New RF test solution ensures quality of automotive wireless modules

The use of modules and devices equipped with a variety of RF interfaces is growing in various vehicles. Because these modules must meet strict reliability requirements, reproducible measurement results must be obtained during adjustment and final testing. With highly effective shielding and rigorous design, Rohde & Schwarz's new RF test chamber equipment can ensure that automotive modules equipped with RF interfaces are free from interference during testing. It supports a wide range of standards, including ISM, GSM, CDMA, WLAN and Bluetooth.

Today, car buyers expect to buy communications and infotainment systems that are well-made, reliable and, most importantly, safe. The challenge facing current and future car manufacturers is to create reliable test methods to ensure the quality of these systems. As product life cycles become shorter and vehicle electronics become more complex, designers need faster and more flexible solutions to meet the challenges of fast time to market. Rohde & Schwarz devices and systems offer excellent measurement accuracy and speed to meet these requirements.

Figure 1: Rohde & Schwarz RF test system for tire pressure sensors.

Wireless modules in cars

In recent years, the number of on-board modules equipped with RF interfaces has grown rapidly. Common applications include: remote keyless entry (RKE) systems with anti-theft protection, transmitters for opening the trunk or controlling the auxiliary heating system. Generally speaking, these modules work in the ISM band, which does not require authorization. There is also a huge demand for GPS navigation systems. More and more GSM modules are also entering the automotive original equipment market. One goal is to improve the quality of mobile radio applications; another goal is to improve the quality of wireless audio communications, where Bluetooth interfaces are used to make calls and receive audio signals among passengers.

Some newer applications include tire pressure monitoring systems for ensuring the safety of cars and trucks, and DVB-T receivers for reliable TV reception. In some cases, diagnostic systems with RF interfaces have been installed in automotive repair centers and emergency support centers. Other applications include sensors for monitoring engine compartment temperature, pressure and speed parameters.

In the near future, we can expect to see RF interfaces based on WiMAX and other standards being used for high data rate mobile reception. Radio communication systems that help prevent collisions between vehicles are also being developed. In all these examples, RF interfaces are needed. Depending on the specific requirements, these interfaces operate in different frequency bands and need to be optimized to support different data rates and safety standards.

Figure 2: Block diagram of the RF test system of Figure 1.

These technologies are highly dependent on the reliable functioning of the RF interface. In safety-related systems, correct operation can be a matter of life and death.

At the beginning of production, these modules must generally be checked and adjusted to ensure compliance with the applicable wireless standards. Safety aspects require that the interfaces be fully tested after final installation in order to be able to cope with extreme environmental conditions. Here, it is necessary to test the effects of large temperature changes and vibration resistance.

In order to obtain reproducible results for RF interface tests, it is essential to ensure that external interference does not affect the test. In addition, it is necessary to ensure that other nearby equipment and test systems are not affected by the test. The only way to meet these requirements is to use an RF cabin with appropriate shielding (Figure 2). The cabin can also be filled with absorbing materials to attenuate the reflection of high-frequency electromagnetic waves and ensure stable and reproducible measurements. Absorbing materials are also effective in audio applications, that is, to reduce internal reflections and environmental noise.

Rohde & Schwarz, with deep expertise in RF technology, is expanding its tried-and-tested line of manual RF test fixtures to a new family of RF test chambers.

RF Test Chamber Product Line R&S TS712x

The new RF test chamber of the R&S TS712x series is oriented to the needs of automatic production lines. Its features include long service life, rugged design and automatic opening and closing of the RF chamber. It has high shielding effectiveness in the range of 300MHz to 6GHz. The test chamber is suitable for testing modules with RF interfaces that meet various standards, including ISM, GSM, CDMA, UMTS, WLAN, Bluetooth and WiMAX.

The product family has two basic models, the difference is the width. To meet different needs, each model has automatic and manual versions. The narrow model is the R&S TS7121, which is only 155mm wide and is mainly used to test smaller devices such as RFID modules, wireless sensors and receivers, RKE and smaller Bluetooth modules.

The R&S TS7123 is ideal for automotive testing due to its 330 mm wide handle for testing onboard electronics in double DIN slots. This model is suitable for testing car radios, navigation systems and infotainment systems. The wider RF chamber provides more space to integrate subsystems that generate special environmental conditions, a good example of which is the pressure chamber for testing pressure sensors for TPMS. By combining the two chambers, the RF interface can be tested and the tire pressure sensor can be checked for proper operation under a wide range of typical pressure conditions.

Table 1: Application of various wireless standards in the automotive industry.

The automation industry requires its suppliers to perform extensive tests, including the documentation of the test results. Only an automated test system like the R&S TS7180 equipped with an RF test chamber can meet this requirement.

The pressure chamber simulates the tire pressure inside the RF test chamber. A waveform generator stimulates the tire pressure sensor to send data (ID number, pressure and temperature) with a 125kHz LF data telegram. The RF data telegram is picked up by the ISM antenna in the test chamber and demodulated in the spectrum analyzer. Its system software can evaluate this information and give a GO/NoGo message.

The automotive RF test chambers are primarily used for production tests. The manual version is designed for maintenance work, quality assurance, research and development. Since the automatic and manual RF test chambers have the same design, identical measurement conditions are ensured for development, production and service work. If combined with suitable antennas, these RF test chambers can be used to quickly implement a wide range of applications. They offer an optimized solution for situations where rapid reorganization of the production process is critical. Ensuring the superior quality of the final marketed product is equivalent to a decisive advantage in future competition.

By Gert Heuer

Product Manager

Rohde & Schwarz