C-Band Pulse Amplifiers (5600–5800 MHz): 10 W vs. 50 W Selection and Sub-Microsecond Integration

For radar, transponder, and instrumentation systems operating in the 5600–5800 MHz band, short pulse widths down to 0.3 µs (300 ns) create specific requirements for pulse fidelity and RF gating. At 300 ns, an uncompressed pulse corresponds to an ideal range resolution of approximately 45 m, calculated from ΔR = (c · τ) / 2. Selecting and integrating solid-state power amplifiers for these platforms requires evaluating both the RF gain budget and how the module behaves as a dynamic load on the DC bus.

MCW’s standard catalog Solid State RF Pulse Amplifiers include two complementary GaN units covering this band: the 10 W MCW5700M40A and the 50 W MCW5700M47A. The two modules cover the same 5.6–5.8 GHz frequency range but serve different positions in the RF chain. The M40A is intended for lower-power driver stages, while the M47A provides 50 W peak output as a final RF stage in a compact transmitter.

Parametric Overview: 10 W Driver vs. 50 W Output Stage

Parameter	MCW5700M40A (Driver / Low Power)	MCW5700M47A (Output Stage / Medium Power)	Integration Guidelines
Operating Frequency	5600–5800 MHz	5600–5800 MHz	Full band coverage without mechanical or electrical tuning.
Peak Output Power	10 W peak (+40 dBm)	50 W peak (+47 dBm)	Peak output power under specified factory test conditions.
Nominal Power Gain	30 dB nominal	37 dB nominal	Small-signal/nominal gain; actual gain depends on drive level.
Estimated Input Drive	~+10 dBm (first-order estimate)*	~+10 dBm (first-order estimate)*	Estimated from nominal gain; verify against factory drive curves.
Maximum Pulse Width	0.3 µs (300 ns)	0.3 µs (300 ns)	Rated pulse width ceiling; duty cycle and PRF are system-defined.
Operating Voltage	28 VDC nominal (24–32 VDC range)	28 VDC nominal (24–32 VDC range)	Tolerates typical airborne and vehicular DC supply variations.
Catalog Listed Current	0.5 A listed	1.0 A listed	Catalog benchmark; not the instantaneous peak pulse current.
RF Connectors	SMA Female (50 Ω)	SMA Female (50 Ω)	Standard coaxial interfaces for input and output ports.
Dimensions & Mass	140 × 85 × 25 mm (1.0 kg max)	160 × 90 × 25 mm (1.5 kg max)	Compact conduction-cooled aluminum chassis.

*Note: Input drive values are first-order engineering approximations derived by subtracting nominal gain from target peak power (+40 dBm − 30 dB = +10 dBm; +47 dBm − 37 dB = +10 dBm). They do not represent a guaranteed drive specification at saturation; actual required drive must be confirmed using factory-measured output-power-versus-input-power data.

Which Module Should You Specify?

The choice mainly depends on the required output power and the position of the amplifier in the RF chain, alongside system-level thermal constraints.

Specify the MCW5700M40A (10 W) when:

• Driving Higher-Power Downstream Stages: You need an intermediate driver for a higher-power tube or solid-state output stage requiring +37 to +40 dBm input drive.
• Operating Under Strict SWaP-C Constraints: The host platform is an unmanned aerial vehicle (UAV) pod or small mast where saving 0.5 kg (1.0 kg vs. 1.5 kg) and 20 mm of enclosure length is critical.
• Sizing for Lower Prime Power: The platform power supply cannot accommodate the higher transient current demand of a 50 W final stage.

Specify the MCW5700M47A (50 W) when:

• Final Stage in a Compact Transmitter: You are designing a transmitter for localized coastal surveillance, weather sensing, or tactical transponders where 50 W peak power provides the necessary target return without an additional booster stage.
• Minimizing Upstream Gain Stages: With 37 dB of nominal gain, radar exciters outputting between 0 dBm and +10 dBm can drive the transmitter directly, eliminating the cost and footprint of a separate pre-driver module.

Input Drive Budgeting and Interstage Cascading

A common engineering question is whether exciter outputs can push these units directly, or whether the 10 W unit can serve as the direct pre-driver for the 50 W unit.

• Exciter Level Compatibility: Based on their nominal gain figures (30 dB and 37 dB), the first-order input level corresponding to rated output is approximately +10 dBm for both modules. The actual drive required to reach rated peak power should be established from measured output-versus-input-power data. Whether the exciter can directly drive the module should be checked against its specified output power and the amplifier’s measured drive requirement.
• Cascading Precautions: The MCW5700M40A must not be connected directly to the input of the MCW5700M47A. The 10 W module produces +40 dBm, while the 50 W module requires a drive level far below this to operate safely. Feeding +40 dBm directly into the M47A would substantially exceed acceptable input levels and could damage the input stage.
• Benchtop Testing with an Attenuator: If you are using the M40A on a test bench to evaluate the M47A, an external high-power RF attenuator must be placed between them. The exact attenuation must be calculated from the measured output of the driver and the factory-confirmed maximum input threshold of the final stage.

