Stable Phase Center Research Articles

A miniaturized UWB stepped-slot antenna for medical diagnostic imaging

A novel compact planar UWB stepped-slot antenna optimized for medical diagnostics is presented in this article. This antenna can be placed directly on the skin to allow more energy to be radiated into the human body for obtaining a stronger signal for processing. The design of the antenna is based on the differential feed for two symmetrical-elliptically shaped monopoles, where the radiation direction of the main beam is found to be very stable over a broad frequency range due to the phase center being in the middle of the antenna, as shown in the results. The stepped-slot design enables a further miniaturization of the size and enhancement in the bandwidth. Characterization of the antenna is done from 1 to 9 GHz on a phantom emulating the human body, where the antenna gain and near E-field are investigated. The performance of the antenna is then verified using a near-field measurement setup. With features such as a very small size, low operational frequency, stable phase center over the whole operated frequency range and high front-to-back ratio, this design shows a high potential for applications for the detection of breast cancer, stroke in human brain and other relevant medical diagnostics. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:105–109, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27222

Broadband Integrated Lens for Illuminating Reflector Antenna With Constant Aperture Efficiency

A new integrated shaped lens antenna configuration is described with frequency stable radiation pattern and phase center position across a broad 1:3 frequency band, which can be used for focal plane reflector feeding in quasi-optical radio telescope systems. The lens is compatible with the integration of ultrawideband uniplanar printed feeds at its base and equally broadband mixing devices, like the Hot Electron Bolometer (HEB), although these are not used in the present work. Measurements on a scaled mm-wave lab prototype have confirmed stable performance versus frequency, with only dB directivity variation, and better than 94% Gaussicity, thanks to the possibility to impose a predefined output radiation pattern template. Simulations were performed to test the illumination of an off-set parabolic reflector by the lens radiation pattern, which confirmed reasonably constant aperture efficiency in the order of 78% across the 100% bandwidth.

A Miniature Planar Antenna for Bluetooth and UWB Applications

The paper puts forward a miniature microstrip antenna at the operating frequency of 2.4–2.5 GHz (Bluetooth) and 3.1–10.6 GHz (UWB). The omnidirectional radiation patterns can be obtained at the whole operating frequency band by cutting the ground conductor and adding a branch at the top of the antenna. Simulated results show that the antenna has attractive characteristics such as stable phase center, constant group delay, linear phase and good time-domain impulse response. Both the reflection coefficient and radiation patterns of the antenna are in good agreement with measured results. Experiment also shows that the cross polarization level is very low with flat gain. Consequently, the proposed antenna can well meet the requirements of wireless communication in both the Bluetooth and UWB bands.

A WIDE BAND ANTENNA FOR MULTI-CONSTELLATION GNSS AND AUGMENTATION SYSTEMS

Local Area Augmentation System (LAAS) based on multi- constellation GNSS can provide improved accuracy, availability and integrity needed to support all weather category II and III precision approach landing of aircraft. In order to receive satellite signals of GNSS, an antenna working over wide frequency band and high phase center stability is preferred. Commonly used antennas like crossed dipoles, patch etc. are inherently narrow band. This paper describes the design and development of half-cardioid shaped dual arm, wide band printed circuit antenna. The antenna has low VSWR of < 3 : 1, a stable phase center and good right hand circularly polarized radiation patterns covering full L-band frequencies. The simulated and measured results compare well. This compact antenna can also be used on ground, ship and airborne platforms to receive signals from multiple GNSS satellites above the horizon.

Two-Layer Dielectric Rod Antenna

A dielectric rod antenna (DRA) design that consists of two concentric dielectric cylinders and achieves more than 4:1 bandwidth is described. The new DRA is composed of a launcher section, followed by a waveguide section and ends in a radiation section. The utilization of two-layer structure avoids the excitation of high-order modes, thus extending the operational bandwidth. Properly chosen radii and dielectric constants of each layer in conjunction with a properly tapered radiation tip ensure frequency-insensitive radiation properties (gain and pattern) and stable phase center. The design example of a two-layer dual-polarization DRA presented in this paper operates from 2 to 8 GHz and produces symmetric radiation patterns with half-power beamwidth greater than 55deg. The current design is one of the most ideal antennas to be used as a near-field probe or reflector feed.

Low Profile GALILEO Antenna Using EBG Technology

A dedicated low profile antenna for geodesic applications is presented. This type of antenna requires mitigation of multipath signals to achieve sub-centimeter level of precision. Typically, bulky and heavy choke ring structures have been used to reduce the effects of multipath interference. The antenna presented here consists of a low temperature co-fired ceramic (LTCC) patch antenna immersed in an electromagnetic bandgap (EBG) substrate. The EBG substrate reduces the effects of multipath by blocking the propagation of surface waves. The result is an antenna showing good multipath rejection and a stable phase center. The advantage of printed EBG substrates is that they can be realized in a low-weight, low-price, and low-profile fashion. First prototypes have been manufactured and tested, and its performance has been compared to that of a more classical choke ring antenna.

The Ultrawideband Leaky Lens Antenna

A novel directive and nondispersive antenna is presented: the ultrawideband (UWB) leaky lens. It is based on the broad band Cherenkov radiation occurring at a slot printed between different infinite homogeneous dielectrics. The first part of the paper presents the antenna concept and the UWB design. The issues that are specifically addressed include the impedance matching, the radiation pattern and the phase purity. Subsequently the hardware demonstrator and the results of the measurement campaign are shown. The results fully validate the antenna concept. The antenna presents decade bandwidth impedance matching, directive and frequency independent patterns in the H-plane over two octaves, negligible cross-polarization levels, weak amplitude dispersivity and, according to the authors, the most stable phase center for a directive antenna over an ultra wide frequency range.

PHASE CENTRE OPTIMIZATION IN PROFILED CORRUGATED CIRCULAR HORNS WITH PARALLEL GENETIC ALGORITHMS

Achieving a high stability of the phase centre position in horn antennas with respect to frequency is a very desirable aim in reflector antenna design; a highly stable phase centre reduces efficiency dropping for defocusing at the frequency band extremes. By using an appropriate profile for the horn antenna it is possible to obtain horns both compact and with a stable phase centre. In this paper an automatic design procedure, based on Genetic Algorithms, to obtain such horns is described. The algorithm operates on many horn profile parameters, including corrugations, and is based on an accurate fullwave mode matching/combined field integral equation analysis code. To keep computing time down a full parallel algorithm over a 12 CPU parallel virtual machine is described.

An ultrawide-bandwidth tapered resistive TEM horn antenna

A novel stable beamwidth, ultrawide-bandwidth low-scattering antenna is presented. This antenna is a modified version of the conducting slotline bowtie hybrid (SBH) antenna with resistive sheets (Rcards) introduced into the guiding structure design. Since the resistive sheets can attenuate creeping wave fields, much smaller rolled edges are needed in the Rcard SBH antenna. Moreover, due to the Rcard's partially transparent nature with respect to electromagnetic fields, the radar cross section (RCS) associated with this new antenna is smaller than the original conducting rolled edge one. By employing an optimization process based on the concept of the genetic algorithm, one can easily design the Rcard SBH antenna to obtain a very stable antenna beamwidth and phase center in both the E- and H-planes across the entire operating frequency bandwidth. Because of its constant beamwidth, low RCS, and broad-band features, the Rcard SBH antenna is an ideal antenna for many applications such as a compact range feed. Calculated and measured results are presented to demonstrate the performance of this new antenna.