{"id":37355,"date":"2026-10-15T10:54:49","date_gmt":"2026-10-15T02:54:49","guid":{"rendered":"https:\/\/www.bestpcbs.com\/blog\/?p=37355"},"modified":"2026-10-15T11:23:58","modified_gmt":"2026-10-15T03:23:58","slug":"rf-insertion-loss","status":"publish","type":"post","link":"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/","title":{"rendered":"RF Insertion Loss in PCBs: Causes, Measurement, and Reduction"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_85 ez-toc-wrap-left counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#What_Is_Insertion_Loss_in_RF\" >What Is Insertion Loss in RF?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#What_Is_the_Difference_Between_Insertion_Loss_and_Return_Loss\" >What Is the Difference Between Insertion Loss and Return Loss?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#What_Causes_RF_Insertion_Loss_in_a_PCB\" >What Causes RF Insertion Loss in a PCB?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#How_Do_PCB_Materials_Affect_RF_Insertion_Loss\" >How Do PCB Materials Affect RF Insertion Loss?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#How_Do_Frequency_Trace_Length_and_PCB_Stackup_Affect_RF_Insertion_Loss\" >How Do Frequency, Trace Length, and PCB Stackup Affect RF Insertion Loss?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#How_Do_You_Measure_RF_Insertion_Loss_Using_a_VNA\" >How Do You Measure RF Insertion Loss Using a VNA?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#What_Is_an_Acceptable_RF_Insertion_Loss_Value_for_RF_PCBs\" >What Is an Acceptable RF Insertion Loss Value for RF PCBs?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#How_Can_You_Reduce_RF_Insertion_Loss_in_PCB_Design\" >How Can You Reduce RF Insertion Loss in PCB Design?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#How_Can_EBest_Circuit_Support_Low%E2%80%91Loss_RF_PCB_Manufacturing\" >How Can EBest Circuit Support Low\u2011Loss RF PCB Manufacturing?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#FAQs_About_RF_Insertion_Loss\" >FAQs About RF Insertion Loss<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/#Conclusion\" >Conclusion<\/a><\/li><\/ul><\/nav><\/div>\n<div class=\"yzp-no-index\"><\/div><div id=\"article-rf-insertion-loss\" style=\"color:#202830;word-break:normal;overflow-wrap:normal;hyphens:none;max-width:100%;\">\n<style id=\"article-rf-insertion-loss-presentation-fixes\">body.single-post h1.entry-title,body.single-post .post-37355 h1._title{word-break:keep-all!important;overflow-wrap:normal!important;hyphens:none!important;white-space:normal!important;}#article-rf-insertion-loss h2,#article-rf-insertion-loss p,#article-rf-insertion-loss li{word-break:keep-all!important;overflow-wrap:normal!important;hyphens:none!important;}.ez-toc-wrap-left .ez-toc-title{color:#202830!important;}.ez-toc-wrap-left .ez-toc-list li,.ez-toc-wrap-left .ez-toc-list li::before{color:#666!important;}.ez-toc-wrap-left .ez-toc-link,.ez-toc-wrap-left .ez-toc-link:visited{color:#666!important;text-decoration:none;}.ez-toc-wrap-left .ez-toc-link:hover,.ez-toc-wrap-left .ez-toc-link:focus{color:#444!important;text-decoration:underline;}@media(max-width:480px){#article-rf-insertion-loss table,#article-rf-insertion-loss tbody,#article-rf-insertion-loss tr,#article-rf-insertion-loss td{display:block;width:100%!important;box-sizing:border-box!important;max-width:100%!important;}#article-rf-insertion-loss table{border:0!important;}#article-rf-insertion-loss thead{display:none;}#article-rf-insertion-loss tr{border:1px solid #000;margin-bottom:12px;}#article-rf-insertion-loss td{border:1px solid #000!important;margin-top:-1px;padding:8px;}#article-rf-insertion-loss td::before{content:attr(data-label);display:block;font-weight:700;margin-bottom:4px;}}<\/style>\n<p>A 50-ohm RF PCB can still show more <a href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/\">RF insertion loss<\/a> than its design allows. At 6 GHz, an S21 reading of -3 dB means only about half the incident power reaches a matched output. The problem may come from the laminate, copper roughness, excessive trace length, or poorly matched transitions.<\/p>\n<p>Before selecting a low\u2011loss material or approving a stackup, it helps to know where <strong>RF insertion loss<\/strong> comes from and how much the signal path can tolerate. This guide covers the main causes, VNA measurement methods, acceptable loss limits, and practical ways to reduce attenuation before PCB manufacturing.<\/p>\n<figure class=\"article-image\" style=\"margin:28px auto;text-align:center;max-width:100%;overflow:visible;\"><img fetchpriority=\"high\" src=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2026\/10\/rf-insertion-loss-hero.jpg\" alt=\"RF insertion loss, https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/\" width=\"600\" height=\"400\" loading=\"eager\" decoding=\"async\" style=\"display:block;width:600px;max-width:100%;height:auto;margin:0 auto;\"><\/figure>\n<h2><span class=\"ez-toc-section\" id=\"What_Is_Insertion_Loss_in_RF\"><\/span>What Is Insertion Loss in RF?