Browsing by Author "Johnston, Michael"
Now showing 1 - 1 of 1
Results Per Page
Sort Options
- ItemWideband Balun design for the pyramidal sinuous antenna(Stellenbosch : Stellenbosch University, 2019-04) Johnston, Michael; Van Niekerk, C.; Van Niekerk, C.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis presents the design of wideband baluns for integration with the pyramidal sinuous antenna. Two different realizations of the Marchand balun are studied, namely a planar coupled-line balun and a rectangular coaxial balun. The planar balun implementation makes use of ground plane apertures to enhance the coupling coeficient of the coupled-line sections, so that higher bandwidths can be achieved compared to standard implementations. It is designed to be able to accommodate a single or dual-linearly polarized sinuous antenna. The designed prototype displays a bandwidth ratio of 3:1 with a 50-300 single-ended to differential impedance transformation. The simulated return loss is better than 10 dB, and the simulated insertion loss is better than 0.84 dB. The amplitude balance is better than ±0.2 dB across most of the band, and the phase balance is better than ±2° across half the band. The performance of the manufactured prototype is shown to be consistent with simulated predictions. The coaxial implementation makes use of a shunted resonate line to provide frequency independent unbalanced current cancellation, and is able to achieve a bandwidth ratio of about 5:1 with a 50-300 singled-ended to differential impedance transformation. The return loss of the final coaxial design is better than 10 dB with an insertion loss better than 0.91 dB. The amplitude balance is better than ±0.2 dB and the phase balance is better than ±1.5° across the entire band. The performance of the manufactured prototype did not agree with simulated predictions and therefore a short follow-up study is conducted explaining the differing results. Performance of the prototype baluns is further veri ed through simulated integration with the single-linearly polarized pyramidal sinuous antenna. Both balun implementations integrate with the antenna in a straightforward manner with relatively small re ections. Reasonably symmetric radiation patterns are achieved for the planar integration with some variation in the reported gain at broadside. Symmetric radiation patterns are also achieved across the band for the coaxial integration, but better consistency is reported for the gain at broadside.