PhD Theses

Permanent URI for this collectionhttp://drsr.daiict.ac.in/handle/123456789/2

Browse

Subject: search.filters.subject.Microstrip antennas

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Compact Circularly Polarized Tri-, Dual- and Single-Band Dielectric Resonator Antennas
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2021) Chaudhary, Pankaj Prabhubhai; Ghodgaonkar, Deepak K.; Gupta, Sanjeev
    The Dielectric Resonator Antennas (DRAs) have received wide attention due to low loss, high radiation efficiency, small size, wider bandwidth and simple feed network as compared to the microstrip antennas. Microstrip antennas have many challenges such as low radiation efficiency, high conductor loss, poor polarization purity, multiple frequency bands and multiple polarizations with a large footprint area of the antenna, low gain and narrow bandwidth. The existing design techniques for tri-, dual- and single-band DRAs reported in the literature have various limitations such as ground plane area of DRA, volume of Dielectric Resonator (DR) and DRA not sufficient for small physical area applications, realization of Circular Polarization (CP) over large ground plane area and unavailability of single DR geometry with multi-mode for multi-band applications. In this thesis, compact CP tri-band (L5, L1 and S-bands) staired Rectangular Dielectric Resonator Antennas (RDRAs) (two port, single port) using tri-, dualand single-sections Wilkinson Power Dividers (WPDs) with wide-band 90◦ phase shifters are designed, analyzed, fabricated and tested. These tri-band RDRAs are used in Indian Regional Navigation Satellite System (IRNSS) and GPS-Aided GEO Augmented Navigation (GAGAN) applications. The ground plane footprint areas of tri-band RDRAs and volumes of staired Rectangular Dielectric Resonators (RDRs) are significantly reduced by using high dielectric constant of DR materials and high dielectric constant of dielectric substrates. The broadside radiation patterns of triband RDRAs are produced by TEy 111, TEy 113 and TEy 112 modes for L5, L1 and S-bands, respectively. Various parameters of tri-band RDRAs like return loss, Right Hand Circularly Polarized (RHCP) - Left Hand Circularly Polarized (LHCP) radiation patterns, RHCP gains and axial ratios are analyzed and measured. Compact CP dual-(L5 and L1) and single-band RDRAs are designed, analyzed, fabricated and tested using feed networks of dual- and single-sections WPDs with wide-band 90◦ phase shifters. The miniaturized volumes of RDRs and ground plane areas of dual- and single-bands RDRAs are achieved using high dielectric constant of DR materials and high dielectric constant of dielectric substrates. The broadside radiation patterns of dual-band RDRA are produced by TEy 111 and TEy 113 modes for L5 and L1-bands, respectively. The TEy 111 modes are produced in three single-band RDRAs for L5, L1 and S-bands. The simulated and measured parameters of dualand single-band RDRAs are return loss, RHCP-LHCP far field radiation patterns, RHCP gain and axial ratio. The design and analysis of finite ground plane single-band CP RDRAs using WPD with wide-band 90◦ phase shifter for L1 and L5-bands are carried out by using high dielectric constant of DRs and dielectric substrates. Also, the effect of different radii of finite circular ground planes of single- and dual-band RDRAs are investigated by using the Method of Moments (MoM). The effect of different radii of circular ground plane on single- and dual-band RDRAs are analyzed for return loss and gains.
  • Thumbnail Image
    ItemOpen Access
    Broadband microstrip antennas with switchable polarizations
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2010) Bombale, Uttam Laxmanrao; Gupta, Sanjeev
    Microstrip antenna consists of a patch of metallization on grounded substrate. These are low profile, lightweight antennas, most suitable for aerospace and mobile application. They are replacing many conventional antennas used in defense and commercial applications. They have got certain drawbacks such as narrow bandwidth, low gain, and low power handling capability and polarization impurity. Many researchers are trying to overcome these drawbacks. In this thesis also some efforts have been done to overcome certain drawbacks of microstrip antenna. One of the serious limitations of the microstrip antennas is its narrow bandwidth. The impedance bandwidth of MSA is around 1% only for thin substrates. The bandwidth of the MSA can be increased by increasing thickness of the substrate. If the thickness is increased it creates problems for impedance matching, produces radiations from the feed and distortions in the radiation patterns due to higher order modes. Therefore to avoid these problems thicker substrate is not used. The common techniques to improve bandwidth are Planner multiresonator configurations, Electromagnetically coupled MSA; Aperture coupled MSAs, Impedance matching networks for broad band MSAs & Log periodic MSA configurations. It is advantageous to use Electromagnetically coupled MSA because of its small size and no back radiations. Therefore Electromagnetically coupled MSA is used to design the antenna. The MSA gives linear polarization. Many times we need circular polarization with low cross polar level (generally below 10-12 dB). This circular polarization is obtained in this antenna using a shorting pin. This is the major achievement. Many papers discuss about bandwidth only, a few papers discuss just about polarizations using shorting pins. Many times we need large bandwidth, desired polarization and high gain. In order to obtain high gain we have to form an array of antennas. It is convenient to feed the array elements using microstrip feed. Therefore the Electromagnetically coupled MSA is fed using a microstrip line as described in chapter 4. Some times we need right circular or left circular or linear polarization depending on situation. These polarizations can be obtained using two shorting pins instead of one as described in chapter 4. In satellite TV transmission vertical and horizontal polarizations (Eθ and EФ) are used. In order to minimize adjacent channel interference they are placed alternately on vertical and horizontal polarizations. These additional Eθ, EФ polarizations as well as RHCP and LHCP are obtained using additional shorting pins as described in chapter 4. for satellite TV transmission we need high gain around 30 dB. This can be obtained using an array of above elements. The design is given in chapter 4. Various feeding techniques, transmission lines, bends, power dividers and quarter wave transformers are discussed. Spacefed microstrip antennas are also designed, simulated and studied in chapter 5. Recently fractal antennas are becoming very popular because of their small size, multiband response and high efficiency. The basic types of fractal antennas are designed and simulated in chapter 6. Bandwidth is the major problem in microstrip antennas. In chapter 7, it is discussed how do we get large bandwidth, and the concept is used to obtain very large or ultra-wide bandwidth using rectangular microstrip antenna. The same concept is used to obtain very large bandwidth using sierpinski fractal antennas.