Optenni Lab — Calculation of radiation efficiency

Optenni Lab calculates the antenna radiation efficiency from the impedance and measured total efficiency data, which do not have to use the same frequency grid. The impedance (S-parameter) data is read from a Touchstone file and the radiation efficiency data is read from a text file where possible comment rows will be ignored and the data can be specified using different frequency units (e.g. MHz or GHz) and either in linear of dB scale. The coupling to other antenna ports will be taken into account in the calculation of the radiation efficiency.

In addition, when a matching circuit has been constructed, Optenni Lab calculates the total efficiency through the circuit, taking into account impedance mismatch, losses in the matching circuit, the radiation efficiency and coupling to the other antennas.

Optenni Lab — Calculation of electromagnetic isolation

When we consider isolation between a pair of antennas, the result depends upon the impedance mismatch of each antenna. This means that an apparently good isolation may simply be due to mismatch, and when the antennas have properly been matched, the isolation can actually be very poor.

Optenni Lab provides a so called electromagnetic isolation analysis where this effect is factored out, and the isolation is calculated as if both ports were perfectly matched. If there are more than two antennas in the system, the electromagnetic isolation is calculated for each antenna pair with the assumption that the other ports are either left open or terminated at their impedances (typically 50 Ohms, but the termination impedance can also be different and frequency-dependent).

Electromagnetic isolation calculation allows you for example to

Study the effect of antenna placement to isolation – this works great also in a 2-port measurement, as the calculation of electromagnetic isolation is carried out essentially real time with the VNA measurement
Design a proper band allocation in a multi-antenna system such that the coupling is minimized

EM isolation of a 3-antenna system: antenna 2 can be paired with either of the antennas 1 or 3 to form a MIMO system at 2.4 GHz, but antennas 1 and 3 must operate at different bands.

More information:
For more information about the concept of electromagnetic isolation, see for example J. Rahola and J. Ollikainen, Analysis of Isolation of Two-Port Antenna Systems using Simultaneous Matching, Proceedings of the EuCAP 2007 conference, Edinburgh, November 11-16, 2007.
J. Rahola (invited), Bandwidth potential and electromagnetic isolation: Tools for analysing the impedance behaviour of antenna systems, Proceedings of the EuCAP 2009 conference, Berlin, March 23-27, 2009.

Optenni Lab — Automatic matching circuit synthesis

Automatic matching circuit synthesis is the core functionality of Optenni Lab. Over the years of development, this same standpoint has refined into highly sophisticated algorithms and use cases. The synthesis capabilities include

automatic determination of the optimal number of required matching components
more than 100 component series from top vendors to choose from
tolerance analysis with design sensitivity ranking
synthesis using full EM-simulated layout model
generic “black box” synthesis blocks to be used in a long RF chain
lumped, microstrip or hybrid matching circuits
synthesis blocks as subcircuits to enforce symmetry
optimization for multiple impedance environments or variants in one go
co-matching of coupled antenna system
matching circuit synthesis to optimize antenna array total system efficiency

The automation brings enormous advantage for the designer, as much of the work would otherwise require manual setup for potentially hundreds of design candidates. This makes the designer’s work both productive and motivating.

Optenni Lab — Estimation of obtainable bandwidth

Optenni Lab offers tools for estimating the obtainable bandwidth from antenna impedance curves using the bandwidth potential and Q factor approaches.

Bandwidth potential

In the bandwidth potential calculation, Optenni Lab synthesizes for each frequency an optimal two-component matching circuit and calculates the obtained maximal impedance bandwidth. The analysis is carried out for all frequencies in the data, and results in a curve that shows the obtainable bandwidth at each center frequency.

With the bandwidth potential calculation you can

Uncover ”hidden” bandwidth that may not be evident by looking at the impedance curve
Verify if the bandwidth is large enough for the desired application even if the antenna was not originally resonant
Make a proper bandwidth comparison of prototypes, factoring out easy-to-fix mismatch
Check on which frequencies the antenna gives maximal bandwidth

The bandwidth potential calculation speeds up the antenna design process. You can quickly estimate the obtainable antenna bandwidth from a measured or simulated prototype without explicitly tuning the antenna to resonance at the desired frequency range. If the bandwidth is not sufficient, you can modify the design until the bandwidth potential meets the specifications, and only then consider the actuai implementation of the matching circuit.

Repeating the bandwidth potential analysis for different reference S11-levels, you can create a ”map” for a quick assessment of given antenna’s bandwidth behavior.

Example of standard and optimized bandwidth potential. The vertical axis is relative bandwidth as a percentage of the center frequency.

Q factor estimation

In addition, Optenni Lab can estimate the antenna Q factor based on the impedance data directly. This method is less accurate than the bandwidth potential calculation especially if the impedance data is noisy or if multiple resonances are present.

More information

For the theory of the bandwidth potential calculation, see for example

J. Rahola (invited), Bandwidth potential and electromagnetic isolation: Tools for analysing the impedance behaviour of antenna systems, Proceedings of the EuCAP 2009 conference, Berlin, March 23-27, 2009.

The Q factor calculation is explained in

A. D. Yaghjian and S. R. Best: Impedance, Bandwidth, and Q of Antennas, IEEE Transactions on Antennas and Propagation, Vol. 53, 2005, pages 1298-1324.

Optenni Lab — Conjugate matching

In addition to general matching circuit optimization, Optenni Lab calculates two-component matching circuits that obtain conjugate matching to the generator impedance at a single frequency (critical coupling) or maximize the bandwidth around the starting frequency at a given matching level (overcoupled matching). Either the total bandwidth or the symmetric bandwidth around the starting frequency is maximized. Also the two-component matching circuit generation works with an arbitrary frequency-dependent complex termination impedance. When the termination impedance is real (e.g. 50 Ohm), an exact match can be obtained at a single frequency.

The difference between the two matching circuit generation approaches in Optenni Lab is that the general matching circuit generation tries to obtain as good matching as possible over a given frequency range and a given number of components, whereas the two-component matching tries to maximize the bandwidth at a given matching level.

The conjugate matching and symmetric bandwidth maximization procedures are used in the calculation of the bandwidth potential.