A Dual Band Microstrip Branch Line Coupler with Harmonics Suppression Using LPF and Open Ended Stubs

A dual band branch line coupler (DB-BLC) with wide harmonics rejection band is designed. The designed coupler can work at 2.6 and 4 GHz and also, provides ultra-wide suppression band of 5.2 GHz-30 GHz with better than 20 dB rejection level. In this design four low pass filters and four open ended stubs are utilized to provide dual operating frequencies and harmonics rejection at higher frequencies. Applied low pass filter has a 4.8 GHz cut off frequency and a size of $0.18 \lambda_{g} \times 0.12 \lambda_{g}$. The obtained values of S
12
and S
13
at 2.6 GHz (lower pass band) are 3.2 dB and 2.8 dB, which show lower than 0.2 dB insertion loss at the first working band. The obtained values of S
11
and S
14
are lower than 33 dB at the lower pass band. Moreover, the obtained values of S
12
and S
13
at 4 GHz (higher pass band) are 2.9 dB and 3.4 dB, which show lower than 0.4 dB insertion loss at the higher pass band. The obtained values of S
11
and S
14
are lower than 22 dB at the higher pass band.