radiation eﬃciency, and wide frequency range to name a few. Moreover, DRA is a 3-D structure whereas microstrip antenna is a 2-D structure. In addition, DRAs are well suited for low-loss applications for the reason that there is no conductor loss in them.
get trapped along the substrate. Due to this trapped electromagnetic energy, the efficiency and gain of the antenna reduces significantly. A significant amount of energy gets trapped into the substrate, resulting in unwanted surface wave loss, which if suppressed, can enhance the gain of antenna. Several methods have been proposed to reduce the effects of surface waves -. One approach suggested, is the synthesized substrate, which lowers the effective dielectric constant of the substrate either under or around the patch , . Other approaches are to use parasitic elements ,  or to use a reduced surface-wave antenna -. Electromagnetic band-gap structures, also known as photonic crystals , are commonly used to improve the antenna performance -. The surface waves can be suppressed by creating electromagnetic band-gap structures in the substrate. These structures have the ability to open a band-gap, which is a frequency range for which the propagation of electromagnetic waves is forbidden i.e., EBG blocks the surface waves from propagating in a certain band-gap. Reduction of mutual coupling and co-site interference are other benefits of these EBG antennas.The surface wavesare reduced by the EBG structure, but the antenna gain enhancement is also due to the coupling between the dielectric resonator antenna and the EBG structure. By appropriately using these artificial materials (EBG structures), the antenna aperture efficiency is significantly improved without increasing the antenna size. Several studies have shown that EBG structures, when combined with microstrip antennas or dielectric resonatorantennas, can significantly enhance its performance in terms of directionality, gain, bandwidth, return loss and reduction of size etc.. Due to incorporation of resonant artificial materials, the surface-waves are radiated by the antenna and add up the gain of antenna. Within the band-gap, around the resonant frequency of the antenna, it does not allow surface-waves to propagate in the substrate. As a result, the whole radiations go up in the vertical direction and enhance the gain. In every design using EBG structure, the antenna is designed with its resonant frequency lying in the band-gap of EBG substrate. Various microstrip patch antennas as well as dielectric resonatorantennas have been designed by the researchers in past few years with EBG substrates for the gain enhancement.
Diﬀerent basic dielectric resonatorantennas (DRAs) are reported in the literature such as hemispherical, cylindrical, and rectangular DRAs [1–3]. The main drawback of these basic DR antennas is the narrow bandwidth. For a standard rectangular DRA, up to 10% impedance bandwidth can be achieved . Many approaches have been used to enhance the bandwidth of DRA. One of the approaches to widen the impedance bandwidth is to remove portions from DRA structure. In , the central portion of the rectangular DRA is removed which enhanced the bandwidth up to 28%. Another method to improve the bandwidth is to modify the geometry of the DRA to get diﬀerent shapes such as a split cylinder , conical DRA , a tetrahedron and triangular , truncated tetrahedron . These modiﬁed geometries have more degree of freedom for the design parameters than all basic DRAs geometries. By using this approach, the largest bandwidth reported so far is 72% using U-shaped DRA covering frequency ranges from 3.87 to 8.17 GHz . Another approach is investigated by using hybrid DRAs. In a hybrid DRA, combination of a DRA with other resonators such as microstrip patch, quarter wave monopole MP, or a slot radiator is used to improve the impedance bandwidth. Multiple modes of the resonators are excited and merged at adjacent frequencies [10–13]. In , a fractional bandwidth of 3 : 1 (100%) is demonstrated by using a hybrid conﬁguration of quarter wave electric monopole and annular DR. The monopole (MP) in this conﬁguration is used as an exciting element for the DR and as a loaded radiating structure. The ultra-wideband response of this conﬁguration was characterized by three resonances. The quarter-wave resonance of the MP is responsible for the lowest resonance frequency of the impedance bandwidth whereas the excitation of the TM 01 δ mode of the DR is generated the highest resonance.
Dielectric resonatorantennas (DRAs) have been sub- jected to many investigations since their introduction in 1983 . The DRA is useful for high frequency applica- tions where Ohmic losses become predominant for con- ventional metallic antennas. In addition, they offer higher bandwidths and gain when compared with microstrip patch antennas. Over the past few years researchers have tried to improve the impedance bandwidth of these DRAs to increase its functionality. Wideband DRA has been demonstrated for cylindrical DRA (CDRA) by Chair et al.  and for rectangular DRA by Li and Leung . System- atic analysis of improving bandwidth using this mode merging technique has been reported by Young and Long . In  it was revealed that the actual reason for wideband operation of CDRA was due to unequal rate of variation in resonant frequency of the TM 110 and TM 111
bandwidth than ordinary dielectric resonatorantennas. The feeding mechanism is chosen with the proper parameters to achieve broadband impedance match and good circular polarization characteristic. The simulated results demonstrate that the proposed antenna offers a 3- dB AR bandwidth of 15.9% (6.22–7.28 GHz) and a 10-dB impedance bandwidth of 21.3% (5.78–7.16 GHz). Neither external quadrature feed network nor complex shape of DR are required in this design. The rest of the letter is organized as follows. The antenna geometry and design are presented in Section 2. Experimental results are also provided in Section 3. Conclusions are given in Section 4.