The modified aperture coupled MicroStrip Antenna (MSA) and Planar Inverted F Antenna (PIFA) for mobile applications are studied and presented in this dissertation. The designed antennas are improved multi-band and broad-band characteristics by the modification of radiating elements and/or the ground plane. The novel modified aperture coupling annular-ring antenna fed by stripline is the hybrid structure of the aperture coupling feed MSA and the proximity feed MSA. The proximity feed enable to concentrate the field strength toward the direction of the radiating element and the modified aperture layer contributes to provide the maximum coupling to the radiating element. The measurement bandwidths of the Aperture Coupling Proximity Feed Hybrid MSA #1(ACPF-HMSA#1, design #1) and ACPF-HMSA #2 (design #2) are 185MHz (7%) and 105MHz (4.1%), VSWR in less than 2, respectively. Two layers Planar Inverted F Antenna (PIFA) with the modification of the ground and radiating element was studied. The inserted T-shaped or L-shaped ground and inserted a slot and slits on radiating elements help to adjust the resonant frequencies to the target applications. The result of PIFA #3 (design #3) is presented a significant board-band characteristic on the upper band by 910MHz (from 1.45GHz to 2.36GHz) with VSWR less than 2.5. It covers GPS, DCS, PCS, and UMTS bands. Novel internal loop planar inverted F antennas (L-PIFA) with Inserted Concentrated Annular Rings (ICAR) and Inserted Loop Inductors (ILI) are presented as design #4 (ICAR-L-PIFA #4) and design #5 (ILI-L-PIFA #5), respectively. The simple loop structure consists of a meandered line. It increases the capacitance between adjacent lines. The Inserted annular-rings and loop inductors provide inductance values to the main loop antennas. Therefore, the impedance bandwidth of the design #4 is 570MHz (from 1.69GHz to 2.26GHz) with VSWR less than 2.5. And, the impedance bandwidth of the design #5 is 275MHz (from 1.63GHz to 1.905GHz) and 465MHz (from 2.19GHz to 2.655GHz) with VSWR less than 2.5.

Yes / A compact dielectric resonator antenna for ultra-wideband vehicular communication applications is proposed. Two cylindrical dielectric resonators are asymmetrically located with respect to the center of an offset rectangular coupling aperture, through which they are fed. Optimizing the design parameters results in an impedance bandwidth of 21%, covering the range from 5.9 to 7.32 GHz in the lower-band and a 53% relative bandwidth from 8.72 to 15 GHz in the upper-band. The maximum achieved gain is 12 dBi. Design details of the proposed antenna and the results of both simulations and experiment are presented and discussed.

Yes / A compact dielectric resonator antenna (DRA) for wideband applications is proposed. Two cylindrical dielectric resonators which are asymmetrically located with respect to the center of a rectangular coupling aperture are fed through this aperture. By optimizing the design parameters, an impedance bandwidth of about 29%, covering the frequency range from 9.62 GHz to 12.9 GHz, and a gain of 8 dBi are obtained. Design details of the proposed antenna and the results of both simulation and experiment are presented and discussed.

