My name is Tomasz Walensky and I'm a product manager and a marketing manager at RF elements.

And today we'll continue with our series of webinars on antennas 101.

Today about the patch arrays.

So in the previous webinar, we looked in detail at the horn sectors.

Today we'll speak about the patch array sectors.

So where does the name come from?

What they're built from?

How do they function?

And we'll look at their advantages and disadvantages in terms of application and unlicensed five gigahertz risk networks.

To begin with, take the word sector.

So why is an antenna called sector?

Because it's beam width in the azimuth plane is not 360 degrees, meaning that it's not an omni, but only a part of the whole circle is covered.

And this part is called sector, that's it.

So sector is not an inherent quality of patch array antennas.

It has to do with the beam width in the azimuth plane.

Just a small recap from the previous part about horns.

A great sector antenna has plenty of parameters that WISPs would ideally observe in order to choose the best possible antenna for a particular application.

But of course, we understand compromises are inevitable as you move in your daily life.

But if you happen to have the time to be thorough, definitely look through these parameters and give it a minute to see whether besides gain, beam width or bandwidth, any other parameters might make sense to consider.

And especially the amount of silos when if the noise is what you're battling with in your networks.

So patch arrays and horns are very different types of antennas, which results in fundamental differences in their performance and properties of each of these types of antennas.

So no longer only the price is the major decision factor when choosing between these two.

Because of the interference conditions and the flight of all kinds of antennas to the market, one should be really careful about what antenna technology to go with.

In comparing horns and patch arrays, there are differences in many, if not most of the parameters you're looking at.

So if you haven't seen the first part of this webinar series, make sure you check it out.

The part one about horns, so that you have the complete picture of both technologies.

And you can find a recording of the first part about horns on our YouTube channel already.

So this was a short intro, and now we can move on to the details of the patch array antennas.

Why are these antennas called patch arrays?

So the core of this antenna is the printed circuit board with a number of patches stacked in the vertical direction and connected with the feeding lines, which all originate at the coaxial connectors to which you connect the radio.

So while the building unit is a single rectangular patch etched on the surface on the printed circuit board, as soon as you stack two or more patches above each other and feed them with the same signal, they form an antenna array.

And this is valid regardless of the shape or size of the patches.

Two or more patches makes a patch array or an antenna array.

A single patch etched on the surface of a PCB laminate is a resonant type of an antenna.

So the resonance is a phenomenon that occurs when the length of the patch is equal to half of the wavelength of the signal that is fed to it, where by wavelength we mean the distance over which the feeding signal repeats its shape.

So if this condition is fulfilled, the antenna radiates the signal into free space.

How does the resonant frequency change with the size of the patch?

So as many things in the world of RF engineering, the resonant frequency is inversely proportional to the size of the patch.

As we increase the size of the patch, the resonant frequency is decreasing and vice versa.

When we decrease the size of the patch, the resonant frequency is growing.

So the graph is indicating where the resonant frequency, FR, is located.

And the VSWR, or voltage standing wave ratio, is an antenna parameter that tells us how much of the input signal is reflected from the antenna connectors.

So the smaller the VSWR is, the less signal is reflected, which is what we want.

So in other words, it is radiated by the antenna.

So eventually you recognize the resonant frequency as a dip in the VSWR graph, as you can see from this animation.

It's not only the size of the patch that influences the properties of patch array antenna, but also the substrate on which it is etched.

So it has three main parameters that the patch antenna designers work with.

So first is the substrate height, or H, and this one influences the resonant frequency and the amount of unwanted radiation.

Second is their permittivity, epsilon R, which is the property of the material of the substrate and tells us how strongly the substrate material influences the electric fields.

And the third one is the loss tangent of the substrate.

This one tells us how much power is dissipated in the material of the substrate, which influences the resulting gain of an antenna.

So naturally, the higher the loss tangent, the more signal is lost, dissipated in the heat inside the substrate.

This is how typical substrates look like.

