Compact tunable bandstop filter with wideband balun using IPD technology for frequency agile applications

A multi-chip module tunable bandstop filter with wideband balun using integrated passive device (IPD) technology is proposed. By integrating barium strontium titanate (BST) based varactors with the bandstop filter, a widely continuous tuning range of 20-dB rejection from 1.3 - 2.3 GHz is achieved. A measured insertion loss of less than 1-dB is maintained up to 5 GHz. Furthermore, a novel compact wideband balun is presented. It is built by combining distributed elements with lumped elements in the IPD platform. The measured results of the balun demonstrates an operating range of 0.5 - 2.5 GHz with ±1 dB amplitude imbalance and 180 ± 20° phase imbalance in a footprint of 1.9 × 2 mm².