Monday, February 17, 2014

Multiport matching in Optenni Lab, part 2

Guest post by Jussi Rahola, Managing Director, Optenni Ltd.
As discussed in the previous blog entry, when we at Optenni were designing the multiport features in the Optenni Lab matching circuit optimization software, one of the key questions was the choice of an appropriate cost function in the matching circuit optimization. We identified two distinct cases for the multiport matching, each with its own optimization goals. The radiating antenna case was discussed before, and this time I’ll be focusing on multiport matching of non-antenna devices.

In radiating antenna applications, coupling between the antennas is undesirable as it reduces the antenna efficiency. However, in many other matching applications (for example, amplifier and filter matching, matching of coil-type antennas for maximal power transfer in wireless charging, and near-field communication), coupling between the external ports is actually desired. The picture below describes the various loss mechanisms affecting the transfer of power between the ports.

In this matching application, the main optimization goal is to maximize some of the S-parameters of the system describing the transmission (e.g. S21), but at the same time stop bands for the same S parameters can also be specified. Optenni Lab designs matching circuits that obtain an optimal balance between the different loss terms. Note that it is not enough to minimize the reflected power alone (i.e. S11); losses in the matching network may reduce the transferred power dramatically.

Losses in general multiport matching

The design flow for multiport matching using CST STUDIO SUITE® and Optenni Lab is very simple. First, simulate the multiport structure in CST MICROWAVE STUDIO®. With a macro command, the simulated impedance data can be transferred straight to Optenni Lab. Next, depending on the application, start either the multiantenna matching or the general multiport matching procedure, enter the relevant frequency bands that the efficiencies or S-parameters should be optimized over, along with the number of matching components and component series to be used from the component library. Optenni Lab will quickly calculate multiple suitable optimized matching circuit configurations. The sensitivity of the results to component tolerances can be analyzed, allowing you to quickly optimize and analyze different multiport matching configurations.  The matching circuits can then be transferred back into CST DESIGN STUDIO™ with a single command for further analysis and inclusion in the full 3D model.

If you’re interested in matching circuit optimization and the link between Optenni Lab and CST STUDIO SUITE, more information is available at the Optenni Ltd website and in the CST-Optenni whitepaper.

Friday, February 14, 2014

Accepting Research Papers for CST Uni Publication Award 2014

When submissions for the CST University Publication Award come in, we’re always excited to see not only the electromagnetic (EM) simulation techniques being used, but also the wide scope of research applications.

Last year we granted the award for papers that looked into metamaterials, MIMO antennas, impedance cardiography and particle beam focusing. Now in our 11th year of granting the award, we are quite sure that we’ll be discovering more interesting and novel areas of application.

If you’re interested in sending us a research paper for consideration, read about the submission procedure below.

What is the CST University Publication Award?
The Award is granted to universities for their work in the application of 3D EM field simulation – shown through published research papers. The winners of the Award are provided with a one year extension to their current CST STUDIO SUITE® license.

What are the prerequisites for participation?
For a paper to be eligible for consideration, it must:
  • be authored or co-authored by university researchers,
  • be published in either a scientific journal or conference proceeding,
  • use numerical results that are either entirely or in part obtained through simulation using CST software products and
  • be published between April 1, 2013 and March 31, 2014.
How can my university participate?
Universities can apply by sending their research paper in electronic format to CST. The submission must be in English and should also state the place of publication. Only one paper per candidate will be considered so please limit your submission to one paper.

How are the winners chosen?
Research papers are evaluated on a number of criteria, including originality of the application or the theory, clarity of presentation, as well as the skilful usage of CST software features.

When is the deadline?

March 31, 2014.

For more information on the CST University Publication Award and to find out about our University Program, feel free to visit

Monday, February 3, 2014

Multiport antenna matching in Optenni Lab - MIMO

Guest post by Jussi Rahola, Managing Director, Optenni Ltd.

Losses in a device with two radiating antennas.
Optenni Lab is a software tool for matching circuit design and optimization. Developed to support the design process for RF components and antennas, Optenni Lab can improve the efficiency of a system designed using full-wave simulation. We at Optenni Ltd are always developing new features to extend the usefulness of the software, and have recently introduced multiport matching.

When we were designing the multiport features in Optenni Lab, one of the key questions was “Which cost function is most appropriate for matching circuit optimization”. In other words, “What variables exactly do we want to optimize?” Rather quickly it became clear that the optimization goal should not just be to obtain the best possible impedance match at all ports. This can be easily achieved by just adding enough resistive losses in the matching network, but obviously, adding such large losses reduces the efficiency of the antenna.

Instead, we identified two distinct cases for the multiport matching, each with their own optimization goals: systems with multiple radiating antennas (e.g. MIMO antennas) where the goal is to maximize transmitted power and minimize the coupling between elements, and systems with both radiating and transmitting elements (e.g. wireless power transfer) where the best efficiency is instead achieved by maximizing the coupling between antennas. In this blog entry I’ll be discussing the case where we are designing the matching for multiple radiating antennas in the same device. The other case will be covered in another blog entry.

When designing devices with multiple antennas, the goal of matching circuit design should be to maximize the antenna efficiency. The picture describes the different loss mechanisms affecting antenna efficiency: loss due to impedance mismatch, losses in the matching components, coupling to the other ports and losses in the antenna structure (described by antenna radiation efficiency). The antenna system is supposed to radiate as much of the input power as possible, to be captured by receiving antennas at the other end of the link (not shown). Any energy that is coupled to the other device antenna at right reduces the efficiency of the antenna at left.

Without careful antenna and matching circuit design, you could end up with a nicely matched but inefficient antenna system, in which most of the power is coupled to the other antenna port. When the matching circuits are optimized for maximal total efficiency, we might actually want to have some impedance mismatch because it will reduce the coupling to the other port and thus increase the overall efficiency. Optenni Lab designs matching circuits with optimized balance between the different loss terms, giving optimal total efficiency. Optenni Lab’s simultaneous multi-antenna matching can handle any number of antennas and also supports the optimization of tuning and decoupling components that are placed within the antenna structure.

Of course, in other cases, a strong coupling between elements is actually desired. In these cases, we want a very different sort of matching circuit. Look out for the next blog post, explaining multiport matching for power transfer and explaining how Optenni Lab can fit into the multi-antenna matching design flow with CST STUDIO SUITE®.