Accelerate Design Flow with Optenni Lab – Volume II

Posted by Olli Pekonen | 16 April 2024

Introduction

In this Optenni blog article, the themes introduced in the previous blog on Feb 12^th, 2024 will be expanded to multiport antennas, in particular to tunable antennas. We also rely on the teachings of an Optenni blog article on preassessments from Nov 28^th, 2023.

Antenna to Study

Let’s take a look into a schematic representation of an aperture tuned antenna in the figure below.

In the picture, there is a simplified view of a three-throw switch with two capacitors and an inductor as tuning component in a tuning port (let’s call this port 2), and the Antenna feed port (to be called port 1), to which the matching circuit is to be connected. Let’s further assume that this antenna is to be used at three different bands, calling them low band (700 – 800 MHz), mid band (1800 – 2000 MHz) and high band (2600 – 2900 MHz), as implied by the three throw port components.

At first blush, the design of this kind of an antenna seems simple in conventional RF circuit simulators, at least if we perform the optimization of the device in the return loss sense, and not in the efficiency sense. Just minimize the S₁₁, and we are done, right?

Well, how are you going to treat the tuning components and the states of the switch? How about just looping them all through, one optimization for one band, a total of three, with the target of minimizing S₁₁.

This rises three further questions:

Q1: How do you really know if the component in the tuning port is going to be an inductor or a capacitor, even if you get its value optimized?
Q2: With the three proposed optimization runs, you will get three different matching circuits for the feed port. But you only can have one, catering for all the three bands and the three tuning components (through the states of the switch) at the same time. How to cope with this?
Q3: And how would you synthesize the topology of even one matching circuit, and not resort to guessing and optimizing the values of the components of a fixed topology, which is also based on a guess?

The answers are as follows:

A1: In general, you do not. You have to try everything out, 2³ = 8 times for three inductors or capacitors.
A2: Frankly, the only answer we know is: Use Optenni Lab… namely, the current RF circuit simulators are not well suited for this kind of a problem.
A3: See A2.

Of course, with Optenni Lab, you would do the design to maximise the total efficiency, not just focus on S₁₁. Remember that you get excellent S₁₁with a lossy system, with a 50 Ohm resistor in the extreme. Obviously, this is not the path we should take.

Using Preassessment Results

It is good to remember that Optenni Lab has preassessment tools for the antenna data which can be used even before any matching circuit design is attempted. We covered this already in our blog article on 28^th November 2023 (which conveniently relates to the same antenna) .

With the teachings of the said blog, we know that for the high band, we can likely cope with a simple short circuit as the tuning component, for the mid band we are best off with a small inductor, and for the low frequency, Optenni Lab should choose. This kind of preassessment will save us a lot of time, as nothing is to be optimized for the high band, and no capacitors need to be considered for the mid band.

Posing the Design Task to Optenni Lab

The secret of Optenni Lab handling the various bands each having a different tuning component, and a same matching network so smoothly is called a “frequency configuration”. You simply make three frequency configurations in the Optenni Lab interface, in the Multiport Antenna Matching mode (for example), as show in the figure below. We call the frequency configurations set 1, 2 and 3 for low, mid and high bands, respectively.

Then you assign the targets, one for each of the frequency configurations. You may use classical efficiency targets, and boost the process with impedance targets. Below, we have examples for set 1 and 2 (set 3 settings are obvious and thus not repeated)

Finally, we need to set the switch to follow the frequency configurations. For example, for frequency configuration set 1, set the switch to state SP3T_100, for set 2 to state SPT3_010 etc.

The tuning port setup now looks like this:

Please remember that that the tuning components at switch ports RF2 and RF3 were deduced from the preassessment results. Different states of the switch (and their corresponding frequency configurations) are shown with colored dashed lines.

Finally, the overall synthesis task looks like this, with the somewhat condensed contents of circuit 2 shown above.

Note how trivially easy it is to ask Optenni Lab to keep the synthesis results the same in the feeding port 1. We simply place an automatic 0-6 component synthesis block to the port, and Optenni Lab takes care of the rest, using the same (but yet to be synthesized) topology for all three frequency configurations and states of the switch.

After some 60-90 seconds of number crunching, we get the following promising result.

For example, for the high frequency band, the result is as follows, nicely catering for the needs at that band, only -1.8 dB off from the perfect efficiency result of 0 dB.

