Wee Kian Toh

Spectrum Survey in Singapore: Occupancy Measurements and Analyses

We study the 24-hour spectrum usage pattern in Singapore in the frequency bands ranging from 80 MHz to 5850 MHz. The objectives are to find how the scarce radio spectrum allocated to different services is utilized in Singapore and identify the bands that could be accessed for future opportunistic use due to their low or no active utilization. The results from the spectrum measurements taken over 12 weekday periods reveal that a significant amount of spectrum in Singapore has very low occupancy all the time. The occupancy is quantified as the amount of spectrum detected above a certain received power threshold. The outcome of this study suggests that Singapore has a great potential for employing emerging spectrum sharing technology such as the cognitive radio technology to accommodate enormous demands for future wireless services. However, this study of spectrum survey is preliminary in its nature and future long term studies need to be performed to determine any potential secondary usage on those channels that have low or no active utilization.

A Planar UWB Diversity Antenna

A planar dual-port diversity antenna, operating with broadside and/or conical radiation patterns in H-planes, is presented for ultrawideband (UWB) applications. The proposed antenna consists of a suspended square patch with a thick stem underneath. A broadband differential feeding strip is used to feed the square patch. The measured gain for the broadside mode is 8.4-10.3 dBi from 3.1 GHz to 5.2 GHz (50.6%), and the conical mode 3.2-5.1 dBi from 3.1 GHz to 4.9 GHz (45%). The measured reflection coefficients (|S 11|, |S 22|) are less than -10 dB over the frequency ranges and the isolation |21| between the two ports is greater than 13.5 dB. The operation of the differential feeding strip on the antenna is discussed. Both pattern diversity and partial polarization diversity are achieved for this antenna.

Ultrawideband Suspended Plate Antenna With Enhanced Impedance and Radiation Performance

We describe an ultrawideband (UWB) suspended plate antenna (SPA) with enhanced impedance and radiation performance. This antenna consists of two layers. The bottom plate is suspended above a ground plane and fed by a tapered down feeding strip. The top layer consists of four identical radiating plates, each connected to the bottom plate by a vertical strip. The design is optimized numerically and validated experimentally. The measured results show that the antenna achieves an enhanced impedance bandwidth of 72.7% (2.8-6.0 GHz) for VSWR les 2 with stable radiation performance in terms of gain from 8.0-9.9 dBi, direction of maximum radiation, and high copolarization-to-cross-polarization ratio of ges 12 dB across the lower UWB band of 3.1-4.8 GHz.

A Planar UWB Antenna With a Broadband Feeding Structure

A planar antenna with a broadband feeding structure is presented and analyzed for ultrawideband applications. The proposed antenna consists of a suspended radiator fed by an n-shape microstrip feed. Study shows that this antenna achieves an impedance bandwidth from 3.1-5.1 GHz (48%) for a reflection of coefficient of iotaS11iota < -10 dB, and an average gain of 7.7 dBi. Stable boresight radiation patterns are achieved across the entire operating frequency band, by suppressing the high order mode resonances. This design exhibits good mechanical tolerance and manufacturability.

Antennas for WiFi Connectivity

Wireless fidelity (WiFi) is a superset of the IEEE 802.11 standards for communications over several tens of meters. A WiFi device connects to the network via an access point. The design of commercial WiFi antennas is a compromise between cost, size, manufacturability, and performance. This paper describes the design considerations of antenna from a WiFi system perspective with state-of-the-art solutions. The omnidirectional and multiband antenna solutions with diversity characteristics, particularly for access points and portable devices, are discussed. Case studies of a compact multiband antenna with omnidirectional coverage for access point application and a dual-band antenna system for portable devices are presented.

A Planar Dualband Antenna Array

A planar dual-band antenna array for point-to-point communication is presented. The proposed compact antenna array operates at 2.4-2.5 GHz (4%) and 5.1-5.5 GHz (7.5%) with |S11| <; -10 dB, and corresponding gains of 11-13.3 dBi and 10.6-14.5 dBi respectively. It consists of four branches suspended at a height of 5 mm above a 250 × 250 mm ground plane. Each quarter consists of a series-fed meandered step-impedance filter connected to a L-shaped radiator, and they transverse horizon tally away from the epicenter. The insertion loss method with non-redundant synthesis for filter design is applied to control the radiation aperture of the antenna array, allowing both the 2.4 GHz and 5.5 GHz radiators to co-exist and operate independently. A stable broadside radiation pattern and gain are achieved.

A Planar UWB Patch-Dipole Antenna

A planar dipole antenna is presented for ultrawideband applications. The proposed antenna consists of two patches forming a half-wavelength center-fed dipole. The differentially-fed dipole couples with an integrated balun-transformer and ground plane to achieve a stable broadside radiation pattern and consistent gain of 7.5-8.8 dBi. An impedance bandwidth from 3.1-4.8 GHz (43%) for a reflection coefficient of |S11 | <; -10 dB has been achieved.

A broadband planar antenna

A broadband planar antenna with stable radiation patterns is presented. It consists of a suspended radiator fed by a vertical feed through an n-shaped microstrip. The measured impedance bandwidth is 3.1-5.1 GHz for a return loss of |S11| < -10 dB, and an average gain of 7.7 dBi is achieved. There is no beam squinting across the operating frequency band. Also, this cost effective design has a high manufacturability and good mechanical tolerance.