A　compact　planar　sensor　is　presented　in　this　letter,　which　could　measure　the　dielectric　constants　of　solid　materials　at　microwave　and　sub-THz　frequencies,　simultaneously.　The　lower　band　resonator　is　based　on　a　complementary　split　ring　resonator　(CSRR),　fed　by　a　coplanar　waveguide　line　on　the　board　operating　at　4.76　GHz,　and　the　upper　band　sensor　is　a　3　×　3　CSRR　array,　excited　by　a　pair　of　WR-10　open-ended　waveguide　probes　operating　at　112　GHz.　The　upper　band　CSRR　array　is　nested　in　the　lower　band　CSRR　resonator,　but　their　sensing　functions　are　independent　of　each　other.　A　coincident　sensing　area　is　obtained　that　needs　a　testing　sample　with　small　volume.　Dielectric　films　composed　of　polydimethylsiloxane　and　barium-titanate　with　different　volume　fractions　are　used　to　verify　the　performance　of　the　sensor　in　both　frequency　scales.　The　advantages　of　the　proposed　design,　including　compact　size,　high　sensitivity,　low　sample　volume,　and　dual-scale　operation,　make　it　a　competitive　solution　for　detecting　solid　materials　with　similar　dielectric　properties　in　a　single　frequency　band,　for　application　such　as　the　food　industry,　material　quality　control,　and　biomedical.　　©　2017　IEEE.