Selection and performance considerations of GPS smart antenna modules in system integration

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Selection and performance considerations of GPS smart antenna modules in system integration [Copy link]

In recent years, GPS has evolved from an integrated product to part of a comprehensive system solution. The driving force behind this transformation is the miniaturization of GPS and the pursuit of cost reduction. Highly integrated signal mixing chips complete the RF front-end functions. The entire system consists of chips including GPS hardware, powerful processing cores, embedded memory, and small electronic components, which makes GPS miniaturization possible. OEMs can choose to use GPS chipsets, GPS modules , or smart antenna modules to achieve system integration. Each solution has its own advantages and disadvantages: chipset-based designs can provide high flexibility, but at the same time require a lot of design effort and require the design engineer to have a wealth of RF knowledge; while smart antenna modules are the right choice for rapid system integration. In rapid system integration applications, based on this fully designed GPS subsystem, integration requires only the shortest development time, the lowest development cost, and the least development risk. When starting mass production, the use of smart antenna modules will significantly simplify the material procurement and stockpiling work and the product testing process.

Figure 1: GPS system requirements analysis.

Currently, there are a wide variety of affordable GPS receivers on the market to meet the different needs of OEMs. GPS manufacturers offer products with different performance and different levels of system integration. Even if today's GPS receivers seem to be suitable for simple and straightforward system integration, it is still difficult for OEMs to make the most appropriate choice due to the large number of products available on the market. Therefore, it is recommended that OEMs determine the requirements that the GPS receiver needs to meet before making a choice, including technical and non-technical factors, as shown in Figure 1.

Technical and non-technical requirements of the system

Technical requirements include features (such as power-saving modes and SBAS support), ease of use (especially ease of configuration), and both qualitative and quantitative performance criteria. Quantitative indicators refer to measurable parameters such as accuracy, startup performance, tracking sensitivity, and power consumption, while qualitative indicators include the expected positioning results obtained from field testing. Some GPS receivers may have good technical indicators measured in the laboratory, but they may not be good in field testing. Field testing reveals weaknesses or defects in technical characteristics. No matter how GPS receiver technology develops, there will still be performance compromises due to certain trade-offs. For smart antenna modules, the miniaturization of patch antennas and their ground planes comes at the expense of sensitivity. The pursuit of low power consumption brings another performance trade-off: power consumption can be reduced by reducing the hardware architecture, such as reducing the number of channels and time/frequency search windows, but at the same time, startup performance will be compromised.

Engineers tend to focus on technical requirements and ignore the importance of non-technical requirements. Limited project cycles, budgets, and available internal R&D resources all have an impact on product design. Engineers need to carefully decide the level of system integration, which is best viewed as a measure of the technical depth of their R&D work. The selected level of system integration affects project complexity, schedule, cost, product, and material procurement. Cost factors play an important role in evaluating GPS receivers. For projects with small product batches, the initial development cost accounts for the largest part of the total product cost and must be considered. For projects with large product batches, the impact of development costs on the project itself can be ignored. In order to optimize product costs, sufficient time and resources need to be invested in the R&D process.

The fierce competition among GPS manufacturers has resulted in low prices for GPS products. Engineers and purchasing managers are easily attracted by price factors and choose the cheapest one. Please note that simply focusing on product cost while ignoring other requirements is likely to lead to disappointing results, such as project delays and product quality defects. Poor performance, quality that does not meet expectations, and dissatisfied users are the last things you want to see in GPS embedded products.

The level of system integration that must be determined early in the project will influence the choice of an OEM GPS receiver. The selected level of system integration is a trade-off between design complexity and limited cycles, skills, and available resources.

Design based on GPS chipsets can provide the greatest flexibility and product optimization. Design based on chipsets requires development engineers to have rich skills and experience in RF design to complete product development and provide a comprehensive and thorough supporting product testing system. The design and development cycle of chipset-based products usually exceeds one year, the cost is high, and the technical risks cannot be ignored. Generally, three or more product prototype tests will be carried out before the product can be finalized. It is strongly recommended to work closely with GPS manufacturers during the development process. In short, the high design costs, greater risks and complex material sources (20-40 components from different semiconductor companies) make this method only suitable for products with large-scale application potential.

GPS modules can be an alternative to chipsets. Modules contain full GPS functionality, allowing development engineers to quickly integrate systems without having to deal with the hassle of RF and GPS design flaws during development. Development engineers only need basic RF knowledge to specify the antenna type and design the antenna to the module's link. The module uses surface mount pads and is suitable for automatic placement and soldering lines, making it an attractive option for medium and high-volume production projects. From a material preparation perspective, using modules is easier than purchasing a large number of components. At the same time, since the supplier has fully tested the GPS module, only relatively simple product testing is required.

