RF Filter vs. RF Duplexer: Key Differences Explained

This page compares RF filter and RF duplexer and describes the difference between them with respect to various comparison parameters.

RF Filter

The component used to filter out undesired RF signals in a particular band is called an RF filter. It’s mainly used to block a certain range of frequencies and pass others. Based on functionality, various filter types have been developed, including low pass, high pass, band pass, and band stop. It helps to improve the SNR (Signal to Noise Ratio) of the system.

Low Pass Filter (LPF)

The figure depicts an LPF response. As shown, this filter type passes signal frequencies below a certain cut-off frequency and blocks all frequencies above it. It is mainly used to remove high-frequency components from the RF signal.

High Pass Filter (HPF)

The figure depicts an HPF response. As shown, this filter type passes frequencies above a certain cut-off frequency and blocks all frequencies below it. It is mainly used to eliminate low-frequency components from the RF signal.

Band Pass Filter (BPF)

The figure depicts a BPF response. As shown, this filter type passes frequencies within a particular band and blocks signals outside this frequency band. It is mainly used to select a desired frequency range and reject other frequencies outside this band.

Band Stop Filter (BSF)

The figure depicts a BSF response. As shown, this filter type passes frequencies outside the particular band and blocks all the frequencies in the particular band. It is mainly used to remove undesired signals from a specific band.

Based on transmission line type and its construction, RF and microwave filters are divided into microstrip filter, interdigital filter, coaxial line filter, waveguide filter, comb line filter, hairpin filter type, spiral cavity type filter, ceramic di-electric filter, lumped filter, etc.

The common specifications of an RF filter are as follows:

• RF Center Frequency
• Passband Bandwidth
• In-Band Insertion Loss
• Out-of-band suppression
• Passband ripple

RF Duplexer

The device which allows an RF transceiver with a single antenna to operate simultaneously on the same frequency. It allows the receiver to continue receiving the signals while the transmitter is transmitting the signals and vice versa. It consists of filters and other RF components which helps to segregate signals by frequency, time, or polarization.

• For example, in FDD topology, a duplexer uses filters which helps to separate incoming signal and outgoing signal by frequency. FDD-based duplexer allows the transmitter and receiver to operate at the same time on different frequencies without any kind of interferences. This is shown in the figure for a GSM system.

• In TDD topology, a duplexer uses a switch or filter which helps to separate incoming signals and outgoing signals by time. In this case, the transmitter and receiver use the same frequency band but performs their respective operations in different time slots.

In addition to simultaneous transmission and reception, RF duplexers provide isolation to the output of the transmitter and prevents damage to the receiver. Hence, it protects sensitive components of the receiver.

As mentioned above, both RF filters and duplexers are used in wireless systems for different functions.