How to Choose the Right Cellular Antenna Type for Your Application

There’s no shortage of options when choosing a cellular antenna: embedded, external, monopole, dipole, and cabled, to name just a few possibilities. How do you navigate all those options and choose the one that best meets your application’s unique requirements for performance, size, bands, mobile operators, and more?

Start by understanding that antennas should never be an afterthought during the application design process. Take the example of an application where the form factor requires an internal antenna, such as for aesthetics. If the size and layout of that device’s printed circuit board (PCB) are finalized first, it limits the antenna choices. Another example is the device enclosure, which must be made out of a material that doesn’t attenuate signals. That rules out metal and carbon fiber.

This can have enormous ripple effects. For instance, pre-certification might reveal that the antenna, the cellular module, or both cannot meet mobile operator and regulatory requirements. (For more information about how the carrier certification and pre-certification processes work, click here.) Now a major redesign of the PCB may be necessary, which is an additional cost that can make it difficult to achieve the application’s price and profit goals.

If the enclosure is the issue, then a seemingly simple change to an RF-transparent polymer could mean the device no longer meets ruggedization specs, which becomes a major problem for applications such as automotive and law enforcement. Whatever the reason, a redesign also delays the application’s market debut, potentially giving competitors a first-mover advantage.

Another risk is that no off-the-shelf antenna will work because it’s too late or too expensive to make major design changes, such as using a larger enclosure. A custom antenna is an ideal way to accommodate a rigid design. However, the antenna supplier will need enough lead time to design, test, and refine the antenna to ensure that it meets the application’s performance requirements, as well as carrier and operator certification, and then ramp up production. All of this can delay the application’s time to market, revenue potential, and competitiveness.

How to Narrow Down the Options

The two main types of antennas are embedded and external. For example, vehicular applications such as asset tracking, autonomous/robot taxis, fleet telematics, and driver access to cloud services typically use external antennas. Figure 1 uses a police cruiser to illustrate many common external types for vehicular applications.

Figure 1: Common Types of External Antennas for Vehicular Applications

There are two types of external antennas for fixed and mobile applications:

• Terminal mount antennas are attached to the device via a connector on its housing, like the 4G router in Figure 2. Some terminal mount antennas are monopoles and thus need to sit atop a large metallic surface — such as a vehicle’s roof — so they have a ground plane to radiate efficiently. Others are dipoles, which means they have a built-in ground plane.

Figure 2: Cellular Router with Terminal Mount 4G Dipole Antenna

• Cabled antennas are mounted several inches or feet away from the device, such as with as adhesive on a windshield. They’re a good fit for new products that need to get to market quickly because if the cable is longer than 20 cm, then the antenna doesn’t have to go through carrier certification. Another benefit is the distance from the device’s electronics minimizes the risk of undermining the antenna’s total isotropic sensitivity (TIS).

Embedded antennas, meanwhile, are mounted inside the device’s housing, just like in smartphones. There are two types, both of which are subject to carrier certification:

• On-PCB embedded antennas are typically monopoles and a relatively low-cost option. One key consideration is their location on the PCB, which serves as the ground plane and thus affects the antenna’s efficiency. The size of the PCB ground plane also affects the antenna’s total radiated power (TRP). Each mobile operator has its own set of TRP requirements for carrier certification; these vary based on factors such as band and technology (4G vs. 5G). One rule of thumb is that the lower the band, the larger the ground plane, which highlights the importance of considering antenna options early on in the device design process.
• Off-PCB embedded antennas are attached to the device housing rather than to the PCB. Although this provides design flexibility because the PCB doesn’t have to serve as a ground plane, the distance from the antenna becomes an important consideration because it affects TRP and efficiency. Off-PCB antennas also cost slightly more than on-PCB types, which is a consideration for highly price-sensitive applications such as IoT sensors.

That’s a lot to consider, which is why device OEMs, systems integrators, IoT service providers, and other companies frequently turn to an antenna expert to make informed choices. To get started, contact our Engineering team directly by clicking the button below.