Simplify radar designs with antenna-on-package technology
Article By : Kishore Ramaiah
Simplify radar designs with a highly-compact form factor that eliminates the need for expensive PCB substrate materials.
Millimeter-wave (mmW) radar is one of the primary sensing modalities for automotive and industrial applications because of its ability to detect objects from a few centimeters to several hundred meters with high distance, angle, and velocity accuracy, even in challenging environmental conditions.
A typical radar sensor consists of a radar chipset along with other electronic components such as the power-management circuit, flash memory, and interface peripherals assembled on a PCB. Transmit and receive antennas are also typically implemented on the PCB, but achieving high antenna performance requires a high-frequency substrate material such as Rogers’ RO3003, which adds PCB cost and complexity. In addition, antennas can take up as much as 30% of the board space (Figure 1).
Figure 1 A radar sensor antenna on the PCB occupies about 30% of the board space. Source: Texas Instruments
Antenna-on-package technology
It’s possible to design mmW sensors with antenna elements integrated directly into the package substrate, thus reducing the size of the sensor and the complexity of the sensor design. Figure 2 depicts a cavity-backed E-shape patch antenna element that radiates the mmW at 60 or 77 GHz into the free space. Arranging several such antenna elements on the package of a device creates a multiple-input multiple-output (MIMO) array, which can sense objects and people in a 3D space.
Figure 2 A cavity-backed E-shape patch antenna element radiates mmW into the free space. Source: Texas Instruments
Figure 3 shows the arrangement of the three transmitter and four receiver antenna elements on the AWR6843AOP automotive radar sensor. This antenna enables a wide field of view (FoV) in both the azimuth and elevation directions.
Figure 3 The AWR6843AOP device with antenna elements on the package forms a MIMO array. Source: Texas Instruments
Antenna-on-package technology provides the following benefits to developers:
- Smaller size enables the design of extremely small form-factor sensors. Radar sensors designed with an antenna on package are approximately 30% smaller than antennas on PCB sensors.
- Lower bill-of-material (BOM) costs can be achieved by bypassing the need for expensive high-frequency substrate material in the PCB stackup.
- Lower engineering costs can be achieved because there’s no need for antenna engineers to design the antenna, simulate the performance through tools, and design the actual board to characterize the performance for different parameters.
- Higher efficiency and reduced power loss can be achieved because of shorter routing from the silicon die to the antennas.
For MIMO systems, it’s very challenging to implement high-performance antennas on a small and cost-efficient package solution. Existing solutions implement antenna elements on the top or bottom side of a mold compound; the radiated signal travels through this lossy mold material, which reduces efficiency and excites substrate modes that cause spurious radiation. Flip-chip package technology, on the other hand, makes it possible to place antennas on a mold-less substrate. In addition, antennas and silicon die can overlap on a multilayer substrate, which results in a more compact solution.
How antenna-on-package helps in-cabin sensing
Regulatory bodies like the European New Car Assessment Program are addressing the problem of child deaths when left behind in a hot car. Automakers and Tier-1 manufacturers are turning to 60-GHz mmW sensors to accurately detect children and pets inside cars in challenging environmental conditions.
Given that vehicles can have very different interior designs, it is essential for the form factor of the sensor to be extremely small for a seamless integration. For example, it may be difficult to integrate a sensor into the roof of a car with a panoramic roof; instead, it must be integrated in space-constrained locations like the overhead console around the rearview mirror, or in the pillars.
Figure 4 A sensor with an antenna on a PCB is shown beside an antenna on the package. Source: Texas Instruments
The single patch wide FoV antenna on sensors are ideal for placement under the headliner or even pillars of the vehicle in front-facing positions. It enables in-cabin sensing use cases like detection and localization of children, pets, or occupants across two rows of the car, including in the footwell. The sensor, in a low-power mode of operation, can also detect intruders under challenging environmental conditions.
Developers can also benefit from the integrated DSP, MCU, radar hardware accelerator, and on-chip memory. The integration of the RF, digital, and antenna components on a single chip takes away a lot of design complexities and enables simpler and faster design.
A child-presence and occupant-detection reference design using a 60-GHz antenna-on-package mmW sensor captures the test results for detection of children and adults in various seating positions. The sensor was placed in an overhead position in the car. Figures 5-7 illustrate the results, and you can watch this video for more details.
Figure 5 Here are the test results for a baby doll simulating a breathing child in the rear seat of a vehicle. Source: Texas Instruments
Figure 6 This test detected and located four occupants: driver, passenger, an adult, and a child in the rear seat. Source: Texas Instruments
Figure 7 This test detected an intruder near the vehicle. Source: Texas Instruments
Antenna-on-package technology helps radar sensor designers create very small form-factor sensors with less effort and faster time to market, while also providing system-level cost benefits. TI’s 60-GHz AWR6843AOP sensors simplify in-cabin sensing by enabling multiple applications such as child presence detection, seat belt reminders, driver vital-sign detection, and gesture control.
This article was originally published on EDN.
Kishore Ramaiah is a product marketing manager for mmWave radar at Texas Instruments.
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