RF engineers play an important role in developing many revolutionary technologies in the field of telecommunications, physics, and astronomy to name a few. Their innovations have revolutionized our lives in different ways. They are responsible for introducing the amazing technologies we use every day such as cell phones, satellite communication (SATCOM), and radar systems.
There are approximately 22,000 Radio Frequency Engineers currently employed in the United States. This number grows with each passing year due to the growing importance of RF technologies and the high compensations these professionals receive.
We discussed the skill sets necessary to succeed as an RF engineer in the modern era in an earlier article (click here to read the article). In this article, we will examine the various steps an RF engineer must perform when designing a product for manufacturing and mass production. Each of these steps is summarized in Fig. 1. We will elaborate on each step in this article.
Figure 1. The workflow from design to manufacturing of an RF product
Obtaining and Reviewing Design Requirements
The design requirements for products are usually obtained in one of two ways. They may be provided by the customer. Alternatively, they may be contemplated by the R&D team to solve a specific problem. In many cases, they might change along the way or they could become more complex or less complex based on the budget. They may also incorporate additional parameters if the design is a part of a larger design.
The first step of the design process, i.e. defining the design requirement, functions as a stepping stone that leads to the creation of a successful product. This makes it vital to place realistic, economical, clear, and practical requirements for the project.
Some key points to keep in mind prior to starting the design process include:
Set a Deadline
A project without a fixed deadline may likely continue forever. Therefore, you must set a realistic deadline that keeps the project on-track towards completion. Such a deadline should take many factors into account. This includes the time devoted to:
- Designing a prototype
- PCB fabrication and assembly
- FCC certification
- Test fixture design and implementation
Designers should ensure they communicate with their team regularly. This helps reduce the odds of delays or mistakes occurring.
Get a Second Opinion
Designers should also consider getting a second opinion from their peers. This could be in relation to their assessment of the design and how it could potentially be improved. If a designer feels they need help, they should seek it out immediately to speed up the design process.
This is important, as the goal is to complete the design correctly and as efficiently as possible. Therefore, it is beneficial to utilize skills and knowledge from your colleagues.
Use Resources Only as Needed
French Philosopher Voltaire famously stated, “the best is the enemy of the good”. If the product’s current design enables it to perform as needed, there is no benefit to putting in additional resources such as time and money to improve it. The only exception exists if the customer is willing to pay for the improved performance.
Here is an example of the type of the design requirements an RF engineer would typically receive from a client:
We need to design an RF-frontend consisting of an LNA and PA to increase the range of communication. The board is supplied by an external 5V supply. The output power of the PA needs to be 2W and the operational bandwidth is 2.5 GHz-2.7 GHz. The LNA needs a noise figure less than 1.5 dB and a gain of at least 17 dB. Our budget for a board shouldn’t exceed xx dollars. The project needs to be finished by xxxxx.
Once the design requirements have been received, the next step is to implement a block diagram design of the system based on these requirements.
For example, the block diagram for the frontend design described in the previous section resembles the following:
The block diagram approach is especially useful when designing sophisticated systems that include RF, digital, and analog subsystems.
One of the most important steps in this stage is to calculate the system parameters such as gain/loss, 1dB compression point, noise figure, IP3 (third order intercept point) of the whole chain. This helps ensure that the system performs as expected. Software such as ADS, AWR, or even Excel spreadsheets can be utilized to predict system performance at this stage of the design process.
This step converts the block designs discussed in the earlier sections into actual components. As mentioned in the previous article (click here), there are numerous high-performance and low-cost chip solutions available for different RF applications.
The availability of such solutions enables RF engineers to focus on system level design instead of component level design. This helps significantly accelerate the time-to-market for RF products. However, the RF engineer may still need to design a component themselves in certain situations. In both cases, the RF engineer can save on resources by using a simulator. This helps optimize the board’s performance, thereby bypassing the lengthy and costly process of prototyping. Powerful RF simulation tools such as ADS and AWR are often utilized for this purpose.
Several considerations must be kept in mind when choosing components. This includes:
One key consideration is to select components that offer adequate product performance. It doesn’t make sense to give your customer a Ferrari when they asked for a Toyota Camry!
The statement “Price is king” rings true even in choosing or designing components. A higher-priced component may offer better performance. However, you may not necessarily need to spend on the best quality component to achieve the target performance.
Therefore, RF designers should find a compromise that offers a good ratio of price to performance. For example, if you need to achieve a noise figure of 1.5 dB, it doesn’t make sense to pay more for a device with a noise figure of 0.5 dB.
Designers should also ensure the part they intend to use is available on the market and that it won’t become obsolete in the near-future. Changing a design can cost a lot, so it is best to avoid parts that are unavailable or could become obsolete soon.
Availability of Simulation Models
If you are planning to use simulations to assess design performance, it is vital to seek out components that have S-parameters. This is especially important for components such as amplifiers.
