Design of low profile planar antennas incorporating electromagnetic ancillary structures for diversified applications

Abstract

With the growing trend of miniaturisation in personal communication systems, the need for multi band compact antennas is on a rise. The development of modern planar microstrip antenna designs have resulted in replacement of conventional antennas in many applications. But the presentday communication systems require compact and high-performance antennas which cannot be catered by simple microstrip based designs. Many new technologies have emerged in the modern antenna design arena and one exciting breakthrough is the development of electromagnetic ancillary structures. This thesis focus on the design and development of low profile compact planar antennas incorporating electromagnetic ancillary structures for diversified applications. Simple design equations are provided for proposed antennas with the required electrical characteristics. The design equations are verified by practical implementation and measurements. One of the investigation involves bandwidth improvement in microstrip antennas by using suitable feeding technique and by adding parasitic elements. A novel design is proposed to increase the bandwidth of a vertical monopole and patch antenna. The vertical monopole antenna is a broadband capacitive coupled fed quarter-wave microstrip antenna mounted on a ground plane operating at 5 GHz (5.180 5.825 GHz) Industrial, Scientific and Medical (ISM) radio band. The proposed antenna is a compact structure as the length of the antenna is half the length of the usual rectangular microstrip antenna and it provides 1 GHz bandwidth (5.4 6.4 GHz). The bandwidth is improved when parasitic elements are added with the monopole antenna and a large impedance bandwidth of about 3 GHz (5.1 8.1 GHz), which is three- fold improvement over the one without parasitic patches is observed. The prototype of the antenna that operates at 5.8 GHz frequency range is fabricated and characterized using a near-field measurement system. A good agreement is found between the simulation and measured results. The microstrip patch antenna with the capacitive feed is developed for analysing parasitic patches for bandwidth improvement and it provides a -10dB bandwidth of 410 MHz which is 130 MHz greater than the antenna with embedded air cavity. These novel antennas are truly compact and hence finds applications where small-sized antennas with wider bandwidths are needed. Subsequently, a Coplanar Waveguide (CPW) fed dual band antenna is examined with Defected Ground Structure (DGS) for notching applications. The proposed antenna comprises of a tapered ring radiator and two half-dumbbell- shaped slots in the ground plane, producing dual band notch features. By adjusting the position of the dumbbell slots in the ground plane, two distinct notching bands with bandwidths of 400 MHz and 1200 MHz are achieved around 2.5 GHz and 4.5 GHz. The measured results indicate that the Omni- directional radiation pattern with a significant gain of 2.4 dB and 3.5 dB over the operating bands. newline