Seeking advice on selecting an antenna for wireless modules

I have a project I’m working on that requires WIFI/BLE. I have found some wireless modules, like the ESP32 or some others from Laird. However I’m new to IoT and wireless design and I’m not sure how to select an antenna… some modules have built in PCB or chip antennas and other modules give some suggested u.fl antennas that are also certified for use with the module.

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How does one know if the PCB or chip antenna is sufficient or if you need a u.fl type antenna? What selection criteria or analysis would you recommend to help decide which path to go down?

The circuit board will be sitting in a plastic enclosure. The only real metal in the product will be the circuit itself and some screws or what not for assembly.

This is an RF system design question.

The short and cryptic answer is the link budget tells you how much performance you need. The real answer is the continual subject of many masters and doctoral theses.

Like most engineering problems it’s a bag of jello - squeeze it one place and it squirts out somewhere else. Not really optimization but rather trade-offs. Better antenna performance gives you better range, or requires less transmit power so you get better battery life, or … Better antenna performance also leads to directions of poorer performance. Search on “Antenna Patterns” for more reading.

So, get advice, test to verify, and make sure you have lots of margin for the stuff you haven’t considered.

The TL:DR is that RF connections are described by a “link budget.” The link budget is transmit power plus all losses and gains, and the receiver sensitivity. If the total number is positive, things work. If it’s negative, they don’t. [Note to the pedants: I’m including any processing gain effects, so shut up about negative S/N.]

Simple, small antennas tend to be poor performers and show up as losses in the budget. Antennas with gain have patterns - some directions have gain, and others have (even higher) losses. If you can be sure your receiver and transmitter are in the area where the antenna has gain, you have the option of the higher gain antenna.

The distance between the receiver and transmitter is a loss factor all it’s own. It’s a square law relationship - double the distance and the loss increases by a factor of four (~6 dB) Search on “Free Space Path Loss” Wikipedia has a decent intro article. Note that few cases are actually “free space” so the path losses have a lot of other loss terms that I won’t bore you (even more) with other issues like fading, mutlipath, and a bazillion other considerations.

An ideal point source antenna that radiates in all directions is called an isotropic radiator. Antenna gains are often specified in dBi (dB relative to an isotropic radiator.) Antenna gains are also frequently described in dBd (dB referenced to a dipole.) A dipole is a simple, fairly fundamental and common antenna type with a gain in it’s main lobe of ~2.15 dBi. The gain off the end of a dipole is a null, so infinite loss. A tradeoff.

Antennas develop gain by squeezing signal energy in some direction. An isotropic radiator’s gain plot is a sphere - equally good (and poor) in all directions. A dipole’s antenna pattern is a torus. Better in a direction normal to the axis of the antenna, and (theoretically) zero off the ends along the axis. [Note to pedants, shut up about infinite Q and the infinitesimal dipole.]

You need to look at the specified gain of the antenna and your link budget. If you have gain to burn, a simpler antenna is generally better. If your budget is negative, you need a better receiver, more transmit power, a better antenna, or another trick up your sleeve.

All these things have limits. We’ll talk abut receiver noise limitations another day.

Rich

Is there anyway one could get a sense if the PCB trace antenna on a module is good enough to work with a typical WIFI router/receiver in such a situation? Or do I basically have to built it and test to see?

The short answer is: Yes, build it and try it out.

The longer answer is that a good PCB trace antenna implementation isn’t really inferior to your other antenna options. The only catch is that you need to carefully observe any implementation details and avoid detuning it with nearby components or enclosure walls. Most vendors will provide a reference design with some guidelines (PCB material, nearby ground plane requirements, keep-out areas around antenna). Always start with that.

The reality is that you can’t make an IoT device work in every possible user scenario. I prefer to set a reasonable benchmark against my . If I can stream YouTube on my over WiFi in a certain location, my low-bandwidth IoT device should also work there. Your has the advantage of a highly optimized, sensitive front-end, but your IoT device has the advantage of ultra-low bandwidth.

Users can generally understand that if their can’t get WiFi in a location, it’s unreasonable to expect any other device to work there. On the other hand, they’re not going to be happy if their works fine but your IoT device cannot.

