This paper presents highly selective, low-loss, and miniaturized balun devices fabricated using the integrated passive device (IPD) technique for the GSM band (900/1800 MHz) and the WiFi band (2400 MHz) in mobile applications. Balun devices were fabricated on a gallium arsenide (GaAs) substrate using the IPD fabrication process to reduce the overall size (0.05λg × 0.036λg at 900 MHz). Each device is the combination of lattice lumped structure with a low-pass filter and a high-pass filter configuration. This structural formation of lumped elements helps to reduce the phase mismatch error in the balun devices. For all the balun devices, the measured results indicated a minimum amplitude imbalance (
