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

GPS has evolved from an integrated product to a part of a comprehensive system solution. Original equipment manufacturers (OEMs) can choose to implement system integration with GPS chipsets, GPS modules or smart antenna modules. Each option has its own pros and cons, and the OEM needs to evaluate it based on the requirements of its entire system before making a choice. This paper provides a smart antenna solution selection idea, and discusses the performance comparison between the chip antenna and the helical antenna and the factors affecting the embedded antenna application in the terminal product.

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In recent years, GPS has evolved from an integrated product to a part of a comprehensive system solution. The motivation for this shift is the miniaturization process of GPS and the pursuit of cost reduction. The highly integrated signal mixing chip completes the RF front-end functionality. The entire system consists of GPS hardware, a powerful processing core, embedded memory chips, and small electronic components that make GPS miniaturization possible. OEMs can choose to implement system integration with a GPS chipset, GPS module or smart antenna module. Each solution has its own advantages and disadvantages: chipset-based design provides a high degree of flexibility, but at the same time the design requires a lot of effort and requires the design engineer to have a wealth of RF knowledge; smart antenna module is the right choice for rapid system integration In rapid system integration applications, based on this well-designed GPS subsystem, integration requires only minimal development time, minimal development costs, and minimal development risk. At the beginning of mass production, the use of smart antenna modules will significantly simplify the material procurement reserve work and product testing process.

Figure 1: GPS system requirements analysis.

At present, there are a wide variety of GPS receivers on the market that can meet the different needs of OEMs. GPS manufacturers offer products with different performance and different system integration levels. Even though today's GPS receivers seem to be used for simple and straightforward system integration, it is still difficult for OEMs to make the most appropriate choices due to the large number of products available on the market. Therefore, OEMs are advised to 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 or non-technical requirements of the system

Technical requirements include features such as power-saving modes and support for SBAS, ease of use (especially ease of configuration), and performance criteria that are both qualitative and quantitative. Quantitative indicators refer to measurable parameters such as accuracy, start-up performance, tracking sensitivity, and power consumption. Qualitative indicators include predictable positioning results obtained from field tests. Some GPS receivers may have good technical indicators measured in the lab, but it is likely that field tests will not work. Field tests expose weaknesses or defects in technical characteristics. Regardless of how GPS receiver technology evolves, there will still be performance tradeoffs due to some trade-offs. For smart antenna modules, the miniaturization of the patch antenna and its ground layer is at the expense of sensitivity. The pursuit of low power brings another performance trade-off: power reduction can be achieved by reducing the hardware architecture, such as reducing the number of channels and the time/frequency search window, but at the same time the startup performance is compromised.

Engineers tend to focus on the importance of technical requirements while ignoring non-technical requirements. Limited project cycles, budgets, and available internal R&D resources all have an impact on product design. Engineers need to carefully determine the level of system integration, which is best seen as a yardstick for measuring the depth of their R&D work. The selected system integration level affects project complexity, schedule, cost, product, and material acquisition. Cost factors play an important role in evaluating GPS receivers. For projects with small batch sizes, the initial development cost is the largest part of the overall product cost and must be considered. For projects with large batches of products, the impact of development costs on the project itself can be neglected. 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 caused the low price of GPS products. Engineers and purchasing managers are easily attracted by price factors and choose the cheapest one. Please note that simply focusing on product costs and ignoring other requirements is likely to lead to disappointing results, such as project delays and product quality defects. Poor performance, unsatisfactory quality and unsatisfactory users are the least desirable for GPS embedded products.

At the initial stage of the project, the level of system integration must be determined, which affects the choice of the OEM GPS receiver. The selected system integration level is similar to a trade-off between design complexity and limited cycles, techniques, and available resources.

The GPS chipset design provides maximum flexibility and product optimization. Chipset-based design requires development engineers with extensive skills and experience in RF design to complete product development and provide a comprehensive and complete product testing system. The chipset-based product design and development cycle usually exceeds one year, the cost is high, and the technical risk cannot be ignored. Three or more product prototype tests are generally performed, and the product can be finalized. It is strongly recommended to work closely with GPS vendors during the development process. In summary, high design costs, high risk and complex material sources (20-40 components from different semiconductor companies) make this approach only suitable for products with large-scale application potential.