It's a thin sheet of a semi-rigid material with copper metallization on one, or maybe even both surfaces.

So there are many types of substrates with varying quality and properties, with prices spanning quite a wide range.

So naturally, the very low loss and precise dielectric constant substrates tend to be on the more expensive side.

Patch antennas come in many different shapes.

These different shapes with various cutouts, as you can see from these images, are another tool in the hands of the antenna designer.

They all influence the bandwidth gain, manufacturability, or price of the final product, as well as other parameters like, for example, the stability of the radiation pattern and so on.

So the intricacies of the patch array antenna design reside in knowing the effect of these modifications and be aware of the trade-offs that are always present.

When we change one thing in a desired way, well, something else might go a little bit worse, but it depends on the application what trade-offs are acceptable.

The radiation pattern tells us how well an antenna radiates in any direction, and single patch array antenna has wide radiation pattern in all directions, as you can see.

So sometimes you can also see the 2D version of the radiation pattern.

It is important to understand that the 2D radiation pattern gives rather limited information about the antenna behavior because it shows only a single slice of the whole 3D image.

Nevertheless, it still depends, of course, on the application, whether you should be interested in the full 3D radiation pattern or the 2D version gives enough information.

And for WISPs, the 3D radiation pattern definitely makes more sense because the side lobes of the antennas are the root of the interference issues in unlicensed WISP networks.

So the 3D radiation pattern will show you the whole information with all the side lobes, so you have the full image and know if you want to avoid or use the antenna you're looking at.

The reason why single-patch antenna is not good for sector coverage is that its radiation pattern is wide and fixed, and eventually its gain is also rather low.

So there are the parameters that are fixed, which is why the single-patch is used in applications where low gain and wide radiation angle are desirable, which is definitely not the WISP networks.

Another problem with the single-patch antennas is their narrow band of operation, which is connected to the narrow band nature of the resonance we mentioned earlier, so typically resulting to around half a gigahertz bandwidth, which would not be enough for unlicensed WISP networks operating in the five gigahertz frequency range, but again, in other types of applications, it might be fine.

To improve the shortcomings of a single-patch antenna, we can form an antenna array of two or more patches, and this is the general principle you can apply with any radiating element.

Stack two or more of them, and you get an antenna array.

Here we show a one-dimensional patch array antenna, and what happens with the radiation pattern as we keep adding more and more patches?

So clearly, the more patches in the array, the higher the gain of the antenna will be, and at the same time, the radiation pattern is changing as well.

You can see that the bandwidth is shrinking in the elevation plane, so when the patches are stacked in the vertical direction, the bandwidth is shrinking in the elevation plane, while in the azimuth, the pattern keeps the shape of a single-patch antenna, and also the side lobes start to appear as we stack more and more patches, which is the result of the physics of antenna arrays, regardless what is the single or the building block of the radiating element.

The array principles work in a similar way for two-dimensional arrays.

So adding more patches, the main bandwidth is shrinking, but now in both azimuth and elevation planes at the same time, because we're adding more patches in horizontal and vertical directions.

Same is valid for the side lobes.

These images show results of simulation in an EM simulation software, so it's nicely visible how the side lobes progress as we increase the size of the array.

And by now, I'm sure you're getting the intuitive understanding of how the antenna arrays work.

So if we, for example, stacked patches only along the horizontal direction, the radiation pattern would be getting narrow in the azimuth plane, and elevation would, vice versa, remain the same.

To align the line of thought with the first part of this webinar about horns you might have watched before, we will start looking at the patch arrays in terms of their side lobes performance.

There are two major causes of the side lobes patch arrays suffer from.

So one of them, as we mentioned earlier, is the physics of the antenna arrays.

And to be a little bit more precise, it's the interference of the waves that are radiated from each and every single patch, or interference, or in this case, addition.

You can also call it an addition of the waves.

So here it is nicely visible how the wave from two and more sources add up.

In the areas where they add up constructively, there is a maximum, so you get a side lobe.

