Portable Impedance Measurement System

The Microwave Division (DIMAS) of the ITACA Research Institute develops specific equipment for microwave processes to be used according to industrial conditions: simple, affordable and robustness, while retaining a useful subset of their current functionality. Aside from these applications, portable, accurate and low cost network analyzer provide an accessible platform for new and interesting applications of network analysis at industrial level to be developed.

Figure 1 shows the block diagram of a low power network analyzer developed for off-line impedance measurements in industrial environments.

Fig. 1. Schematic diagram of the reflectometer system based on two AD-8302 radio receiver

 Microwave source is implemented as a close- loop PLL microwave synthesizer. Receiver is composed by two AD8302 integrated RF detectors shifted 90º, to avoid phase ambiguity. Due to the dual Matched Logarithmic Amplifiers with Phase Detector of the IC, the receiver presents a dynamic range of 45 dB and a high stability with the temperature (-25ºC to 50ºC) from low frequencies up to 2.7GHz.

The separation of forward and reverse waves is carried out by two directional couplers to increase directivity. Output voltage signals from the detectors are digitalized in a multichannel analog to digital converter and processed in a microprocessor connected with a serial link to a personal computer or PLC controller. Digital lines for the control of the synthesizer are also driven by the microprocessor to synchronize the whole measurement procedure.

Fig. 2 shows a picture of a low power network analyzer developed for off-line measurements in magnitude and phase of impedance (reflection) at 2.45 GHz in a standard WR340 waveguide. The equipment is a complete solution for network analysis which includes all necessary components to perform the generation, separation, control and analysis of microwave signals and display of results.

Fig. 2. Picture of low power Vector Reflectometer around 2.45 GHz manufactured from the schematic of Fig.1

Calibration or adjustments with reference loads is not necessary and measurements are simple and fast. The waveguide reflectometer allows a non-experienced user in high frequency measurements a fast tuning or adjusting of a microwave applicator.

CONTROL SOFTWARE

The Vector reflectometer is driven from a PC or PLC controller, connected through a USB, RS-232 or CAN serial link. For PC interface, a Labview-based software has been developed to perform all the necessary functions with a user-friendly interface (Windows XP/Vista/7).

The control software permits the automatic measurement of module and phase of the reflection coefficient and impedance. Representation modes include: logarithmic magnitude, phase and Smith Chart.

TECHNICAL SPECIFICATIONS:

  • Frequency range: 2.2 to 2.6 GHz (extended to other ranges)
  • Waveguide: WR340
  • Microwave power level: 0 dBm
  • Dynamic Range: 40/45 dB
  • Uncertainty: +-0.1dB / +- 1º
  • Measurement rate: up to 4 sweeps per second
  • Operating Temperature: 10-50 °C

One Response to Portable Impedance Measurement System

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