We can also study e.g. the power balance diagram at the center of the high band, with the following outcome:

This clearly illustrates that we have achieved more or less perfect matching condition at this band, but the always present resistive losses and component losses make the result less than ideal.

The same observations can be naturally repeated for other bands.

Note how well Optenni Lab keeps the designer up-to-date of his/her design progress. More information means less guessing, less errors, better product quality and a faster time-to-market.

Conclusion

Handling multiple bands in antenna matching, each requiring both identical (static) matching portions, and band-dependent (dynamic) matching portions is very easy with Optenni Lab. All this can be done

relative to the total efficiency of the antenna which is the true figure of merit of an antenna system, and
with full synthesis capability for matching and tuning circuit topologies.

We encourage the antenna community to stop wasting time in guessing their matching and tuning networks. Instead, please use Optenni Lab. Hit that Start Free Trial button at Optenni homepage now!

Olli Pekonen
Sales Director
Email: olli.pekonen (at) optenni.com

Accelerate Design Flow with Optenni Lab – Volume I

Posted by Olli Pekonen | 12 February 2024

Introduction

In this Optenni blog article, we take a look into some of the ways many Optenni Lab accelerates the design flow of antenna designs, and antenna matching in particular. We first focus on a straightforward one-port antenna, and then in later blog articles expand the story e.g. to the challenging domain of multiport (aperture tuned) antennas.

Designers responsible for a high performance antenna of a small electronics device are facing hard times when the size of the radiator is mostly dictated by mechanical constraints of the device. At the same time, the antenna has to cater for many bands, and have a high-enough radiation efficiency.

It is like the designer is in the middle of a Bermuda triangle, with i) small antenna size, ii) wide bandwidth requirements and iii) good radiation efficiency as the corners.

In fact, the three factors in the corners counteract each other – for example, it is relatively easy to make a small antenna that radiates well if it has to operate only on a very narrow band. Remember that in the extreme case, following the teachings of basic radio engineering, any load can be matched with just two components, but at a single frequency only. Similarly, a small sized multiband antenna is quite easy to create if any efficiency is allowed. In the extreme, the “antenna” is a small 50 Ohm resistor, resulting in an excellent wideband match, and in a dismal radiation.

Traditional Antenna Matching Design Flow

With traditional circuit simulation based tools, the design flow of a one-port antenna matching is based on the following:

A. Obtain the S₁₁ of the antenna.

B. Neglect the efficiency and other radiation aspects of the antenna.

C. Guess a matching circuit topology for the antenna into a static topology (e.g. a ladder of inductors and capacitors) and connect it to the one-port representing the S₁₁ of the antenna.

D. Optimize the values of the statically placed inductors and capacitors to get a suitable notch (return loss) to the S₁₁ at the input of the matching circuit at the desired frequency bands.

This traditional process faces many challenges, however. Let’s go through them one by one:

Step A is fine – we will need the S₁₁ always anyhow
Step B is problematic: Neglecting efficiency of the antenna makes the solution suboptimal, as the total efficiency is the true figure of merit. This is because the total efficiency takes both matching and radiation into consideration.
Step C is fine if the designer happens to guess the right combination of inductors and capacitors. But what if the designer makes a bad guess? In fact, there is no way to know this, so to be sure, every combination must be manually entered and tried out. For the possibility of either inductor or capacitor in shunt or in series (4 possibilities / component), there are 4^N combinations to go through. So for 2 components, there are 16 topologies, for 3 components, 64 topologies etc. In fact, it is highly unlikely that the designer guesses the right topology, and to counter this, a lot of manual placement is needed.
Step D is OK as such, but suffers badly from the inadequacy of steps B and C. For example, what good are optimal element values if the topology is bad in the first place.

The Optenni Lab Way

Optenni solves the challenges of the method steps A – D in one sweeping stroke. Namely,

Optenni Lab is efficiency aware, and the main target for optimization is very often simply the total efficiency of the antenna system. By reading in the radiation patterns of the antenna (or a tabulated radiation efficiency file), efficiency is fully integrated into everything Optenni Lab does. This solves challenge of step B.
Instead of manual placement of components, Optenni Lab synthesizes circuits automatically. So there is no need to tinker with a schematic circuit diagram, interchanging components from inductors to capacitors or wise versa (it should be added that for the users wanting more control, manual placement is possible, however). With this, challenges of step C are solved.

