{"id":382702,"date":"2024-09-15T02:51:30","date_gmt":"2024-09-15T02:51:30","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/180-degree-phase-shift-when-measuring-s21\/"},"modified":"2024-09-15T02:51:30","modified_gmt":"2024-09-15T02:51:30","slug":"180-degree-phase-shift-when-measuring-s21","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/180-degree-phase-shift-when-measuring-s21\/","title":{"rendered":"180 Degree Phase Shift When Measuring S21"},"content":{"rendered":"

<p>Hi,<\/p><p>I’m running a parametric sweep by rotating a probe around a central horn antenna. I’m showing a few images below for illustration.<\/p><p><\/p><p>Fig 1: At Theta = 0 degrees.<\/p><p><\/p><p>Fig 2: At Theta = 10 degrees<\/p><p><\/p><p>Fig 3: Theta = 20 degrees<\/p><p>…And so on…<\/p><p>When I measure the phase of the S21 results, I see random 180 degree shifts in the measurements. I am not able to see any pattern in these shifts either.<\/p><p>I thought perhaps it was because I was initially using 2 FE-BI boundaries and that might be causing an issue. So I tried a single Radiation boundary instead, but that also didn’t help.<\/p><p> <\/p><table style=”border-collapse: collapse; width: 186pt;” border=”0″ width=”248″ cellspacing=”0″ cellpadding=”0″><colgroup><col style=”mso-width-source: userset; mso-width-alt: 3474; width: 71pt;” width=”95″> <col style=”mso-width-source: userset; mso-width-alt: 5595; width: 115pt;” width=”153″> <\/colgroup><tbody><tr style=”height: 15.0pt;”><td style=”height: 15.0pt; width: 71pt;” width=”95″ height=”20″>theta_rotation [deg]<\/td><td style=”width: 115pt;” width=”153″>S21 Phase Results [deg]<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>-10<\/td><td align=”right”>101.2924367<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>-9<\/td><td align=”right”>103.7009139<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>-8<\/td><td align=”right”>105.601412<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>-7<\/td><td align=”right”>107.5837877<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>-6<\/td><td align=”right”>109.0814497<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>-5<\/td><td align=”right”>110.6225511<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>-4<\/td><td align=”right”>-68.19983945<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>-3<\/td><td align=”right”>112.7819268<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>-2<\/td><td align=”right”>-66.46548137<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>-1<\/td><td align=”right”>-65.96723292<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>0<\/td><td align=”right”>114.1349591<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>1<\/td><td align=”right”>114.08219<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>2<\/td><td align=”right”>113.6846084<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>3<\/td><td align=”right”>-66.93414481<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>4<\/td><td align=”right”>112.1847997<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>5<\/td><td align=”right”>111.1811682<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>6<\/td><td align=”right”>109.7736687<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>7<\/td><td align=”right”>-71.78552943<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>8<\/td><td align=”right”>106.3168243<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>9<\/td><td align=”right”>104.558732<\/td><\/tr><tr style=”height: 15.0pt;”><td style=”height: 15.0pt;” align=”right” height=”20″>10<\/td><td align=”right”>102.4050767<\/td><\/tr><\/tbody><\/table><p>As you can see from these results, at random points the phase shifts down by ~180 degrees.<\/p><p>For example at Theta = -4, the phase measurement is -68.2 degrees, whereas at Theta = -5 it is 110.6 degrees, and at Theta = -3 it is 112.8 degrees. The -68.2 measurement seems to be shifted down by 180 degrees (-68.2 + 180 = 111.8). 111.8 degrees seems like a more reasonable measurement. This occurs again at random points with no discernible pattern.<\/p><p> <\/p><p>Can I please get some feedback on why this issue might be occuring and how I can fix it?<\/p><p> <\/p><p>Thank you,<\/p><p>Shyam<\/p><p> <\/p><\/p>\n","protected":false},"template":"","class_list":["post-382702","topic","type-topic","status-publish","hentry","topic-tag-ansys-hfss","topic-tag-hfss"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["449801","39445"],"_bbp_author_ip":["137.122.64.52"],"_btv_view_count":["690"],"_bbp_topic_status":["unanswered"],"_edit_lock":["1726368789:449801"],"_bbp_topic_id":["382702"],"_bbp_forum_id":["27793"],"_bbp_engagement":["39445","449801"],"_bbp_voice_count":["2"],"_bbp_reply_count":["7"],"_bbp_last_reply_id":["388272"],"_bbp_last_active_id":["388272"],"_bbp_last_active_time":["2024-10-05 20:05:30"]},"test":"spate035uottawa-ca"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/382702","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":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/382702\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=382702"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}