A Highly Selective and Compact Bandpass Filter with a Circular Spiral Inductor and an Embedded Capacitor Structure Using an Integrated Passive Device Technology on a GaAs Substrate

As one of the most commonly used devices in microwave systems, bandpass filters (BPFs) directly affect the performance of these systems. Among the processes for manufacturing filters, integrated passive device (IPD) technology provides high practicality and accuracy. Thus, to comply with latest development trends, a resonator-based bandpass filter with a high selectivity and a compact size, fabricated on a gallium arsenide (GaAs) substrate is developed. An embedded capacitor is connected between the ends of two divisions in a circular spiral inductor, which is intertwined to reduce its size to 0.024 &lambda
g &times
0.013 &lambda
g with minimal loss, and along with the capacitor, it generates a center frequency of 1.35 GHz. The strong coupling between the two ports of the filter results in high selectivity, to reduce noise interference. The insertion loss and return loss are 0.26 dB and 25.6 dB, respectively, thus facilitating accurate signal propagation. The filter was tested to verify its high performance in several aspects, and measurement results showed good agreement with the simulation results.