Example

The designer is faced with the design of a dual-band antenna operating in frequencies 1695 MHz – 2020 MHz and 2570 MHz – 2620 MHz. Both S₁₁ (in Touchstone format) and efficiency files are available, from 0.1 MHz to over 5 GHz.

The designer simply needs to read in the S₁₁ and efficiency files, enter the number of components the matching circuit may have (for two bands, 2 x 2 = 4 is a good guess, two components making a “resonator”) and the two bands of interest. This takes about 30 seconds to specify in the user-friendly user interface of Optenni Lab. Compare this with entering every possible combination of inductors and capacitors manually – we would have 4⁴ = 256 options to go through. Assuming that it takes a minute to change the topology and note for any improvement (this is likely a bit optimistic), the task would take more than 4 hours.

The synthesis run takes less than a second in an average laptop. This is the best topology Optenni Lab gives:

And this is the frequency response result

So in all, a manual tinkering worth of more than 4 hours in a traditional RF circuit simulation and optimization tool was reduced to a design task taking less than 40 seconds in a Optenni Lab.

But wait – when we write “the best result”, exactly what do we mean?

To cut the long story short, the best result (in this case) is the result with the best worst-case performance of the efficiencies over the two frequency bands. So the S₁₁ of the matching circuit is just a starting point, and it is the efficiency that counts. Note, however, that the S₁₁ has the valleys / notches at the frequencies where the efficiency peaks. This is reflected also in the Smith chart with S₁₁ arches that loop around the center of the Smith chart as closely as possible at the bands of interest as the frequency varies. If the S₁₁ would go through the Smith chart center, the matching would likely be excellent, but only in that single spot frequency, and far off in the other frequencies.

Conclusion

This was maybe one of the most simple use cases of Optenni Lab but it goes a long way to illustrate one of the prime ways Optenni Lab accelerates the design flow by

focusing on the most important figure of merit in making well-radiating antennas, the optimization total efficiency, and
by synthesizing circuits automatically instead of forcing the user to manually tinker with horde of circuit topologies.

Of course Optenni Lab offers so much more even for a single-port matching, with built in support for library components, their statistical, sensitivity and tolerance analyses, versatile user interface for result management and post processing etc. And things get even more exciting with multiport matching. We will cover the ways Optenni Lab can accelerate your design work in later blog articles.

If this blog article aroused your interest and Optenni Lab is new to you, do not hesitate to hit that “Start Free Trial” button at our WWW site.

Olli Pekonen
Sales Director
Email: olli.pekonen (at) optenni.com

Power Balance Plots and Napoleon

Posted by Jussi Rahola | 18 December 2023

In this blog article, I will present the background and different variants of Optenni Lab’s power balance plots, which are used to illustrate power flow in RF circuits and antennas. But what has Napoleon to do with all this? Read through the blog and find out!

When delivering courses on matching circuit design at various conferences, I have used the following diagram to illustrate the power flow in matching circuits connected to antennas:

With this figure, it is easy to explain that the goal of matching circuit design is not to minimize the reflected power but to maximize the radiated power of the antenna system. The resistive losses of the matching components can indeed reduce the reflected power, but naturally this happens at the expense of radiated power and antenna efficiency.

Based on the above idea, back in 2019 we introduced power balance plots into Optenni Lab so that you can easily see the propagation of power in your antenna system and see the changes when you tune interactively any of the matching components. The figure below shows an example of the power balance plot for a single-antenna system, where also the absolute and relative power levels of the various loss mechanisms are shown numerically.

In addition to single-port matching, Optenni Lab can easily treat antenna systems with an arbitrary number of ports. The starting point is multiport antenna data coming typically from an electromagnetic (EM) simulator. Optenni Lab can synthesize matching circuits for each of the EM ports and wire the circuits to a number of external ports. In addition, Optenni Lab can optimize the type and value of components to be placed in the aperture or tuning ports of the EM model. The two figures below illustrate some possible multiport circuit synthesis setups in Optenni Lab.

Optenni Lab can easily plot the power propagation in multiantenna systems. The multiantenna power balance plot can show the power lost to other ports (labeled “Coupling losses”) and depending on the setup the component losses can be in some cases shown for the feed port and for the other ports separately.

