Investigations on Reconfigurable Planar Antennas and Devices

Abstract

In this growing technological trend, there always has been a requirement of multifunctional wireless devices which can provide all-around connectivity with assorted entertaining
features. To incorporate different features in these devices, multiple radios are integrated into a single wireless platform which increases the density and complexity of hardware following Moore’slaw. Along with multiband wireless support, the requirement of enhanced
signal quality at diverse climatic conditions for stability of connectivity and high data-rate adjoin more complications to the radio frequency (RF) end terminals. Therefore, the antenna reconfigurability approach has become the principal attraction for all researchers which is considered as one of the best ways to overcome the above-discussed problems. In other words, it can be said that reconfigurability has become salient and most desired attribute for state-of-the-art RF systems used in wireless and satellite communications, imaging and sensing.

This dissertation is aimed at building new design methodologies about multifunctional
antennas/microwave devices to overcome the above-discussed challenges as well as enhance overall microwave system performance by proposing new structures and setups.

In this research work, the design of a frequency reconfigurable square shaped microstrip antenna with an ability to provide both right and left hand circularly polarized radiation (RHCP and LHCP) is investigated. The frequency tuning and radiation characteristics of
the antenna are evaluated by a mathematical modelling, full-wave analysis as well as its physical measurement. The antenna generates very consistent circularly polarized radiation patterns with a wide 3 dB beamwidth of 150◦ ( for both LHCP & RHCP) at all the tunable bands within 1.98 GHz-2.44 GHz. The antenna shows a maximum realized gain of 2.2 dBc at 2.43 GHz and has a very wide CP bandwidth (21%) which is the same as its total tunable range.

A frequency, circular polarization as well as pattern reconfigurable microstrip triangular patch array is introduced in this research work which can withstand both spectrum and climatic or orientation based signal quality concerns. From physical measurement, it is found that the operating frequency of the antenna can be altered between 1.97 GHz to 2.54 GHz (25.3% tunable bandwidth). Investigation confirms that the antenna produces both
types of CP radiation with minimum axial ratio of 0.98 dB and beamwidth >24◦ at all tunable frequency bands using the proposed feed network. In pattern reconfiguring mode,
antenna pattern can also be rotated at 120◦ angle in the complete azimuth plane at different frequencies.

This thesis also describes a wideband (2.7 GHz-4.0 GHz) cylindrical dielectric resonator antenna (DRA) array with four types of polarization variability. Full-wave analysis of the antenna was carried out using the simulated and measured responses of the phase shifting cum switching network. From the analysis, it is revealed that the antenna shows a wide axial ratio bandwidth of 39% and 19.4% when operated in LHCP and RHCP mode respectively. It is also verified that the antenna can be fairly operated in horizontal and vertical linear polarization mode within the whole bandwidth of 39%. During the CP modes, the antenna
shows the maximum realized gain value of 9.95 dBc whereas, in LP modes, it has a maximum gain value of 9.75 dB.

At the end of this research work, an active elements based wideband frequency reconfigurable rat-race hybrid is presented which has many attractive characteristics like
wide operational bandwidth of 68.4%, smaller size (30% of conventional design), insertion loss of 4.8 dB, maximum amplitude imbalance of 0.4 dB, maximum phase imbalance of 5◦
and ease of design. The device performances are evaluated from mathematical modeling, full-wave analysis, as well as physical measurement and it is found that the device is a good candidate to challenge today’s multifunctional requirements.