Figure 2: System integration levels.

The GPS receiver board itself has dedicated RF and I/O connectors. Although it is larger than the GPS module , it further simplifies system integration. In addition to selecting an active GPS antenna with a suitable connecting cable and connector, no other RF-related design work is required during use. When ease of use and cost-effective product reliability are key considerations, the plug-in receiver board is the best choice.

When the ability to quickly finalize a product or quickly launch it into the market is the determining factor for the success of a product, GPS smart antenna modules are the best choice. Smart antenna modules contain a complete GPS receiver with a built-in antenna. Smart antenna modules have two application forms: one is an OEM smart antenna module for terminal integration, and the other is to encapsulate the smart antenna into a component.

Select smart antenna module in the design

Due to the characteristics of fast system integration and low risk, GPS smart antenna modules are the most appropriate choice for applications that require rapid product finalization, small batch production, and strict time-to-market requirements. Even if the smart antenna module includes a completely independent GPS function, there are still some design work to be done during use, including the selection of antenna type (chip antenna or helical antenna) and embedding the smart antenna module into the terminal product.

Most smart antenna modules use either ceramic patch antennas or helical antennas. Patch antennas are directional and have maximum gain in the plane orthogonal to the radiator. In other words, the radiator in the horizontal plane has the maximum gain for signals sent from the apex of the sky. This high-center sensitivity is greatly affected when the reception elevation range in the horizontal plane is very narrow. Patch antennas are suitable for end products that are mainly facing upward, such as in car navigation, mounted on the exhaust hood against the windshield. In addition, the size of the antenna aperture, which is determined by the size of the radiator and the size of the ground plane below it radiates through, will also affect the signal reception sensitivity.

Helical antennas have relatively wide directional characteristics: they have a wider receiving elevation angle, but the peak gain is relatively low. Helical antennas are suitable for terminal products that require free use in all directions, such as mobile handheld devices. Since they interfere with signal reception when close to the human body, the impact of using helical antennas in this case is relatively small, so GPS reception can be achieved when the terminal product is held in all directions at a distance or near the human body. However, helical antennas also have a disadvantage: the antenna aperture is small, which limits the overall receiving sensitivity.

The following are some factors that affect the embedded application of smart antenna modules in terminal products:

1. Before selecting a smart antenna module, you should understand the main positioning direction and usage of the terminal product: for example, whether the electronic device is placed on a flat surface for operation or held in the hand at a certain angle to the horizontal plane and close to the human head for use.

2. The antenna should not be integrated close to noise sources, such as internal processors and illuminated LCD displays.

3. The shell material of the end product has an impact on the antenna performance. The dielectric constant, thickness and spacing of the shell or shielding material to the antenna surface will affect the resonant frequency of the sheet antenna. Therefore, well-designed OEM smart antenna modules use packaging shells according to manufacturer specifications and have zeroed the offset resonant frequency.

Packaged smart antenna

Packaged smart antennas are an alternative to OEM smart antenna modules. When it is required that the product embedded with GPS does not make hardware changes, choosing a packaged smart antenna has certain advantages. There are two types of packaged smart antennas: discrete smart antennas and closely coupled smart antennas. Discrete smart antennas can be placed in a location with a good view of the sky, such as GPS mice. They communicate through RS-232, USB or Bluetooth, and are powered by the host (for example, through a USB power cable) or a rechargeable battery. Closely coupled smart antennas can be directly inserted into the end product, such as through a CF slot (Compact Flash slot).

Packaged smart antennas are ideal for system solutions running on standard portable hardware platforms such as portable PCs and PDAs.

Conclusion

Using a well-designed smart antenna in the integrated design work can provide the same high performance level as using GPS modules and chipsets. In Japan, Shinjuku is one of the most demanding cities for drive testing. The high-rise buildings on both sides of the city roads and the limited view of the sky put a severe test on the multipath suppression capability of the receiver. The smart antenna module contains 16 channels of ANTARIS positioning technology, which can still provide excellent performance in such a harsh positioning environment.

When the end product design needs to be realized quickly, the development cost needs to be reduced, or the internal R&D resources are limited, the smart antenna module is a practical option. Carefully selected smart antenna modules can provide performance comparable to traditional GPS chipsets and module integration.

By Georg zur Bonsen