top view of a microstrip 32 on the upper substrate 10 fig3 b shows a planar log periodic antenna structure 31 beneath the upper substrate 10 fig3 c shows a wire structure 34 beneath the lower substrate 13 as shown in fig3 b the planar log periodic antenna structure 31 comprises a first segment 311 and a second segment 312 wherein the first segment 311 further comprises a plurality of first subsegments 3111 perpendicular to the first segment 311 and the second segment 312 further comprises a plurality of second subsegments 3121 perpendicular to the second segment 312 those skilled in the art can easily understand the cpw fed planar log periodic antenna structure of the present invention through fig3 a to 3 c fig4 a to 4 c are top views partially showing a microstrip 42 of the cpw fed planar log periodic antenna according to the present invention wherein fig4 a shows the left part of the microstrip 42 fig4 b shows the middle part of the microstrip 42 and fig4 c shows the right part of the microstrip 42 as shown in the drawings the microstrip 42 comprises a signal ground region 420 and a signal transmission region 421 wherein the width of the signal transmission region 421 increases towards two edges of the upper substrate a first dielectric region 422 a second dielectric region 423 and a third dielectric region 424 are formed around the signal transmission region 421 the first dielectric region 422 and the second dielectric region 423 extend towards two edges of the upper substrate and form an angle with the third dielectric region 424 a fourth dielectric region 425 and a fifth.