Energy Sensitive Bandpass Filter to Protect Ku-Band LNAs from HPEM Threats

Abstract

This letter introduces an energy sensitive bandpass filter (ESBPF) to protect Ku-band low noise amplifiers (LNAs) from high power electromagnetic (HPEM) threats. The ESBPF circuit has anti-parallel Schottky Barrier diodes mounted on a planar bandpass filter (BPF) circuit. The ESBPF operates as a BPF at a power level below the maximum permissible power level (MPPL) of the LNAs. However, the circuit works like a variable attenuator at the power level equal to or higher than the MPPL of the LNAs. To increase attenuation and selectivity functions, a 63 degrees line section between two planar filter circuits loaded transversely along WR-75 waveguide has been inserted to cascade. The development of the circuit model has been started with lumped elements under the condition of a 0 dBm MPPL of LNA. Then, the model has been simulated, optimized with HFSS, and fabricated. Measurement results show that the ESBPF has insertion loss less than 1.27 dB at the power level lower than -2 dBm for the frequency range from 11.8 to 12.3 GHz. At the power level higher than -2 dBm, the circuit provides different levels of attenuation depending on the input power within the identical frequency band; 31 dB insertion loss, which provides isolation characteristic, has been measured at the power level of 30 dBm.