Compact 915MHz RF Filter for LoRa and ISM band Interference

In crowded ISM bands such as 868MHz and 915MHz, receivers often suffer from strong out-of-band interference.This reduces sensitivity, increases noise floor and can cause packet loss in LoRa and SDR systems.

Many available filtering solutions are either too large, too expensive or not optimised for embedded systems.SDR and IoT developers often lack a small, inline RF filter that can be easily integrated into existing setups.

This project presents a compact 915MHz RF filter module designed for inline use between antenna and receiver front-end.It provides high out-of-band rejection while maintaining low insertion loss in the passband.

Key Design Features

Compact 10mm by 12mm footprint

u.fl rf connectors for direct integration

Designed for 50 ohm systems

Optimised for 915MHz ISM band applications

Inline module form factor (plug-and-play integration)

The filter was evaluated using a fully calibrated VNA to verify insertion loss and rejection performance.Results show strong attenuation outside the 915MHz band while maintaining minimal signal degradation within the passband.See plots below of filter performance:

This filter module is suitable for:

SDR receivers in noisy rf environments

LoRa/IoT gateway front-ends

RF prototyping and lab setups

Embedded wireless development systems

This project demonstrates a compact, practical approach to improving RF receiver performance in real-world environments where interference is a limiting factor.