In wireless product development, what happens behind the scenes when selecting, designing, and integrating an antenna into a product? What is the journey of a PCB antenna, or more specifically, a PCB-mounted embedded antenna?

Designing and integrating an antenna may seem complex, but it can be broken down into manageable steps. It begins with defining the product’s requirements, which drive the antenna specifications. Next, you select and design the appropriate antenna type. Then, verify the design’s performance through simulations. After building and testing prototypes, manufacturing begins.

Each step demands careful attention. This article offers a clear, step-by-step guide to the PCB antenna design process, explaining each stage and providing practical tips to help you successfully integrate the antenna into your wireless product.

The first step in designing an antenna for wireless solutions is to identify and document the product's essential needs. This process is known as Requirements Engineering (RE).

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RE focuses on understanding what needs to be designed, not how. To effectively define these requirements, the design team must conduct a thorough problem analysis. This analysis should address several critical questions to ascertain the operational and environmental conditions under which the product will function. These include:

• What types of communication protocols will the product support (e.g., WiFi, cellular, GPS)?
• What operating frequency and bandwidth are required?
• What are the coverage, gain, and cost expectations?
• Will the product operate indoors, outdoors, or under specific environmental conditions such as extreme temperatures or high humidity?
• How much space can be afforded for antenna clearance on the PCB?

The product requirements define the necessary antenna specifications, which help narrow down the possible antenna technologies. When proposing antenna solutions, include a detailed assessment of the costs, timeline, and, if possible, recommendations for placement and orientation.

Document all antenna and product requirements in a way that supports testing. These requirements should guide the design process and serve as a checklist during testing to ensure the design meets the goals.

The design stage starts by using the requirements defined in the RE phase to select the appropriate antenna type and design its specifications to meet those needs.

The antenna must be designed to cover the required frequency and range. Its key parameters, such as efficiency and directionality, should align with the product’s needs. The polarization of both the transmitting and receiving antennas must match to maximize power transfer. The Voltage Standing Wave Ratio (VSWR) should be kept low and the return loss high.

When attaching the antenna to a PCB, match the antenna's impedance with the characteristic impedance of the feed line connecting it to either a transmitter or a receiver. Impedance mismatches can significantly reduce the RF link budget, lowering the antenna's efficiency and range.

Remember, an antenna is a sensitive component. Its performance is greatly influenced by its placement, surrounding components, the ground plane, and the enclosure or casing.

To shorten and ensure reliable design cycles for PCB antennas, designs must be verified early on. However, predicting antenna performance is challenging, as solving Maxwell's equations requires complex algorithms. Electromagnetic simulators can help predict performance and optimize antenna designs before building physical prototypes.

Remember, however, these simulators are tools, not replacements for the designer. They can predict performance based on the designs you give them, but you need a strong understanding of antenna theory to use them effectively.

Choosing the right simulation method is also important. Popular algorithms include the Method of Moments (MoM), Finite Element Method (FEM), Finite Difference Time Domain (FDTD), and Finite Integration Technique (FIT). Each has specific advantages and disadvantages summarized below:

AlgorithmAdvantagesLimitationsMethod of Moments (MoM)

• Analyzes complex layered structures effectively.
• Simulates designs with many ports efficiently, without added time costs.

• Cannot handle general 3D structures, limiting its use to planar designs.
• Demands large storage and increases computational time sharply with the size of the problem.

Finite Element (FEM)

• Can analyze arbitrarily shaped 3D structures, not just layered setups, offering an advantage over the MoM.
• Simulates designs with many ports efficiently, without added time costs.
• Offers the most flexible approach to electromagnetic analysis.
• Serves as a frequency-domain solver, making it ideal for problems with periodicity like phased arrays, frequency-selective structures, and band gap antennas.

• Simulating complex antenna structures uses significant computer memory.

Finite Difference Time Domain (FDTD)

• Can analyze 3D structures.
• It has an advantage over the FEM method in that it does not require solving a matrix, allowing it to handle very large problems with relatively small amounts of computer memory.
• Highly suitable for parallel processing, which allows it to leverage modern GPUs to speed up simulations.
• Simpler to implement a basic FDTD solver compared to MoM and FEM solvers.
• Well-suited for simulating specific antenna types such as horn antennas, waveguides, microstrip antennas, conformal antennas, and small planar array antennas.

