Design And Analysis Of Adaptive And Reconfigurable Antennas For Wireless Communication

Modern radar and communication systems have experienced a tremendous increase in the number of antennas onboard, on the ground, and in orbital space. This places a burden due to the confined volume and limited weight requirements especially in space applications. The reconfigurable antenna is a promising and exciting new type of antenna, where through the use of appropriate switches the antenna can be structurally reconfigured, to maintain the elements near their resonant dimensions for several frequency bands. This increases the bandwidth of the antenna dramatically, which enables the use of one antenna for several applications. Four novel reconfigurable antenna elements were designed to work at 2.45 GHz and at 5.78 GHz, to cover the transition period when wireless communication will shift to the 5.78 GHz band. The four elements designed are: the reconfigurable Yagi, the reconfigurable corner-fed triangular loop antenna, the reconfigurable center-fed equilateral triangular loop antenna and the reconfigurable rectangular-spiral antenna. None of these antennas have been reported in the literature. Simulation results for all four antennas were obtained using IE3D. Fabrication and measurements for the Yagi antenna was done and the measured results agree with simulations. All four antennas have very good performance with respect to the 3dB beamwidth and directivity. However the reconfigurable rectangular-spiral antenna is the most compact in size among all four antennas. It is (20 mm x 20 mm) in size. At 2.45 GHz it has a 3dB beamwidth of 87° and directivity of 6.47dB. As for the 5.78GHz frequency the 3dB beamwidth is 82.5° and the directivity is 7.16dB. This dissertation also introduces the use of reconfigurable antenna elements in adaptive arrays. An adaptive array that can null interference and direct its main lobe to the desired signal while being reconfigurable to maintain functionality at several frequency bands has the potential to revolutionize wireless communications in the future. Through several examples, at both the design frequencies, it is shown that the reconfigurable and adaptive antenna arrays are successful in nulling noises incident on the array. These examples illustrate how reconfigurable elements and adaptive arrays can be combined very beneficially for use in wireless communication systems

RF-MEMS switches for a full control of the propagating modes in uniplanar microwave circuits and their application to reconfigurable multimodal microwave filters

This is a copy of the author 's final draft version of an article published in the journal Microsystem technologies. The final publication is available at Springer via http://dx.doi.org/10.1007/s00542-017-3379-8In this paper, new RF-MEMS switch configurations are proposed to enable control of the propagating (even and odd) modes in multimodal CPW transmission structures. Specifically, a switchable air bridge (a switchable short-circuit for the CPW odd mode) and switchable asymmetric shunt impedances (for transferring energy between modes) are studied and implemented using bridge-type and cantilever-type ohmic-contact switches, respectively. The switchable air bridge is based in a novel double ohmic-contact bridge-type structure. Optimized-shape suspension configurations, namely folded-beam or diagonal-beam for bridge-type switches, and straight-shaped or semicircular-shaped for cantilever-type switches, are used to obtain robust structures against fabrication-stress gradients. The switches are modelled using a coupled-field 3D finite-element mechanical analysis showing a low to moderate pull-in voltage. The fabricated switches are experimentally characterized using S-parameter and DC measurements. The measured pull-in voltages agree well with the simulated values. From S-parameter measurements, an electrical model with a very good agreement for both switch states (ON and OFF) has been obtained. The model is used in the design of reconfigurable CPW multimodal microwave filters.Peer ReviewedPostprint (author's final draft

Effect of PIN Diode Integration on Patch Antennas for Frequency Reconfigurable Antenna Applications

PIN diodes are commonly used to design reconfigurable antennas owing to their sufficient isolation, lower cost, and ease of fabrication. This study aims to explore the effect of biasing conditions of a PIN diode radio frequency (RF) switch on a frequency-reconfigurable antenna. This approach investigates the contribution of the forward diode current and the reversed biased voltage on the shift in the operating band, the impedance matching, and the radiation efficiency of a reconfigurable antenna. The benefits and drawbacks of different approaches to modeling PIN diode RF switches are demonstrated on Ansys electromagnetic switch. The result shows a significant match between simulated and measured operating bands, impedance matching, and radiation efficiency. The proposed RF switch model can be used as a practical simulation model for implementing various reconfigurable microwave components

