Radar System Design with the Infineon BGT24LTR11N16 24GHz Transceiver

The proliferation of radar technology into consumer and industrial applications demands highly integrated, cost-effective, and reliable solutions. The Infineon BGT24LTR11N16, a 24GHz ISM band transceiver, stands out as a pivotal component for designing compact and efficient radar systems for motion detection, presence sensing, and distance measurement.

This monolithic microwave integrated circuit (MMIC) incorporates a complete RF front-end in a single package. It features a voltage-controlled oscillator (VCO), a power amplifier (PA) for the transmit (TX) chain, a low-noise amplifier (LNA), and mixers for the receive (RX) chain. This high level of integration drastically simplifies the system architecture, reducing both the bill of materials (BOM) and the required PCB footprint, which is critical for space-constrained applications.

A fundamental advantage of the BGT24LTR11N16 is its Doppler radar capability. It operates as a homodyne or direct-conversion receiver. The transmitted 24GHz signal, reflected by a moving target, undergoes a frequency shift (the Doppler effect). This reflected signal is received and mixed with a portion of the transmitted signal directly on the chip, producing a baseband output signal. The frequency of this low-frequency output is directly proportional to the velocity of the target, while its amplitude relates to the target's radar cross-section. This makes the IC exceptionally suitable for motion sensing and speed measurement.

When designing a radar system around this transceiver, several key considerations must be addressed:

1. Antenna Design: The antenna is a critical part of any radar system. For 24GHz operation, patch antenna arrays are commonly used on the PCB. The design must ensure good gain and directivity to achieve the desired sensing range and field of view. Proper isolation between the TX and RX antennas is paramount to prevent signal leakage from saturating the sensitive receive path.

2. PCB Layout: At 24GHz, the PCB layout is not merely a connection but an integral part of the RF circuit. A controlled-impedance microstrip design is mandatory for all RF traces. The use of a Rogers material or an FR-4 substrate with carefully modeled characteristics is recommended. The ground plane must be solid and uninterrupted beneath RF components. Vias should be used generously to connect top-layer ground pours to the main ground plane, minimizing parasitic inductance.

3. Baseband Signal Conditioning: The output of the BGT24LTR11N16 is a low-frequency, small-amplitude signal often contaminated with noise and DC offset. This signal must be passed through a high-pass filter (to remove DC offset from clutter and leakage) and a low-pass filter (to anti-alias and limit noise bandwidth). Subsequently, a programmable gain amplifier (PGA) is essential to amplify the signal to a level suitable for sampling by a microcontroller's analog-to-digital converter (ADC).

4. Digital Processing: The conditioned analog signal is digitized for further processing. A microcontroller unit (MCU) or a digital signal processor (DSP) performs Fast Fourier Transform (FFT) analysis to convert the time-domain signal into the frequency domain. This allows the system to identify the precise Doppler frequency shift, from which target velocity can be calculated. More advanced algorithms can be implemented for frequency modulation (FMCW) to enable distance measurement, though this requires additional control circuitry for the VCO.

The BGT24LTR11N16 finds its strength in applications such as smart lighting systems (activating lights upon detecting human movement), building automation (for occupancy counting and HVAC control), vital signs monitoring (detecting respiration or heartbeat through subtle chest movements), and industrial sensing (e.g., conveyor belt speed monitoring).

ICGOOODFIND: The Infineon BGT24LTR11N16 is an exemplary solution for modern radar design, offering a superior blend of high integration, performance, and cost-efficiency for 24GHz Doppler radar applications, accelerating development and enabling innovative sensing products.

Keywords: 24GHz Radar, Doppler Effect, MMIC Transceiver, RF Design, Motion Sensing