Bandpass-Filtering Power Amplifier With Compact Size and Wideband Harmonic Suppression

This article proposed a codesign of a power amplifier (PA) and a bandpass filter (BPF) named filtering PA using metal integrated and substrate integrated suspended line (MI-SISL). Two BPFs are designed separately as the input and output matching network to realize bandpass filtering response and good harmonic suppression at the same time. The BPF matching circuits are implemented using SISL-based dual-layer interdigital capacitors for miniaturization and SISL-based dual-layer spiral inductors for low loss. The suspended substrate of the PA is patterned according to the shape of the PA core circuit, which helps to reduce the circuit loss and improve efficiency. Moreover, the metal integrated technique is also proposed by replacing the top and bottom substrates of the conventional SISL structure with metal plates with good electrical and thermal conductivities for heat dissipation. A filtering PA on the MI-SISL platform at 0.9 GHz is fabricated and measured as a demonstration case. An ultrasmall size of
$0.12\,\,\lambda _{g} \times 0.07\,\,\lambda _{g}$
is achieved, where
$\lambda _{g}$
is the guide wavelength at 0.9 GHz. To the best of our knowledge, this is the most compact filtering PA on the board level to date. In addition, a harmonic suppression level of 40 dBc in up to the fifth-harmonic frequency is achieved.