Narrow Resonant Double-Ridged Rectangular Waveguide Probe for Near-Field Scanning Microwave Microscopy

  • Kim, Byung-Mun (Department of Electrical Electronics, Gyeongbuk Provincial College) ;
  • Son, Hyeok-Woo (Hanwha Corporation) ;
  • Cho, Young-Ki (School of Electronics Engineering, Kyungpook National University)
  • Received : 2017.02.01
  • Accepted : 2017.09.08
  • Published : 2018.01.01


In this paper, we propose a narrow resonant waveguide probe that can improve the measurement sensitivity in near-field scanning microwave microscopy. The probe consists of a metal waveguide incorporating the following two sections: a straight section at the tip of the probe whose cross-section is a double-ridged rectangle, and whose height is much smaller than the waveguide width; and a standard waveguide section. The advantage of the narrow waveguide is the same as that of the quarter-wave transformer section i.e., it achieves impedance-matching between the sample under test (SUT) and the standard waveguide. The design procedure used for the probe is presented in detail and the performance of the designed resonant probe is evaluated theoretically by using an equivalent circuit. The calculated results are compared with those obtained using the finite element method (Ansoft HFSS), and consistency between the results is demonstrated. Furthermore, the performance of the fabricated resonant probe is evaluated experimentally. At X-band frequencies, we have measured the one-dimensional scanning reflection coefficient of the SUT using the probe. The sensitivity of the proposed resonant probe is improved by more than two times as compared to a conventional waveguide cavity type probe.

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Fig. 1. Block diagram of an waveguide probe for near-fieldscanning: (a) the conventional probe (b) theproposed probe

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Fig. 2. Waveguide probe and substrate SUT

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Fig. 3. Equivalent transmission-line model for the proposedprobe with open-ended DRWG: (a) with an idealtransformer, (b) without an ideal transformer, (c) if=∞ in the case of Fig. 3(b)

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Fig. 4. Reflection coefficient

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Fig. 5. Turn ratio n2 of the transformer and the normalizedradiation admittance

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Fig. 6. Normalized input admittance at the interfacebetween the input RWG and the DRWG

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Fig. 7. Calculated reflection coefficients of the proposedprobe

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Fig. 8. Optimum length of the open-ended DRWG for theproposed probe

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Fig. 9. Electric field intensity distribution on the SUTsurface (

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Fig. 10. Peak intensity of electric field

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Fig. 11. Experimental equipment arrangement

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Fig. 12. Layout of a PCB with seven strips with width of0.5 mm

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Fig. 13. Measurement results of the SUT in Fig. 12 atresonant frequencies of 9.642 GHz and 10.330 GHz

Table 1. Dimensions of the proposed probe

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Supported by : National Research Foundation of Korea (NRF)


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