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In recent years, the use of Gallium Nitride (GaN) transistors as active device inpower amplifier circuits has increased. The advancement in the technology forsuitable substrate has allowed the use of this very promising material. In this thesis,a Radio Frequency (RF) power amplifier is designed using GaN HEMT fromCree, 4600 Silicon Drive, Durham, North Carolina 27703, USA. The work presentsdetailed theory of amplifier including design and simulation of single and multistageamplifiers with different matching circuits. The design was implementedwith the help of large signal model from Cree. Amplifier presented here is observedto be stable over a frequency range of approximately 400 MHz (2.2GHzto 2.6GHz). Also the harmonics pose problems with power amplifiers. The harmonicscause wastage of power. The second and the third harmonics are givendue consideration because high order harmonics are not so prominent. Also, dueto the harmonic currents, the device gets overheated, and for a power amplifierthe current values would be high enough to pose serious heating problems. Herethe constraints were laid upon 2nd and 3rd harmonics (provided by SAC ISRO),and the simulation results are observed to be in accordance. The output powerachieved is 31.23 dBm (at input power 10 dBm) which shows the gain to be around21 dB even at such high input power level.

In this thesis, an issue of bandwidth is considered in a rectangular dielectric resonator antenna (RDRA). Two techniques (merging of modes and stacking) of bandwidth im- provement are introduced with miniaturized resonator. Single narrowband in RDRA is also introduced and investigated. Dual narrowband is proposed in a L-shaped DRA. It is compact structure as compared to a conventional DRA structure.

This thesis reviews and analyses the designing of wideband low noise amplifier. All the parameters required for designing a low noise amplifier are properly analysed. This thesis includes the design of basic single stage low noise amplifier and later wideband low noise distributed amplifier.The first stage of thesis covers the basics of LNA design and the design of single stage LNA at centre frequency 3.2 GHz. In this device, GaAs pseudomorphic High Electron Mobility Transistor(pHEMT) is used from PH25 process provided by UMS foundry (United Monolithic Semiconductor, Germany). We are using 0.25?m pHEMT technology. This process is suitable to design MMICs. The common-source(CS) topology is used along with inductive source degeneration to combat the noise figure. The results are reported after both circuit and EM simulation.The second stage includes the design of wideband low noise distributed amplifier. This device covers the bandwidth from 1-6 GHz. Distributed amplification wideband technique is used in this device. In this device, four stages are cascaded in parallel. All the components in this device are from D01PH process provided by OMMIC (Ohmic MMIC, France). We are using 0.13?m pHEMT technology. We are getting noise figure less than 2.5dB over entire bandwidth with minimum noise figure of 1.4dB. All the results are reported in this thesis after both circuit and EM simulation.

Estimation of a complex permittivity is achieved using the moment method formulation of electric field integral equation. In addition to numerical results for three dimensional biological bodies, thesis also describes formulation of inverse problem, forward problem and the evaluation of matrix element. For excitation of the 36-cell human body with electric field, short dipole is used as transmitter, which is located in front and back side of the body. Thus, electric field at cell centroid locations are calculated using near field equation and electric field at N receiving dipole locations are stimulated using MAT LAB and thus complex permittivity are estimated from the inverse problem. This procedure is an ideal approach. But, in practical scenario, random and systematic errors occur which cannot be calculated in stimulation. Hence, it is taken into consideration by addition of Gaussian error to the received electric field at the receiver locations. Due to this process, error in the complex permittivity of a buried cells occurs in a large amount. Hence, multiple view technique is introduced in order to obtain the reduction in the error of complex permittivity of buried cells.

Wireless communication play a imported role in our daily life. Present scenario of communication, all wired ones becoming as wireless. So, to achieve efficient and affordable communication in wireless technology, compact and efficient radiators are required. One of the efficient radiators is dielectric resonator antenna (DRA). Almost all the applied power will be lost in the radiated fields only, with this attractive feature DRAs become popular in wireless communication field at microwave frequencies. At high frequency, patch and other metallic antennas have significant amount of energy losses due to conductor which cannot be negligible. Generally, dielectric Resonator antennas have more attractive features compared to general microstrip patch antennas because of absence of conductor material in DR antennas. Dielectric resonating antenna uses a basic type of cavity resonator. It uses various combinations of dielectric materials, different and varied shapes of conducting material, various coupling techniques to produce the desired radiation pattern. In this thesis, DR antenna array is designed with microstrip feed, using High Frequency Simulation Software (HFSS) version 14. The basic design of first antenna which was to be used as a test case for validation of results obtained by the antenna designed in software from a real data set. The second and third antenna which was designed was based on 6.2 GHz band. Its design parameters had two element array mechanisms with dielectric resonator incorporated in every single element separated with a calculated distance to achieve the requisite radiation pattern and desired gain. The only difference was third one was stacked Dielectric Resonator antenna for better coupling and bandwidth improvement purpose. In third arrangement higher permittivity material placed over lower permittivity material because high permittivity material gives better coupling results and low permittivity material gives better Bandwidth.

Meta materials are artificially designed materials that exhibit very high transmission values within a frequency range. Double Negative (DNG) Meta material shows both negative permittivity and negative permeability within a certain frequency range. It is composed by an array of Split Ring Resonators (SRRs) and an array of Capacitive Loaded Strips (CLSs). This paper presents the design of a new meta material structure. As compared to conventional Double Negative Metamaterial in Reference[3], the size of the new structure is 70% reduced and hence this leads to a size miniaturization in various meta material applications specially in antenna application. It can also be used in very high frequency applications, as its operating frequency is considerably high (30-40 GHz). Both the conventional and new metamaterial structure is simulated by CST Microwave Studio. In the metamaterial structure, dimensions has been varied many times and simulated in CST to observe the behavior of meta material and also theoretical explanations have been given for the observed shift in resonance frequency.