In this paper, a novel miniaturized microstrip branch-line coupler (BLC) with good harmonic suppression using radial stub loaded resonators is proposed. The novel structure has two significant advantages, which not only effectively reduces the occupied area to 10.3% of the conventional BLC at 0.5 GHz, but also has high 14th harmonic suppression performance. The measured results indicate that a bandwidth of more than 121 MHz has been achieved while the phase difference between S21 and S31 is within 90° ± 1.5°. The measured bandwidth of |S21| and |S31| within 3 ± 0.4 dB are 146 MHz and 151 MHz, respectively. Furthermore, the measured insertion loss is comparable to that of a conventional BLC. To validate the design concept, a new miniaturized planar BLC with good harmonic suppression using radial stub loaded resonators is designed and fabricated. Simulated and experimental results are achieved with good agreement.
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