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><strong><a href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/\">RF insertion loss<\/a> is the reduction in signal power transmitted through an RF path, expressed in decibels (dB).<\/strong> In a PCB, this path may include copper traces, vias, connectors, and transmission\u2011line transitions.<\/p>\n<p>Insertion loss is commonly calculated from the forward transmission parameter S21:<\/p>\n<p><strong>Insertion Loss (dB) = -20 log10(|S21|)<\/strong><\/p>\n<p>For example, an <strong>S21 reading of -3 dB corresponds to approximately 50% power transmission<\/strong> into a matched output. The remaining power may be dissipated, reflected, or radiated, depending on the RF structure.<\/p>\n<p>Lower insertion loss generally means more signal power reaches the intended destination.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"What_Is_the_Difference_Between_Insertion_Loss_and_Return_Loss\"><\/span>What Is the Difference Between Insertion Loss and Return Loss?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><strong>Insertion loss measures signal attenuation through an RF path, while return loss measures reflected signal power caused by impedance mismatches.<\/strong> Both are expressed in decibels but evaluate different aspects of RF transmission.<\/p>\n<table style=\"border-collapse:collapse;width:100%;max-width:100%;table-layout:fixed;border:1px solid #000;word-break:normal;overflow-wrap:break-word;\">\n<thead>\n<tr>\n<th style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Parameter<\/th>\n<th style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Insertion Loss<\/th>\n<th style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Return Loss<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td data-label=\"Parameter\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">S\u2011Parameter<\/td>\n<td data-label=\"Insertion Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">S21<\/td>\n<td data-label=\"Return Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">S11<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Parameter\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Measurement<\/td>\n<td data-label=\"Insertion Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Forward transmission<\/td>\n<td data-label=\"Return Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Input reflection<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Parameter\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Formula<\/td>\n<td data-label=\"Insertion Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">-20 log10(abs(S21))<\/td>\n<td data-label=\"Return Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">-20 log10(abs(S11))<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Parameter\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Main Purpose<\/td>\n<td data-label=\"Insertion Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Evaluate signal attenuation<\/td>\n<td data-label=\"Return Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Evaluate impedance matching<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Parameter\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">VNA Reading<\/td>\n<td data-label=\"Insertion Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">S21 typically negative in dB for a passive attenuating path<\/td>\n<td data-label=\"Return Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">S11 typically negative in dB<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Parameter\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Preferred Result<\/td>\n<td data-label=\"Insertion Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Lower positive loss<\/td>\n<td data-label=\"Return Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Higher positive return loss<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Parameter\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Example<\/td>\n<td data-label=\"Insertion Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">S21 = -1 dB means 1 dB insertion loss<\/td>\n<td data-label=\"Return Loss\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">S11 = -20 dB means 20 dB return loss<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>The return\u2011loss measurement assumes the other VNA port is terminated in the reference impedance.<\/p>\n<p>For example, <strong>20 dB return loss indicates approximately 1% reflected power<\/strong>, but good impedance matching does not guarantee low insertion loss. A long transmission line can still lose significant energy through conductor and dielectric attenuation.<\/p>\n<p><strong>S21 and S11 should be evaluated together<\/strong> to distinguish transmission attenuation from reflection\u2011related problems.