The baluns are the key components in balanced circuits such balanced mixers, frequency multipliers, push–pull amplifiers, and antennas. Most of these applications have become more integrated which demands the baluns to be in compact size and low cost. In this thesis, a new approach about the design of planar balun is presented where the 4-port symmetrical network with one port terminated by open circuit is first analyzed by using even- and odd-mode excitations. With full design equations, the proposed balun presents perfect balanced output and good input matching and the measurement results make a good agreement with the simulations. Second, Yagi-Uda antenna is also introduced as an entry to fully understand the quasi-Yagi antenna. Both of the antennas have the same design requirements and present the radiation properties. The arrangement of the antenna’s elements and the end-fire radiation property of the antenna have been presented. Finally, the quasi-Yagi antenna is used as an application of the balun where the proposed balun is employed to feed a quasi-Yagi antenna. The antenna is working in the S-band radio frequency and achieves a measured 36% fractional bandwidth for return loss less than -10 dB. The antenna demonstrates a good agreement between its measurement and simulation results. The impact of the parasitic director on the antenna’s performance is also investigated. The gain and the frequency range of the antenna have been reduced due to the absence of this element. This reduction presents in simulation and measurement results with very close agreement.

Made available in DSpace on 2014-12-17T14:55:33Z (GMT). No. of bitstreams: 1 FlaviaCC_Capa_ate_pag15.pdf: 8751469 bytes, checksum: df79b8a134d4a6869e65f7ed508775af (MD5) Previous issue date: 2009-11-17 / ln this work, planar quasi- Y agi antennas are investigated based on the concept of the classic Y agi_Uda antennas. These antennas represent improvements on the topologies of the antennas existing printed because they present characteristics of broad bandwidth, excellent radiation diagrams and simple construction. New configurations are adapted for the driver of the antennas, introducing patches elements into the driver. These new configurations are named Patches Elements Anteonas (PEA). This adaptation is obtained from simulations that are executed usiog the software C8T Microwave 8tudio 5. After doing the optimizations, procedures for construction and measurement ofthe prototypes are executed in order to improve the performance of the antennas in such way that they could be used in wireless communication applications, such as Bluetooth, WLAN' s and Wi-Fi. Next, the quasi- Y agi antennas are studied in order to implement them in arrangements. The arrangements construction is based 00 the best driver configuration of the antenna developed in this work. First, a linear arrangement composed by two elements of quasi?Yagi antennas is constructed in such way that the radiation characteristics and the mutual coupling effects could be analyzed. After that, a 90? angle arrangement composed by two elements is studied to observe the effect of circular polarization. Experiments are executed in order to evaluate the arrangements performance. The experimental results show that the analysis made in this work is efficient and accurate. The numerical values obtained for the analyzed parameters of each structure developed are compared with the experimental values. 80, it is possible to observe a good concordance between them. Finally, some future works proposals are presented / Neste trabalho, antenas planares quasi-Yagi s?o estudadas com base no conceito das antenas Yagi-Uda cl?ssicas. Estas antenas representam melhorias sobre as topologias das antenas impressas existentes por apresentarem caracter?sticas de banda larga, excelentes diagramas de irradia??o e constru??o simples. Novas configura??es s?o adaptadas para o driver das antenas, introduzindo elementos patches sobre o driver. Essas novas configura??es s?o chamadas de Antenas de Elementos Patches (AEP). Esta adapta??o ? obtida realizando simula??es de otimiza??o com o aux?lio do software CST Microwave Studio 5. Ap?s as otimiza??es, procedimentos para constru??o e medi??o dos prot?tipos s?o realizados com o objetivo de melhorar o desempenho das antenas para aplica??es de comunica??es sem fio, tais como Bluetooth, WLAN's e Wi-Fi. Posteriormente, as antenas quasi- Yagi s?o estudadas com o intuito de implement?-Ias em arranjos. A constru??o dos arranjos baseia-se na melhor configura??o do driver da antena desenvolvida por este trabalho. Primeiramente, um arranjo linear com dois elementos de antenas quasi-Yagi ? constru?do de tal forma que as caracter?sticas de irradia??o e o efeito do acoplamento m?tuo pudessem ser analisados. Em seguida, um arranjo composto por dois elementos dispostos sob um ?ngulo de 900 ? estudado para se observar o efeito da polariza??o circular. Experimentos s?o executados para avaliar o desempenho dos arranjos. Os resultados dos experimentos demonstram que a an?lise efetuada neste trabalho ? eficiente e precisa. Os valores num?ricos obtidos para os par?metros analisados em cada estrutura desenvolvida s?o comparados com os valores experimentais. Com isso, ? poss?vel observar uma boa concord?ncia entre eles. Por fim, algumas propostas para a realiza??o de trabalhos futuros s?o apresentadas