The animation below shows the power balance plot for the multiport antenna case when the user changes the visualization frequency.

We also generalized the power balance plots to general RF systems, which do not have an antenna component. In this setup, Optenni Lab can easily show the power flow between a pair of external ports, where the goal is to maximize the power coupled to the target port (marked as “Output power”) and the power coupled to any other ports is considered as a loss (labeled “Coupling losses” in the image below).

All the examples above assume that only one port is fed at a time. But Optenni Lab can also calculate the power balance plots for a simultaneous multiport excitation, such as in antenna arrays, where special emphasis needs to be placed on the active reflection coefficient and the dependence of the radiation efficiency on the feeding amplitudes and phases.

How does Napoleon then enter the picture? Well, during the IMS2023 exhibition I was demonstrating Optenni Lab and the power balance visualization to various customers and then two engineers independently remarked that the power balance plots resemble the visualization of the losses of Napoleon’s army during his infamous invasion to Russia during 1812.

Indeed, I studied Wikipedia and discovered the visualization by French engineer Charles Joseph Minard from 1869, which indeed uses related visualization techniques:

Source: Wikimedia commons.

From the visualization one can see the dramatic loss of life during this ill-fated campaign: over 400 000 solders started the march to Russia. Only some 100 000 reached Moscow and out of those only 4000 solders returned alive, others being eliminated by disease, exhaustion, and bitter cold. Quite a path loss!

In summary, we adopted a data visualization technique which is more than 150 years old to describe the power balance in antenna matching circuits and in general RF circuits. If your boss insists on focusing on the minimization of reflected power, you can use these plots to highlight the importance of maximizing the antenna efficiency instead.

CEO Jussi Rahola
Email: jussi.rahola (at) optenni.com

Exploring Antennas With Optenni Lab

Posted by Olli Pekonen | 28 November 2023

Introduction

With the blog article of September 2023, we touched the main design philosophy of Optenni Lab, where the user may Explore the antenna, Accelerate the design of antenna matching, and Maximise the impact of matching.

In this blog article, let me focus on the first aspect of this philosophy, Explore.

Before matching circuits are synthesized and time is spent to gain adequate performance, it is very beneficial to get an overview of the theoretical limits of the antenna’s radiator. If the radiator has very little chance of surviving the communication task at hand, it is better to go back to the drawing board and try to redesign the radiator. After all, if a failure is to happen in engineering, it always pays off to fail fast and in early stages of the design, and then move on.

Optenni Lab Preassessment tools

There are three main preassessment tools in Optenni Lab: Bandwidth potential, electromagnetic isolation and total scan pattern.

Electromagnetic isolation can reveal that the isolation between two antenna ports is, in fact, caused by poor matching. If we take away the effect of poor matching, it may become evident that the two antenna ports are quite strongly coupled. This can become a problem for antenna systems with many radiators.

Total scan pattern is an important feature in assessing the ability of array antennas to direct radiation over the solid angle enclosing the array.

Preassessment Workhorse – The Bandwidth Potential

Bandwidth potential is likely the most frequently used preassessment tool in Optenni Lab. It gives a quick overview on the following: What is the width of the frequency band at each of the frequencies available in the antenna impedance data (Touchstone file) if we wish to reach a certain matching level (using an ideal two-port matching circuit).

A typical bandwidth potential graph is given in Figure 1 below. It shows that the antenna in question will be difficult to match to -10 dB return loss level at frequencies below 1.3 GHz. At approximately 1.8 GHz a massive bandwidth of 700 MHz is easily achievable. Again, at around 3.6 GHz a broadband matching of more than 100 MHz (twice the indicated potential of 50 MHz for a two-port matching) will likely be hard. And finally, around 4.4 GHz, a 700 MHz bandwidth will again be a simple task.

It is very typical that the bandwidth potential tapers out at both edges of the frequency spectrum, as the number of frequency points runs out (the closer we get to the start or end of the frequency data, the more narrow the bandwidth potential becomes out of necessity). Also at low frequencies, antennas tend to be short in terms of wavelength, and thus the ability of the antenna to radiate is quite limited, dropping the bandwidth potential further.

With single port antennas, the usage of bandwidth potential computation is very straightforward. Just go to the Assessment menu and choose Bandwidth Potential, set the matching level, and off you go, as in Figure 1.

