In modern wireless systems such as 5G, DAS (Distributed Antenna Systems), private networks, SATCOM, and public safety communications, engineers often focus on baseband units, RF modules, spectrum resources, and algorithms. However, once a system is deployed in real environments — office buildings, airports, tunnels, ships, or macro sites — the actual performance ceiling is usually determined by a less visible part: the RF passive chain.

Power dividers, combiners, couplers, feeders, jumpers, connectors, and antennas directly influence signal coverage and interference levels. Among all specifications, two of the most critical yet frequently overlooked parameters are:

Low PIM (Passive Intermodulation) and Low Insertion Loss.

Simply put:
Low Insertion Loss = Deliver more signal.
Low PIM = Generate less interference.

1. What Is Low PIM (Passive Intermodulation)?

1.1 Where Does PIM Come From?

PIM (Passive Intermodulation) occurs when multiple high-power RF signals pass through passive components that contain microscopic nonlinear points. These nonlinear effects cause new unwanted frequencies to be generated inside devices that should ideally be linear.

Common sources include:

• Poor metal contact
• Oxidation of plated surfaces
• Material impurities
• Micro gaps in structures
• Uneven mechanical pressure
• Magnetic effects from screws or springs

Ideally, passive components only transmit signals. But under high power, even tiny nonlinearities can behave like semiconductor junctions and generate intermodulation products.

For example, if two carriers exist:

• f1 = 1800 MHz
• f2 = 1900 MHz

They may produce intermodulation such as:

• 2f1 − f2
• 2f2 − f1

If these fall into the uplink band, the passive component itself becomes an interference source.

1.2 Impact of High PIM on Networks

Excessive PIM typically results in:

• Raised uplink noise floor
• Reduced receiver sensitivity
• Lower cell-edge throughput
• Call drops and unstable connections
• Persistent interference that is difficult to locate

Many field issues that appear to be coverage problems are actually caused by PIM from the RF passive chain.

1.3 What Does Low PIM Mean?

Low PIM means that a passive component generates extremely low intermodulation products under high-power, multi-carrier operation.

Typical engineering specifications:

• PIM ≤ -150 dBc
• PIM ≤ -155 dBc
• PIM ≤ -160 dBc

The more negative the value, the better the performance. In base stations, DAS, and 5G MIMO systems, low PIM is no longer optional — it is a necessity.

2. What Is Low Insertion Loss?

2.1 Understanding Insertion Loss

Insertion Loss describes how much signal power is lost when a component is inserted into the RF path.

In simple terms:

How much signal goes in, and how much comes out.

For example:

• Input power: 100 W
• Output power: 80 W
• Insertion Loss ≈ 1 dB

All passive devices introduce some loss, but professional RF design aims to minimize it.

2.2 What Does Low Insertion Loss Mean?

Low Insertion Loss means minimal signal attenuation and high transmission efficiency.

Typical values:

• 0.05 dB
• 0.1 dB
• 0.2 dB
• 0.3 dB

Smaller numbers indicate better signal preservation.

2.3 How Insertion Loss Affects Coverage

Insertion loss may look small, but it accumulates quickly in real networks.

Engineering experience shows:

Every additional 1 dB of loss may reduce coverage distance by 10–15%.

High insertion loss leads to:

• Shorter downlink coverage
• Lower uplink SNR
• Higher PA loading
• Increased energy consumption
• Reduced system capacity

2.4 Where Does Insertion Loss Come From?

• Conductor loss
• Dielectric loss
• Reflection loss (poor VSWR)
• Structural discontinuities
• Impedance mismatch at interfaces

3. Low PIM vs Low Insertion Loss

In short:

Low insertion loss ensures efficient transmission, while low PIM protects the network from internal interference.

4. Understanding Them in a Real RF Chain

A typical RF path looks like:

RRU → Jumper → Power Divider → Feeder → Coupler → Antenna

If insertion loss is high, coverage is naturally limited. If PIM is high, uplink performance is permanently disturbed.

Even with advanced AAU, Massive MIMO, and modern algorithms, poor RF passive performance creates a hard ceiling for system quality.

RF passive components are therefore not accessories — they are part of the system performance architecture.

5. How to Achieve Low PIM and Low Insertion Loss

• High-purity, non-magnetic metals
• Stable silver or copper plating
• Precision CNC machining
• Consistent mechanical pressure control
• Non-magnetic screws and fasteners
• Strict PIM testing procedures

These manufacturing disciplines separate professional RF suppliers from ordinary mechanical parts producers.

6. Conclusion

In modern wireless networks, real user experience is not defined only by baseband and algorithms, but also by every silent working passive component in the RF chain.

Low insertion loss ensures maximum signal delivery, and low PIM prevents passive devices from becoming interference sources.

Only when the RF passive chain delivers high efficiency and low interference can 5G, DAS, private networks, and SATCOM systems achieve their true performance potential.