DESIGN AND FABRICATION OF 12 GHZ MICROSTRIP DIRECTIONAL COUPLER FOR RF/MICROWAVE APPLICATION

Microstrip coupled line is parallel coupled transmission lines formed by coupling two conducting strips (resonator) with the same width together at a certain distance. This paper presents the design of microstrip directional coupler without the prior knowledge of the physical geometry. A general configuration directional coupler will be determined by creating a layout in the Agilent Advanced Design System (ADS) and momentum. In order to perform simulation, a substrate as well as metallization and mesh should be defined. Hence, the required s-parameter response of the coupler could be obtained. The design will then fabricate on top of RT Duroid 6010 substrate, and finally undergo measuring through Vector Network Analyzer (VNA) to evaluate their S-parameter characteristics. Simulated results show insertion loss, isolation, coupling (10.82 dB), and return loss were within the acceptable limits. Directivity of better than 23 dB was achieved in the simulated response. The coupling (9.99 dB) of fabricated circuit shows a good agreement with the required specification (10 dB), but the directivity 10.61 dB is quite low in practice. The reason for the discrepancy could, however, due to discontinuities, measuring errors, and fabrication error. However, coupling values show a good agreement between the simulation and measured results