Documentation
Skaha-Drone
Skaha-Drone
  • Introduction: Digital L-Band (1.4 GHz) Polarimeter for UAVs
  • Microwave Polarimetry
    • Radio Wave Polarization
  • Technical Description
    • Mounting Options
    • Antenna
    • Control Unit
    • RF Signal Chain
    • A/D Converter and Digital Correlator
    • Receiver Noise Temperature
    • Internal Calibration
    • Radio Interference Filter
  • Ground Station and User Interface
    • Ground Station
    • Labels and Tags
    • Status
    • Settings
    • Rawdata
    • Map
    • Internal
  • Online Processing
    • Introduction
    • Sanity Check and Filtering
    • Gain Calibration
    • Conversion to Volumetric Water Content
    • Data Storage in Google Drive
  • Working with the Sensor and Data
    • HDF5 File Structure
    • Python Scripts
    • Test Observations
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  1. Technical Description

RF Signal Chain

The following is a description of the chain consisting of the RF amplifier and filter.

PreviousControl UnitNextA/D Converter and Digital Correlator

Last updated 5 months ago

The radiometer's RF section (also known as the front end of the receiver) comprises a 50-Ohm termination, a low-loss RF switch, a low-noise amplifier (LNA), a bandpass filter, and a 2nd stage amplifier. As the receiver captures both polarizations, the signal chain is replicated for both hands of polarization.

A 50-Ohm termination (load) is used for calibration purposes, similar to a Dicke receiver. As the radiometer is not kept in a temperature-controlled environment, the physical temperature of the calibration load may vary, affecting its noise figure. To account for this, a temperature sensor is placed near the load to measure and adjust for any temperature changes. The temperature is measured every 10 seconds.

The RF switch, one for each polarization, is used to switch between the antenna and the calibration load approximately every 350 ms. The RF switch is followed by the LNA, filter, and 2nd stage amplifier. The bandpass filter has a passband from 1290 to 1515 MHz. The combined gain of the LNA and 2nd stage amplifier is 40 dB. From here, the RF signals go into the A/D converter and digital correlator.

The following components are used:

  • RF switch: Analog HMC545

  • LNA: NXP USA Inc. BGU8052X

  • Bandpass filter: Mini-Circuits CBP-1400BD+

  • 2nd stage amp: Analog Devices Inc. HMC741ST89E

Schematic of the dual-amplifier chain.
Schematic of the dual-amplifier chain.