Terminology » Suspended Substrate Vs Traditional Stripline:Key differences

Suspended Substrate Vs Traditional Stripline:Key differences

suspended substrate stripline traditional stripline stripline rf filter microwave

Introduction : Both are high performance planar transmission lines. They have their unique advantages such as low loss, broad bandwidth and TEM behavior. Both of these striplines differ greatly in structure, dielectric use and manufacturing complexity.

Traditional stripline

A planar transmission line where the signal trace is sandwiched between two ground planes fully embedded in a solid dielectric substrate. The key points are as follows.

Supports pure TEM mode, not quasi-TEM ; with good shielding and low radiation
Advantages : Offers wide bandwidth, good isolation, lower attenuation compared to microstrip line.
Disadvantages : Complex and costly fabrication, narrow trace widths, difficulty in tuning or troubleshooting

Suspended substrate stripline

It is a transmission line in which conductor is printed on very thin dielectric substrate suspended in air between two ground planes. In this type, most of the EM field propagates through air, leading to exceptionally low loss and higher Q. The key points are as follows.

True TEM propagation
Advantages : High Q, wide bandwidth, robust temperature stability, wide impedance options, broadside coupling, layout flexibility etc.
Disadvantages : Manufacturing complexity

Traditional Vs Suspended Substrate Stripline

The figure depicts traditional stripline as well as suspended substrate stripline structure versions.

Key differences

Feature	Suspended Substrate Stripline	Traditional Stripline
Dielectric medium	Primarily air with minimal dielectric support	Solid dielectric material throughout
Loss/ Q-factor	Very low loss with high Q	Low loss but lower Q
Temperature stability	Excellent, minimal effect from dielectric variations	Good, but more susceptible to dielectric shifts
Shielding / Radiation	Excellent shielding, no radiation	Well shielded, minimal emissions
Fabrication complexity	High	Moderate
Miniaturization	Challenging due to physical housing and air gaps	Good; compact multi-layer layouts possible

Conclusion: Suspended substrate stripline offers pristine performance, lower loss, higher Q factor and wider bandwidth due to air as dielectric. Traditional stripline excels in compactness and ease of PCB integration. Selection of appropriate stripline depends on performance goals versus manufacturability and space constraints.