Several broadband dual-polarized patch antenna designs are presented and studied. Good isolation (< ¡V30 dB) between the two feeding ports of the proposed broadband dual-polarized patch antenna has been obtained. This dissertation reports four different innovative designs. Firstly, a new design of the aperture-coupled patch antenna with modified H-shaped coupling slots for achieving dual-polarized radiation with high isolation over a wide bandwidth is studied. Secondly, Optimized feeding of the dual-polarized aperture-coupled patch antenna with H-shaped coupling slots for achieving highly decoupled feeding ports is experimentally investigated. Thirdly, an aperture-coupled patch antenna with a cross slot for compact dual-polarized operation in the 1800-MHz band suitable for applications in personal communication system is presented. Finally, new designs of the broadband dual-polarized patch antenna with hybrid feeds suitable for DCS base-station application are proposed.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The objective of this thesis is to develop a 9.2 GHz low phase noise oscillator with a cylindrical cavity resonator. A cylindrical metal cavity with air as dielectric was used as a resonator. To minimise the phase noise of the oscillator, the resonator must be designed to have a high Q-factor. A high Q-factor was obtained by designing the resonator to operate in the TE011 mode. A tuning screw was used to tune the resonant frequency without significantly affecting the Q-factor. The tuning screw also separates the resonant frequencies of the degenerate TE011 and TM111 modes. The signal is coupled to the resonator by means of rectangular apertures. The coupling was designed to minimise the phase noise of the oscillator. A dual mode waveguide filter was developed and inserted into the oscillator loop in order to prevent oscillation at unwanted frequencies. Due to the excellent phase noise performance of the oscillator, it was not possible to measure the phase noise directly with the available phase noise meter. A measurement setup using two similar oscillators tuned to oscillate at frequencies differing by about 60 MHz was implemented. The output signals were down-converted to the difference frequency where the phase noise could be measured accurately. The output signal of the oscillator was measured at different locations in the loop and clearly showed that the resonator can be used as a filter to minimise the phase noise. The performance of the oscillators met all expectations. Phase noise levels of -115 dBc/Hz and -146 dBc/Hz were obtained at offset frequencies of 10 and 100 kHz. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om ‘n 9.2 GHz lae faseruis ossillator met 'n silindriese holte resoneerder te ontwikkel. 'n Silindriese metaal golfleier holte met 'n lug diëlektrikum was gebruik as die resoneerder. Om die faseruis van die ossillator te minimeer moet die resoneerder ontwerp word om 'n hoë Q-faktor te hê. Om 'n hoë Q-faktor te behaal was die resoneerder ontwerp om in die TE011 orde te werk. Die resoneerder is toegerus met 'n verstelskroef wat die bedryfsfrekwensie verstel sonder om die belaste Q-faktor aansienlik te beïnvloed. Die verstelskroef skei ook die frekwensie van die degeneratiewe TE011 en TM111 ordes. Drywing word na die resoneerder gekoppel deur middel van reghoekige openinge. Die koppeling is ontwerp om die faseruis van die ossillator te minimeer. 'n Tweede orde dubbelmodes golfleier filter is ontwerp en in die ossillatorlus ingevoeg om ossillasie by ongewenste frekwensies te voorkom. Vanweë die baie lae faseruis van die ossillator was dit nie moontlik om die faseruis direk met die beskikbare faseruismeter te meet nie. 'n Meetopstelling met twee soorgelyke ossillators waarvan die frekwensies met ongeveer 60 MHz verskil is geïmplementeer. Die uittreeseine van die ossillators is afgemeng na die verskilfrekwensie waar die meetinstrument meer sensitief is en die faseruis akkuraat gemeet kan word. Die uittreesein van die ossillator is by verskillende punte gemeet en het duidelik getoon dat die resoneerder as filter gebruik kan word om die faseruis te minimeer. Die ossillators se werkverrigting het aan die verwagtinge voldoen. Faseruis vlakke van -115 dBc/Hz en -146 dBc/Hz by afsetfrekwensies van onderskeidelik 10 en 100 kHz is verkry.

This thesis reports the analysis of the rectangular shaped defected ground structure (RS-DGS) and the application of the structure on some microwave devices. DGS is analyzed in terms of its superior properties, which enables the designers to easily realize many kind of microwave devices which are impossible to achieve with the standard applications. Within the scope of this thesis, the focus is on the rectangular shaped DGS and its characteristic properties. The basic slow wave and high impedance characteristics are utilized in the design of some microwave devices. The design is carried on at the two different frequency bands: X-band and Ka band, centering at 10 GHz and 35 GHz, respectively. Finally, using the high impedance property and the coupling between the defects, a wide band 1 : 4 beam forming network is designed and implemented at 10 GHz.