Bedri A. Cetiner

Integrated Bluetooth and UWB Antenna

A small-sized, low-profile, and planar integrated Bluetooth and ultrawideband (UWB) antenna is presented. The antenna exhibits a dual-band operation covering 2400-2484 MHz (Bluetooth) and 3100-10600 MHz (UWB) frequency bands. It is fed by a microstrip line and built on a FR-4 substrate with 42times46 mm2 surface area. The impedance, radiation, phase linearity, and impulse response properties of the antenna are studied both theoretically and experimentally. The calculated and measured results agree well. The antenna shows acceptable gain flatness with stable omnidirectional radiation patterns across the integrated Bluetooth and UWB bands. The average group delay is approximately 0.2 ns across UWB frequencies. The impulse response is very good, with some level of ringing observed.

A MIMO System With Multifunctional Reconfigurable Antennas

A multiple-input-multiple-output (MIMO) system equipped with a new class of antenna arrays, henceforth referred to as multifunction reconfigurable antenna arrays (MRAAs), is investigated. The elements of MRAA, i.e., multifunction reconfigurable antennas (MRAs) presented in this work are capable of dynamically changing the sense of polarization of the radiated field thereby providing two reconfigurable modes of operation, i.e., polarization diversity and space diversity. The transmission signaling scheme can also be switched between transmit diversity (TD) and spatial multiplexing (SM). The results show that the reconfigurable modes of operation of an MRAA used in conjunction with adaptive space-time modulation techniques provide additional degrees of freedom to the current adaptive MIMO systems, resulting in more robust system in terms of quality, capacity and reliability. A performance gain up to 30 dB is possible with the proposed system over conventional fixed antenna MIMO systems depending on the channel conditions

RF MEMS Integrated Frequency Reconfigurable Annular Slot Antenna

A new kind of double- and single-arm cantilever type DC-contact RF MEMS actuators has been monolithically integrated with an antenna architecture to develop a frequency reconfigurable antenna. The design, microfabrication, and characterization of this ¿reconfigurable antenna (RA) annular slot¿ which was built on a microwave laminate TMM10i ( ¿r = 9.8, tan ¿ = 0.002), are presented in this paper. By activating/deactivating the RF MEMS actuators, which are strategically located within the antenna geometry and microstrip feed line, the operating frequency band is changed. The RA annular slot has two reconfigurable frequencies of operation with center frequencies f low = 2.4 GHz and f high = 5.2 GHz, compatible with IEEE 802.11 WLAN standards. The radiation and impedance characteristics of the antenna along with the RF performance of individual actuators are presented and discussed.

Circular Beam-Steering Reconfigurable Antenna With Liquid Metal Parasitics

A novel antenna reconfiguration mechanism based on the displacement of liquid metal sections is presented. The liquid nature of the moving parts of the antenna helps avoid the main disadvantage of mechanically-actuated reconfigurable antennas which is the mechanical failure of their solid parts due to material fatigue, creep or wear. Furthermore, the displacement of liquid elements can be more effectively performed than in the case of solid materials by applying precise microfluidic techniques such as continuous-flow pumping or electrowetting. The reconfiguration mechanism is demonstrated through the design, fabrication and measurement of a radiation pattern reconfigurable antenna. This antenna operates at 1800 MHz with 4.0% bandwidth and is capable of performing beam-steering over a 360° range with fine tuning. The antenna is a novel circular Yagi-Uda array, where the movable parasitic director and reflector elements are implemented by liquid metal mercury (Hg). The parasitics are placed and rotated in a circular microfluidic channel around the driven element by means of a flow generated and controlled by a piezoelectric micropump. The measured results demonstrate good performance and the applicability of the microfluidic system.

Frequency, Radiation Pattern and Polarization Reconfigurable Antenna Using a Parasitic Pixel Layer

This communication presents a reconfigurable antenna capable of independently reconfiguring the operating frequency, radiation pattern and polarization. A switched grid of small metallic patches, known as pixel surface, is used as a parasitic layer to provide reconfiguration capabilities to existing antennas acting as driven element. The parasitic pixel layer presents advantages such as low profile, integrability and cost-effective fabrication. A fully operational prototype has been designed, fabricated and its compound reconfiguration capabilities have been characterized. The prototype combines a patch antenna and a parasitic pixel surface consisting of 6 × 6 pixels, with an overall size of 0.6 λ×0.6 λ and 60 PIN-diode switches. The antenna simultaneously tunes its operation frequency over a 25% frequency range, steers the radiation beam over ±30° in E and H-planes, and switches between four different polarizations (x̂, ŷ, LHCP, RHCP). The average antenna gain among the different parameter combinations is 4 dB, reaching 6-7 dB for the most advantageous combinations. The distance between the driven and the parasitic layers determines the tradeoff between frequency tuning range (12% to 25%) and radiation efficiency (45% to 55%).

