A miniaturized lumped element directional coupler with parasitics compensation

This paper presents a miniaturized coupled line directional coupler carefully designed in a lumped element configuration. Due to the fact that all the parasitics (i.e. ohmic losses, inductances and capacitances) were taken into consideration at different stages of the design process, this resulted in a measured response which is in very close agreement with the simulated one. The measurements showed an input return loss and isolation of 22.43 dB and 15.76 dB respectively at 1 GHz with a 10-dB fractional bandwidth of almost 10.85%. The measured coupling and thru coefficients are 3.48 dB and 4.01 dB respectively at the same operating frequency. These values agreed quite well with the ones from the electromagnetic simulations. The reduction in the measured thru coefficient is mainly due to the added losses of solders and co-axial connectors. A phase error of about 2.4° with respect to the expected 90° phase difference was noticed.