Where they add up destructively, there is a minimum, and there is a dip in that radiation pattern.

So in the symmetry axis of the array is located the main beam, which is the strongest.

That's what we're interested in.

Any other lobes outside that main beam are side lobes, which in the RF engineering lingo, they're called grating lobes, if you will.

And these are the side lobes a typical patch array has in the elevation plane.

So when looking at the antenna from the side.

Second major cause of the side lobes of patch arrays is parasitic radiation.

And here we look at two components.

First is the radiation of the feeding lines.

So to bring the feeding signal to each patch in the array, a network of feeding lines is used, which is basically symmetrical division of the line until we get as many outputs as possible, I mean, or as needed, as is the number of patches.

In this case, in this example, you can see two.

So at the top, there is a vertical line and that's branching to two.

So we can feed our two patches.

So the feeding line is composed of metal strips of varying width and shapes.

And these have their own resonances that help on one hand, extend their bandwidth of the whole antenna, which is a good thing, but also makes them radiate part of the energy before it reaches the patches, which is a negative feature for a WISP sector antenna.

Looking at the patch from the side.

So a lot more is happening there than we would actually like to.

And main portion of the wave is radiated from the patch itself, which is of course what we want.

But portion of the energy is traveling inside the substrate as a so-called surface wave, causing lateral radiation and diffraction at the edges of the substrate.

And these parasitic sources of radiation cause additional side lobes in the azimuth plane of a typical patch array sector.

In fact, we can actually simulate how the feeding lines themselves radiate in the absence of the patches on the substrate.

So here we can see the result of such simulation.

While the feeding lines are inevitable when designing a patch array, they introduce additional side lobes in the resulting antenna radiation pattern, which is a very common thing with vast majority of patch arrays on the WISP market.

One of the ways manufacturers try to deal with the azimuth side lobes are various shields and shrouds that are attached to the back of the original antenna structure.

Be it the aftermarket kits or the shielding kits provided by the manufacturer.

So what is the effect of these shields on the radiation pattern of patch arrays?

While the shield might help improve the front-to-back ratio a little bit, the azimuth side lobes they aim to suppress are actually still strongly present as we can see from these near-field plots.

On the left side is the generic patch array antenna when we're looking at it from the top.

And a lot of radiation finds its way in the backward direction, causing the side lobes that are harmful to WISP networks.

And on the right side is the same antenna, but with the shield, which you can see as the two slanted lines at the edge of the antenna body.

So the difference in the radiation is noticeable, but altogether the desired effect of suppressing the side lobes is practically non-existent.

The side lobes are merely rearranged slightly, but are equally strong whether a shield is used or not.

This slide shows the same comparison, but the far-field radiation patterns.

So on the left is the patch array radiation pattern without the shield.

And you can see the strong side lobes pointing backwards.

On the right is the patch array radiation pattern with the shield.

The change is noticeable.

I won't be denying that, but as you can see, the strength of the side lobes didn't really change and some got actually even worse.

So the conclusion for the shields is that they will really not help you mitigate the side lobes as intuitive as it sounds.

Like one would think if I put that shield around it, well, surely it must be doing something.

But in this case, this intuitive understanding does not apply.

Like some things in the art of engineering or in physics in general are just weird.

So some are intuitive, some are not, and this one is definitely not.

But the conclusion here is that the shield, unfortunately, do not help to mitigate the side lobes.

Here is another viewpoint on how the patch arrays perform with the shields.

So the colorful images show the coverage pattern, in this case, the MCS zones.

So the dark blue, for example, says you can have the MCS rates of one or less.

Or for example, the green area says that the links can perform with the MCS rate from four to seven and so on.

So instead of the typically expected oval shape of the coverage area, you can see on the left one, for the antenna without the shield, you get this wild flower-like looking area, which is way different from what you expect when you use the shield.

And this adds yet another set of issues, especially to the customers close to the edges of the sectors, as you can imagine.

Some of them will find themselves outside the coverage zone.

Never before you install the shield and that will make their internet slow down.