Design of a Microstrip Line to CPS Transition With 1:300 Bandwidth for the HF and VHF Bands

A PCB based planar back-to-back microstrip line to coplanar strip line (CPS) transition is presented for the HF and VHF band applications. A metallic via and a slot is used to convert the unbalanced microstrip line mode to the balanced CPS mode. The measured results show a return loss better than 10 dB over 1–300 MHz. Over the band, measured insertion loss is less than 0.7 dB. Removal of any frequency dependent physical parameter helps to achieve 1:300 bandwidth. The dimension of a single transition fabricated on a RO4003C substrate with a dielectric constant of 3.55 is just 105 mm × 40 mm.