Ming-Iu Lai

Compact Switched-Beam Antenna Employing a Four-Element Slot Antenna Array for Digital Home Applications

In this paper a compact switched-beam antenna is proposed. The antenna is composed of a four-element antenna array based on L-shaped quarter-wavelength slot antenna elements. Such an antenna element is a planar structure and presents a directional radiation pattern in the azimuth plane. Its maximum radiation direction is toward near the direction of the open end of the slot. As a result, the open ends of the four slot antennas are arranged toward 0, pi/2, pi, and 3pi/2 , respectively. The statuses of these antennas are controlled by some diodes. Consequently, by carefully controlling the diodes, an antenna with several switchable patterns can be achieved. To prove the concept, a 2.4-2.5 GHz switched-beam antenna for WLAN applications is designed and implemented. Its size is 52 mm in square. The antenna possesses eight directional patterns and many nearly omnidirectional patterns in the azimuth plane. The experiment results fully demonstrate the performance of the proposed design. The envelope correlations and the characteristics of the designed antenna are also discussed. Due to the compact size and low manufacture cost, such a design can be a promising solution for digital home applications to overcome multipath problems and increase the transmission data rate.

Compact microstrip dual-band bandpass filters design using genetic-algorithm techniques

An optimization scheme based on hybrid-coded genetic-algorithm (GA) techniques is presented to design compact dual-band bandpass filters with microstrip lines. A representation scheme is proposed to represent an arbitrary microstrip circuit as a set of data structures. Each data structure in the set describes a simple two-port network with the corresponding connection method and electrical parameters. The optimization algorithm based on conventional GAs is then applied to simultaneously search for the appropriate circuit topology and the corresponding electrical parameters with dual-band characteristic. Two examples are designed and implemented to validate the proposed algorithm. In the first example, the 3-dB fractional bandwidth of the low and high bands is 35% and 17%, respectively. It has return losses larger than 10 dB from 2.14 to 2.96 and 5.14 to 6.06 GHz. In the second example, the 3-dB fractional bandwidth of the low and high bands is 9.9% and 7.9%, respectively. The return losses are larger than 10 dB from 3.37 to 3.64 and 5.27 to 5.62 GHz. The sizes of the proposed filters are nearly half as small as those of the filters presented before. All the studies are completed on a computer with a 2.4-GHz microprocessor, and the computing time of two examples is 6 and 3 min, respectively

Design of Matching Circuits for Microstrip Triplexers Based on Stepped-Impedance Resonators

New matching circuits for microstrip triplexers are proposed based on half-wavelength tapped-connected (or fed) stepped-impedance resonators. The stepped-impedance resonators play important roles for the matching circuits, either to serve as a through pass at the center frequency of a bandpass filter or to provide a short circuit at the center frequency of another bandpass filter. First, three tapped-connected stepped-impedance resonators together with suitable branch transmission lines are utilized to develop the matching circuits for a microstrip triplexer. The design procedure for these matching circuits is much simpler than that for the conventional triplexer structures due to the use of tapped-connected stepped-impedance resonators. Second, to reduce the number of stepped-impedance resonators and to improve the spurious resonances associated with the proposed matching circuits, modified matching circuits for the triplexer are also proposed. Agreement between measured and simulated results is observed and supports the usefulness of the design procedure

A microstrip three-port and four-channel multiplexer for WLAN and UWB coexistence

This paper proposes a microstrip three-port four-channel multiplexer for wireless systems where wireless local area network (WLAN) and ultra-wideband (UWB) coexist. The proposed multiplexer has two channels, from 2.15 to 2.89 GHz and from 5.13 to 5.84 GHz, for WLAN and two channels, from 3.22 to 4.83 GHz and from 6.07 to 8.22 GHz, for UWB. The measured scattering parameters agree well with the simulations. To determine a proper circuit topology and overcome the interference problems between ports, the genetic algorithm (GA) technique is exploited. The GA search takes approximately 3 min on a personal computer with a 2.4-GHz microprocessor. Additionally, the analysis of the circuit behaviors, the problem on the size of the multiplexer, and the isolation issues between WLAN and UWB ports are discussed.

