Microstrip antennas

Abstract

In the last ten years a revolution has taken place at microwave frequencies. These frequencies ranging from 1 to 300 GHz have been produce, amplified and mixed using solid-state and microstrip components which are more reliable, compact and cheaper than the tubes previously used. Hence use is being made nowadays of microwave equipment for domestic use such as burglar alarms, small dappler radar installations on cars, medical instruments, etc. In microwave communications the antenna always played an important part in the design of a system since a good antenna design could save a lot of power in transmission by not radiating, in unwanted directions. Without a good antenna design at these frequencies (because of line of sight propagation) the power needed quite the transmitter would not be feasible or even possible. Since the performance of an antenna depends on the physical size, the antenna problem also tends to be a mechanical one. In the last decade various types of revolutionary antennas have shown up namely the frequency independent antennas and the phased array antennas. These type of antennas have found a great use and most of the present equipment is being equipped with such antennas. In the last five years another antenna has gone into study, namely the microstrip antenna. The advantages of microstrip antennas on previous antennas used are the simplicity in construction, the relatively small size, the compatibility with solid-state devices, the flat profile and streamline structure. Because of these valuable advantages they may well replace the existing antennas used on aircrafts, missiles and satellite stations. So much so there have already been considerations for the use of such antennas on satellites and missiles. The work on this project, entitled mostly a detailed study of propagation of microwave energy in various types of media with a special reference to microstrip and the apparatus available in the laboratory. Use was then made of this knowledge to produce various types of microstrip antennas in order to study their radiation properties. Some problems were encountered in the construction of such antennas because of lack of dielectric material to work with and also because of lack of an appreciable varying frequency which could have very much aided the design. The first chapters are therefore of a rather theoretical nature, leading to wave propagation in the waveguide system available and also to the propagation and radiation from the microstrip. For the understanding of the theory special treatment used especially in the use of vectors and social functions. A brief study of microwave apparatus has been included in the fifth chapter before going into the experimental work that was carried out. The construction and polar pattern results of five different types of radiating elements has been included in chapter six. The types of radiating elements being the dipoles, half wavelength resonators wide slots, annular and zig-zag structures, the last two being of original design. In chapter seven the knowledge of the microstrip techniques was used to construct an omni directional small antenna at 50 MHz. The theoretical aspects use flat microwave frequencies were adopted and applied in the design of this antenna.