The Study and Design of a Miniaturized Microstrip Balun With a Wider Bandwidth

In this letter, a miniaturized microstrip balun is presented. It replaces the half-wavelength open microstrip line in Marchand balun with a quarter-wavelength short microstrip line. Also, to improve the insertion loss, an I-shaped slot is etched in the ground. Finally, a rectangular slot is etched in the ground near port 2 to further eliminate the imbalance. The measured result shows that the bandwidth of the proposed balun for |S
₁₁
| ≤ -10 dB is from 1.19 to 3.23 GHz, and the relative bandwidth is about 92.3%. In the operating band, the maximum amplitude and phase imbalance are 0.49 dB and 6.5°, respectively. The realized balun has a dimension of 17.5 × 18 mm
²
, equal to 0.1λ
_g
× 0.1λ
_g
(λ
_g
is the guided wavelength at 1.17 GHz, the lowest operating frequency).