{"id":455998,"date":"2026-04-08T07:37:55","date_gmt":"2026-04-08T07:37:55","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/evaluating-loss-using-eigenmode-and-modal-network\/"},"modified":"2026-04-08T07:41:16","modified_gmt":"2026-04-08T07:41:16","slug":"evaluating-loss-using-eigenmode-and-modal-network","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/evaluating-loss-using-eigenmode-and-modal-network\/","title":{"rendered":"Evaluating loss using Eigenmode and Modal Network"},"content":{"rendered":"

<p><p data-start=”65″ data-end=”80″>Hello everyone,<\/p><p data-start=”82″ data-end=”258″>I am trying to compare the loss of a lumped LC resonator coupled to a shortened CPW line placed in different positions relative to the resonator.<\/p><p data-start=”260″ data-end=”499″>First, I performed an Eigenmode<\/strong> simulation where I modeled the external loading by assigning a lumped RLC boundary of 50 Ω at the launcher of the CPW line. With this setup, I obtain a mode at approximately 5.717 GHz with a Q of about 5.47e5.<\/p><p data-start=”501″ data-end=”909″>Then, I ran a Driven Modal<\/strong> (Modal Network) simulation by assigning a lumped port (50 Ω) for the Excitations at the same launcher and sweeping from 5 to 6 GHz. In this case, I observe a feature close to the expected frequency (~5.7 GHz), but the dip in S11 is extremely shallow (on the order of 1e-8). The result is also not very stable: depending on the parameter sweep, sometimes I see a dip, and sometimes even a peak instead.<\/p><p data-start=”911″ data-end=”1090″>I expected that by fitting the S11 feature I could extract a linewidth consistent with the Q obtained from the Eigenmode simulation, but this does not seem to be the case.<\/p><p data-start=”1092″ data-end=”1109″>My questions are:<\/p><ul data-start=”1110″ data-end=”1363″><li data-section-id=”1b0vp2m” data-start=”1110″ data-end=”1191″>Are Eigenmode<\/strong> and Driven Modal<\/strong> simulations directly comparable in this context?<li data-section-id=”1rhurwv” data-start=”1192″ data-end=”1268″>Should I expect to extract the same linewidth from S11?<li data-section-id=”12fgru0″ data-start=”1269″ data-end=”1363″>Or am I missing something in the Driven Modal setup or in how I am interpreting the results?<p data-start=”1365″ data-end=”1512″>I attach here the design and two S11 profiles, as you can see, the structure is relatively simple: a resonator coupled to a shortened CPW line, with the launcher used as the boundary\/excitation port.<\/p><p data-start=”1514″ data-end=”1560″ data-is-last-node=”” data-is-only-node=””>Thanks in advance for any help or suggestions!<\/p><p>\"\"\"\"\"\"<\/p><\/p><\/p>\n","protected":false},"template":"","class_list":["post-455998","topic","type-topic","status-publish","hentry","topic-tag-compatibility-1","topic-tag-eigenmode","topic-tag-excitations","topic-tag-hfss","topic-tag-linewidth-1","topic-tag-Qfactor-1"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_forum_id":["27793"],"_bbp_topic_id":["455998"],"_bbp_subscription":["673445","15859"],"_bbp_author_ip":["2001:760:4211:0:8d23:69bb:1693:73a2"],"_bbp_last_reply_id":["456113"],"_bbp_last_active_id":["456113"],"_bbp_last_active_time":["2026-04-09 07:32:28"],"_bbp_reply_count":["2"],"_bbp_reply_count_hidden":["0"],"_bbp_voice_count":["2"],"_bbp_engagement":["673445","15859"],"_btv_view_count":["17"],"_bbp_topic_status":["unanswered"],"_edit_last":["673445"],"_bbp_revision_log":["a:1:{i:455999;a:2:{s:6:\"author\";i:673445;s:6:\"reason\";s:17:\"Adding more plots\";}}"]},"test":"gobbo-marco98gmail-com"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/455998","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":1,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/455998\/revisions"}],"predecessor-version":[{"id":455999,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/455998\/revisions\/455999"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=455998"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}