The GPS module can be used as an alternative to the chipset. The module includes full GPS functionality, allowing development engineers to perform rapid system integration without the hassle of RF and GPS design flaws during development. Development engineers only need to have basic RF knowledge, specify the antenna type and design the antenna to the module's link. The module's surface mount pads make it suitable for automated placement and soldering lines, making it an attractive option for medium and high volume production projects. From the perspective of stock preparation, it is easier to use modules than to purchase a large number of components. At the same time, since the supplier has thoroughly tested the GPS module, only relatively simple product testing is required.

Figure 2: System integration level.

The GPS receiver board itself has dedicated RF and I/O connectors, which are larger than the GPS module, but further simplify the system integration. In addition to selecting an active GPS antenna with suitable connecting cables and connectors, no other RF-related design work is required. Plug-in receiver boards are the best choice when ease of use and cost-effective product reliability are key considerations.

The GPS Smart Antenna Module is the best choice when it is possible to quickly complete product sizing or quickly place the product on the market as a decisive factor in the success of the product. The Smart Antenna Module contains a complete GPS receiver with built-in antenna. The smart antenna module has two application forms: one is an OEM smart antenna module for terminal integration, and the other is to package a smart antenna into a component.

Choose to use smart antenna module in the design

Due to the fast system integration and low risk, the GPS smart antenna module is the most appropriate choice in applications requiring rapid product sizing, small batch production and strict time-to-market. Even though the smart antenna module contains completely independent GPS functions, there are still some design work to be done during use, including the choice of antenna type (chip antenna or spiral antenna) and embedding the smart antenna module into the end product.

Most smart antenna modules do not use ceramic chip antennas or spiral antennas. The patch antenna has directivity and has a maximum gain on the orthogonal faces of the radiating elements. In other words, the radiating elements on the horizontal plane have the greatest gain for the signal from the vertex of the Scorpio. When the range of the receiving elevation angle on the horizontal plane is very narrow, this sensitivity to the height-centered type is greatly affected. The chip antenna is suitable for use in terminal products that are mainly oriented upwards, for example in car navigation, mounted on the exhaust hood against a windshield. In addition, the size of the antenna aperture, which is determined by the size of the radiating element and the size of the ground plane through which it radiates, also affects signal reception sensitivity.

The helical antenna has a relatively wide directional characteristic: it has a wider receiving elevation angle, but the peak gain is also relatively low. The helical antenna is suitable for use in end products that require free use in all directions, such as mobile handheld devices. Since the proximity to the human body interferes with signal reception, the effect of using the helical antenna in this case is also relatively small, so that GPS reception can be realized when the terminal product is held in all directions from a position far or near from the human body tissue. However, the helical antenna also has a disadvantage: the antenna aperture is small, which limits the overall receiving sensitivity.

The following points affect the factors that affect the smart antenna module embedded in the end product:

1. Before selecting the 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 the plane or is held in the hand and is close to the human head at a certain angle with the horizontal plane.

2. The position of the antenna integration cannot be close to noise sources such as internal processors and illuminated LCD displays.

3. The housing material of the terminal product has an impact on the antenna performance. The dielectric constant, thickness, and spacing to the antenna surface of the outer casing or shield material can affect the resonant frequency of the patch antenna. Therefore, the well-designed OEM Smart Antenna Module uses the package housing in accordance with the manufacturer's specifications, and the offset resonant frequency has been zero-calibrated.

Packaged smart antenna

The packaged smart antenna is an alternative to the OEM smart antenna module. In the case of products that require embedded GPS without hardware changes, the choice of packaged smart antennas has certain advantages. There are two types of packaged smart antennas: discrete smart antennas and tightly coupled smart antennas. Discrete smart antennas can be placed in locations with better sky views, such as GPS mice. They communicate via RS-232, USB or Bluetooth and are powered by the host (eg via a USB power cable) or a rechargeable battery. The tightly coupled smart antenna can be plugged directly into the end product, for example via a CF slot (Compact Flash slot).

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

Conclusion of this paper

The use of well-designed smart antennas in integrated design work provides the same high performance levels as GPS modules and chipsets. In Japan, Shinjuku is one of the most demanding cities in the road test environment. There are many high-rise buildings on both sides of the city, and the sky has limited horizon, which puts a strict test on the multipath suppression capability of the receiver. The smart antenna module contains 16 channels of ANTARIS positioning technology, which still provides excellent performance in such a harsh positioning environment.

Smart antenna modules are a viable option when it is required to quickly implement end product design, reduce development costs, or have limited internal R&D resources. Carefully selected smart antenna modules provide performance comparable to traditional GPS chipsets and module integration.