For example, designers should ensure their chosen components are compatible with simulator tools such Modelithics.
PCB design is a core aspect in the creation of RF systems. In most cases, PCB technicians typically work alongside RF engineers to design the layout of a board. However, the RF engineer will still need to understand the layout principles to minimize the issues such as impedance mismatch, couplings, noise, and unwanted resonances.
The board layout is also essential for avoiding electromagnetic compatibility (EMC) issues that could jeopardize system performance and create issues related to FCC certification.
The PCB design part consists of a schematic and a layout. The layout is usually based on the schematic created.
There are various PCB software tools on the market such as Altium designer, Eagle, and KiCad suited for this purpose. Each of the aforementioned software vary in terms of their price, capabilities, and ease of use. Designers should have a good understanding of the strengths and drawbacks of each PCB software tool before selecting one for their needs.
Once this part has been completed, it should be sent to your peers for review. This step is important, as other designers and engineers may spot issues or improvement areas that you may have overlooked. This strategy is especially important for complex designs, as it can be easy to miss issues and design elements that could potentially cause problems in the finished product.
In some cases, it can be necessary to use simulation tools such as ADS or HFSS to optimize the routing or layout. This is especially important as frequency goes higher and reaches X band and above. In such cases, the results from simulation must be implemented in the final PCB layout.
The final step here is to have a clean bill of materials (BOM). This bill of materials should take the aforementioned considerations such as part availability into account before being finalized.
After this, the board is sent for manufacturing and assembly. It is essential to use a reliable manufacturer to build your design. This is because the assembly and manufacturing quality can have a direct impact on the circuit performance. This consideration is important as the quality of the manufacturing and assembly matters more as the frequency increases.
Designing a good enclosure can be a challenging task. After all, an enclosure performs many vital functions. It not only protects the PCB from damages, it also shields the components so that radiation coming out of the enclosure and mutual coupling between the components on the board are minimized.
An RF engineer usually works with a mechanical engineer or a technician for the enclosure design. Extra attention needs to be devoted when high power circuits such as power amplifiers are on the board. This is because they need to have an extra shield, such as a shield can, on-hand.
Once the prototype manufacturing process is complete, RF engineers must shift their focus to troubleshooting and optimizing the board’s various performance factors. For this purpose, an RF engineer must be capable of working with various test and measurement equipment.
One essential piece of equipment they must use is a network analyzer. This allows them to perform component level characterization such as gain, loss, and matching.
For system level characterization such as error vector magnitude (EVM), adjacent channel power ratio (ACPR), harmonics, and intermodulation measurements, a spectrum analyzer is used.
In this stage, the matching, harmonics, spurs, gain, noise and other parameters are optimized. This stage sometimes requires the board to be reworked. This task is usually performed by an RF technician. If a critical component or a subsystem needs to be changed or optimized, the design will need to be reiterated as shown in Fig. 1.
All commercial products must pass specific tests designated by the Federal Communication Commision (FCC) before they can be sold on the market. Such compliance tests ensure the product does not cause unwanted interference with other equipment or frequency channels, and that it meets other telecommunications requirements.
If system issues do occur, the PCB design or components will need to be changed or redesigned. For example, this may occur if the system’s radiated harmonics are higher than expected.
RF engineers must be familiar with EMC concepts to avoid such occurrences. They must also possess a good understanding of the relevant FCC limitations and requirements before updating their design to meet these requirements.
Once the product has received FCC certification, it must be tested in the production line. The process of designing a RF product can be vastly different from the perspective of mass producing in a production line. In-factory RF testing consists of unique challenges and requires well-designed test processes and test fixtures that streamline the production process.
RF engineers need to work together with software developers to create automated test processes using software such as LabView, Python, or Matlab. They will also need to work with a mechanical engineer to create a mechanical test fixture where the product goes in for testing purposes.
Such fixtures include a “lick” mechanism or a type of push mechanism that connects the PCB or product with various test equipment and probes. Once the connection is established, an automatic test process runs and generates a measurement report that indicates if the test has been failed or passed.
As you can see, RF engineers must possess various skills to be able to design and test RF systems as required. Such skills can take a long time to understand, and even longer to master. This creates bottlenecks in the industry and research where RF engineers are required to be knowledgeable in these areas before working on advanced technologies that need the knowledge of RF system design.
Key RF technology developments can be accelerated if the time RF engineers spend developing such skills is minimized. This is exactly what we aim to do at Quaxys Academy.
Quaxys offers exceptional skill-based RF courses that bring the RF engineers up to speed with key RF concepts and teach them the essential skills they need to solve the real-world problems in industry and research. Most importantly, we offer a road map that accelerates the learning process and focuses on key areas where the RF engineers need training. This learning process is supported by interactive online simulators, calculators and valuable PDF resources and videos. We also offer RF educational kits for some of our courses to deepen participants’ understanding of these concepts.