Using the RF Signal Generator Module

This module generates a fixed 6.3 GHz RF signal and delivers it through an SMA connector. The design uses a voltage‑controlled oscillator (VCO) and a high‑gain amplifier to produce a clean, high‑frequency output. Although rated to 6 GHz, the amplifier can operate up to about 8 GHz, giving this module a broad range for lab experiments and RF system testing.

Project Description

The bullets below describe the essential circuits that create and deliver the 6 GHz signal. Understanding their roles will guide you in adapting the design to other frequencies.

• Signal generation – The core of the module is the HMC358MS8GE VCO, tuned to generate a 6.3 GHz carrier. A dual‑rail regulator provides bias voltages for the VCO and sets its tuning voltage. The output is AC‑coupled into a HMC637ALP5E power amplifier which provides about 13 dB gain.
• Output interface – The amplifier feeds an SMA connector via a bias‑tee circuit. The bias‑tee isolates the DC supply from the RF path while maintaining the desired passband. Choose inductor and capacitor values so that the tee’s cutoff frequency lies well below 6 GHz to minimize insertion loss.
• Power supplies – A low‑noise regulator produces the primary supply voltage, while a dual‑rail regulator generates positive and negative gate voltages for the amplifier. Proper decoupling and filtering ensure a low‑noise RF output.

Using The Module

The guidelines here explain how to power and operate the module, adjust its frequency and interface with test equipment safely.

• Power input – Apply the recommended supply voltage (typically 5 V) to the module. Ensure that the current rating meets the amplifier’s requirements.
• Frequency control – An optional header exposes the VCO’s VTUNE pin. By applying a control voltage, you can tune the output frequency within the VCO’s range. For fixed‑frequency operation, leave VTUNE unconnected and the module will output approximately 6.3 GHz.
• Connecting to equipment – Use a high‑quality 50 Ω coaxial cable from the SMA connector to your test equipment or system. The output is AC‑coupled, so no external bias is required.
• Bias‑tee usage – If you wish to inject DC bias onto the RF line, use the onboard bias‑tee. Select appropriate inductor and capacitor values to achieve the desired isolation and passband.

Design Considerations

RF circuits demand special attention to layout, impedance and filtering. The points below outline best practices for achieving a clean signal.

• Layout and stack‑up – The PCB uses a four‑layer stack with coplanar waveguide routing for the RF traces. A low‑dielectric‑constant FR4 material is chosen to minimize loss at 6 GHz. Separate the RF section from the power regulators to reduce parasitic coupling.
• AC coupling and impedance – The RFIN and RFOUT lines are AC‑coupled to block DC offsets. Maintain a 50 Ω characteristic impedance on all RF traces and keep trace lengths short.
• Regulator selection – The TPS562201 and LM27762 regulators provide clean supplies and gate voltages. Place decoupling capacitors close to each regulator’s pins to limit ripple and noise.

With proper biasing, this module delivers a stable 6 GHz signal for RF experiments, calibration and small‑signal testing. Engineers can adjust the tuning voltage to explore the VCO’s frequency range or modify the bias‑tee for specific applications.

For greater frequency agility, replace the fixed tuning network with a digitally controlled voltage source, allowing the VCO to sweep across its operating band. Filtering on the power rails is critical; use low‑ESR capacitors and ferrite beads to suppress supply noise that could modulate the RF output. The amplifier’s bias current should be set according to the desired output power; consult the datasheet for recommended gate voltages. If more output power is required, cascade an additional amplifier stage, but be aware that gain increases can also raise the noise floor and spurious emissions.

Additional Resources

Read the full guide article on Altium Resources for a deep dive on this project. The video below shows the design approach and preparation for manufacturing of the Rev A release of this project, starting from schematic review and completing the PCB layout.