Automotive applications are requiring increased use of RF/microwave frequency bands, from low RF signals through millimeter-wave frequencies at 77 GHz. As these high-frequency signals become more integral parts of the worldwide driving experience, effective test solutions become more critical for designers developing new automotive RF/microwave circuits, as well as production facilities seeking efficient methods for verifying the performance of these added circuits. While lower-frequency testers are in abundance, and automotive applications employ a wide range of wireless frequencies—including remote keyless entry (RKE) systems at 433 and 868 MHz—a growing concern in automotive markets is for the accurate and cost-effective testing of 77-GHz automotive radar systems. This interest stems from the fact that historically, measurement equipment at such high frequencies has neither been commonplace nor cost-effective.
A number of different automotive radar-based safety applications make use of frequencies from 76 to 77 GHz, for adaptive cruise control (ACC), blind-spot detection (BSD), emergency braking, forward collision warning (FCW), and rear collision protection (RCP). For example, in a collision warning system, an automotive radar sensor can detect and track objects within the range of the transmitted and returned radar signals, automatically adjusting a vehicle’s speed and distance in accordance with the detected targets. Different systems can provide a warning of a potential collision ahead and also initiate procedures leading to emergency braking as required.
This millimeter-wave frequency band is not the only frequency range currently in use for automotive radar systems. A “temporary” frequency band has also been established at 24 GHz for short-term automotive electronics systems. Unfortunately, this band is already occupied by other electronic devices, including microwave radios, which add to the congestion faced by radar systems within this band (and with radar signals becoming interference for the existing microwave radio devices). The band has been deemed as “temporary” for such applications as automotive radar because it will be closed to those devices when the signal levels become too dense at 24 GHz.
This band was made available in Europe to European Union (EU) members by means of European Commission Decision 2005/50/EC. Said regulation also sets requirements for automatic deactivation devices for 24-GHz when too close to existing systems (such as radio astronomy sites), and also sets guidelines for transition to a more permanent frequency band. In Europe, the “permanent” band for automotive radar service has been allocated at 79 GHz, per European Commission Decision 2004/545/EC, which requires that this band to be made available in all EU member states.
The band from 76 to 77 GHz had been allocated to the Radio Astronomy Service (RAS) in the US, but the Federal Communications Commission (FCC) made amendments to sections of its allocations and regulations, allowing automotive radar system in that frequency band. The modifications also impacted fixed radar applications in the 76-to-77-GHz band at airport locations, using fixed radar systems to detect foreign object debris (FOD) on runways and monitor aircraft traffic as well as service vehicles on taxiways and other airport vehicle service areas that have no public access. In Europe, the European Telecommunications Standards Institute (ETSI; www.etsi.org) sets similar guidelines for radar systems at 24 and 77 GHz.
Both system and components suppliers have supported the different automotive frequency bands. TRW Automotive, for example, has developed automotive radar system solutions at 24 GHz (model AC100) for ACC and FCW applications as well as at 77 GHz (model AC3). Numerous semiconductor suppliers have enjoyed business in supplying transceiver solutions for 77-GHz automotive radar systems, including Texas Instruments with its model MRD2001 automotive radar chip set. Devices in the chip set are housed in low-loss packaging (usable through 100 GHz) which simplifies assembly for automotive manufacturers and is scalable to 4 transmit channels and 12 receive channels so that a single radar system can provide radar beams across a wide field of view for near-field, mid-field, and far-field applications.
Freescale Semiconductor has used its silicon-germanium (SiGe) BiCMOS semiconductor process as the basis for its Xtrinsic 77-GHz automotive radar semiconductor devices. And TriQuint Semiconductor supports the long- and medium-range automotive radar market with a wide portfolio of 77 GHz MMICs for front-end applications such as ACC and FCW systems. Additional semiconductor and component suppliers include Altera, Analog Devices, Fujitsu, Infineon, Millitech, NXP Semiconductors, and Skyworks Solutions.
A Matter Of Power
Of course, testing these systems and their components at millimeter-wave frequency bands such as 76 to 77 GHz requires the generation and analysis of pulsed millimeter-wave frequencies at sufficient power levels. Signal sources for such high frequencies are usually produced with the aid of frequency doublers and triplers, while analyzers rely on frequency-downconversion techniques for such instruments as spectrum analyzers. Most major instrument makers, including Agilent Technologies, Anritsu Co., Rohde & Schwarz, and Tektronix, offer solutions for testing at automotive millimeter-wave frequencies.
Even smaller instrument suppliers, such as Roos Instruments, offer testers for 77 GHz, including the firm’s model RI8564A test set. Based on a modular approach to instrumentation, the company’s instrument solutions work with tester instrument modules (TIMs) to achieve the required functionality for a number of different automotive radar tests at 77 GHz. For example, tests with Roos’ Cassini modular automatic-test-equipment (ATE) systems include efficiency (for power amplifiers, full S-parameter measurements, output power at 1-dB compression, third-order intermodulation (IM3), and leakage current.
Some of the essential measurements required for automotive radars at 76 to 77 GHz include system-level tests such as transmit and receive frequencies and frequency bandwidths, transmit and receive power levels, modulation, radar system measurement distance and resolution, antenna beamwidth, and power supply requirements. Additional measurements tend to apply to component-level testing, such as gain and noise figure for amplifiers and phase noise, spurious levels, and harmonic levels for signal sources. Many of the leading test-and-measurement equipment suppliers offer benchtop solutions, with signal generators and analyzers (such as spectrum analyzers, scalar network analyzers, and vector network analyzers), for measurements through 79 GHz. However, the availability of portable 77-GHz measurement systems for automotive radar testing was been extremely limited to this point.
Yet such portable measurement capabilities will be invaluable to automotive manufacturers and service shops as the number of automotive radar systems worldwide increases. The challenge for test-equipment suppliers will be to supply such traditionally exotic millimeter-wave measurement capabilities to automotive customers in need of watching tight budgets.