• Requires running a separate simulation for each port in a design, making it less efficient for designs with many ports.
• Not optimal for certain types of antennas like wire antennas, aperture antennas, reflector antennas, and those with electrically large structures.

Finite integration technique (FIT)

• Effective for analyzing antennas with inhomogeneous materials, wideband issues, and ultra-wideband (UWB) applications.
• FIT underpins many commercial simulation tools because it can handle the entire spectrum of electromagnetics, from DC to high-frequency and optical applications.

• Not well-suited for simulating wire antennas.

Learn more about the challenges of RF PCBA design now.

Selecting the appropriate EM(Electromagnetic) analysis tool depends on factors like ease of model creation, integration with circuit simulation tools, and the level of EM expertise required.

For planar structures, such as PCB interconnects and planar antennas, the MoM is most effective. For fully 3D structures like connectors, packages, and 3D antennas, FEM or FDTD methods are better.

For complex 3D structures with many ports, FEM is ideal. FDTD is best for large structures with fewer ports, such as antenna placements on vehicles or aircraft, and for evaluating antenna performance near detailed human body models.

After optimizing the designs, prototypes are built for testing. These tests take place in an anechoic chamber designed to absorb all sound waves. Key measurements include return loss, efficiency, maximum gain, Effective Isotropic Radiated Power (EIRP), Total Radiated Power (TRP), Total Isotropic Sensitivity (TIS), and impedance. These measurements fully assess the antenna’s performance. If the results show any issues, the design can be adjusted.

Testing falls into two categories: passive and active.

Passive antenna testing evaluates the antenna alone, without the influence of the rest of the device. The antenna port is isolated from the RF front end and connected to a vector network analyzer (VNA) set to specific frequencies and amplitudes. The VNA measures data, which is then used to calculate efficiency, gain, directivity, and EIRP.

Active antenna testing measures the antenna as part of the entire system, including the RF front end. The main measurements are TRP and TIS.

TRP measures the total power radiated by the antenna when it is transmitting across a frequency band. TIS measures the average sensitivity of the receiving antenna system over a frequency band. TRP and TIS are key indicators of signal quality, offering a reliable gauge of the system’s overall performance.

The final step is manufacturing. Success in this stage depends on a stable design, a reliable production process, and effective end-of-line testing. Even the best designs are useless if they can't be produced efficiently and with high quality. To achieve this, consider the following when selecting and collaborating with a manufacturer:

• Early Collaboration: Involve the manufacturer early in the design process. Close collaboration between design, manufacturing, and materials teams throughout all stages—from design and prototyping to production—ensures a smooth transition to manufacturing, saving time and costs.
• Quality Assurance: Choose a manufacturer that offers robust quality assurance, including innovative end-of-line testing methods. Ensure any overseas facilities comply with local legal standards and maintain strict confidentiality agreements.
• Timely Production: The manufacturer must meet your deadlines and pricing requirements without compromising on quality. Confirm their average lead time to ensure they will deliver on schedule and within budget.
• Fabrication Tolerances: Select a fabrication process capable of meeting tight tolerances. Use prototyping and testing to evaluate the manufacturer’s capabilities and limitations and how their fabrication tolerances impact antenna performance.

Listen to this classic Circuit Break podcast episode to hear about the Wireless Research Center and FCC Pre-Cert Testing.

Designing and manufacturing antennas is a complex process. It is crucial for the success of any wireless product. Choosing the right partner is essential. The design team must work closely together. They need to understand the product’s requirements. They must also follow regulations on frequency, power output, EMC, and testing.

The design should consider factors like PCB size, ground plane, casing, placement, and nearby components. Early design verification is important. Rapid prototyping helps speed up production. Ultimately, even the best designs are only valuable if they can be manufactured efficiently.

Contact us to discuss your requirements of PCB antenna manufacturer. Our experienced sales team can help you identify the options that best suit your needs.