Design and implementation of passive microstrip circuits

Abstract

The radio and microwave frequency spectrums permit high-speed data transmission over communication lines and media. The ever increasing high frequency applications must cater for certain losses and effects which come into play in such scenarios. Electronic circuits operating beyond 1 GHz are difficult to realize with discrete components because the wavelength becomes comparable with the physical element dimensions, resulting in various losses that severely degrade the circuit performance. Thus, the lumped component circuits must be converted into distributed element realizations. This work consisted in the design, simulation and implemention of passive microstrip circuits. In particular, narrowband and broadband quarter wavelength transformers and microwave filters were considered. The passive microstrip designs were targeted to operate correctly in the microwave frequency spectrum whilst making sure that maximum power transfer is preserved. As a general rule, the design procedure consisted of an initial calculation of the geometry of the microstrip sections based on the transformation of lumped element circuits into distributed element circuits, followed by verification and optimisation via circuit and electromagnetic simulators. The designed passive microstrip devices were then fabricated and implemented on an FR-4 printed circuit board. Following the implementation, they were characteristed and tested in terms of the scattering parameters, in order to determine the amount of reflection and transmission of energy over a wide range of frequencies. Prior to the actual implementation of the microstrip passive circuit designs, a number of microstrip transmission line characteristics were analysed and studied, in order to guarantee that the quality and response of the fabricated transmission line sections was close enough to that of the electromagnetic simulated counterparts. This was also aided by means of a developed estimation algorithm impelmented in MATLAB. The designed and measured passive microstrip circuits exhibit a performance which is in good agreement to the simulation results.