Yes! There is a trade-off between insertion loss and isolation of Ka-band circulators. This trade-off is mainly reflected in the selection of materials, structures, and processes during the design optimization process:
Specific manifestations of the trade-off
Influence of materials and structures
Ferrite thickness and magnetization: For example, the increase in the thickness of the BaM hexagonal ferrite substrate will increase the insertion loss (increase in S21), but after optimization, a high isolation of 53dB and a minimum insertion loss of 0.85dB can be achieved.
This shows that the two must be balanced by adjusting the thickness and the center disk radius (R0).
Impedance matching design: The strontium ferrite self-biased circulator with multi-branch short-line impedance matching has an insertion loss of 3.4dB at 29 GHz but an isolation of 29.5 dB. If you pursue higher isolation, you may need to sacrifice some insertion loss performance.
Bandwidth and performance trade-off
The microstrip circulator achieves ≤0.1dB insertion loss and ≥23dB isolation in a bandwidth of 33–41GHz; while the similar design achieves insertion loss <0.3dB but isolation >20dB in a bandwidth of 31–40GHz. Wider bandwidth may make it difficult to optimize both at the same time.
Process limitations
Point out that the miniaturized design (7mm×7mm×0.4mm) requires fine-tuning of the Y junction size to balance return loss (S11) and isolation, while
The commercial microstrip embedded circulator achieves an insertion loss of 2.2dB, but isolation is only > 20 dB.
Typical data comparison
Case Insertion loss Isolation Key design factors Source
BaM ferrite optimization design ≤1dB ≤53dB Y junction size and substrate thickness optimization
HFSS simulation microstrip circulator ≤0.1dB ≥23dB "Double peak" structure widens bandwidth
L/S band commercial circulator ≤0.35dB ≥20dB (non-Ka band but reflects the general trade-off trend)
Conclusion
When designing Ka-band circulators:
High isolation usually requires a stronger magnetic field or a more complex impedance matching structure (such as multi-branch stubs), which may increase insertion loss.
Low insertion loss requires simplifying the transmission path or optimizing the conductivity of the material (such as a thin ferrite substrate), but may limit the ability to control the magnetic field.
Broadband design requires sacrificing some performance peaks (such as the "double peak" curve reduces the overall index).
Therefore, engineers need to optimize according to specific application requirements (such as satellite communication requires low insertion loss and radar requires high isolation).
Reference:
1. Niharika Narang, Pushparaj Singh. "Metal contact RF MEMS switch design for high performance in Ka band." IOP Conference Series: Materials Science and Engineering
2. A. White, G. H. Ahn et al. "Integrated passive nonlinear optical isolators." Nature Photonics