A Wide Stopband Balun Bandpass Filter with Its Application to Balanced Quasi-Yagi Antenna

Abstract EN

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.