Low PIM Diplexers

A Low PIM (Passive Intermodulation) diplexer is a passive RF component designed to either split or combine two frequency bands with minimal interference. It isolates high and low frequency bands to enable multiple signals to travel over a single path while ensuring extremely low levels of intermodulation distortion, which is critical in high-performance RF systems.

Low PIM is essential in systems where multiple high-power signals share components, such as:

• Cellular base stations (4G/5G)

• DAS (Distributed Antenna Systems)

• Satellite and radar systems
  Uncontrolled PIM can cause self-interference, degraded signal quality, and reduced system capacity.

PIM is caused by:

• Nonlinearities in passive materials (e.g., ferrous metals, poor-quality plating)

• Mechanical junctions (e.g., loose connectors, poor solder joints)

• Contaminants like dirt or corrosion at interfaces

PIM is typically measured in dBc (decibels relative to the carrier), with two tones injected at high power (usually 2 × 43 dBm = 20 W), and the intermodulation products (e.g., 3rd-order) are measured.

• Low PIM rating: –150 dBc or better (often –160 dBc in critical applications)

• Cellular infrastructure (e.g., BTS, RRH)

• Distributed Antenna Systems (DAS)

• In-building wireless systems

• Public safety and critical communications

• Multi-band antenna systems

To reduce PIM, manufacturers use:

• High-purity, non-ferromagnetic metals (e.g., aluminum, silver-plated brass)

• Low-PIM dielectric materials

• High-quality connectors (like DIN 7/16 or 4.3-10)

• Silver plating to reduce surface resistance and non-linear junctions

• PIM rating: –150 dBc or better

• Insertion loss: ≤ 1 dB (usually lower)

• Isolation: ≥ 60 dB between ports

• Return loss: > 18 dB (VSWR < 1.3:1)

• Power handling: Up to 300 W or more (depends on application)

• Use Low PIM-rated cables and connectors

• Ensure tight, torque-specified connections

• Avoid bending or straining cables

• Keep connectors clean and corrosion-free

• Avoid using ferrous tools near the RF path

A Low PIM diplexer separates or combines two different frequency bands, while a Low PIM duplexer is typically designed to allow simultaneous transmit and receive operation within closely spaced bands. Duplexers generally require even higher isolation and stricter PIM control, especially in full-duplex cellular systems.

High-quality Low PIM diplexers are designed to maintain stable PIM performance over many years. However, factors such as thermal cycling, vibration, connector wear, and environmental exposure can degrade PIM over time. Regular inspection and proper installation help preserve long-term performance.

Yes, reputable manufacturers perform factory PIM testing on Low PIM diplexers using standardized two-tone test methods. Some suppliers test 100% of units, while others use sample-based testing. Factory test reports are often available for critical infrastructure deployments.

Wider bandwidth designs can be more challenging to maintain ultra-low PIM because they require more complex internal structures and additional junctions. Narrower, band-optimized diplexers typically achieve better PIM performance due to simpler signal paths and fewer nonlinear interfaces.

Key trade-offs include:

• Cost vs PIM level (lower PIM requires premium materials and manufacturing)

• Size vs power handling (high power often means larger structures)

• Bandwidth vs isolation (wider bands can reduce selectivity)

• Connector type vs compactness (rugged connectors are larger but offer better PIM stability)

Understanding these trade-offs helps ensure the diplexer meets both performance and budget requirements.

When selecting a Low PIM (Passive Intermodulation) diplexer, you’re often working in high-performance RF systems where signal clarity and reliability are critical — especially in cellular infrastructure, DAS, public safety, and multi-band antenna systems.

Here are the key parameters you should consider:

1. PIM Performance (Passive Intermodulation Level)

• Definition: The level of unwanted intermodulation products generated within the passive diplexer itself.

• Measured in: dBc (decibels below carrier)

• Target:

  • –150 dBc or better (standard)

  • –160 dBc or better (premium systems)

• Why it matters: PIM causes self-interference, reduces signal-to-noise ratio, and limits system capacity—especially in high-power, multi-carrier systems like 4G/5G.

2. Frequency Bands

• Definition: The two (or more) frequency ranges the diplexer separates or combines.

• Why it matters: Must match the Tx/Rx bands or co-located services (e.g., 700 MHz and 2600 MHz in LTE/5G systems).

• Tip: Choose a diplexer specifically designed for your exact band pairing to ensure proper filtering and isolation.

3. Bandwidth (Per Port)

• Definition: The width of each passband the diplexer supports.

• Why it matters: Needs to accommodate the entire operating band including any carrier aggregation or channel overlap.

4. Insertion Loss

• Definition: The amount of signal attenuation introduced by the diplexer in each passband.

• Typical Values:

  • < 0.5 dB (excellent)

  • < 1 dB (good)

• Why it matters: Lower insertion loss = better signal strength, less need for amplification, and improved link budget.

5. Isolation Between Ports

• Definition: The attenuation between the two frequency bands’ signal paths.

• Typical Values:

  • ≥ 50–60 dB is desirable

• Why it matters: High isolation prevents cross-band interference, especially in shared-antenna systems.

6. Return Loss / VSWR

• Definition: A measure of how well the diplexer is impedance-matched to your system (typically 50 ohms).

• Typical Values:

  • Return loss > 18 dB

  • VSWR < 1.3:1

• Why it matters: Poor return loss causes signal reflections, degrades performance, and increases the risk of PIM.

7. Power Handling

• Definition: The maximum RF power the diplexer can handle per port.

• Typical Values:

  • Up to 300 W (for DAS and macro cells)

  • Lower for small cell or indoor applications

• Why it matters: Ensure the diplexer can safely handle peak and average power levels without overheating or generating PIM.

8. Connector Type and Quality

• Common Options:

  • 7/16 DIN (rugged, high power)

  • 4.3-10 (compact, low PIM, modern systems)

  • N-type (lower power, common in indoor)

• Why it matters: Connector quality and torque affect both PIM and signal integrity. Use Low PIM-rated connectors and cables.

9. Environmental Ratings

• Definition: Ability to operate in harsh conditions (temperature, moisture, vibration).

• Look for:

  • IP65/IP67 for outdoor use

  • Wide temp range (e.g., –40°C to +85°C)

• Why it matters: Especially important in outdoor, rooftop, or tower-mounted deployments.

10. Mechanical Size and Mounting Options

• Why it matters: In dense rack or antenna environments, size and weight can be critical.

• Tip: Look for compact, lightweight, and mounting-flexible designs if needed.

11. Certification and Compliance

• Why it matters: Especially for public safety or commercial wireless infrastructure, diplexers may need to comply with:

  • RoHS/REACH

  • Carrier-grade requirements

  • UL, FCC, CE, or regional telecom regulations

12. Customizability

• Why it matters: For non-standard or multi-band deployments, you may need:

  • Custom frequency pairs

  • Tri-/quad-plexer configurations

  • Special packaging or connector options

To place an order for Low PIM diplexers please contact us and we will help you!