Design of a Modified Compact Coupler with Unwanted Harmonics Suppression for L-Band Applications

This paper presents the design, analysis, and fabrication of a new miniaturized microstrip branch line coupler (BLC) with high harmonics suppression. The T-shaped resonators, open stubs cross-shaped resonators and radial stubs are used in the proposed coupler design. The designed BLC operates at 1 GHz frequency, which can suppress up to 5th spurious harmonics with a 20 dB level of attenuation. High miniaturization of about 86% is obtained for the proposed BLC, which is corresponding to the normalized size of 0.009 λg2. The measured values of isolation and return loss are obtained 28 dB and 29 dB, respectively, while the measured insertion loss of better than 0.2 dB is achieved at the operating frequency. Additionally, the operating bandwidth of the designed coupler ranges from 0.905 GHz up to 1.105 GHz, which shows a 200 MHz operating bandwidth or a fractional bandwidth (FBW) of 20%. The presented BLC is fabricated and measured, where the measurements confirm the simulated results. The designed coupler shows desirable performance compared to the recent designed couplers