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Insertion Loss Benchmarks for High-Frequency Micro Coaxial Cables: What to Expect

High-frequency micro coaxial cables are essential for connecting sensitive components in modern electronics like smartphones, radar systems, satellite communications, medical devices, and high-speed digital circuits. One of the most critical performance parameters for these tiny cables is Insertion Loss. Understanding typical benchmarks is vital for designing reliable systems.

What is Insertion Loss?

Simply put, insertion loss measures how much signal power disappears (“is lost”) as it travels through the cable. It’s expressed in decibels (dB). A lower dB value indicates less signal loss, meaning more of your valuable signal reaches the other end. Think of it like water pressure dropping over a long, thin pipe – insertion loss is the measure of that drop for electrical signals.

Why is Insertion Loss Critical at High Frequencies?

As signal frequencies increase (think GHz ranges), insertion loss becomes increasingly significant. This is due to:

Skin Effect: High-frequency signals travel mostly near the conductor’s surface. This reduces the effective conducting area, increasing resistance and thus loss.
Dielectric Loss: The insulating material (dielectric) between the center conductor and shield absorbs some signal energy as heat.
Radiation Loss: Tiny cables can leak small amounts of signal energy, especially if not shielded perfectly or bent sharply.
Losses add up quickly over distance and frequency, potentially degrading signal strength below usable levels or distorting it beyond recognition.

Typical Insertion Loss Benchmarks for Micro Coax

Crucial Note: Insertion loss HIGHLY depends on several factors:

Exact Cable Type/Series: Manufacturers have many specific series (e.g., 0.047″, 0.034″, 0.027″, 0.020″ diameter are common micro coax sizes).
Frequency: Loss increases dramatically with frequency. Benchmarks must specify the GHz point.
Dielectric Material: PTFE-based dielectrics generally offer lower loss than polyethylene.
Length: Always specified per unit length (e.g., dB per meter or dB per foot).
Construction: Conductor material (often silver-plated copper), shield effectiveness (braid + foil vs. braid only), center conductor size.

Here’s a table showing representative insertion loss benchmarks for common commercial micro coaxial cable types at popular frequency points:

Cable Diameter (Approx.)	Common Series Examples (e.g.)	Frequency	Typical Insertion Loss Benchmark (Approx.)
~0.047″ (1.19 mm)	RG-178B/U, UFB136A, C091	3 GHz	1.1 – 1.5 dB/ft (3.6 – 4.9 dB/m)
		6 GHz	1.8 – 2.5 dB/ft (5.9 – 8.2 dB/m)
~0.034″ (0.86 mm)	RG-316/U, M17/065, UFB112A	3 GHz	1.6 – 2.0 dB/ft (5.2 – 6.6 dB/m)
		6 GHz	2.4 – 3.2 dB/ft (7.9 – 10.5 dB/m)
~0.032″ (0.81 mm)	RG-188A/U, UFB127A	3 GHz	1.3 – 1.8 dB/ft (4.3 – 5.9 dB/m)
		6 GHz	2.0 – 2.8 dB/ft (6.6 – 9.2 dB/m)
~0.027″ (0.68 mm)	–	3 GHz	1.7 – 2.3 dB/ft (5.6 – 7.5 dB/m)
		6 GHz	2.8 – 3.8 dB/ft (9.2 – 12.5 dB/m)
~0.020″ (0.51 mm)	RG-405/U, M17/135, UFB091A	3 GHz	2.0 – 2.7 dB/ft (6.6 – 8.9 dB/m)
		6 GHz	3.3 – 4.5 dB/ft (10.8 – 14.8 dB/m)
		26.5 GHz	12.0 – 18.0 dB/ft (39.4 – 59.0 dB/m) *
		40 GHz	16.0 – 24.0 dB/ft (52.5 – 78.7 dB/m) *

(* Important MM-Wave Note): Extremely high-frequency signals (e.g., 26.5 GHz, 40 GHz) used in 5G mmWave, radar, and advanced SATCOM demand ultra-low-loss micro coax (often 0.020″ or smaller). Benchmarks vary even more significantly here depending on specific materials and construction (e.g., solid vs. stranded center conductor, premium dielectrics). Losses become very high per foot/meter, making cable length critically important.

Key Considerations Beyond Raw dB Numbers:

Datasheets Are King: The benchmarks above are general ranges for popular cable types. ALWAYS consult the specific datasheet for the exact cable you plan to use. Manufacturers like Times Microwave, Molex, Samtec, Gore, TE Connectivity, Huber+Suhner, and Carlisle provide detailed insertion loss vs. frequency graphs.
Connectors Matter: The connectors soldered or crimped onto the cable ends add their own significant loss (easily 0.2 to 0.5 dB per connector for micro types, often rising with frequency). This is separate from the cable loss. Total system loss = Cable loss + Connector loss at both ends.
Bend Radius: Bending micro coax beyond its specified minimum bend radius sharply increases loss at the bend point.
Phase Stability: For precise timing/phase applications (like phased arrays), low loss AND stable phase characteristics are needed. Low-loss cables often correlate with better phase stability.

Conclusion:

Expect insertion loss for high-frequency micro coax to range from roughly 1.0 dB/ft at 3 GHz for larger (~0.047″) cables to over 20 dB/ft at 40 GHz for the smallest (~0.020″) cables. Loss increases steeply with both frequency and decreasing cable diameter. While the benchmarks provided give a realistic starting point, always rely on the official manufacturer’s datasheet for the precise cable you select. Factor in connector losses and bend effects to accurately predict overall system performance, especially in demanding applications like mmWave communications. Choosing the right micro coax with known low-loss characteristics is fundamental to ensuring your high-frequency signal arrives intact.