Radio frequency wideband Wilkinson’s microstrip power couplers

Abstract

Designing high frequency circuits is a challenging endeavour. At high operating frequencies in the gigahertz range and beyond, discrete passive components, such as resistors, capacitors and inductors, start to behave in a non-ideal manner, and their correct operation is limited by their self-resonating frequency which depends on their size and shape. Microstrip structures are used so that the limitations of discrete passive components are circumvented when designing at such high frequency ranges. In this work, the design, simulation, and implementation of various microstrip structures such as the Wilkinson’s Power Divider (WPD) was carried out. The design methodology consisted of designing and investigating the performance of a number of microstrip transformers, which were then integrated in the design of a wideband WPD. Initially, specifications were established so that the microstrips could be designed around these requirements. The dimensions of the printed circuit board (PCB) copper tracks were determined using analytical equations and numerical calculators. In addition, rule-of-thumb strategies were adopted to further optimise the microstrip circuits, aided with simulations performed using an electromagnetic (EM) simulator. Once the performance adhered to the established specifications, the design was implemented using a PCB CAD software. After finalising the designs, these were then sent off for fabrication. The designed structures were fabricated using an FR-4 based double sided PCB. Finally, the microstrip circuits were characterised and tested using a vector network analyser (VNA) and the measured scattering parameters were compared to those simulated using the EM simulator. Overall, consistent performance was achieved between the analytical, numerical, and empirical analysis which contribute towards a sound approach in the design of a wideband microstrip WPD.