Custom antennas for cellular applications

I'm an Antenna Engineer at Digi Wireless Design Services. I'm going to talk to you today about custom antennas, and specifically, custom antennas for cellular applications. So if you watched the last video, we talked about custom versus off-the-shelf and some pros and cons of each. So today, I really want to dive into why custom from cellular? Well typically, cellular designs are going to be higher volume, so you're looking at a lower cost solution. You might have mechanical constraints where an off-the-shelf antenna is not going to fit and lower risk.

Is a custom cellular antenna is going to be the lowest risk solution?

So this is the point I really want to drive home today, is why a custom cellular antenna is going to be the lowest risk solution. Now, when you're designing a cellular product, you're going to have to go through additional approvals. So you're going to have to go through like Verizon approvals, AT&T or T-Mobile in addition to, say, CTA, PTCRB and FCC. So there's going to be some additional requirements than just what you might be used to if you've done a Wi-Fi or a Bluetooth device.

Key tests for cellular network approval

Some key tests from those network approvals are TRP and TIS. TRP is "total radiated power" which is a measurement of power delivered from the antenna in all angles from the antenna and integrated. And TIS is a measure of sensitivity over all angles from the antenna and integrated. So this is going to give you two numbers that are going to drive antenna efficiency requirements.

Which gets us right into our antenna design process and that's what start with is, what are the requirements?

We'll just need to know where do you plan on shipping the product and which carrier do you plan on using? Because AT&T and Verizon are going to have different OTA requirements, different TRP and TIS requirements. And that's going to drive the antenna design, some electromagnetic modeling, and the simulation portion. And the beautiful thing about custom antennas is that we can simulate the design before we build anything, and we can do trade off studies and save a lot of time that way. So here's an example of a PCB trace antenna. So we have the antenna over here. We have a ground plane with length L. And so what we can do is we can vary the length of the ground plane and measure efficiency versus frequency. And we can put a bunch of plots together and see the performance of the antenna as we increase the size of the antenna and/or the ground plane.

And then we can take those simulation results, we can pick an antenna that's going to meet our carrier requirements here in red and has the margin of all those requirements. And then we can build prototypes based on those models. And then we'll tune and test those prototypes. And we're doing the testing by looking at the gain, we're looking at the efficiency and far-field pattern of the antenna. And we're going to compare that to our original requirements. And at this point, we're going to have a lot of confidence with the antenna and the mechanical design and we'll be able to finalize the industrial design because we're going to know that our antenna requirements are going to meet these efficiency requirements that we extrapolated from the carrier requirements.

So, we can go into the PCB assembly integration with a lot of confidence that we're not going to have to redesign the mechanicals. Now, this is the big difference between just implementing an off-the-shelf antenna is that you're going to know all of these before you even do an integration, so that's going to give you a lot of confidence. Now, I hope this showed why a custom cellular antenna is the lowest risk path when you're dealing with a cellular application.