Ku-Band GaN BUC (200W to 300W): Saturated Output Power, Linear Back-Off, and Uplink Spectral Purity

Satellite ground stations and professional VSAT uplinks operating in the standard and extended Ku-band require high-efficiency solid-state amplification capable of operating at defined linear output power levels under multi-carrier loading. The Ku-Band BUC (200W, 250W, 300W GaN) series integrates Gallium Nitride (GaN) solid-state power amplifier (SSPA) stages, an upconversion architecture covering 13.75 GHz to 14.5 GHz, and internal telemetry monitoring (lock status, temperature, and RF output power) into an IP66-rated chassis measuring 330 mm × 200 mm × 180 mm with a total mass of 15.5 kg.

RF Power Sizing: Psat vs. Plinear Across 200W, 250W, and 300W Configurations

Transmitter sizing for satellite uplinks depends on the distinction between saturated output power (Psat) and rated linear power (Plinear), with the difference between the two defining the operating back-off used to limit intermodulation distortion:

• 200W Hardware Tier: Delivers a saturated output power (Psat) of 53 dBm (200 W) and a rated linear output power (Plinear) of 50 dBm (100 W).
• 250W Hardware Tier: Achieves a Psat of 54 dBm (250 W) with a rated Plinear of 51 dBm (125 W).
• 300W Hardware Tier: Delivers a Psat of 54.8 dBm (300 W) with a rated Plinear of 51.8 dBm (150 W).
• Linear Operating Margin: Across all three power ratings, Plinear is set at approximately 3 dB of back-off from saturation, defining the rated linear operating point for multi-carrier transmission formats.

Parameter	200W Model	250W Model	300W Model
Operating Frequency Range	13.75 GHz – 14.5 GHz	13.75 GHz – 14.5 GHz	13.75 GHz – 14.5 GHz
Saturated Output Power (Psat)	53 dBm (200 W)	54 dBm (250 W)	54.8 dBm (300 W)
Rated Linear Power (Plinear)	50 dBm (100 W)	51 dBm (125 W)	51.8 dBm (150 W)
Small-Signal Gain	≥73 dB	≥73 dB	≥73 dB
Gain Flatness	±2 dB typical	±2 dB typical	±2 dB typical
Input VSWR (Max)	1.8:1	2:1	2:1
Output VSWR (Max)	1.3:1	1.3:1	1.3:1
RF Output Waveguide	WR75 Grooved	WR75 Grooved	WR75 Grooved

Gain Characteristics and Dynamic Level Adjustment

Gain stability over temperature helps keep link-budget variation predictable across the operating range:

• Gain Magnitude: The block upconverter maintains a nominal small-signal gain of ≥73 dB across the entire 13.75 GHz to 14.5 GHz passband.
• Passband Flatness: Gain flatness across the full operating band is specified at ±2 dB typical, limiting gain variation across the operating band.
• Thermal Gain Stability: Integrated compensation circuitry limits gain variation over temperature to ±1 dB across the operating window of -40°C to +60°C, helping limit gain-related variation in link-budget margins.
• Gain Attenuation Control: An internal digital attenuator provides a 20 dB gain adjustment range in nominal 0.5 dB increments, configurable via remote control interfaces.
• Port Impedance Matching: The IF input presents a maximum VSWR of 1.8:1 on the 200W model and 2:1 on the 250W and 300W models, while the RF output waveguide maintains a maximum VSWR of 1.3:1.

Linearity, Intermodulation, and Spectral Purity Specifications

Uplink signal fidelity is governed by intermodulation limits, phase noise masks, and spurious suppression to meet satellite operator transmission requirements:

• Third-Order Intermodulation (IMD3): Intermodulation products are rated at -25 dBc maximum relative to the sum of two equal carriers spaced 5 MHz apart when operating at rated Plinear.
• Spurious Emissions: Non-harmonic spurious signals are suppressed to a maximum level of -55 dBc across the operating band.
• Phase Noise Profile: The internal frequency conversion chain complies with the following single-sideband phase noise ceiling:
  • 100 Hz offset: -63 dBc/Hz maximum
  • 1 kHz offset: -73 dBc/Hz maximum
  • 10 kHz offset: -83 dBc/Hz maximum
  • 100 kHz offset: -93 dBc/Hz maximum
• Reference Stability: Frequency stability over temperature is maintained within ±0.1 ppm using an external 10 MHz reference, or ±0.02 ppm when utilizing the internal reference option.
• Noise Power Density (NPD): Thermal and active noise output is held to -70 dBm/Hz maximum in the transmit band (13.75–14.5 GHz) and -150 dBm/Hz maximum in the receive band (Rx band), helping limit transmit-noise coupling into co-located LNB receive paths.

RF and Waveguide Interfacing Boundaries

The physical interface boundaries align standard IF modem cabling with antenna feed assemblies:

• IF Input Connection: The intermediate frequency drive signal connects via a standard 50-ohm N-type female connector.
• RF Output Flange: Transmit power exits through a WR75 SQ Cover-Grooved waveguide flange, providing a direct waveguide interface to the feed horn or orthomode transducer (OMT).
• Enclosure Constraints: All RF stages, local oscillator circuitry, and GaN matching networks reside within a unified IP66-rated chassis (330 mm × 200 mm × 180 mm, 15.5 kg) designed for outdoor deployment.

Frequently Asked Questions (RF Performance & Sizing)

Q: Why is Plinear specified 3 dB below saturated power (Psat) on this BUC series?

A: GaN solid-state amplifiers experience non-linear compression as they approach saturation. The specified Plinear point is set approximately 3 dB below Psat (50 dBm for 200W, 51 dBm for 250W, and 51.8 dBm for 300W), with IMD3 specified at ≤-25 dBc under the stated two-tone test conditions, supporting reduced spectral regrowth and adjacent-channel interference under multi-carrier operation.

Q: How does the receive-band Noise Power Density specification protect the ground terminal?

A: In single-antenna VSAT systems sharing common reflector optics through a diplexer or OMT, transmit noise leakage into the downlink band can elevate the receiver noise floor. The BUC’s receive-band noise power density of -150 dBm/Hz maximum minimizes broadband noise injection into the receiving chain, helping limit degradation of terminal G/T performance.

Q: What is the primary difference in port VSWR between the 200W model and the 250W/300W models?

A: The primary difference lies in the specified IF input VSWR across the power tiers: the 200W model specifies a maximum of 1.8:1, while the 250W and 300W models specify a maximum of 2:1. The RF output waveguide maintains an identical 1.3:1 maximum VSWR across all three power levels.