A Parasitic Layer-Based Reconfigurable Antenna Design by Multi-Objective Optimization

A parasitic layer-based multifunctional reconfigurable antenna (MRA) design based on multi-objective genetic algorithm optimization used in conjunction with full-wave EM analysis is presented. The MRA is capable of steering its beam into three different directions (θi = -30°, 0°, 30°) simultaneously with polarization reconfigurability (Pj = Linear, Circular) having six different modes of operation. The MRA consists of a driven microstrip-fed patch element and a reconfigurable parasitic layer, and is designed to be compatible with IEEE-802.11 WLAN standards (5-6 GHz range). The parasitic layer is placed on top of the driven patch. The upper surface of the parasitic layer has a grid of 5 5 electrically small rectangular-shaped metallic pixels, i.e., reconfigurable parasitic pixel surface. The EM energy from the driven patch element couples to the reconfigurable parasitic pixel surface by mutual coupling. The adjacent pixels are connected/disconnected by means of switching, thereby changing the geometry of pixel surface, which in turn changes the current distribution over the parasitic layer, results in the desired mode of operation in beam direction and polarization. A prototype of the designed MRA has been fabricated on quartz substrate. The results from simulations and measurements agree well indicating ~8 dB gain in all modes of operation.

A Beam-Steering Reconfigurable Antenna for WLAN Applications

A multifunctional reconfigurable antenna (MRA) capable of operating in nine modes corresponding to nine steerable beam directions in the semisphere space {-30°,0°, 30°}; φ ∈ {0°, 45°, 90°, 135°}) is presented. The MRA consists of an aperture-coupled driven patch antenna with a parasitic layer placed above it. The surface of the parasitic layer has a grid of 3 × 3 electrically-small square-shaped metallic pixels. The adjacent pixels are connected by PIN diode switches with ON/OFF status to change the geometry of the parasitic surface, which in turn changes the current distribution on the antenna, thus provides reconfigurability in beam steering direction. The MRA operates in the IEEE 802.11 frequency band (2.4-2.5 GHz) in each mode of operation. The antenna has been fabricated and measured. The measured and simulated impedance and radiation pattern results agree well indicating an average of ~ 6.5 dB realized gain in all modes of operation. System level experimental performance evaluations have also been performed, where an MRA equipped WLAN platform was tested and characterized in typical indoor environments. The results confirm that the MRA equipped WLAN systems could achieve an average of 6 dB Signal to Noise Ratio (SNR) gain compared to legacy omni-directional antenna equipped systems with minimal training overhead.

Reduced Overhead Training for Multi Reconfigurable Antennas with Beam-Tilting Capability

This paper proposes low overhead training techniques for a wireless communication system equipped with a Multifunctional Reconfigurable Antenna (MRA) capable of dynamically changing beamwidth and beam directions. A novel microelectromechanical system (MEMS) MRA antenna is presented with radiation patterns (generated using complete electromagnetic full-wave analysis) which are used to quantify the communication link performance gains. In particular, it is shown that using the proposed Exhaustive Training at Reduced Frequency (ETRF) consistently results in a reduction in training overhead. It is also demonstrated that further reduction in training overhead is possible using statistical or MUSIC-based training schemes. Bit Error Rate (BER) and capacity simulations are carried out using an MRA, which can tilt its radiation beam into one of Ndir = 4 or 8 directions with variable beamwidth (≈2π/Ndir). The performance of each training scheme is quantified for OFDM systems operating in frequency selective channels with and without Line of Sight (LoS). We observe 6 dB of gain at BER = 10-4 and 6 dB improvement in capacity (at capacity = 6 bits/sec/subcarrier) are achievable for an MRA with Ndir= 8 as compared to omni directional antennas using ETRF scheme in a LoS environment.

Integrated bluetooth and UWB antenna

This paper presents a microstrip-fed integrated bluetooth and ultra-wide band (UWB) antenna that is small, low-profile, and planar. Antenna occupies an area of 42 times 46 (mm) on a printed circuit board (PCB). The design of the antenna is optimized to provide high performance for the operation at 3100-10600 MHz (UWB) and 2400-2484 MHz (bluetooth) bands. The antenna was fabricated and its return loss and radiation patterns were measured and compared to the simulations results showing a good agreement between theoretical and measured results.

A reconfigurable spiral antenna for adaptive MIMO systems

We present a reconfigurable spiral antenna for use in adaptive MIMO systems. The antenna is capable of changing the sense of polarization of the radiated field. It is fabricated by using an RF-MEMS technology compatible with microwave laminate substrates developed within the authors group. The proposed antenna structure is built on a number of rectangular-shaped bent metallic strips interconnected to each other with RF-MEMS actuators. Two senses of polarization, RHCP and LHCP, are achieved by configuring the physical structure of the antenna, that is, by changing the winding sense of the spiral, through judicious activation of MEM actuators. The fabrication process for the monolithic integration of MEM actuators with bent microstrip pixels on RO4003-FR4 microwave laminate substrate is described. The measured and calculated radiation and impedance characteristics of the antenna are given. The operating frequency of the presented antenna design can easily be adjusted to be compatible with popular IEEE networking standards such as 802.11a.