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Miniaturized Broadband 3-dB / 90 deg and 180 deg Power Splitters for GPS/GNSS Anti-Jam Systems

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Technical memo.

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This document reports on compact broadband rat-race and branch-line hybrids designed in the 1.15-1.6 GHz frequency band using microstrip technology. Two relatively simple design techniques using a conventional unilayer fabrication process have been investigated. The technology described in this document has been specifically developed for designing antenna feeding circuits for GPSGNSS anti-jam systems, but it can be used for other wideband applications. A miniaturized two-section 180 deg hybrid using microstrip space-filling curves has been designed and fabricated to operate between 1.15 and 1.6 GHz on an FR4 substrate. The miniaturized geometry area is 31 of the broadband two-section 180 deg hybrid area. The obtained performance is as good as the conventional geometry. A 3-dB coupling with maximum amplitude imbalance of less than 0.15 dB has been measured over the 1.15-1.6 GHz band. Over this frequency band, the phase variation is -2 deg. The measured insertion loss is approximately 0.9 dB, and is mainly due to the substrate loss. To further reduce the footprint of the compact hybrid and the insertion loss, a second circuit has been designed on a substrate having a higher dielectric constant and lower loss Cer10. The area of the second circuit is 54 of the hybrid area on the FR4 substrate. The measured performance is very similar, except that the insertion loss has been reduced by about 0.4 dB. The lumped distributed element method has been applied to miniaturize a two-section branchline hybrid. The obtained geometry area is 65 of the two-section branch-line hybrid area and 54 when considering only the width of the circuits. Over the 1.15-1.6 GHz band, the maximum coupling imbalance obtained by measurement is 1 dB, and the phase variation is 4 deg. Higher than expected maximum coupling imbalance has been measured because this parameter is sensitive to the impedance values of the two-section branch-line.

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  • Navigation and Guidance
  • Radiofrequency Wave Propagation

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