In this paper, the design, analysis, and characterization of reconfigurable antennas based on radio frequency micro-electro-mechanical systems (RF MEMS) operating in the United States' public safety (PS) bands are presented. The design methodology of these antennas, which are different from the normal antenna design, is also reported. In this thesis, two electrically small reconfigurable antenna designs have been presented, with two and three modes of operation, and central frequencies of 718 and 4960 MHz and of 857,809 and 4960 MHz, respectively. The maximum frequency tunable ratio achieved in these designs is 7. The recongurability between the modes is achieved by one and three RF MEMS switches in all three designs. These switches enable a change in the length of the current flow path, thereby changing the resonance frequencies. The measurement results for impedance and radiation characteristics of the fabricated antennas prototypes are also presented, and agree reasonably well with the simulations results from An-soft HFSS.

A compact, frequency-reconfigurable filtenna with sharp out-of-band rejection in both its wideband and continuously tunable narrowband states is presented. It is intended for use in cognitive radio applications. The wideband state is the sensing state and operationally covers 2.35-4.98 GHz. The narrowband states are intended to cover communications within the 3.05-4.39 GHz range, which completely covers the Worldwide Interoperability for Microwave Access (WiMAX) band and the satellite communications C-band. A p-i-n diode is employed to switch between these wide and narrowband operational states. Two varactor diodes are used to shift the operational frequencies continuously among the narrowband states. The filtenna consists of a funnel-shaped monopole augmented with a reconfigurable filter; it has a compact electrical size: 0.235 lambda(L) x 0.392 lambda(L), where the wavelength lambda(L) corresponds to the lower bound of its operational frequencies. The measured reflection coefficients, radiation patterns, and realized gains for both operational states are in good agreement with their simulated values.

Yes / In this paper, we present a simple reconfigurable multiband antenna with two PIN diode switches for WiMAX/WLAN applications. The antenna permits reconfigurable switching in up to ten frequency bands between 2.2 GHz and 6 GHz, with relative impedance bandwidths of around 2.5% and 8%. The proposed antenna has been simulated using CST microwave studio software and fabricated on an FR-4 substrate. It is compact, with an area of 50 × 45 mm2, and has a slotted ground substrate. Both measured and simulated return loss characteristics of the optimized antenna show that it satisfies the requirement of 2.4/5.8 GHz WLAN and 3.5 GHz WiMAX antenna applications. Moreover, there is good agreement between the measured and simulated result in terms of radiation pattern and gain. / Engineering and Physical Science Research Council through Grant EP/E022936A.

No / 5th Generation mobile networks (5G) and mobile communications technologies beyond 2020 will need to be energy aware so as to support services that are likely to be intelligent and bandwidth hungry, as well as to support multi-mode operation (LTE, LTE+, HSDPA, 3G among others) in a HetNet environment. This imposes stringent design requirements on the RF transceiver, a key consumer of power in networks today. This chapter will investigate the key RF subsystems forming part of the 5G RF transceiver, where energy efficiency and full radio flexibility are at the forefront of system design. In particular, we target advanced designs on antenna systems, RF power amplifiers and the challenges facing cross-talk in MIMO architectures.

Research on multiple antenna systems has been a hot topic in recent years due to the demands for higher transmission rate and more reliable link in rich scattering environment in wireless communications. Using multiple antennas at both the transmitter side and the receiver side increases the channel capacity without additional frequency spectrum and transmitted power. However, due to the limited space at the size-limited terminal devices, the most critical problem in designing multiple antennas is the severe mutual coupling among them. The aim of this thesis is to provide compact, decoupled and efficient multiple antenna designs for terminal devices. At the same time, we propose a simple and cost effective method in multiple antenna measurement. All these efforts contribute to the development of terminal devices for the fourth generation wireless communication. The background and theory of multiple antenna systems are introduced first, in which three operating schemes of multiple antenna systems are discussed. Critical factors influencing the performance of multiple antenna systems are also analyzed in details. To design efficient multiple antenna systems in compact terminals, several decoupling methods, including defected ground plane, current localization, orthogonal polarization and decoupling networks, are proposed. The working mechanism and design procedure of each method are introduced, and their effectiveness is compared. Those methods can be applied to most of the terminal antennas, reducing the mutual coupling by at least 6dB. In some special cases, especially for low frequency bands below 1GHz, the chassis of the device itself radiates like an antenna, which complicates the antenna decoupling. Thus, we extend the general decoupling methods to the cases when the chassis is excited. Based on the characteristic mode analysis, three different solutions are provided, i.e., optimizing antenna locations, localizing antenna currents and creating orthogonal modes. These methods are applied to mobile phones, providing a more reliable link and a higher transmission rate, which are evaluated by diversity gain and channel capacity, respectively. In order to measure the performance of multiple antenna systems, it is necessary to obtain the correlation coefficients. However, the traditional measurement technique, which requires the phase and polarization information of the radiation patterns, is very expensive and time consuming. In this thesis, a more practical and convenient method is proposed. Fairly good accuracy is achieved when it is applied to various kinds of antennas. To design a compact and efficient multiple antenna system, besides the reduction of mutual coupling, the performance of each single antenna is also important. The techniques for antenna reconfiguration are demonstrated. Frequency and pattern reconfigurable antennas are constructed, providing more flexibility to multiple antenna systems. / QC 20120604

Recently, reconfigurable antennas have attracted significant interest due to their high adaptation with changing system requirements and environmental conditions. Reconfigurable antennas have the ability to change their radiation pattern, frequency or polarization independently according to the application requirements. In this thesis, three different reconfigurable antenna structures have been designed / beam-steerable meanderline antenna, dual circularly polarized meanderline antenna and dual-frequency slot-dipole array. Traveling wave meanderline antenna arrays are investigated in detail and a beam-steerable traveling wave meanderline antenna array has been introduced for X-band applications. Beam-steering capability of the antenna array has been achieved by loading the antenna elements with varactor diodes. Theoretical analysis and computer simulations of the proposed antenna have been verified with experimental results. Radiation direction of the 8-element meanderline array can be rotated 10&deg / by changing the varactor diode&rsquo / s bias voltage from 0V up to 20V. Also, a polarization-agile meanderline antenna array has been designed and simulated. Polarization of the circularly polarized meanderline array can be altered between right hand circularly polarized and left hand circularly polarized by using RF MEMS switches. The third type of reconfigurable antenna investigated in this thesis is a dual frequency slot-dipole array operating at X- and Ka-band. Electrical length of the slot dipoles has been tuned by using RF MEMS switches. Antenna prototypes have been manufactured for &lsquo / on&rsquo / and &lsquo / off&rsquo / states of RF MEMS switches and it has been shown that the operating frequency can be changed between 10 GHz and 15.4 GHz.