Suppression of Second and Third Harmonics Using $\lambda /$ 4 Low-Impedance Substrate IntegratedWaveguide Bias Line in Power Amplifier

In this letter, a low-impedance substrate integrated waveguide (SIW) bias line is proposed to suppress second and third harmonics in power amplifier. Such a bias line consists of a 4 low-impedance microstrip line and a shorted SIW that can operate as a radio frequency block and suppress any harmonic signals from entering the dc source. Since the frequency of the second harmonic components is lower than the inherent cutoff frequency of the SIW, second harmonic components are blocked. At the same time, third harmonic components are shorted by the shorted SIW. Measured results show that second and third harmonic components can be reduced by 25 dB and 13 dB, respectively, compared to the outcomes using conventional 4 high-impedance microstrip bias line. Also, both 1 dB compression point and power added efficiency are improved slightly.