Based on stub loaded meandrous coupled lines, a novel microstrip coupler is designed, fabricated and measured for wireless applications. It is very compact with high performance. The size of this coupler is only 0.0028λ g2, where it operates at 875 MHz. The values of S11, S21, S31 at the operating frequency are -24.97 dB, -3.058 dB and -3.033 dB respectively. Therefore, the insertion losses are very low and the magnitudes of S21 and S31 are well balanced. The phase imbalance at the operating frequency is 0.5°. From 790 MHz up to 1.18 GHz, S11 is better than -10 dB, the maximum phase imbalance is lower than 4.5° and the maximum magnitude imbalance is lower that ±0.5 dB. Therefore, it has 40% fractional bandwidth (FBW) that covers 0.79 GHz to 1.18 GHz. Its in-band isolation factor is better than -25 dB. The important advantages of this coupler compared to most of the previous designs is having a filtering frequency response and having flat passbands with a maximum group delay of 1 ns.