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"What_Causes_RF_Insertion_Loss_in_a_PCB\"><\/span>What Causes RF Insertion Loss in a PCB?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>RF insertion loss in PCBs mainly comes from conductor resistance, dielectric dissipation, radiation or leakage, and impedance discontinuities. Their effects become more noticeable as operating frequency increases.<\/p>\n<ul>\n<li><strong>Conductor Loss:<\/strong> Skin effect concentrates high\u2011frequency current near the copper surface, increasing effective resistance. Rough copper surfaces can contribute additional attenuation.<\/li>\n<li><strong>Dielectric Loss:<\/strong> Electromagnetic energy is dissipated within the PCB insulating material. Higher dissipation factors generally produce greater dielectric attenuation under comparable conditions.<\/li>\n<li><strong>Radiation and Leakage:<\/strong> Discontinuous reference planes, unsuitable transitions, and poorly contained electromagnetic fields may allow energy to escape the intended signal path.<\/li>\n<li><strong>Impedance Mismatch:<\/strong> Variations in trace geometry, connector launches, or via structures create reflections and reduce measured forward transmission.<\/li>\n<\/ul>\n<p>Conductor and dielectric losses typically increase with frequency, while impedance discontinuities can create ripples or sharp dips in the S21 curve.<\/p>\n<p><strong>If the measured S21 response contains sudden fluctuations, inspect the connector transitions, vias, and test fixture before attributing the problem to PCB materials.<\/strong><\/p>\n<h2><span class=\"ez-toc-section\" id=\"How_Do_PCB_Materials_Affect_RF_Insertion_Loss\"><\/span>How Do PCB Materials Affect RF Insertion Loss?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>PCB materials influence RF insertion loss through dielectric properties, copper roughness, and environmental stability. <strong>Dissipation factor (Df) is a primary indicator of dielectric attenuation<\/strong>, while dielectric constant (Dk) affects transmission\u2011line impedance and electrical length.<\/p>\n<figure class=\"article-image\" style=\"margin:28px auto;text-align:center;max-width:100%;overflow:visible;\"><img src=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2026\/10\/rf-pcb-materials-and-copper-loss.jpg\" alt=\"RF insertion loss, https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/\" width=\"600\" height=\"400\" loading=\"lazy\" decoding=\"async\" style=\"display:block;width:600px;max-width:100%;height:auto;margin:0 auto;\"><\/figure>\n<table style=\"border-collapse:collapse;width:100%;max-width:100%;table-layout:fixed;border:1px solid #000;word-break:normal;overflow-wrap:break-word;\">\n<thead>\n<tr>\n<th style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Material Property<\/th>\n<th style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Effect on RF Performance<\/th>\n<th style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Selection Consideration<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td data-label=\"Material Property\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Dissipation Factor (Df)<\/td>\n<td data-label=\"Effect on RF Performance\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Higher Df increases dielectric loss<\/td>\n<td data-label=\"Selection Consideration\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Low Df at operating frequency<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Material Property\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Dielectric Constant (Dk)<\/td>\n<td data-label=\"Effect on RF Performance\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Affects impedance and signal propagation<\/td>\n<td data-label=\"Selection Consideration\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Stable Dk and controlled tolerance<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Material Property\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Copper Roughness<\/td>\n<td data-label=\"Effect on RF Performance\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Increases conductor attenuation<\/td>\n<td data-label=\"Selection Consideration\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Suitable low\u2011profile copper<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Material Property\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Dielectric Thickness<\/td>\n<td data-label=\"Effect on RF Performance\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Changes transmission\u2011line geometry<\/td>\n<td data-label=\"Selection Consideration\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Controlled thickness tolerance<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Material Property\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Moisture Absorption<\/td>\n<td data-label=\"Effect on RF