Terence Wu

Equivalent-Circuit Analysis of a Broadband Printed Dipole With Adjusted Integrated Balun and an Array for Base Station Applications

A printed dipole with an integrated balun features a broad operating bandwidth. The feed point of conventional balun structures is fixed at the top of the integrated balun, which makes it difficult to match to a 50-Omega feed. In this communication, we demonstrate that it is possible to directly match with the 50-Omega feed by adjusting the position of the feed point of the integrated balun. The printed dipole with the hereby presented adjustable integrated balun maintains the broadband performance and exhibits flexibility for the matching to different impedance values, which is extremely important for the design of antenna arrays since the mutual coupling between antenna elements commonly changes the input impedance of each single element. An equivalent-circuit analysis is presented for the understanding of the mechanism of the impedance match. An eight-element linear antenna array is designed as a benchmarking topology for broadband wireless base stations.

Switchable Quad-Band Antennas for Cognitive Radio Base Station Applications

A novel antenna configuration for quad-band operation is presented. The quad-band antenna has a directional radiation pattern in four frequency bands, i.e., B1 (800-900 MHz), B2 (1.7-2.5 GHz), B3 (3.3-3.6 GHz), and B4 (5.1-5.9 GHz), covering all spectrums for existing wireless applications, such as GSM, PCS, WCDMA, WiFi, and WiMax. The operating frequency of the quad-band antenna can be adjusted by the use of a MEMS switch, making it suitable for cognitive radio applications. First a switchable quad-band antenna element is introduced. Then a two-element antenna array is developed to increase the antenna gain for base station applications featuring a gain value of about 9-11 dBi over all four frequency bands.

Passive wireless smart-skin sensor using RFID-based folded patch antennas

Folded patch antennas were investigated for the development of low-cost and wireless smart-skin sensors that monitor the strain in metallic structures. When the patch antenna is under strain/deformation, its resonance frequency varies accordingly. The variation can be easily interrogated and recorded by a wireless reader. The patch antenna adopts a specially chosen substrate material with low dielectric attenuation, as well as an inexpensive off-the-shelf radiofrequency identification (RFID) chip for signal modulation. Since the RFID chip harvests electromagnetic power from the interrogation signal emitted by the reader, the patch antenna itself does not require other (internal) power sources and, thus, serves as a battery-less (passive) and wireless strain sensor. In this preliminary investigation, a prototype folded patch antenna has been designed and manufactured. Tensile testing results show strong linearity between the interrogated resonance frequency and the strain experienced by the antenna. Through experiments, the strain sensing resolution is demonstrated to be under 50 μϵ, and the wireless interrogation distance is shown to be over a few feet for this preliminary prototype.

A Scalable Solar Antenna for Autonomous Integrated Wireless Sensor Nodes

A novel scalable low-profile omnidirectional antenna that can be integrated underneath a solar panel is presented. The topology alleviates the effect of solar panel to the antenna while achieving a monopole-like radiation performance above a ground plane. A 72 × 72 × 11.5 mm3 solar antenna 3-D structure operating around 2.4 GHz demonstrates the potential of the presented configuration for the implementation of autonomous integrated wireless sensors nodes.

A dual-band unidirectional coplanar antenna for 2.4–5-GHz wireless applications

A dual-band unidirectional antenna has been developed. The dual-band antenna consists of a long dipole for the lower frequency band and two short dipoles for the higher frequency band. All dipoles are printed coplanar on a thin substrate. The printed dipole antenna is excited by a microstrip line. The higher-order mode in the higher frequency band has been suppressed, leading to a good unidirectional pattern in the both frequency bands. This dual-band unidirectional antenna may find application in base stations and/or access points for 2.4/5- GHz wireless communications.

A broadband printed dipole and a printed array for base station applications

A printed dipole with an adjustable integrated balun is presented, featuring a broadband performance and flexibility for the matching to different impedance values. As a benchmarking topology, an eight-element linear antenna array is designed and built for base stations used in broadband wireless communications.

Sensitivity Modeling of an RFID-Based Strain-Sensing Antenna With Dielectric Constant Change

An radiofrequency identification (RFID)-based folded patch antenna has been developed as a novel passive wireless sensor to measure surface strain and crack, for the structural health monitoring of metallic structures. Up to 2.5 m of read range is achieved by a proof-of-concept prototype patch antenna sensor with a strain sensitivity around -760 Hz/με, which is equivalent to a normalized strain sensitivity of -0.74 ppm/με. In this paper, we propose to consider the change of the substrate dielectric constant due to strain when modeling the antenna sensor. An enhanced strain sensitivity model is introduced for more accurately estimating the strain sensing performance of the hereby introduced smart skin antenna sensor. Laboratory experiments are carried out to quantify the dielectric constant change under strain. The measurement results are incorporated into a mechanics-electromagnetics coupled simulation model. Accuracy of the multi-physics coupled simulation is improved by integrating dielectric constant change in the model.

A triple-band unidirectional coplanar antenna for 2.4/3.5/5-GHz WLAN/WiMax applications

A triple-band unidirectional coplanar antenna is developed for WLAN/WiMax wireless applications. The triple-band planar antenna consists of a top-loaded dipole for the 2.4-GHz band, two longer dipoles for 3.5-GHz band, and 2 shorter dipoles for the 5-GHz band. The triple-band antenna is printed on a coplanar substrate. The antenna achieves a similar directional radiation pattern at all of the three frequency bands with gains of 7.5 dBi for the lowest band, 8.5 dBi for the middle band, and 9–10 dBi for the highest band.

A triple-band low-profile planar antenna for wireless applications

A triple-band low-profile planar antenna is developed for wireless applications. The triple-band planar antenna consists of a two-strip monopole for the 2-GHz band, a horizontal monopole for the 3.5-GHz band, and a vertical monopole for the 5-GHz. The planar antenna is printed on a very thin substrate (0.254 mm in thickness) with a very low profile (8 mm in height). The antenna achieves a bandwidth of ~35% at the 2-GHz band, ~10% at the 3.5 GHz, and ~15% at the 5-GHz band, which may find applications in wireless/mobile devices.

A multiband/scalable reconfigurable antenna for cognitive radio base stations

A four-band MEMS-based reconfigurable antenna is designed and tested. Future work would focus on the reduction of the effect of second harmonic resonances. Due to the highly scalable nature of the design, this topology can be a good basis for building future cognitive base stations that could provide higher bandwidth, large number of bands and multi-standard support for end users and the communication backbone.