Impact of point contacts in antenna simulations

Point contacts -when two faces have only one point in common- are problematic for antennas and other electromagnetic devices. The problem is we cannot determine if current is going through the point junctions or not (as different simulation methods have different results).

What we get in the real world is slightly connected, or separated, which are similar structures with different outputs. In our recent paper "Point Contacts in Modeling Conducting 2-D Planar Structures" ¹ published in IEEE Antennas Wireless Propag. Letters, We have a clear message for readers: "AVOID POINT CONTACTS" since manufacturing errors make the performance of your device unpredictable.

More details:

It is customary to look for the optimum shape of electronic devices with optimization methods. A common method to generate new geometries is by placing small rectangular patches at random places. A common problem of this routine is that it often yields to exotic shapes which include faces that do not touch except in one common point which is called point contact. These points are source of uncertainty in modelling, fabrication, and measurement of electronic and radiating systems.

It is not possible to fabricate such single point junctions in the real world. However, one often gets junctions that are slightly shifted, rounded, bridged, or chamfered. In the other words, it is either connected or not connected. To examine the issue, we simulated the similar structures with different junctions by using different computational methods. Impact of various junctions on dipole and loop antennas were modeled by method of moments (MoM), finite-difference time domain (FDTD), and finite-element method (FEM) solvers.

In this research, we studied current distribution, radiation pattern, and impedance properties. Radiation pattern defines the area that is going to be under antenna coverage (shape of the coverage), and impedance determines the maximum power that an antenna can radiate (extent of coverage). Different computational methods do not agree on modelling of the point crossing junctions which is a warning about uncertainty in using such junctions. For example, integral methods, believe that current cannot pass a point junction, while differential methods model the exact opposite results (current goes through the junction). In addition to current, other parameters like radiation pattern and impedance support that argument. On the other hand, solvers agree that a negligible change in the junction would significantly change antenna performance.

For example, some people can get out of the coverage if a piece of metal fills the gap between two chamfered cells (in the BTS antenna) and make two unconnected parts connected. Another impact is on power which leads to huge reduction of the  coverage radius. For instance, if the output power of transmitter for FM radio is decreases by a factor of 10, then the range of coverage would be just 100 meters instead of 10km.

We proposed that one should consider bridging and chamfering of the conflicting cells to find optimized structures. This is a new approach which not only reports the problem, but also provides a solution which can revolutionize both antenna industry and optimization algorithms.

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1 Thiel, D.V.; Shahpari, M.; Hettenhausen, J.; Lewis, A., "Point Contacts in Modeling Conducting 2-D Planar Structures," IEEE Antennas Wireless Propag. Letters , vol.14, no., pp.978,981, 2015 DOI:10.1109/LAWP.2014.2387437  arXiv: 1504.05944  ^↩