DC Bus Sizing: Average Draw vs. Instantaneous Pulse Current

The catalog current ratings (0.5 A for the M40A and 1.0 A for the M47A) serve as baseline system references. When sizing DC power supplies and cable harnesses, keep two design factors in mind:

• Catalog Current vs. Peak Pulse Current: The catalog-listed current is not the instantaneous peak pulse current. During the active pulse, the amplifier experiences a rapid change in electrical load. The resulting current waveform depends on device operating conditions, pulse duty cycle, bias architecture, and internal power conversion. The manufacturer should be consulted for the measured pulse-current waveform when sizing the supply and local decoupling network. At low operational duty cycles, the time-averaged current remains low, but the DC supply must tolerate rapid load steps without tripping over-current protection.
• Mitigating Harness Inductance: Long power cables between the system 28 V bus and the amplifier introduce line inductance (V = L · (di/dt)). During sub-microsecond pulse transitions, this inductance causes transient voltage sag directly at the module supply pins, contributing to pulse droop or edge ringing.
• Decoupling Recommendations: Place a local capacitor bank (low-ESR electrolytic or polymer capacitors paired with high-frequency ceramic bypass units) directly at the amplifier’s DC supply interface to supply localized charge during the 300 ns pulse without dragging down the main 28 V rail.

Control Timing and Thermal Integration

Generating clean 300 ns microwave bursts requires coordinating DC bias and RF path switching. Attempting to switch the main 28 V DC rail at 0.3 µs intervals is impractical due to supply capacitance and lead inductance.

Instead, modern radar architectures keep the 28 V rail active, pre-bias the amplifier stages via an enable line, and use fast internal RF switching to carve the active 300 ns microwave pulse. Gating the amplifier off during receive windows may help reduce unwanted emissions and unnecessary power dissipation, depending on overall system architecture.

For mechanical integration:

• Both modules are housed in aluminum enclosures (140 × 85 × 25 mm for the 10 W unit; 160 × 90 × 25 mm for the 50 W unit) equipped with standard SMA Female connectors.
• A suitable thermal path should be provided through the mounting structure. Depending on average dissipation, ambient conditions, and required thermal margin, this may use a conduction-cooled plate, forced-air heatsink, or another qualified thermal solution that meets manufacturer thermal limits.
• Apply a thin, uniform layer of high-conductivity thermal interface material (TIM) between the module baseplate and mounting surface to minimize contact thermal resistance.

Technical Data Checklist Before Specifying

Before finalizing module selection and releasing your transmitter architecture, request the following factory verification data:

• Output Power vs. Input Power Curves: Measured saturation characteristics across 5600–5800 MHz to establish actual drive requirements across temperature.
• Pulse Rise and Fall Times: 10–90% RF envelope rise and fall response at 0.3 µs pulse widths.
• Pulse Droop: Measured amplitude variation across the rated 300 ns pulse width under specified duty-cycle conditions.
• Maximum Safe Input Power: Absolute maximum continuous and pulsed RF input thresholds to safeguard the input stages.
• Maximum Duty Cycle and PRF: Thermal and electrical boundaries under continuous pulsed transmission.
• Pulse Current Waveform: Oscilloscope captures of the transient current demand on the 28 V rail during active RF bursts.
• Control Interface Specifications: Logic levels, pinout assignments, and required lead/lag timing between the bias enable and RF gating controls.
• Baseplate Thermal Limits: Maximum allowable baseplate operating temperature and baseplate-to-heatsink mounting requirements.

Frequently Asked Questions

Q: What input drive level is required for the 10 W and 50 W amplifiers?

A: Using a first-order calculation from nominal gain (30 dB for the 10 W unit and 37 dB for the 50 W unit), both modules require an estimated input drive around +10 dBm to reach rated peak power (+40 dBm and +47 dBm, respectively). However, because gain compresses near saturation, the actual drive power required depends on frequency and operating temperature. Integrators should confirm the exact drive level from factory output-power-versus-input-power curves.

Q: Can the MCW5700M40A be cascaded directly into the MCW5700M47A?

A: No. The 10 W output (+40 dBm) from the MCW5700M40A would substantially overdrive the input of the 50 W module and could cause damage. The 37 dB nominal gain of the MCW5700M47A reduces upstream gain requirements, but any benchtop cascade requires an external, power-rated attenuator inserted between the stages to bring the drive down to safe operating levels.

Q: Why is sub-microsecond pulse shaping performed in the RF path rather than on the DC bus?

A: Switching the main 28 V power rail at 0.3 µs speeds is limited by power-supply capacitance and cable inductance, which cause severe voltage ringing and pulse degradation. Maintaining a stable 28 V DC bus while gating the RF signal allows fast edge transitions and preserves pulse fidelity.

For the MCW5700M40A and MCW5700M47A, matching your exciter output and DC decoupling network to the module’s gain and transient current profile ensures clean, repeatable sub-microsecond pulse performance across the 5600–5800 MHz band.