A device can have a well-designed radio and still fail certification, or perform poorly in the field, because of the antenna. Choosing one is less about finding the highest-gain part on a catalogue page and more about matching the electrical, mechanical and environmental limits of the product around it. The questions below are the ones worth settling before you request samples, roughly in the order they tend to matter.

1. Start with the network requirements, not the antenna

The antenna follows the radio plan, not the other way round. Before comparing parts, write down what the device actually has to do:

• Which bands and standards must be supported — for example LTE, NB-IoT, LoRa, Wi-Fi, Bluetooth, GNSS, or a combination of them
• Which regions the product ships to, since regional band variants may need different antennas
• Whether the device transmits continuously or in short bursts, which affects how much efficiency matters
• How much physical space the layout can realistically give up

Bandwidth affects how an antenna performs across different frequencies. A narrowband antenna can be optimized for a specific frequency range, while a wideband design needs to operate across a broader range, often with some trade-offs in efficiency and peak gain. Antenna gain also depends on the radiation pattern: higher gain in one direction does not necessarily mean better coverage in every direction. These factors are worth considering early in the design process, especially when the antenna must fit into a fixed enclosure or PCB layout.

2. Decide between an internal and an external antenna early

This decision affects the overall product design, so it is usually considered during the early layout stage rather than after tooling is completed.

Internal antennas, including FPC, PCB trace, stamped metal, and ceramic designs, help maintain a sealed enclosure and a clean product appearance. They are widely used in wearables, trackers, and compact sensors. However, their performance can be affected by nearby components such as the ground plane, battery, display, and housing materials, which may require additional tuning during development.

External antennas are generally easier to optimize because they are positioned away from components that can absorb or detune RF signals. An omni antenna installed on a device or vehicle provides coverage around the mounting point, making it suitable for applications such as tracking and telemetry where the signal direction may change. The main considerations are mechanical requirements, including the connector, cable routing, and mounting structure needed for the operating environment.

In many wireless products, a combination of internal and external antennas is used, with each antenna serving different radio functions according to the design requirements.

3. Give the antenna space and a ground plane

Most compact antennas are not independent radiating elements. They rely on the PCB ground plane as part of the RF structure, which means the size and layout of the ground plane directly affect antenna performance. A design that works well on a large evaluation board may perform differently on a smaller production PCB, and re-tuning is often required after the final board size is confirmed.

Two layout considerations are especially important. First, reserve a proper antenna keep-out area and avoid placing copper, components, or metal parts within this region. Second, consider any conductive materials located near the antenna in the final assembly, such as batteries, speakers, metal brackets, or coated labels. These materials can shift the resonant frequency and reduce efficiency.

For compact IoT antenna designs, the surrounding structure has a direct impact on RF performance. If the enclosure is made of metal, an internal antenna may not provide the expected performance because the enclosure can block or detune the signal. In such cases, an external antenna or a dedicated RF opening in the enclosure is usually required to provide a suitable signal path.

For applications requiring wider coverage, an omni antenna can also be considered when the device needs communication in multiple directions rather than a fixed point-to-point link.

4. Check the mechanical and environmental requirements

An antenna that performs well in the lab may still behave differently after installation. The working environment should be considered when selecting the right antenna design.

• Ingress protection – Outdoor and industrial products may require IP67 or higher protection, which affects sealing design and antenna structure.
• Operating temperature – Materials and cable assemblies have temperature limits, and long-term exposure can affect performance and reliability.
• Mechanical conditions – Vibration, cable bending, and connector stress should be considered for vehicle and industrial installations.
• Weather resistance – UV exposure, moisture, and salt spray can affect housing materials and connector selection for outdoor use.
• Mounting requirements – Screw, adhesive, magnetic, and through-panel mounts suit different equipment structures and applications.

Defining these requirements before selecting or sampling an IoT antenna helps ensure the antenna matches the actual installation environment. For applications requiring coverage in multiple directions, an omni antenna can be considered based on the system requirements.

5. Keep the RF path short: connectors and cable

When an antenna is installed away from the radio module, the cable becomes an important part of the RF path. Cable loss directly affects the link budget, and the loss increases with cable length and operating frequency. A cable that works well for lower-frequency applications may introduce noticeable loss at higher bands.

