A 3D RF impedance matching circuit used to package of multi-channel parallel EML array

In this paper, a novel three-dimensional (3D) RF impedance matching circuit has been designed to match the characteristic impedance of RF transmission line and reduce the reflection of RF signal. It consists of a coplanar RF transmission line array circuit and a non-coplanar termination resistor array circuit. The latter is vertically installed on the RF transmission line array circuit by soldering. The resistor array is fabricated on the two sides of circuit board that helps to increase the heat dissipation and power density of resistor. Simultaneously, the thermal characteristic is greatly improved. Moreover, the structure overcomes the limitation of conventional microwave circuit design which only focuses on two-dimensional (2D) plane. In the design, electrical crosstalk between transmission lines is comprehensively investigated by building simulation model based on three-dimensional electromagnetic field simulator. Finally, as the measurement result demonstrates, the RF impedance matching circuit we fabricated, which is only 5mm×4mm×1.2mm in size, has a good performance with reflection response of less than -10dB at about 22GHz and the 3-dB transmission bandwidth has reached up to 20GHz. The circuit can be used to the compact package of multi-channel parallel electro-absorption modulator laser (EML) array, electronic absorption modulator (EAM) array and Mach-Zehnder modulator (MZM) array.