Here’s what you need to know about energy storage capacitors, wideband filters, bypass capacitors and other radar components.
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Radar systems are continuously evolving as threats become more diverse. These systems are expected to register anything from drones to hypersonic missiles. As a result, modern radars are becoming more agile. Increasingly, that means they rely on a multifunction array (MFA), where one array can be used for search, track and targeting as well as electronic warfare and communications functions.
The need for a single-array configuration, paired with the desire to improve signal-to-noise ratio (SNR) with an analog-to-digital converter (ADC) on every antenna element, was a catalyst for the adoption of fully digital beamforming.
With fully digital beamforming, shown below, each antenna element can transmit and receive multiple beams or split them in different directions simultaneously without interference. In addition, each element is software-defined, so control and tuning can occur on an application-specific basis. Designs that leverage fully digital beamforming use space more efficiently while achieving more comprehensive radar coverage.
Radar systems and other military applications have always been restricted by size, weight and power (SWaP) requirements. Now, engineers are up against additional size constraints to support electronics with fully digital beamforming. In addition to managing higher power consumption, integrated devices must fit in a denser phased array with an antenna pitch measuring half the wavelength (i.e., λ/2) or less for optimal array performance. Wavelength decreases as frequency increases, so size requirements only become more restrictive in high-frequency applications.
Under these conditions, there’s a variety of components that must fit into a smaller amount of board space. Here are some component selections that deserve special consideration:
Energy storage capacitors
Energy storage capacitors in radar T/R modules support pulsed operation in power amplifiers, and with high-performance expectations and little space, these passive devices are especially SWaP-challenged. Low-profile aluminum electrolytic capacitors like the MLPS Flatpack series, designed and manufactured by Knowles Precision Devices’ subsidiary Cornell Dubilier, offer high capacitance density in a flat configuration for space-saving. These military-grade capacitors are optimized for 10,000 hours at 105 °C, making them ideal for T/R modules and other system electronics that maintain high performance and reliability in a small footprint.
Wideband filters
Wideband filters with high rejection are similarly challenged by strict SWaP requirements. To protect the receiver, these filters must be positioned at every element, and as mentioned above, they must be sized at λ/2 or less to fit in the phased array antenna pitch.
Knowles Precision Devices’ 10 GHz surface mount bandpass filters support direct sampling receivers enabled by high-speed RF-ADCs. With deep expertise in high-reliability ceramic devices, Knowles Precision Devices fabricates its DLI brand filters on high-k ceramic substrate materials to achieve high performance in a footprint smaller than λ/2.
Bypass capacitors
Fully digital beamformers often include devices, like low-noise amplifiers, that can be implemented as high-frequency monolithic microwave integrated circuit (MMIC) dies. MMIC amplifiers with broadband gain need protection from RF noise on the supply line. Bypass capacitors offer an efficient path for RF energy to ground before it enters a gain stage. Look for wire-bondable microwave capacitors (rather than surface-mount) that can provide the right amount of capacitance at a high operating voltage for MMICs in high-frequency applications like radar.
High Q capacitors
Q factor, or quality factor, is a figure used to rate and compare multi-layer ceramic capacitors (MLCCs) based on merit. It’s expressed as the ratio between stored energy and lost energy per oscillation cycle. In resonant circuits, power loss is accounted for via the equivalent series resistance (ESR). Higher ESR indicates higher losses in the capacitor. In high-frequency applications, maintaining efficiency and reliability at the component level is an important contribution to performance optimization. MLCCs built with high Q material are specifically designed to overcome this design challenge.
High Q MLCCs will have a low εr value, and they’re generally built in the pF range to mitigate power loss and minimize the likelihood of overheating. High frequency and low power loss are critical parameters for radar systems. Consider MLCCs based on high Q dielectrics to ensure high performance. Knowles Precision Devices offers ultra-low ESR, high temperature, high power, ultra stable and leaded options.
High-reliability capacitors
Radar systems subject components to intense operating conditions. To ensure quality and performance over time, they must face testing at elevated conditions. Manufacturers perform accelerated life cycle testing to better inform you of a component’s limitations. For example, chip capacitors and dielectric formulations undergo burn-in or voltage conditioning to assess their reliability at a specific voltage and temperature level for a duration of time. Capacitors that fail this test usually lose resistivity under these conditions early in the test cycle.
Common high-reliability military specifications, including MIL-C-55681, MIL-C-123 and MIL-C-49467, each have their own applicable specifications for reliability testing. Work with a manufacturer that has the experience and capacity to run and document these tests. Knowles Precision Devices typically uses a test voltage that is twice the working voltage rating of the device, at 85°C or 125°C for a duration of 96, 100, or 168 hours of test time, and maintains the capacity to process approximately four million parts per month to uphold strict screening criteria.
Supporting innovation in radar systems
While many manufacturers can accommodate MIL-level screening and high-reliability applications, Knowles Precision Devices has designed and tested to these standards for decades with no field failures. The support of an experienced component design and manufacturing company with custom capabilities and extensive testing equipment is key to the continued success and advancement of radar technologies. Whether you’re working with a cutting-edge system or legacy equipment, every component selection makes a difference, so leverage a component manufacturer’s expertise. Knowles Precision Devices’ engineering team monitors current trends that impact your design needs and adapts accordingly, so your team can focus on the core research and development efforts at hand.
For more information on off-the-shelf or custom components for radar or other high-reliability systems, contact Knowles Precision Devices to connect with our engineering team.
