Abstract
This paper is divided into two parts. Part I describes the FR4-fabricated omni-directional bow-the tie antenna, which contains two kinds of balun structures. The first one is for broadband. By changing the structure of the ground, we can generate coupling. And to suppress the common-mode signal (noise), we should transfer the single-ended signal into differential signal. Due to the balanced structure, it is via-less. Another balun is based on the structure of balanced filters. By adjusting characteristic impedance of the ports, the four-port network will be modified into a three-port network. Such balun retains the filtering property and with the ability to control the differential-mode signals. Its combination with bow-tie antenna can be applied to the wireless network system in the frequency of 2.4GHz. The design process and measured results are provided. The second part describes the FR4-fabricated patch antenna, which contains two kinds of structures. The first one is to excite radiation conductor by the coupling between feeding line and cross aperture. Circular polarization will come into existence when the distance between coupled points is equal to quarter-wavelength, and radiation will be reflected back by reflector in the opposite direction to increase the gain. Another structure uses a 2 by 2 antenna array with the same current phases of the feed lines. The polarization of the antenna is linear. By adjusting the distance between the antennas and the spacing between the substrates, we can effectively increase the antenna gain. The design process and measured results are provided.