Performance\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">May alter dielectric properties<\/td>\n<td data-label=\"Selection Consideration\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Stable performance in service<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Material Property\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Thermal Stability<\/td>\n<td data-label=\"Effect on RF Performance\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Influences RF properties across temperature<\/td>\n<td data-label=\"Selection Consideration\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Suitable operating temperature range<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong>Standard FR-4<\/strong> may be adequate for shorter RF paths with moderate insertion\u2011loss requirements. For longer routes or demanding microwave applications, low\u2011loss laminates may provide better attenuation performance.<\/p>\n<p>For reference, <a href=\"https:\/\/www.rogerscorp.com\/advanced-electronics-solutions\/ro4000-series-laminates\/ro4003c-laminates\">Rogers material data<\/a> lists the following typical dissipation factors at 10 GHz:<\/p>\n<table style=\"border-collapse:collapse;width:100%;max-width:100%;table-layout:fixed;border:1px solid #000;word-break:normal;overflow-wrap:break-word;\">\n<thead>\n<tr>\n<th style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Material<\/th>\n<th style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Df at 10 GHz<\/th>\n<th style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Typical Application Consideration<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td data-label=\"Material\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">RO4003C<\/td>\n<td style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\" data-label=\"Df at 10 GHz\">0.0027<\/td>\n<td data-label=\"Typical Application Consideration\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">Low\u2011loss microwave transmission lines<\/td>\n<\/tr>\n<tr>\n<td data-label=\"Material\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">RO4350B<\/td>\n<td style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\" data-label=\"Df at 10 GHz\">0.0037<\/td>\n<td data-label=\"Typical Application Consideration\" style=\"border:1px solid #000;padding:8px;vertical-align:top;text-align:left;word-break:normal;overflow-wrap:break-word;\">RF circuits requiring low loss and UL 94 V-0 flame resistance<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>These figures describe material properties, not the insertion loss of a finished PCB. Actual attenuation also depends on copper roughness, trace geometry, dielectric thickness, and operating conditions.<\/p>\n<p><strong>Material selection should be based on the required RF loss budget rather than Df alone.<\/strong> Compare candidate laminates using equivalent transmission\u2011line structures and supplier data at the intended operating frequency.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"How_Do_Frequency_Trace_Length_and_PCB_Stackup_Affect_RF_Insertion_Loss\"><\/span>How Do Frequency, Trace Length, and PCB Stackup Affect RF Insertion Loss?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><strong>RF insertion loss generally increases with frequency and transmission\u2011line length, while PCB stackup determines how electromagnetic fields interact with the dielectric and copper conductors.<\/strong><\/p>\n<p><strong>Frequency:<\/strong> As frequency rises, skin effect increases conductor resistance, while dielectric attenuation typically becomes more significant. Copper roughness can further increase high\u2011frequency losses.<\/p>\n<p><strong>Trace Length:<\/strong> Longer transmission lines accumulate more attenuation. For a uniform, well\u2011matched structure, insertion loss in dB increases approximately in proportion to length. This relationship allows engineers to estimate attenuation in dB\/in or dB\/cm.<\/p>\n<p><strong>PCB Stackup:<\/strong> Microstrip and stripline structures distribute electromagnetic fields differently. Microstrip fields extend partly into air, potentially reducing dielectric attenuation, while stripline offers stronger field containment and shielding.<\/p>\n<p>The stackup also controls impedance through dielectric thickness, trace dimensions, and reference\u2011plane geometry. Poorly controlled dimensions can introduce mismatches that increase measured RF insertion loss.<\/p>\n<p><strong>Choose the transmission\u2011line structure according to the operating frequency, impedance target, routing requirements, and available loss budget.<\/strong><\/p>\n<h2><span class=\"ez-toc-section\" id=\"How_Do_You_Measure_RF_Insertion_Loss_Using_a_VNA\"><\/span>How Do You Measure RF Insertion Loss Using a VNA?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><strong>RF insertion loss is commonly measured using a vector network analyzer (VNA), which records S21 across the specified frequency range.