A compact branch-line coupler with harmonic suppression using novel circular-shaped resonators for medical imaging systems

This article presents a novel design of a branch-line coupler that possesses the capability to effectively eliminate undesired harmonics while simultaneously achieving a reduction in physical dimensions. The architecture of this coupler incorporates circular-shaped suppressor cells specifically tailored for applications in medical imaging systems (MISs). The proposed coupler has been specifically developed for the central frequency of 2.25 GHz. This scheme demonstrates the capability to eliminate harmonics up to the 5th order and achieve a reduction in size by 80% when compared to its conventional structure. To clarify, the suggested coupler effectively eliminates the second, third, fourth, and fifth harmonics by reducing their amplitudes by −23.3 dB, −33.7 dB, −23.1 dB, and −26.5 dB, respectively. The coupler that has been designed exhibits an insertion loss of less than 0.06 dB in both transmission paths at the specified operating frequency. Furthermore, the measured values for return loss and isolation are −22 dB and −24.1 dB, respectively. The coupler that has been designed demonstrates satisfactory performance within the frequency range of 2.05–2.7 GHz, resulting in a fractional bandwidth (FBW) of 28.8%.