Figure 1: Bandwidth potential reveals the performance of the bare antenna in terms of bandwidths

The Bandwidth Potential of Multiport Antennas

When the antenna is a multiport antenna, for example an aperture tuned two-port structure, things get a lot more interesting!

Consider the basic building blocks of an aperture tuned antenna with a feeding port 1 and tuning port 2 as shown in Figure 2. Green portion marks the meal strips of the radiator, and orange portions are the conducting ground plane. Tuning port 2 has a switch element with various load impedances (inductors or capacitors), that can be dynamically connected to the second port 2.

Figure 2: Basic building blocks of an aperture tuned antenna

Let’s also assume that the antenna is to operate at three distinct frequency bands, and let’s call them

“low band” at 800 – 900 MHz,
“mid band” at 1700 – 1800 MHz, and
and “high band” at 2500 – 2700 MHz,

so that for each of the bands, the switch is at one of its throw positions.

Now the basic design challenge is: What kind of static matching circuit is the best for port 1, and what the three tuning components should be in port 2?

But before we give this task for Optenni Lab to be solved, we can look into the bandwidth potential of the antenna so that we try different tuning port loads at port 2, and see how things look like from port 1.

In version 6.0 of Optenni Lab, studying tuning port loads together with bandwidth potential is really quite simple. In the past, the user had to export one-port S-parameter file and open it in an “auxiliary project” to generate the bandwidth potential graph. Not anymore! As shown in Figure 3, simply first terminate the port 2 with a load you wish to study (say, a 1 nH inductor).

Figure 3: Aperture tuned antenna subjected to 1 nH tuning port load

Then, choose Additional plots… from the plot selection panel,

Figure 4: Bandwidth potential is now accessible through Additional Plots

Add Bandwidth potential and Radiation efficiency as plot types.

Figure 5: Bandwidth potential and efficiency can be turned on or off

Finally, set the bandwidth potential parameters (matching level and symmetry).

At the same time, it is also beneficial to study the radiation efficiency of the radiator. As the tuner port load changes the currents of the radiator, the tuner port changes also the radiation efficiency. This aspect is easily overlooked when designing tunable antennas.

Figures 6 and 7 show typical results for the resulting bandwidth potential and for radiation efficiency, respectively.

Figure 6: Bandwidth potential with a 1 nH load in the tuning port 2

Figure 7: Radiation efficiency with a 1 nH load in the tuning port 2

As an additional plot, bandwidth potential computation is a game changing feature in Optenni Lab 6.0! It makes the generation of bandwidth potential chart (where several bandwidth potential curves are stacked) almost trivial. Simply tune the load at port 2 to get a selection of bandwidth potentials related to various inductance loads. You may then go also through some capacitor values, and short and open circuit options in port 2. Then, push all these results to a User Plot, and you easily get the following kind of chart:

At the same time, it is very easy to generate the following radiation efficiency chart, almost as a by-product.

Figure 8: Bandwidth potential chart

Figure 9: Radiation efficiency chart

Interpreting Bandwidth Potential and Radiation Efficiency Charts

Now let’s see what these two charts reveal for us.

For high band at 2500 – 2700 MHz, the choice of tuning component is clear: The best bandwidth potential is achieved with a short, and as the radiation efficiency is more or less independent of the tuner loading (as the curves are stacked on top of each other around 2500 – 2700 MHz), we can safely assume that the switch should couple to a short when the antenna is operating in the high band.

In the middle band at 1700 – 1800 MHz, both the bandwidth potential and radiation efficiency are at their highest values when there is a small, 1 – 2 nH inductor in the tuning port. Thus, we can let Optenni Lab optimize the inductor value, but there appears to be no need to consider also a capacitor in the tuning port at the middle band.

For the low band at 800 – 900 MHz, the radiation efficiency is again quite good with small inductors, but the bandwidth potential is really poor (more or less zero) for these loads. However, there seems to be a compromise based on a large inductor (10 nH) value, which implies a large impedance. Such a large impedance can also be a small capacitance. Thus, it is likely best that this tuning component is left for Optenni Lab to choose, based on the versatile Generic Reactance component.

Figure 10: Tuner optimization setup (RF1 – low band throw port, RF2 – mid band throw port, RF3 – high band throw port)

Benefits of this approach are clear:

For the high band, nothing needs to be synthesized or even optimized as there is simply a short in this port,
For the middle band, we just need to optimize for inductors, not for capacitors at all.

