A new microstrip balun bandpass filter (BPF) with wide stopband is presented. It is realized by utilizing the out‐of‐phase feature of standing‐wave distribution on a half‐wavelength (λ/2) open‐ended microstrip line and the resonant characteristics of the triple‐mode resonators. For demonstration, a prototype balun BPF operating at central frequency (f0) of 2.34 GHz with fractional bandwidth (FBW) of about 16.7% is designed. The presented balun BPF not only exhibits nice balanced response with 0.47 dB magnitude imbalance and 4.3° phase difference but also achieves 30‐dB harmonic suppression up to 6.40 GHz (2.7f0). Afterward, this presented design is embedded into a balanced quasi‐Yagi antenna to obtain high‐selective radiation and wide stopband rejection. Experimental results of the implemented antenna indicate less than −10 dB reflection coefficient, 4.49–5.38 dBi gain, and 12.71–19.62 dB front‐to‐back ratio within the operating bandwidth.