RF Filters

Purpose: Selectively pass or reject RF signals based on frequency.

Types:

• Low-Pass Filter (LPF): Passes low frequencies, attenuates high.
• High-Pass Filter (HPF): Passes high frequencies, attenuates low.
• Band-Pass Filter (BPF): Passes a specific frequency range.
• Band-Stop Filter (BSF)/Notch: Rejects a specific frequency band.

Key Parameters:

• Center Frequency / Cutoff Frequency
• Bandwidth (BW)
• Insertion Loss (Typical: 0.5–3 dB)
• Rejection / Attenuation (e.g., >40 dB at stopband)
• VSWR (e.g., <1.5:1)
• Power Handling (e.g., 1W to 100W)

Technologies:

• LC Filters: Discrete inductors & capacitors; cost-effective, moderate Q.
• SAW Filters: For MHz–GHz; compact, sharp roll-off.
• BAW Filters: Higher frequency/power than SAW; used in 5G.
• Ceramic Resonator Filters: Compact BPFs for mobile apps.
• Waveguide/Cavity: High-power, low-loss; used in radar/base stations.

Applications:

• Front-end modules in radios/phones
• Transmitter harmonic suppression
• Duplexer sections in transceivers
• Interference mitigation in dense spectrum