Ability to omit these two synthesis steps saves time considerably.

Conclusion

Taking a critical look into the radiator before any matching is attempted is usually very beneficial, especially for tunable antennas where the synthesis times can be long. With the bandwidth potential and radiation efficiency plots, the secrets of a tunable radiator become a lot more visible even when the tuning port load is varied.

If both bandwidth potential and radiation efficiency are low for any tuning port load and at any one of the frequency bands, redesign of the radiator of the tunable antenna should be considered. On the other hand, if any of the tuning components seems to indicate a good performance in both bandwidth potential and radiation efficiency, we can likely choose that component as a starting point for synthesis, and sometimes even set its value (especially for short or open circuits) without doing any synthesis or optimization. This speeds up the synthesis task considerably and gives the antenna designer a firm handle on the potential performance of the tuned antenna radiator, even before any matching is attempted.

Olli Pekonen
Sales Director
Email: olli.pekonen (at) optenni.com

Modeling the layout of RF switches

Posted by Sergei Kosulnikov | 31 October 2023

Introduction

It is well known that compact wireless devices require small antennas whose size is dictated mostly by mechanical, design and aesthetic aspects, and not so much on the efficiency of radiation. Therefore, such small antennas are often made tunable to cater for multiband requirements. To make an antenna tunable, a switch is often incorporated to the antenna radiator. Such a device is also called an aperture-tuned antenna.

Although a typical RF switch is a small component, its layout can have an effect on the operation of the wireless system, especially at higher frequencies. If layout effects (e.g. connecting traces) are not accounted for, simulation results do not always match well with reality. As layout effects introduce complicated interconnections, a combined study of an antenna, a switch and an element representing the layout has been challenging, even with previous versions of Optenni Lab. But not anymore with Optenni Lab version 6.0, introduced in fall 2023!

Optenni Lab’s New Schematic Entry Feature

With Optenni Lab 6.0 and its Schematic Entry mode we can approach the switch+layout design problem with (at least) three methods, named as follows:

Method 1 “No layout”: Antenna and switch are separate blocks wired together, and the layout aspects are simply not accounted for.
Method 2 “Separated”: Layout aspects are separated into a separate layout representation which is wired to the antenna and switch. In other words, antenna, switch and switch layout model are separate elements.
Method 3 “Combined”: Antenna and switch layout are represented in the same element, wired to the switch.

Method 1 – No layout

In this case antenna is assumed to have Port 1 as input feeding port with a static matching circuit (to be synthesized), and Port 2 (2-2’) as a component port. The switch is placed in the component port and has no layout information. The antenna is represented as a 2-port impedance data block and the corresponding efficiency and radiation pattern data for each port, coming from a 3D EM antenna simulation. This model simply neglects the effect of the layout of the switch. In other words, the model assumes that the switch and its interconnections have a zero or negligible electrical length (size). If this is not true, this model runs into difficulties.

Method 2 – Separated

An example of Method 2 with a separated antenna, switch and a switch layout model is given in the following.

Antenna is connected similarly to the switch as in Method 1. The switch throw ports RF1-RF3 are connected to a layout element simulated in a 3D EM model. The layout element connects also the tuning components to be chosen and optimized by Generic Reactances. In this case, the antenna block is aware of radiation aspects (e.g. radiation pattern, efficiency), whereas the layout element is not – only the six-port impedance data of the layout block is used. Thus, this approach is applicable if it is assumed that the radiation and coupling of the switch layout model to the antenna can be neglected.

Method 3 – Combined

Here both the antenna and the switch layout are combined in a single antenna element in a 3D EM simulation. Thus, the switch throw ports RF1-RF3 are directly connected to the antenna block which is also connected to the optimized tuning components.

In this case, the antenna element captures the “full” electromagnetic behavior of both the antenna radiator and the layout. It takes into account any possible couplings between the antenna the layout, and also accounts for any losses due to radiation from the layout’s interconnections.

However, this method is most challenging in terms of the 3D EM analysis, e.g. involving possible accumulated error due to a very large number of mesh elements and very detailed discretization in details of both antenna’s and layout’s surroundings etc. Therefore, it is not certain that this method yields the most accurate solution with 3D EM simulations.

What is the Effect of the Layout?