<\/strong> <a href=\"https:\/\/www.keysight.com\/us\/en\/use-cases\/characterize-rf-components-using-s-parameters.html\">Keysight&#8217;s S\u2011parameter overview<\/a> identifies S21 as forward transmission and explains that calibration establishes the measurement reference plane. Accurate results still depend on the test fixtures, connector quality, and selected reference\u2011plane locations.<\/p>\n<figure class=\"article-image\" style=\"margin:28px auto;text-align:center;max-width:100%;overflow:visible;\"><img src=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2026\/10\/vna-s21-insertion-loss-measurement.jpg\" alt=\"RF insertion loss, https:\/\/www.bestpcbs.com\/blog\/2026\/10\/rf-insertion-loss\/\" width=\"600\" height=\"400\" loading=\"lazy\" decoding=\"async\" style=\"display:block;width:600px;max-width:100%;height:auto;margin:0 auto;\"><\/figure>\n<p>A typical measurement follows five steps.<\/p>\n<p><strong>Step 1: Prepare the Test Setup<\/strong><\/p>\n<p>Connect the PCB transmission path between VNA Port 1 and Port 2 using suitable RF cables, connectors, or fixtures. Configure the operating frequency range and reference impedance, commonly 50 ohms.<\/p>\n<p>For trace characterization, use a test coupon representing the PCB stackup and transmission\u2011line geometry.<\/p>\n<p><strong>Step 2: Calibrate the VNA<\/strong><\/p>\n<p>Perform an appropriate calibration, such as <strong>SOLT (Short\u2011Open\u2011Load\u2011Thru)<\/strong> or <strong>TRL (Thru\u2011Reflect\u2011Line)<\/strong>.<\/p>\n<p>Calibration corrects systematic measurement errors and establishes the reference planes. Connector launches and fixtures beyond those planes may still contribute additional loss.<\/p>\n<p><strong>Step 3: Measure S21<\/strong><\/p>\n<p>Sweep the required frequency range and record the S21 response.<\/p>\n<p>For example, <strong>S21 = -1.2 dB at 6 GHz corresponds to 1.2 dB insertion loss<\/strong> under the specified reference conditions.<\/p>\n<p>Check S11 alongside S21 to identify potential impedance mismatches.<\/p>\n<p><strong>Step 4: Account for Fixture Losses<\/strong><\/p>\n<p>When measuring the PCB transmission line independently, apply a validated de\u2011embedding method or suitable reference structures to account for connector and fixture contributions.<\/p>\n<p>Avoid subtracting assumed fixture losses without supporting measurements.<\/p>\n<p><strong>Step 5: Verify the Results<\/strong><\/p>\n<p>Repeat critical measurements where necessary and record the frequency range, calibration method, reference planes, and S21 readings.<\/p>\n<p><strong>A consistent measurement procedure is essential when comparing prototype and production RF PCB performance.<\/strong><\/p>\n<h2><span class=\"ez-toc-section\" id=\"What_Is_an_Acceptable_RF_Insertion_Loss_Value_for_RF_PCBs\"><\/span>What Is an Acceptable RF Insertion Loss Value for RF PCBs?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><strong>There is no universal acceptable RF insertion loss value for every PCB.<\/strong> The maximum permitted loss depends on operating frequency, signal\u2011path length, receiver sensitivity, available gain, and the RF link budget.<\/p>\n<p>A practical specification defines the maximum attenuation across the required operating band.<\/p>\n<p>Consider an illustrative RF channel with the following requirements:<\/p>\n<ul>\n<li><strong>Operating Frequency:<\/strong> 6 GHz<\/li>\n<li><strong>Maximum Channel Insertion Loss:<\/strong> 1.0 dB<\/li>\n<li><strong>Input Launch Loss:<\/strong> 0.15 dB<\/li>\n<li><strong>Output Launch Loss:<\/strong> 0.15 dB<\/li>\n<li><strong>Transmission\u2011Line Length:<\/strong> 4 inches<\/li>\n<\/ul>\n<p>Assuming sufficiently good impedance matching:<\/p>\n<p><strong>Available Trace Loss = 1.0 &#8211; 0.15 &#8211; 0.15 = 0.70 dB<\/strong><\/p>\n<p><strong>Maximum Average Trace Attenuation = 0.70 \/ 4 = 0.175 dB\/in<\/strong><\/p>\n<p>This preliminary budget leaves 0.70 dB for the transmission line. Actual measurements must also consider mismatch effects, fabrication variation, and measurement uncertainty.<\/p>\n<p><strong>Specify the maximum insertion loss, operating frequency range, measurement reference planes, and acceptance method before PCB fabrication.<\/strong> A board that passes at one frequency may exceed its loss limit elsewhere in the operating band.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"How_Can_You_Reduce_RF_Insertion_Loss_in_PCB_Design\"><\/span>How Can You Reduce RF Insertion Loss in PCB Design?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Reducing RF insertion loss involves controlling conductor and dielectric attenuation while minimizing impedance discontinuities. The following measures can improve transmission performance without unnecessarily increasing PCB manufacturing costs.