High directivity W-band stripline backward coupler based on LTCC technology

Details

Supervisors

Lederer, Dimitri

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil électricien, à finalité spécialisée

Abstract

In the microwave field, the VNA (vector network analyser) is an essential part of the test instrumentation in the RF laboratory. One of the most important measurement uncertainties of a VNA is related to a characteristic of the directional couplers built into the VNA, called directivity. Most of the couplers used in high-frequency VNAs are relatively large waveguide couplers. In collaboration with Farran, a company spe- cialised in millimetre wave technology, this thesis aims to design a W-band coupler with directivity of better than 30dB across the entire bandwidth with a reduced size. A stripline design based on LTCC technology was chosen for its small size and high intrinsic directivity. A design methodology was produced, as well as a study of the different impacts of the structure parameters. The coupler designed in this thesis achieves a minimum isolation better than 50dB for a coupling of 20dB in the entire bandwidth resulting in a directivity better than 30dB. To facilitate the integration of this coupling a microstrip-to-stripline transition has been designed. This transition has a return loss of better than 30 dB in the entire bandwidth. A study of the behaviour of the coupler as a function of certain parameter variations was carried out in relation to manufacturing uncertainties. This study shows that it would be complicated with the envisaged processes to build a coupler that would have a directivity higher than 30dB in the whole bandwidth. However, it would have a directivity greater than 25dB