Kamman Shum

A UWB Bandpass Filter With Two Transmission Zeros Using a Single Stub With CMRC

A compact bandpass filter is proposed for lower-band ultra-wideband applications. It entails the design concept of a stub-tapped half-wavelength line resonator which provides three transmission poles in the passband and two transmission zeros at the high and low rejection bands. The two stubs are replaced by a single dual-band stub and the parallel coupled-line structures are meandered, leading to a compact size of 0.26lambdag by 0.32lambda g

Investigation of microstrip reflectarray using a photonic bandgap structure

A novel approach for the gain enhancement of microstrip reflectarrays is proposed. The measured gain is increased by 2.5 dB when the solid ground plane is replaced by a photonic bandgap structure that consists of a periodic array of perforations on the ground plane. The size of each of the differential phase-shifting patches is properly readjusted as the perforation alternates the phase of the reflected field from the patch.xa0© 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 114–116, 2001.

Active receiving antennas for automotive applications

The Global Positioning System (GPS) provides an affordable worldwide radio navigation capability. However, in a city, where high-rise buildings can block out the satellite signal, navigation has to be supplemented by ground transmitters. By combining a GPS receiver with a wireless communications link, an automatic vehicle location system can be effectively set up. As for satellite radio services, near CD quality music is beamed from a satellite to automobile radio receivers, and this, too, has to be supplemented by ground repeaters for listeners passing through urban areas. Common to these applications is an antenna module that has two antenna elements, namely, a circularly polarized (CP) antenna for receiving satellite signals and a linearly polarized (LP) antenna for terrestrial signals. The CP antenna of each module is integrated with a low-noise amplifier, making it an active antenna. Two active receiving antenna modules are presented. The first module consists of a GPS CP antenna operating at 1.57342-1.57742 GHz and a GSM LP antenna at 880-960 MHz for automotive navigation. The second module consists of a CP and an LP antenna, both operating at 2.3285-2.3485 GHz for satellite radio services.

Curved PBG cell and its applications

An experimental investigation of a novel compact Wilkinson power divider and ring hybrid incorporating a 1-D slow-wave structure, in the form of perforation on the ring, itself, is presented. The size of the structures is reduced by more than 20% due to the slow-wave effect. The inclusion of these PBG cells has no significant effect to the measured insertion loss when compared to the conventional designs.

Wideband L-probe-fed base-station antenna array for PCS communication

In this paper, a 4-element microstrip patch antenna array is designed and studied experimentally for PCS communications. To achieve sufficient bandwidth for the requirement of the PCS 1800 MHz band (1710 MHz - 1880 MHz), we adopt the wideband L-probe feeding technique in our design. The designed array covers the bandwidth from 1550 MHz to 1950 MHz (22.2%) with SWR less than 1.5 to completely fulfill the PCS communications requirement. Array elements are placed with unequal distances and excited with different phases to obtain an asymmetrical radiation pattern. A microstrip feed network is designed for controlling various phase excitation and for the unequal spacing of the patches. The L-probes are mounted at the end of each transmission line.