New S-Band Power Amplifier for Aerospace and Defense Applications

Detailed introduction：

Marine, aerospace and defense applications and weather radars often use what are known as S-band radars. S-band radars typically operate at a frequency of 2–4 GHz. Because of the wavelength and frequency, S-band radars are not easily attenuated. This makes them useful for near- and far-range weather observations, as well as aboard ships, to detect other ships and land obstacles and to provide bearing and distance for collision avoidance and navigation at sea. The National Weather Service (NWS) also uses S-band radars.

Radar System Design Considerations

Designers of S-band radar systems are often focused on improving Size, Weight and Power (SWaP). In this article we demonstrate how our new Microchip 70W, ICP3049P, 2.7–3.5 GHz Power Amplifier (PA) enables the industry’s best-in-class SWaP performance and the highest efficiency for wireless radar systems operating in the S-band.

When radar system designers undertake a new design or add features to an existing platform, they consider many parameters. If the intended use case is mobile (airborne, shipborne or other mobile radar systems), PCB area and integrated circuit component selection/integration quickly become top considerations.

Earlier generations of S-band radar systems commonly used separate PAs for the 2.7 to 3.1 GHz and 3.1 to 3.5 GHz bands. Often, the same PA was used for each band; however, it was uniquely matched/tuned to each band using external components to shift the response up or down in frequency. With a device such as the ICP3049P, this technique is no longer necessary because the entire band is covered with one IC, thereby saving board space by eliminating the need for these external components.

With the increasing popularity of phased array antenna radar systems, many challenging requirements are placed upon the PA. When determining the specifications for a PA transmitter line-up used in a phased array radar system, the requirements of the system must be carefully considered. The following are some common design considerations and design constraints that must be adhered to:

• Printed Circuit Board (PCB) area can be in short supply in a phased array radar. This may result in radiating elements spaced very close together, possibly creating device-to-device EMI issues or heat dissipation challenges.

• The ability to dissipate (sink) additional heat into the system may be quite limited.

• The frequency of operation may vary depending on the radar system. For example, at S-band, it may be necessary to operate across the full 2.7 to 3.5 GHz spectrum.

• The available DC power for a radar system varies depending on the end application. DC power and cooling is typically unlimited for fixed, ground radar, as compared to the more strict requirements imposed on a mobile radar system. In fixed radar, it may be preferable to optimize the PA for output power to increase the range at the expense of DC power consumption and a more complicated cooling system. In the mobile case, the PA could be optimized for PAE to minimize power consumption and simplify cooling requirements.

• Whether the designer should choose a MMIC or power transistor (with external matching networks) for the power amplifier stage.

MMICs vs. Discrete Power Transistors

Monolithic Microwave Integrated Circuits (MMICs) are IC devices that operate at microwave frequencies (300 MHz to 300 GHz). These devices are frequently matched to a characteristic impedance of 50 ohms. This makes MMICs easier to use than individual RFMW power transistors because you would not require an external matching circuit to cascade MMICs, allowing you greater ease in integrating them into upstream and downstream circuits.

For process technology, GaAs has traditionally been an ideal material for MMICs, where active and essential passive components can be readily produced on a single GaAs die. Moving to GaN-on-SiC MMICs for use in higher-power PAs can achieve over 30 percent lower power usage and weight as compared to their GaAs counterparts, which is a huge gain for systems designers and OEMs.

Now, the use of a MMIC device as a PA instead of a discrete transistor can provide a size advantage as MMICs shrink the circuitry required to build complex systems to a relatively small package, saving the designer PCB area. Many MMIC designs also incorporate Electromagnetic Interference Protection (EMI), which obviates the need for the designer to incorporate these additional circuits in the design. Lastly, perhaps key, is if the MMIC is available in a standard semiconductor “package”; this relieves the system designer of having to deal with the requirements around dealing with bare die, which is generally accepted in the industry as being more difficult to process in a manufacturing setting than packaged die.

Discrete RFMW power devices are especially well suited for PA modules in the amplification circuit for several important reasons, but are normally larger in terms of physical size (and the size of the matching networks). Discrete devices typically have substantially higher output power capability than MMIC devices. This means that a designer may be able to generate more power from fewer devices. However, we see with the ICP3049 MMIC standard capability as being able to sustain 70W in S-band, which tends to minimize this earlier advantage of discrete power transistors. Discrete devices do allow the designer to optimize the matching networks surrounding the devices and perhaps choose PCB materials that maximize a circuit’s performance for a specific application, but this may be more desirable for more esoteric applications, not those that may have ×100 radiating elements per board. Finally, since the discrete devices are matched at the board level, the design team can fine-tune or modify the performance of a design in an efficient and less time-consuming fashion than would be available to an MMIC design. However, with the availability of many types of modern PA MMICs out to Ka band and beyond, this advantage becomes more specialized.

GaN-on-SiC Device

Taking a look at the ICP3049P PA and keeping the described design constraints in view, we see the ICP3049P as the only GaN-on-SiC device in the industry with this SWaP maximizing set of performance specs: 7×7 mm plastic QFN package, covering the full S-band BW of 2.7–3.5 GHz at Pout 48–49 dBm across the band with a PAE of 60%. The high efficiency of 60% means this device only needs 24 dBm at the input to achieve 48 dBm out and provides 60+ watts of output power across the 2.8–3.5 GHz band. This kind of efficiency is a step up as compared to historal S-band PAEs in the 40s. For radar upgrades, this means the system will need to dissipate less heat. This freed-up thermal capacity then can be used for new electronic functionality or captured as power savings. Looking into the integration aspects of the ICP0349P MMIC, the device has a hybrid input matching GaN transistor, with an internal passive input matching network fabricated on a cost-effective GaN-on-SiC process. The input of the device is internally matched to 50 Ω across 2.7 to 3.5 GHz.

The ICP3049P small package size of 7.0 × 7.0 × 0.85mm enables new S-band applications with the best-in-class form factor and high performance and requiring only a small PCB area. The ICP3049P requires reduced design effort from the radar designer; it is only necessary to provide the appropriate low frequency decoupling and ensure the package attachment to the PCB provides a reliable electrical ground and thermally conductive path. Our ICP0349 is well suited to both commercial and defense radar applications.

Prev：Microchip Power over Ethernet (PoE) Powers IP Cameras

Next：Canonical Enables Ubuntu on Microchip’s PolarFire® SoC FPGA