We synthesized a matching circuit for 3 bands using Method 1. In the following, let’s compare the results of Method 3 with the results obtained when synthesized component values of Method 1 are inserted into Method 3.

The plots show the comparison between Method 1 (solid lines) vs. the same component values implemented with Method 3 (dashed lines). This comparison brings out the effects of the layout in the synthesis. With the obtained efficiency / S₁₁ results, it is evident that the layout has a major impact: with no layout data, and assuming that the Model 3 represents reality, a realized device based purely on Model 1 data would perform -3.9 dB – (-0.1dB) = -3.8dB worse than predicted. This highlights the value of layout modeling with electrically large elements like switches. As expected, in lower frequencies the effect of layout is not drastic, but at higher frequencies it is!

What is the Effect of Separating Layout from the Antenna?

In this case, we synthesized a matching circuit for 3 bands but using Method 2. Let’s bring the best matching topology from Method 2 as fixed values to the full simulation (Method 3) and compare.

In general, the agreement between Method 2 results (when applied to Model 3) and Model 3 (the full model) is quite good. However, the small shift of the resonance at the highest band indicates that mutual coupling between the layout and antenna physical model may be worth considering. Thus, “to separate or not to separate” the layout from the antenna model needs careful consideration. As usual in engineering, it is ultimately a tradeoff between overall model accuracy and analysis performance.

Summary of the Methods

The teachings of this study can be summarized as follows:

Method 1 (no layout consideration with a simple antenna model):

Has the fastest synthesis.
Not well suited for realistic implementation (at least in frequencies above 1 GHz).
May be used to define an initial matching circuit topology, more accurate methods (2 and/or 3) can continue to optimize the components from this topology.

Method 2 (separate 3D EM simulation of the antenna and the switch layout):

Works as a compromise between high accuracy and good performance. Two simple 3D EM simulations are usually a lot faster than one big 3D EM simulation.
The feasibility depends on the EM coupling of the antenna to the layout structure (pads, interconnecting traces) of the switch. With low coupling, this is a very good method.
The method assumes that the radiation from the switch layout is negligible, and that the layout does not couple electromagnetically to the overall antenna.
Only the S parameter information of the layout is used which speeds up the synthesis task.

Method 3 (simultaneous EM simulation of the antenna and the switch layout):

Most challenging in terms of 3D EM computation.
Takes into account the radiation characteristics of the switch layout and the coupling of the layout to the antenna structure.

Conclusions

Layout effects of switches and tuners may be crucial for accuracy, especially in higher frequencies. The recently introduced Schematic Entry feature of Optenni Lab version 6.0 enables the incorporation of the layout effects accurately and easily with the matching circuit synthesis.

The separation of the EM model into antenna and layout parts speeds up both the 3D EM simulations and the matching circuit synthesis. If the antenna and the layout interact, the accuracy of the method based on such a separation suffers.

As always, modeling is a tradeoff between the desired computation performance and computation accuracy. Optenni Lab version 6.0 offers various ways to easily obtain a good balance between the computation accuracy and time in demanding antenna design and matching tasks.

Sergei Kosulnikov
Field Application Engineer
Email: sergei.kosulnikov (at) optenni.com

Explore – Accelerate – Maximize

Posted by Jussi Rahola | 20 September 2023

With this article I would like to welcome you to the new Optenni blog series. In this blog we will be discussing various matters related to RF circuit synthesis, impedance matching, antenna arrays and our Optenni Lab circuit synthesis software for antenna and RF optimization.

When re-designing the pages, we also re-thought the key messages about our software. The key benefits of Optenni Lab can be condensed in the three verbs: explore, accelerate and maximize.

Using these verbs, let me now explain in more detail what Optenni Lab can offer you.

You may also have noticed a new look and feel for our web pages at www.optenni.com.

Explore theoretical limits:

Optenni Lab has several innovative assessment tools which help to reveal the theoretical upper limits for the wireless performance of your antenna or RF system. If your system requirements are not met with the theoretical upper limits revealed by Optenni Lab, you should likely redesign your antenna radiator structure, and not spend time in vain trying to improve the matching.