Slot Antennas With an Extended Ground for Multiple-Antenna Systems in Compact Wireless Devices

In this letter, new slot antennas with an extended ground are proposed. They are easily built as internal antennas in a compact wireless device. Originated from lambda/4 slot antennas, an additional vertical L-shaped metallic sheet as an extended ground and a main radiator is added to reduce the antenna size. The sheet is designed close to a ground plane, and its height can be chosen according to the available space of a given device. These features offer more design flexibility for antenna and mechanical engineers. In this letter, antennas for WLAN are designed and implemented as examples, and a four-element antenna design using the resultant antennas is demonstrated, showing that the multiple-antenna design occupies only a small region in the system board. With these design examples the proposed structures can be a promising solution for multiple-antenna systems in compact wireless devices.

A compact pattern reconfigurable antenna design for handheld wireless devices

A new topology for designing a compact pattern reconfigurable antenna is proposed in this paper. The antenna consists of a right-angled slot, two diodes, two metal patches, control circuits and a feeding microstrip line. To reconfigure the slot, diodes are used to create short circuits across the slot. As one of the diodes is enabled, the antenna behaves like a quarter-wavelength slot antenna. Since the direction of working slot depends on the status of diodes, the antenna radiation patterns can be configured easily. To prove the concept, a 2.4 GHz antenna for WLAN applications is designed, whose size is comparable to a traditional WLAN antenna. The measured and simulated results agree well. Due to the compactness feature, such a design will be a promising solution for handheld wireless devices.

Compact pattern reconfigurable antenna array based on L-Shaped Slots and PIN diodes for adaptive MIMO systems

In this paper a novel reconfigurable antenna array for 2times2 adaptive MIMO systems is proposed. The array is composed of two reconfigurable slot antennas located at upper-right and upper-left corners of a PCB, where each antenna element consists of a right-angled slot, PIN diodes, lumped capacitors, and bias networks. By carefully controlling these diodes, the induced current distribution around the slot can be changed, resulting in different radiation patterns. Owing to the compact size and ease on manufacture, the proposed antennas can be a promising solution for adaptive MIMO systems in handheld devices such as smart phones and notebook computers.

An RFID Antenna design for multi-layered printed circuit board applications

A passive RFID antenna for multi-layered printed circuit board (PCB) is proposed in this paper. At present most conventional RFID tags cannot be easily attached to a PCB, because the complicated metal planes and wires on a PCB may degrade seriously the radiation properties of RFID tags. The deterioration will greatly reduce the available read distance. Therefore, we propose an RFID antenna fabricated on PCB. Two slots are created on the power and ground planes and the RFID chip is connected over the slot on the ground plane. To get better power transmission between an antenna and a chip and to re-radiate back more power, the conjugate matching method is adopted to design the RFID antenna. According to simulation results, the available read distance is about 18 cm and the size is 30 mm by 20 mm. The small size enhances its use in PCB applications.

A miniature, planar, and switched-beam smart antenna employing a four- element slot antenna array for Digital Home applications

In this paper, a miniature, planar, and switched-beam smart antenna is proposed. The antenna mainly comprises of a four-element array with elements based on an L-shaped quarter-wavelength slot antenna and four pin diodes to control the antenna elements. Since the pattern of a radiation element is directional with maximum at a specific direction, we arrange the four antennas with maximum radiation direction toward 0, 90, 180, and 270 degrees, respectively. Consequently, by carefully controlling the diodes, a switchable beam smart antenna can be achieved. To prove the concept, a 2.4 GHz smart antenna is designed. The experimental results fully demonstrate the performance of the proposed antenna. Due to the miniature and planar features, such a design will be a promising solution for digital home applications.

Design of a multifunctional and cost-effective wideband planar antenna array system for multiple wireless applications

In this paper, a new wideband array antenna system for multiple wireless applications is proposed. It is composed of two equispaced four-element arrays, phase shifters, diplexers, and power dividers. The two arrays are interleaved and connected to diplexers and power dividers. The proposed antenna system associated with feeding network and antenna elements can be integrated in a single substrate. Consequently, such a design is with low fabrication and assembly cost and compact size. A wideband antenna array with bandwidth from 2.0 GHz to 6.0 GHz and main beam pointing to 20 degrees is illustrated as an example