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Paper Abstract and Keywords
Presentation 2026-05-29 13:30
Optimization of Fixture Width for 50 Ω Impedance Matching in Port Extension
Md Zahidul Islam, Masahiro Yoshida, Yoshitaka Toyota (Okayama Univ.) EMCJ2026-13
Abstract (in Japanese) (See Japanese page) 
(in English) High-frequency measurement systems generally use 50~$Omega$ coaxial connectors and cables. When a device under test (DUT) is mounted above a ground plane, a supporting fixture is required to connect the coaxial connector to the DUT. The fixture shape is not specified in standards. However, its parasitic inductance and capacitance depend on the fixture shape. Therefore, an optimized shape is needed in which the influence of parasitic components is minimized. In particular, variations in the stand geometry, especially its width, affect the electrical behavior of the fixture and can degrade the validity of port extension. In this study, a single-conductor transmission structure above a ground plane supported by an L-shaped fixture is investigated using Ansys HFSS over the frequency range from 100~MHz to 1~GHz. First, the parasitic parameters of the supporting fixture are extracted, and the fixture impedance is evaluated as a function of stand width. Then, the optimal stand width providing a near 50~$Omega$ condition is determined. Finally, port extension is applied under the optimized condition and validated by comparison with the ideal wire model. The results show that the fixture impedance decreases from $78.3~Omega$ at $20~mathrm{mm}$ to $49.7~Omega$ at $270~mathrm{mm}$, approaching $50~Omega$ as the stand width increases. For the optimized case, based on the $3~mathrm{dB}$ magnitude-error threshold, the valid frequency range increased from $0.96~mathrm{GHz}$ to above $1~mathrm{GHz}$ for $S_{11}$ and from $0.37~mathrm{GHz}$ to above $1~mathrm{GHz}$ for $S_{21}$. Similarly, based on the $10^circ$ phase-error threshold, the valid frequency range increased from below $0.1~mathrm{GHz}$ to above $1~mathrm{GHz}$ for both $S_{11}$ and $S_{21}$. These findings clarify the relationship among fixture shape, impedance, and the applicability of port extension.
Keyword (in Japanese) (See Japanese page) 
(in English) Impedance / impedance matching / parasitic capacitance / parasitic inductance / port extension / single-conductor transmission structure / supporting fixture /  
Reference Info. IEICE Tech. Rep., vol. 126, no. 41, EMCJ2026-13, pp. 63-68, May 2026.
Paper # EMCJ2026-13 
Date of Issue 2026-05-21 (EMCJ) 
ISSN Online edition: ISSN 2432-6380
Copyright
and
reproduction		 All rights are reserved and no part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Notwithstanding, instructors are permitted to photocopy isolated articles for noncommercial classroom use without fee. (License No.: 10GA0019/12GB0052/13GB0056/17GB0034/18GB0034)
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Conference Information
Committee EMCJ IEE-SPC IEE-EMC  
Conference Date 2026-05-28 - 2026-05-29 
Place (in Japanese) (See Japanese page) 
Place (in English)  
Topics (in Japanese) (See Japanese page) 
Topics (in English)  
Paper Information
Registration To EMCJ 
Conference Code 2026-05-EMCJ-SPC-EMC 
Language English 
Title (in Japanese) (See Japanese page) 
Sub Title (in Japanese) (See Japanese page) 
Title (in English) Optimization of Fixture Width for 50 Ω Impedance Matching in Port Extension 
Sub Title (in English)  
Keyword(1) Impedance  
Keyword(2) impedance matching  
Keyword(3) parasitic capacitance  
Keyword(4) parasitic inductance  
Keyword(5) port extension  
Keyword(6) single-conductor transmission structure  
Keyword(7) supporting fixture  
Keyword(8)  
1st Author's Name Md Zahidul Islam  
1st Author's Affiliation Okayama University (Okayama Univ.)
2nd Author's Name Masahiro Yoshida  
2nd Author's Affiliation Okayama University (Okayama Univ.)
3rd Author's Name Yoshitaka Toyota  
3rd Author's Affiliation Okayama University (Okayama Univ.)
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Speaker Author-1 
Date Time 2026-05-29 13:30:00 
Presentation Time 25 minutes 
Registration for EMCJ 
Paper # EMCJ2026-13 
Volume (vol) vol.126 
Number (no) no.41 
Page pp.63-68 
#Pages 6 
Date of Issue 2026-05-21 (EMCJ) 

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