WIRELESS ANTENNA MULTIPLEXING USING TUNABLE ANTENNA FOR SPACE APPLICATIONS

Recent development in communication technologies shifts the communication paradigm from point to point to multi-user wireless systems. These developments eased the use of mobile telephone, satellite services, 5G cellular, smart application, and the Internet of Things. The proliferation of mobile devices has necessitated an elaborate mechanism to serve multiple users over a shared communication medium, and a multiplexing approach is introduced to serve this purpose. Multiplexing refers to a method that aims at combining multiple signals into one signal such that each user would be able to extract its desired data upon receiving the multiplexed signal. This spectrum sharing allows wireless operators to maximize the use of their spectrum to accommodate a large number of users over fewer channels. In Space applications, where sensors like temperature, attitude, IR, Magnetic, etc. send information using antennas operate at a different frequency, there is a need to collect all or some of these data using a single device. A wideband antenna requires a filtering process in order to remove unwanted signals that lead to a complex circuit design. Furthermore, the use of multiple antennas ends up with a larger size and additional complexity. Therefore, the tunable antenna is an excellent candidate which provides a perfect solution for such scenarios. A tunable antenna whose frequency characteristics shifted by applying tuning action can be used to operate as a multiplexing device that can collect signals from different surrounding antennas; each operates at a fixed frequency. A system architecture for wireless multiplexing using a tunable antenna is proposed in this project. An electronically tunable antenna using varactor diode as a tuning element is used as the multiplexing device that can collect signals from different surrounding antennas. The system consists of an RF front end and a control circuit/system for wireless multiplexing. The RF front end consists of a tunable antenna, tunable phase shifter, tunable bandpass filter, low noise amplifier, mixer, voltage-controlled oscillator, and an intermediate frequency filter. The control unit comprises a microcontroller, DAC, CMOS oscillator, power module, and a USB interface for communication with custom-built software installed on a PC. The device has functions for control, digital signal processing, and de-multiplexing. The device is fed with an input multiplexed signal, and the de-multiplexed output signals are extracted and displayed on the graphical user interface of the software. Due to the reconfigurability and programmability of the device, it presents a flexible, cost-effective solution for a variety of real-world applications

MEMS switches having non-metallic crossbeams

A RF MEMS switch comprising a crossbeam of SiC, supported by at least one leg above a substrate and above a plurality of transmission lines forming a CPW. Bias is provided by at least one layer of metal disposed on a top surface of the SiC crossbeam, such as a layer of chromium followed by a layer of gold, and extending beyond the switch to a biasing pad on the substrate. The switch utilizes stress and conductivity-controlled non-metallic thin cantilevers or bridges, thereby improving the RF characteristics and operational reliability of the switch. The switch can be fabricated with conventional silicon integrated circuit (IC) processing techniques. The design of the switch is very versatile and can be implemented in many transmission line mediums

Multi-Functional Reconfigurable Antenna Development by Multi-Objective Optimization

This dissertation work builds upon the theoretical and experimental studies of radio frequency micro- and nano-electromechanical systems (RF M/NEMS) integrated multifunctional reconfigurable antennas (MRAs). This work focuses on three MRAs with an emphasis on a wireless local area network (WLAN), 5-6 GHz, beam tilt, and polarization reconfigurable parasitic layer-based MRA with inset micro-strip feed. The other two antennas are an X band (8-12 GHz) beam steering MRA with aperture-coupled micro-strip fed and wireless personal area network (WPAN), 60 GHz, inset micro-strip fed MRA for dual frequency and dual polarization operations. For the WLAN (5-6 GHz) MRA, a detailed description of the design methodology, which is based on the joint utilization of electromagnetic (EM) full-wave analysis and multi-objective genetic algorithm, and fundamental theoretical background of parasitic layer-based antennas are given. Various prototypes of this MRA have been fabricated and measured. The measured and simulated results for both impedance and radiation characteristics are given. The work on the MRAs operating in the X band and 60 GHz region focuses on the theoretical aspects of the designs. Different than the WLAN MRA, which uses inset fed structure, the aperture-coupled feed mechanism has been investigated with the goal of improving the bandwidth and beam-tilt capabilities of these MRAs. The simulated results are provided and the working mechanisms are described. The results show that the aperture-coupled feed mechanism is advantageous both in terms of enhanced bandwidth and beam-steering capabilities. Finally, this dissertation work concludes with plans for future work, which will build upon the findings and the results presented herein