<\/p>\n<ul>\n<li><strong>Select Low\u2011Loss Materials:<\/strong> Choose laminates with suitable Df values at the operating frequency. Compare their performance, availability, and manufacturing requirements.<\/li>\n<li><strong>Shorten Critical RF Traces:<\/strong> Reduce unnecessary routing length and avoid detours that increase attenuation.<\/li>\n<li><strong>Maintain Controlled Impedance:<\/strong> Use consistent trace geometry, dielectric thickness, and reference\u2011plane structures to limit reflections.<\/li>\n<li><strong>Optimize Copper Characteristics:<\/strong> Review copper roughness, conductor width, and thickness while maintaining the required impedance.<\/li>\n<li><strong>Minimize Via Transitions:<\/strong> Avoid unnecessary layer changes and review <a href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/08\/via-stub\/\">via stub effects<\/a>, antipads, and return\u2011path connections.<\/li>\n<li><strong>Maintain Continuous Reference Planes:<\/strong> Avoid routing critical RF signals across plane splits or poorly controlled return paths.<\/li>\n<li><strong>Review Surface Finish:<\/strong> Consider finish\u2011related attenuation where high\u2011frequency current flows through exposed conductors, particularly with nickel\u2011containing finishes.<\/li>\n<li><strong>Verify Before Production:<\/strong> Use simulation, impedance coupons, and agreed S21 measurements to check critical RF transmission requirements.<\/li>\n<\/ul>\n<p><strong>Low RF insertion loss depends on the complete transmission path, not only the PCB laminate.<\/strong> Appropriate materials, controlled geometry, and well\u2011designed transitions should be evaluated together.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"How_Can_EBest_Circuit_Support_Low%E2%80%91Loss_RF_PCB_Manufacturing\"><\/span>How Can EBest Circuit Support Low\u2011Loss RF PCB Manufacturing?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>EBest Circuit provides custom RF PCB manufacturing, material guidance, stackup review, and DFM support for high\u2011frequency applications. We help customers identify fabrication risks that may affect impedance consistency, RF performance, and production costs.<\/p>\n<p>Our manufacturing support focuses on the practical requirements of your project:<\/p>\n<ul>\n<li><strong>Choose Suitable RF Materials:<\/strong> Compare available FR-4, low\u2011loss laminates, and hybrid stackups to meet electrical requirements without unnecessary material costs.<\/li>\n<li><strong>Reduce Manufacturing Risks:<\/strong> Review stackup thickness, copper specifications, trace geometry, and tolerances before production to identify potential fabrication issues.<\/li>\n<li><strong>Maintain Impedance Consistency:<\/strong> Manufacture to agreed controlled\u2011impedance specifications and verify relevant parameters according to the approved inspection plan.<\/li>\n<li><strong>Move from Prototype to Production:<\/strong> Support prototype validation, small\u2011batch orders, and volume manufacturing while maintaining agreed fabrication requirements.<\/li>\n<li><strong>Improve Quality Visibility:<\/strong> Provide inspection and production traceability records, with project\u2011specific testing requirements confirmed before manufacturing.<\/li>\n<li><strong>Access Technical Guidance:<\/strong> Work through one sales contact with support from a three\u2011engineer technical team for manufacturability review, process support, and quality coordination.<\/li>\n<\/ul>\n<p>At <strong>EBest Circuit<\/strong>, we manufacture customer\u2011provided PCB designs and provide DFM guidance rather than original circuit design services.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"FAQs_About_RF_Insertion_Loss\"><\/span>FAQs About RF Insertion Loss<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><strong>Q1: Why does a VNA display negative S21 values?<\/strong><\/p>\n<p><strong>A1:<\/strong> A VNA expresses S21 magnitude in dB. For a passive attenuating path, the reading is negative because the transmitted signal is smaller than the incident signal. <strong>S21 = -2 dB corresponds to 2 dB insertion loss.<\/strong><\/p>\n<p><strong>Q2: What causes ripples in an RF PCB S21 curve?<\/strong><\/p>\n<p><strong>A2:<\/strong> Ripples often result from reflections between impedance discontinuities, including connector launches, vias, and trace transitions. <strong>Check S11 and fixture calibration<\/strong> before attributing the behavior to dielectric loss.<\/p>\n<p><strong>Q3: Can PCB transmission loss be expressed in dB per inch?<\/strong><\/p>\n<p><strong>A3:<\/strong> Yes. Compare the insertion loss of two matched\u2011structure test coupons with different lengths. <strong>Divide the measured loss difference by the length difference<\/strong> to estimate attenuation per inch, provided launch and mismatch effects are controlled.<\/p>\n<p><strong>Q4: Is standard FR-4 suitable for microwave PCBs?