The best cellular devices are greater than the sum of their parts. The secret? Careful integration of the antenna system with the module and other components. This ensures that they all work together to achieve technical goals such as link budgets, battery life, throughput, and business goals such as time to market, price point, and competitiveness.
For starters, integration ensures that all components co-exist rather than compromise each other. One indirect way to assess their relationship is total isotropic sensitivity (TIS), which measures the receiver’s ability to maintain a connection when the signal is weak. Components near the antenna can emit spurious radiation, and this noise affects its ability to provide the receiver with as much signal as possible. So, if TIS testing finds that the receiver isn’t performing as expected, don’t overlook the possibility that the root cause is noise undermining the antenna’s ability to do its job.
A related factor is the size of keep-out area, which is exactly what it sounds like: The space on a printed circuit board (PCB) surrounding an embedded antenna that is kept free of anything metallic — such as other components and even copper traces — so they don’t undermine the radiated signals.
Ground Plane Size is Key for Optimized Performance
The PCB also serves as the ground plane, one of the most decisive factors in the antenna’s performance. The antenna’s size — and thus its ground plane size — both vary significantly by band. One rule of thumb is that the ground plane’s length must be at least one-quarter the size of the wavelength—anything smaller and the antenna’s efficiency and bandwidth both plummet.
The 4G and 5G bands currently used in North America range from 600 MHz to 3.5 GHz. At 699 MHz, for example, the minimum ground plane length is 107 mm. At 2400 MHz, it’s 31 mm.
Ground plane size also directly affects the device’s ability to pass carrier certification for all of the mobile operator networks that it will use. Each carrier has its own minimum efficiency requirements for the bands where it holds licenses.
This highlights another essential tip: Integration is something to consider early in the device design process. If it’s addressed later, such as after the device’s form factor is finalized, there’s a good chance that the ground plane, the keep-out area, or both aren’t large enough. Now an extensive, expensive redesign of the PCB may be necessary, leading to cost overruns and delaying the device’s market launch — and potentially giving competitors a first-mover advantage.
Impedance Matching: Waste Not, Want Not
The integration process also covers impedance matching, which ensures that the antenna can broadcast all of the signal that the transmitter provides. If there’s a mismatch, then some of the signal is reflected at the transmitter. This reduces the device’s ability to maintain a reliable, high-performance uplink connection. It also wastes battery life because the transmitter uses power that literally goes nowhere.
Impedance matching focuses on the transmission line. Depending on the antenna type, this is the wire, cable, or PCB trace that connects it to the transceiver. Impedance measures how effectively the signal travels down the transmission line. Aim for a return loss of at least 6 dB. Anything over 10 dB starts to become overkill.
Here’s a matching scheme for a multiband antenna. Using a four-component matching circuit:
- Assign two components to match the low-band resonance. This acts as a high-pass filter.
- Assign two components to match the high band resonance. This acts as a low-pass filter.
The following infographic illustrates the results:
A related measurement is total radiated power (TRP), which is all power that radiates from an antenna over a given band. Because cellular modules have a standardized maximum transmit power, antenna efficiency effectively determines TRP. Operators require a minimum TRP level for any device being approved for use on their networks. If impedance is matched to a 10 dB return loss but TRP is still too low, then the transmission line is not the culprit.
Finally, integration ensures all components work together to take advantage of the latest 3GPP standards. For example, LTE Cat M1 features Power Saving Mode (PSM) and extended Discontinuous Reception (eDRX) to maximize battery life. An antenna with high efficiency can complement those technologies by enabling the transceiver to use less power to transmit a usable signal every time it wakes up.
Integration is a complex process that requires a unique combination of cellular expertise and test tools. So, it’s no surprise that device OEMs, systems integrators, IoT service providers, and other companies frequently consult an antenna expert for guidance. To get started, Taoglas offers Engineers a suite of user-friendly digital tools designed to streamline, simplify, and customize antenna design and integration. These tools help engineers quickly develop their prototypes. The toolset includes the Taoglas Antenna Integrator, Antenna Builder, and Cable Builder.
The latest addition to the suite, the Taoglas Antenna Integrator, allows users to preview their embedded antennas, including the performance of multiple-input multiple-output (MIMO) antenna systems, during the concept phase of a project. This feature accelerates time to market and helps prevent potential issues with component placement inside the product. Discover more by clicking the button below.
