The input impedance of stacked cylindrical dielectric resonator antennas is investigated experimentally. The dielectric resonators are made of different materials. The bandwidth of 25% has been observed for a standing wave ratio better than 2.

Broadband stacked dielectric resonator antennas

The design of a dual-polarization stacked patch antenna to be used in GSM-UMTS base station arrays is presented. The patch shows a high matching level in a broadband and isolation between elements that make it a suitable radiating element for base station arrays. Moreover, the most relevant achievement of this element is the isolation between the two polarization ports of the same element in the antenna operating bandwidth. A prototype has been manufactured and measured. The measurements, that match the design objectives, are also presented.

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A High-Isolation, Wideband and Dual-Linear Polarization Patch Antenna

The principles used in the development of frequency-independent antennas are reviewed. Examples of log-periodic (LP) geometry and the additional requirements that must be met for practical success are given. The evolution of unidirectional, wire-outline, and dipole arrays is presented. Analytical results for LP dipole arrays led to the concept of an active region that remains almost fixed in size relative to the wavelength. Periodic structure theory serves as an aid to understanding LP structures. The analysis of periodically loaded lines shows the problems that may arise from the existence of stop regions on LP antennas and provides procedures for eliminating them. This has led to successful LP monopole and cavity-backed slot arrays. Planar and conical log-spiral antennas are discussed. Frequency-independent, circularly polarized patterns-bidirectional, unidirectional, omnidirectional, and conical-can be provided from log-spiral antennas with two or more arms. Recently, the LP design principles have been applied to low-profile antennas: patches, thin cavities, and spirals over ground. They have also produced flush-mounted aircraft antennas that can respond simultaneously to two different linear of circular polarizations. >

Frequency-independent antennas and broad-band derivatives thereof

An antenna made of a dielectric disk with a high permittivity mounted on top of a grounded dielectric substrate of low permittivity is analyzed. A numerical procedure based on surface integral equations, derived from the equivalence principle, is used to compute the natural resonant frequencies for the HEM/sub 11/ mode from which the radiation Q factor of the antenna is obtained. Then the radiation pattern of the antenna, operating at the resonant frequency evaluated previously, is computed with an electric dipole excitation located within the dielectric substrate under the dielectric disk. The effect of various parameters on the radiation characteristics of the antenna is studied, and presented in the form of diagrams. The low values of the radiation Q, combined with the high values of the dielectric Q and conductor Q, indicate that this antenna promises to be more efficient then the microstrip antenna. >

A numerical study of a dielectric disk antenna above grounded dielectric substrate

A double periodic composite right/left-handed ( DP-CRLH ) substrate integrated waveguide (SIW) is proposed based on the transmission line theory. A new leaky-wave radiation is observed at low frequency below the left-handed passband in addition to the composite right/left-handed property. First, the equivalent circuit of the proposed structure is analyzed, and dispersion characteristics are obtained including the expression for the cutoff frequencies. It is noted that transmission lines double periodically loaded with either alternate capacitances, or alternate inductances will contribute the new leaky-wave behavior. Next, SIW implementation of a DP-CRLH transmission line is designed and illustrated with simulated and experimentally demonstrated results. The electric field distribution plots are extracted from a full-wave simulation tool and exhibit the forward and backward wave propagation in the new leaky-wave region and the typical left-handed region, respectively. Finally, a compact leaky-wave antenna based on the DP-CRLH SIW is designed, and the radiation characteristics are tested and demonstrated to exhibit forward radiation at the new leaky-wave region from 5.2 to 5.8 GHz (covering IEEE 802.11a band) and frequency scanning from backward to forward directions in the left-handed and conventional right-handed region from 12.6 to 17.8 GHz.

Leaky-Wave Radiation Behavior From a Double Periodic Composite Right/Left-Handed Substrate Integrated Waveguide

A method of increasing the bandwidth of low-profile cavity-hacked slot and microstrip patch antennas without appreciably adding to the antenna dimensions is presented. This idea incorporates the stacking of structures which have close resonant frequencies. Energy is coupled between cavities via carefully placed slots in the common wall. An approximate two-and-a-half fold increase in input impedance bandwidth has been observed for a certain cavity-backed slot antenna.

Stacking resonators to increase the bandwidth of low-profile antennas

The dual-feed microstrip patch antenna is presented. This new radiator has broadband match and unidirectional azimuth pattern, desirable characteristics for use in broadband endfire arrays. Design, construction, and experimental results (realized gain, input impedance and far-field patterns) are given for a log-periodic array of dual-feed patches. An array with only ten elements has been demonstrated to operate at nearly constant gain over a 2:1 frequency band with a voltage standing-wave ratio (VSWR) of less than 2:1. >

Log-periodic array of dual-feed microstrip patch antennas

The authors present a theoretical analysis of a stacked antenna system consisting of a driven resonator coupled to a second resonator via an aperture in a common wall. The antennas are thin, rectangular, cavity-backed slot resonators. These resonators consist of five conducting walls, leaving the sixth open to allow radiation. The final structure consists of two identical cavities, one stacked above the other, with the radiating edges on opposing sides. The lower resonator is driven by a probe and coupled to the second resonator through an aperture in a common wall. The cavity model theory developed by W.F. Richards, Y.T. Lo, and D.D. Harrison (IEEE Trans. Antennas Propagat., AP-21, no.1, p.38-46, Jan. 1981) was used to predict the input impedance of this stacked antenna. Preliminary results show good qualitative agreement between theoretical and measured data. The theoretical input impedance clearly shows the effect of coupling between the resonators. In addition, the impedance correctly predicts the effect of changing the dimensions of the coupling aperture. >

Aperture coupling to increase the bandwidth of thin cavity antennas

The antenna presented is an LP (log-periodic) array of dual-mode patches that offers improved performance in a reduced size. A rectangular patch of high aspect ratio is used. This patch is excited simultaneously in two modes from the same feedline, a microstrip line on the opposite side of the ground plane from the patch. A constant-field mode is driven by the capacitively loaded post, which is connected at its base to the microstrip line and is centered under the patch. The post passes through the ground plane in the center of a rectangular slot that serves also to excite the TM/sub 01/ mode. The first array was designed to have a structure bandwidth of two. A scale factor of tau =0.9 was chosen on the basis of the desired overlap of the loading effect of several adjacent elements. The measured S/sub 11/ data (referenced to 50 Omega ) for the array are shown. The operating band of the antenna (1.03 GHz to 1.75 GHz) is reasonably less than the structure bandwidth. Wideband performance at a high-efficiency level has been obtained. >

http://ieeexplore.ieee.org/iel2/724/3074/00094104.pdf

Log-periodic array of dual-mode patch elements

A cavity method that is not restricted to shapes which have separable geometries is described. Metallic surfaces are replaced by perfect electrically conducting walls and radiating sides and apertures are replaced by perfect magnetically conducting walls. The result is a closed cavity. It is also assumed that any prescribed and induced electric currents flow in the z direction, while the prescribed and induced magnetic currents flow in planes transverse to z. This, in effect, states the problem to be transverse magnetic. Input impedance can be calculated by allowing the cavity to radiate and introducing radiation loss and ohmic loss into an effective dielectric constant of the closed cavity. The microstrip patch antenna is considered as a simple example. >

H.K. Smith

Papers

Stacking resonators to increase the bandwidth of low-profile antennas

Log-periodic array of dual-feed microstrip patch antennas

Aperture coupling to increase the bandwidth of thin cavity antennas

Log-periodic array of dual-mode patch elements

A segmentation method for the analysis of thin cavity antennas