Two factors should be considered during antenna integration. First, keep the cable length as short as the product design allows. Second, select a cable type based on its actual loss performance at the highest operating frequency rather than using a general assumption.

Connector selection is also important. SMA, MMCX, U.FL/I-PEX, and N-type connectors differ in size, durability, mating cycles, and suitability for different environments. Each connector transition adds a small amount of insertion loss and creates another point that may affect reliability.

For an IoT antenna system, the antenna, cable, and connector should be evaluated as a complete assembly. Confirming connector compatibility and testing the final configuration can help avoid performance issues that may not appear when individual components are tested separately. In applications using an omni antenna, the complete RF path is equally important because cable and connector losses directly affect the available signal performance.

6. Plan testing and certification before mass production

Antenna performance is typically evaluated through both conducted and over-the-air measurements. Conducted tests, such as VSWR and impedance measurements, check how well the antenna is matched to the RF system. Over-the-air tests measure real-world performance, including efficiency, gain, and radiation patterns with the antenna installed in the actual product.

A VSWR of around 2:1 or better across the operating frequency range is a common target, but it only indicates impedance matching. It does not directly represent radiation efficiency, which means an antenna can show good matching while still having limited performance in the final installation.

For connected products, antenna validation also needs to consider regulatory and carrier requirements. Depending on the market and wireless technology, this may include FCC, CE, carrier certification, or industry-specific testing. For an IoT antenna, testing the complete device with the final enclosure is important because materials, nearby components, and installation conditions can affect RF performance.

Completing pre-compliance testing before final tooling can help identify antenna-related issues earlier and reduce changes during later certification stages. The same approach applies to systems using an omni antenna, where the final mounting position and surrounding environment can influence the measured radiation performance.

7. When a custom antenna is worth considering

Standard antennas can meet many common application requirements and are usually the first choice when size, performance, and production requirements are already defined. A custom antenna design is considered when a standard model cannot meet the project requirements, such as when multiple frequency bands need to be integrated into limited space, the enclosure affects RF performance, the mounting structure is unique, or additional validation is required for certification.

Shenzhen Feisheng Electronics is an RF antenna manufacturer with 13 years of OEM and ODM experience. The company operates a 6,000 m² production facility with an in-house RF laboratory and holds ISO9001, ISO14001, and IATF16949 certifications, along with more than 50 patents. Its product portfolio includes FPC and PCB internal antennas, GNSS and RTK antennas, 5G antennas, drone antennas, magnetic antennas, fiberglass antennas, external antennas, and RF cable assemblies.

For custom antenna projects, the development process typically includes requirement analysis, RF simulation, prototype testing, and production validation. This allows the antenna to be evaluated with the actual enclosure and device structure before moving into mass production. The same process is used for applications such as IoT antenna solutions, cellular communication systems, and omni antenna designs where RF performance depends on the final installation environment.

8. Frequently asked questions about IoT antenna selection

How much ground plane does an IoT antenna need?

The required ground plane size depends on the antenna type, frequency band, and product design. In general, lower-frequency antennas are more affected by ground plane size, and a larger ground plane can help maintain more consistent RF performance. Many compact IoT antenna models provide a recommended ground plane size in the datasheet. If the final PCB layout differs significantly from the reference design, antenna tuning may need to be adjusted.

Can an omni antenna be installed inside a metal enclosure?

In most cases, it is not recommended. A metal enclosure can block and reflect RF signals, which reduces the antenna’s radiation performance. For applications requiring an omni antenna, the common approach is to install the antenna outside the metal enclosure or provide an RF-transparent area, such as a plastic section or opening, for signal transmission.

Is a higher gain antenna always a better choice?

Not necessarily. Antenna gain refers to the direction and concentration of radiated energy rather than an increase in total power. Higher gain antennas usually provide stronger coverage in specific directions but may have a narrower radiation pattern. For many IoT applications, especially mobile or multi-directional deployments, stable coverage and a suitable radiation pattern can be more important than the highest gain value.