The main assessment tools are as follows:

Bandwidth potential: using the impedance of an unmatched antenna, the bandwidth potential calculation quickly reveals the obtainable bandwidth of the antenna through a matching circuit as a function of frequency. Thus, you can quickly determine if your antenna can provide the requested impedance bandwidth after it has been matched.
Electromagnetic isolation: when working with antenna systems, you may initially think that there is a good isolation between two antenna ports. However, most of the isolation may come from impedance mismatch. The concept of electromagnetic isolation removes the effect of impedance mismatch from the calculation and determines the worst-case isolation for each frequency (when the two antennas are simultaneously matched). In converse, for linear amplifiers, the electromagnetic isolation calculation gives the best possible transducer power gain.
Total scan pattern: when working with antenna arrays and beam steering, the beam can only be steered to a certain amount away from the broadside direction before the gain begins to drop and grating lobes start to appear. Optenni Lab implements the total scan pattern calculation, which reveals the maximum gain of the antenna array to any direction. Optenni Lab can also combine the total scan patterns from multiple arrays to determine if they together can provide a more uniform angular coverage of the beams.

Accelerate your design flow:

Accelerating the RF circuit design flow is at the heart of Optenni Lab. Instead of placing and wiring matching components manually, you can leverage the powerful circuit synthesis capabilities of Optenni Lab. After reading in your impedance and radiation data, just specify the desired operation bands and component types, and within seconds Optenni Lab can provide multiple optimized matching circuit topologies. Optenni Lab can optimize broadband and multiband matching circuits also for tightly coupled antenna systems.

The real power of Optenni Lab’s synthesis and optimization algorithms is revealed when tunable and switchable matching circuits are optimized. With Optenni Lab, frequency bands can be grouped into frequency configurations, where each configuration contains the frequency bands which need to be covered by a single switch or tuner state. At the same time, the input port of the system can have a common matching circuit that is to be identical to all states of the system. The optimization of such circuits is a complex task as the total performance depends on the circuit topology, component values and switch and tuner states.

A key part of the acceleration of the design flow is the capability of Optenni Lab to link with leading electromagnetic simulators and measurement equipment. Together with the EM tool vendors we have developed automated links so that simulated S parameters and radiation patterns can be sent from the EM tool to Optenni Lab with a few clicks of the mouse. And in some cases we can send the circuit back to the circuit simulators embedded in the EM tools for further co-simulation.

We also provide links to leading network analyzer models so that you can quickly get the measured data into Optenni Lab and synthesize matching circuits in real time based on the measurements.

Maximize wireless performance:

In impedance matching, the design goal is not to get the best possible impedance match (which can be obtained with sufficiently lossy components), but to transfer maximum amount of power from the antenna or to a load. Optenni Lab’s optimization setup guides you to the maximization of efficiency or maximization of transferred power.

In the optimization we consider all the loss mechanisms in the circuit: impedance mismatch, component losses, coupling to other ports and finite radiation efficiency. Optenni Lab has a wide range of optimization targets for different purposes: passband and stopband efficiency targets, targets to improve the isolation or to move the impedance to a desired location.

For antenna arrays, Optenni Lab is also able to optimize the beamforming coefficients in conjunction with circuit values. The software takes the radiation patterns of each individual element and the coupling between the elements fully into account based on your original simulated or measured data. It is easy to steer the beam to a given direction, control the side lobe levels, nulls and the active reflection coefficient of the array.

More to come:

Stay tuned for additional blog articles from us. We have a lot to tell, as we are very close to releasing Optenni Lab 6.0, our biggest update yet, containing multiple important improvements in circuit synthesis, optimization speed, ease of use and applicability to new problems in RF design.

CEO Jussi Rahola
Email: jussi.rahola (at) optenni.com

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In a matter of seconds, Optenni Lab produces multiple optimized matching circuits for broadband, multiband or tunable matching problems. Optenni Lab can also synthesize and optimize multiple matching circuits for coupled multiantenna systems.

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Optenni Lab can synthesize matching circuit for challenging coupled multiantenna systems, where the matching of all antenna ports must be optimized simultaneously.

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Optenni Lab can display radiation patterns in various formats: Cartesian and polar cuts, two-dimensional pseudocolor plots and 3D plots.

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For tunable antenna design, Optenni Lab uses multiple frequency configurations. Each frequency configuration has its own optimization targets and corresponds to different states of the switches and tuners of the circuit.

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Optenni Lab array module can quickly show the array performance using canonical solutions, such as progressive phase shifts and closed-form amplitude tapering.