<\/strong><\/p>\n<p><strong>A4:<\/strong> FR-4 may work for short microwave transmission paths with sufficient loss margin. Longer routes or tighter attenuation limits often favor low\u2011loss materials. <strong>Evaluate the actual frequency, path length, and insertion\u2011loss budget.<\/strong><\/p>\n<p><strong>Q5: Does lower Dk always reduce insertion loss?<\/strong><\/p>\n<p><strong>A5:<\/strong> No. Dk mainly affects propagation and transmission\u2011line geometry, while <strong>Df is more directly related to dielectric attenuation<\/strong>. Copper properties and conductor dimensions also influence overall loss.<\/p>\n<p><strong>Q6: Will thicker copper improve RF transmission efficiency?<\/strong><\/p>\n<p><strong>A6:<\/strong> Not always. Additional copper thickness may reduce resistance, but skin effect limits the benefit at high frequencies. <strong>Copper roughness, trace width, and impedance geometry<\/strong> should also be considered.<\/p>\n<p><strong>Q7: Can ENIG increase RF PCB attenuation?<\/strong><\/p>\n<p><strong>A7:<\/strong> Yes, in certain structures where RF current interacts with the nickel\u2011containing finish. <strong>Review surface\u2011finish effects on exposed microwave conductors<\/strong>, especially when insertion\u2011loss margins are tight.<\/p>\n<p><strong>Q8: Should RF PCB designs avoid all vias?<\/strong><\/p>\n<p><strong>A8:<\/strong> No. Properly designed vias can provide acceptable RF transitions. <strong>Long unused stubs, impedance discontinuities, and poor return paths<\/strong> are more concerning than the presence of a via itself.<\/p>\n<p><strong>Q9: Why do different VNAs produce different S21 readings?<\/strong><\/p>\n<p><strong>A9:<\/strong> Calibration, reference\u2011plane placement, cables, connectors, and fixture conditions can affect measurements. <strong>Use consistent calibration and test configurations<\/strong> before comparing results.<\/p>\n<p><strong>Q10: Does temperature influence RF transmission attenuation?<\/strong><\/p>\n<p><strong>A10:<\/strong> Yes. Temperature can change copper resistance and dielectric properties. <strong>Check laminate performance over the required operating\u2011temperature range<\/strong> when the design has a narrow loss margin.<\/p>\n<p><strong>Q11: Is individual VNA testing required for every RF PCB?<\/strong><\/p>\n<p><strong>A11:<\/strong> Not necessarily. Testing depends on application requirements and the agreed inspection plan. <strong>RF test coupons, sampling inspections, or individual measurements<\/strong> may be used according to the required assurance level.<\/p>\n<p><strong>Q12: What information should be included in an RF PCB manufacturing RFQ?<\/strong><\/p>\n<p><strong>A12:<\/strong> Provide <strong>Gerber or ODB++ files, operating frequency, stackup, impedance targets, material requirements, and insertion\u2011loss limits<\/strong>. Include test coupon and S21 acceptance requirements where applicable.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Conclusion\"><\/span>Conclusion<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><strong>Reducing RF insertion loss starts with the right material, controlled transmission\u2011line geometry, and a realistic loss budget.<\/strong> VNA measurements help verify whether the PCB meets its RF requirements, while early DFM reviews can identify manufacturing risks before fabrication.<\/p>\n<p><strong>Ready to manufacture your low\u2011loss RF PCB?<\/strong> EBest Circuit supports custom RF PCB prototypes, customer\u2011supplied PCB designs, and volume production with technical guidance throughout the process. Send your PCB files, operating frequency, stackup, and insertion\u2011loss requirements to <strong><a href=\"mailto:sales@bestpcbs.com\">sales@bestpcbs.com<\/a><\/strong> for a manufacturing review and quotation.<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Learn what causes RF insertion loss in PCBs, how to measure S21 with a VNA, set loss limits, and reduce attenuation through materials and stackup.<\/p>\n","protected":false},"author":33247,"featured_media":37352,"comment_status":"open","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"footnotes":""},"categories":[170],"tags":[2927,8863,8861,3311,8862],"class_list":["post-37355","post","type-post","status-publish","format-standard","hentry","category-rf-board","tag-controlled-impedance-pcb","tag-low-loss-pcb-materials","tag-rf-insertion-loss","tag-rf-pcb-design","tag-vna-s21-measurement"],"acf":[],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"Learn what causes RF insertion loss in PCBs, how to measure S21 with a VNA, set loss limits, and reduce attenuation through materials and stackup.\" \/>\n\t<meta name=\"robots\" content=\"max-image-preview:large\" \/>\n\t<meta name=\"author\" content=\"Jessica, Jessica\"\/>\n\t<link rel=\"canonical\" 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