A miniaturized rat‐race coupler with ultra‐wide band harmonic suppression is proposed in this letter. Anti‐parallel lines with open stubs are applied in substitution for the conventional quarter‐wavelength transmission lines. The applied structure provides an excellent harmonic suppression property with a reduced size comparing with the conventional types. The coupler operates at 2.5 GHz with a harmonic suppression up to 17.5 GHz as measured. The amplitude imbalance and phase imbalance are 0.017 dB and 0.018°, respectively.

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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 λ g × 0.013 λ 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.