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Paper Abstract and Keywords
Presentation 2026-07-22 13:30
A Study on the Derivation of the Radiation Unloaded Q Factor of Microstrip Antennas
Hideki Ueda (Murata Mfg.) AP2026-45
Abstract (in Japanese) (See Japanese page) 
(in English) This paper investigates a method to derive the radiation-efficiency-related unloaded Q factor (QU,rad) for miniaturization design of microstrip antennas in millimeter-wave band, motivated by the need to accurately estimate the achievable operational bandwidth at an early design stage. In the millimeter-wave band, both conductor and dielectric losses are significant; therefore, the unloaded Q factor derived from the reflection coefficient or input impedance (QU,Γ) can lead to an overly optimistic bandwidth estimate from the viewpoint of radiation-efficiency bandwidth. To address this issue, we apply de-embedding to a lumped-port-fed model and propose a procedure to derive QU,rad from the fractional bandwidth of radiation efficiency under a matched condition. The results show that QU,Γ and QU,rad agree when losses are small, whereas an opposite trend emerges as conductor and dielectric losses increase, namely, QU,Γ decreases while QU,rad increases. Furthermore, under representative conditions reflecting typical millimeter-wave conductivity and dielectric loss tangent, we confirm that using QU,Γ instead of QU,rad overestimates the bandwidth by 9% and 27%, respectively.
Keyword (in Japanese) (See Japanese page) 
(in English) Unloaded Q-factor / radiation efficiency / microstrip antenna / millimeter-wave / conductor loss / dielectric loss / /  
Reference Info. IEICE Tech. Rep., vol. 126, no. 122, AP2026-45, pp. 23-28, July 2026.
Paper # AP2026-45 
Date of Issue 2026-07-15 (AP) 
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)
Download PDF AP2026-45

Conference Information
Committee SAT AP SANE  
Conference Date 2026-07-22 - 2026-07-24 
Place (in Japanese) (See Japanese page) 
Place (in English) Kobe Port Oasis 
Topics (in Japanese) (See Japanese page) 
Topics (in English) Remote sensing, Sattelite Communication, Radio propagation, Antennas and Propagation 
Paper Information
Registration To AP 
Conference Code 2026-07-SAT-AP-SANE 
Language Japanese 
Title (in Japanese) (See Japanese page) 
Sub Title (in Japanese) (See Japanese page) 
Title (in English) A Study on the Derivation of the Radiation Unloaded Q Factor of Microstrip Antennas 
Sub Title (in English)  
Keyword(1) Unloaded Q-factor  
Keyword(2) radiation efficiency  
Keyword(3) microstrip antenna  
Keyword(4) millimeter-wave  
Keyword(5) conductor loss  
Keyword(6) dielectric loss  
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1st Author's Name Hideki Ueda  
1st Author's Affiliation Murata Manufacturing Co., Ltd. (Murata Mfg.)
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Speaker Author-1 
Date Time 2026-07-22 13:30:00 
Presentation Time 20 minutes 
Registration for AP 
Paper # AP2026-45 
Volume (vol) vol.126 
Number (no) no.122 
Page pp.23-28 
#Pages 6 
Date of Issue 2026-07-15 (AP) 

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