This communication presents a new antenna system designed for cognitive radio applications. The antenna structure consists of a UWB antenna and a frequency reconfigurable antenna system. The UWB antenna scans the channel to discover “white space” frequency bands while tuning the reconfigurable section to communicate within these bands. The frequency agility is achieved via a rotational motion of the antenna patch. The rotation is controlled by a stepper motor mounted on the back of the antenna structure. The motor's rotational motion is controlled by LABVIEW on a computer connected to the motor through its parallel port. The computer's parallel port is connected to a NPN Darlington array that is used to drive the stepper motor. The antenna has been simulated with the driving motor being taken into consideration. A good agreement is found between the simulated and the measured antenna radiation properties.

Implementation of a Cognitive Radio Front-End Using Rotatable Controlled Reconfigurable Antennas

A novel design for a beam-switching antenna using active cylindrical slot frequency selective surface (ACSFSS) is presented. The antenna system is composed of an omnidirectional monopole antenna and the ACSFSS, which employs a new technique of switching slot arrays. The ACSFSS is made up of 12 columns with 8 slots each, dividing the cylinder by 30 $^{\circ}$ . To steer the beam of the antenna the diodes are set off and on, so that the radiation pattern of the antenna is determined by the number of off state columns. To estimate the general dimension of the cylindrical FSS, an equivalent metallic reflector is introduced and optimized, and then parametric studies for the unit cell dimensions are discussed. The fabricated prototype works within the WLAN band, centered around 2.45 GHz, and can agilely select either a narrow-beam or wide-beam operating mode. Simulation and measurements confirm the operation of the ACSFSS antenna, with good matching and gain observed. In particular, the narrow-beam mode $-$ 3 dB beamwidth is 47 $^{\circ}$ which offers enhanced angular resolution compared with other reported beam-sweeping work.

Cylindrical Slot FSS Configuration for Beam-Switching Applications

A frequency-reconfigurable microstrip patch switchable to slot antenna is proposed. The antenna is capable of frequency switching at nine different frequency bands between 1.98 and 3.59 GHz. The patch is resonating at 3.59 GHz, while the slot produces eight different operating frequencies between 1.98 and 3.41 GHz. Five RF p-i-n diode switches are positioned in the slot to achieve frequency reconfigurability. Simulated and measured results are used to demonstrate the performance of the antenna. The simulated and measured return losses, together with the radiation patterns, are presented.

Frequency-Reconfigurable Microstrip Patch-Slot Antenna

The design of a novel partially reflective surface (PRS) antenna with the capability of beam steering is presented in this paper. The beam steering is realized by employing a reconfigurable PRS structure to achieve a changeable reflection phase as well as using a phased array as the source to excite the PRS antenna. A prototype antenna including the biasing network is fabricated and measured. It achieves a consistent beam steering from – 15° to 15° with respect to the broadside direction across an overlapped frequency range from 5.5 to 5.7 GHz with measured realized gains over 12 dBi. Good agreement between the simulated and measured results for the input reflection coefficients and radiation patterns is achieved, which validates the feasibility of the design principle. Compared with other beam steering PRS antennas, the proposed one enables a larger beam steering angle with comparable gains, requires a simpler biasing network, and is more compact.

A Reconfigurable Partially Reflective Surface (PRS) Antenna for Beam Steering

In this paper, we propose a paper-based pattern switchable antenna system using inkjet-printing technology for bi-direction sensor applications. The proposed antenna system is composed of two directional bow-tie antennas and a switching network. The switching network consists of a single-pole-double-throw (SPDT) switch and a balun element. A double-sided parallel-strip line (DSPSL) is employed to convert the unbalanced microstrip mode to the balanced strip mode. Two directional bow-tie antennas have different radiation patterns because of the different orientation of the reflectors and antennas. It is demonstrated from electromagnetic (EM) simulation and measurement that the radiation patterns of the proposed antenna are successfully switched by the SPDT switch.

https://www.mdpi.com/1424-8220/15/12/29851/pdf

Pattern Switchable Antenna System Using Inkjet-Printed Directional Bow-Tie for Bi-Direction Sensing Applications

A basic antenna structure to design pattern and pattern/frequency reconfigurable antennas is proposed. The structure consists of an L-shaped slot, PIN diodes, lumped capacitors and bias networks. The PIN diodes and the lumped capacitors located at specific positions are used to create short circuits across the slot. By carefully controlling these diodes, the induced current distribution around the slot can be changed, resulting in different antenna radiation patterns. Thus, a pattern reconfigurable antenna can be achieved. The proposed structure is then extended to design frequency/pattern reconfigurable antennas by introducing varactor diodes. Two compact reconfigurable antennas based on the proposed structure are designed and implemented to prove the design concepts. The experiment results fully demonstrated the performances of the proposed designs. Owing to the compact size and ease on manufacture, the proposed structure can be a promising solution in compact wireless devices such as smart phones and notebook computers.

Design of reconfigurable antennas based on an L-shaped slot and PIN diodes for compact wireless devices

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.

/pdf/compact-switched-beam-antenna-employing-a-four-element-slot-232uso49ef.pdf

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

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.

A compact pattern reconfigurable antenna design for handheld wireless devices

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.

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

Jung-Chin Hsieh

Papers

Design of reconfigurable antennas based on an L-shaped slot and PIN diodes for compact wireless devices

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

A compact pattern reconfigurable antenna design for handheld wireless devices

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

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