VNA Calibration Techniques Comparison for Waveguide Components
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COMPLEX S-PARAMETER MEASUREMENTS OF WAVEGUIDE COMPONENTS FOR COMPARISON OF VNA CALIBRATION TECHNIQUES Pallavi Saxena*, Kamlesh Patel**, P.S. Negi * Indira Gandhi Institute of Technology, GGS IP University, Delhi Electrical & Electronics Standards, National Physical Laboratory, Delhi **[email protected] Abstract Coaxial and waveguide structures are well established in the field of microwave technology since its invention. Waveguide structures require a different treatment regarding field theory and the related measurements compared to coaxial systems. Now a days various calibration kits are available to characterize any waveguide component using a Vector Network Analyser (VNA) system at microwave frequencies by means of various calibration techniques. This paper discusses the study of various calibration techniques for VNA and the corresponding measurement practices performed on one- port and two-port components i.e., waveguide mismatch (VSWR 1.30) and a rotary vane attenuator (at 30dB setting) as the device under test (DUT). The measured values of three techniques have been compared for both DUTs. This study helps in implementing a particular calibration technique for a specific application for coaxial systems. I. Introduction This paper presents a study of various VNA calibration techniques through the measurements of a laboratory developed waveguide mismatch (VSWR: 1.30) and a rotary vane attenuator of 30 dB at National Physical Laboratory. A number of calibration techniques for VNA have been developed and studied over the decades [1,2,3,4]. A comparison between these techniques is needed for proper use based on device type, application and measurement accuracy. A few comparisons have been performed for coaxial systems earlier, however a comparison study in waveguide system still waits in general [5,6]. The effects of deviation in the coaxial calibration standards in the measured S-parameters are also reported [7,8]. However one should have a proper knowledge and implementation of these techniques through its analysis before applying in real applications for waveguide structures. II. Experiment Three types of VNA calibration techniques were employed, namely, OSLT (Offset Short -Load -Thru), TRL (Thru- Reflect- Line), and LRL (Line- Reflect- Line) using the laboratory developed standards to measure the complex S-parameters of the two DUTs in Magnitude/Phase as well as in Real/Imaginary form on a Wiltron VNA 37247B. The S-parameters of standards used in various calibration techniques were measured using the VNA and their S-parameters used to calculate the S-parameters of the error box for the respective calibration techniques. Using these error terms and the measured S- parameters of the DUT, the actual DUT parameters were calculated through the program codes in C++ developed. The calculated DUT parameters using OSLT and
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The prsent document presents the results of various calibration techniques of vector network analyzer (VNA) for waveguide components. It identifies the effects of standards on the measurement accuracy and range.
Transcript of VNA Calibration Techniques Comparison for Waveguide Components
COMPLEX S-PARAMETER MEASUREMENTS OF WAVEGUIDE COMPONENTS FOR COMPARISON OF VNA CALIBRATION
TECHNIQUES
Pallavi Saxena*, Kamlesh Patel**, P.S. Negi* Indira Gandhi Institute of Technology, GGS IP University, Delhi
Electrical & Electronics Standards, National Physical Laboratory, Delhi**[email protected]
AbstractCoaxial and waveguide structures are well established in the field of microwave technology since its invention. Waveguide structures require a different treatment regarding field theory and the related measurements compared to coaxial systems. Now a days various calibration kits are available to characterize any waveguide component using a Vector Network Analyser (VNA) system at microwave frequencies by means of various calibration techniques. This paper discusses the study of various calibration techniques for VNA and the corresponding measurement practices performed on one-port and two-port components i.e., waveguide mismatch (VSWR 1.30) and a rotary vane attenuator (at 30dB setting) as the device under test (DUT). The measured values of three techniques have been compared for both DUTs. This study helps in implementing a particular calibration technique for a specific application for coaxial systems.
I. IntroductionThis paper presents a study of various VNA calibration techniques through the measurements of a laboratory developed waveguide mismatch (VSWR: 1.30) and a rotary vane attenuator of 30 dB at National Physical Laboratory. A number of calibration techniques for VNA have been developed and studied over the decades [1,2,3,4]. A comparison between these techniques is needed for proper use based on device type, application and measurement accuracy. A few comparisons have been performed for coaxial systems earlier, however a comparison study in waveguide system still waits in general [5,6]. The effects of deviation in the coaxial calibration standards in the measured S-parameters are also reported [7,8]. However one should have a proper knowledge and implementation of these techniques through its analysis before applying in real applications for waveguide structures.
II. ExperimentThree types of VNA calibration techniques were employed, namely, OSLT (Offset Short -Load -Thru), TRL (Thru- Reflect- Line), and LRL (Line- Reflect- Line) using the laboratory developed standards to measure the complex S-parameters of the two DUTs in Magnitude/Phase as well as in Real/Imaginary form on a Wiltron VNA 37247B. The S-parameters of standards used in various calibration techniques were measured using the VNA and their S-parameters used to calculate the S-parameters of the error box for the respective calibration techniques. Using these error terms and the measured S-parameters of the DUT, the actual DUT parameters were calculated through the program codes in C++ developed. The calculated DUT parameters using OSLT and
TRL techniques were then compared with measured DUT parameters over the X-band frequency range i.e. 8.2 to 12.4 GHz. Also a comparison of the measured values of the S-parameters of the two DUTs obtained using the three calibration techniques: TRL, LRL and OSLT is presented by means of graphs in Fig.1 and Fig.2.
III. ResultsThe measured S-parameters of mismatch obtained from TRL and OSLT have a similar pattern; those obtained from LRL are different. However, at some frequency points TRL magnitude-phase values differ widely from those obtained from OSLT but can be verified from the corresponding real-imaginary values. For two port components, the measured values for OSLT and TRL are same and a slight difference exists in magnitude values. However, the magnitude and phase values obtained using LRL differ largely from the values obtained using TRL or OSLT. This indicates that the LRL values depend largely on the difference of lengths between the two line standards used.
8 9 10 11 12-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
Im(S
11 )
Re(
S 11)
Frequency(GHz)
ReOSL ReTRL ReLRL
-0.14
-0.12
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
ImOSL ImTRL ImLRL
8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5
-18
-17
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-15
-14
-13
-12
Mag
(S11
) (d
B)
Frequency (GHz)
MagOSL MagTRL MagLRL
-150
-100
-50
0
50
100
150
Phase
(S11 ) (D
eg)
PhOSL PhTRL PhLRL
(a) (b)Fig 1 (a) S
11 (Real-Imaginary), (b) S
11 (Magnitude-Phase) of waveguide mismatch measured using SOLT, TRL and LRL
8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5-0.04
-0.03
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
Im(S
21 )
Re(
S 21)
Frequency (GHz)
ReOSL ReTRL ReLRL
-0.04
-0.03
-0.02
-0.01
0.00
0.01
0.02
0.03
ImOSL ImTRL ImLRL
8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5
-30.6
-30.4
-30.2
-30.0
-29.8
-29.6
Mag
(S21
) (d
B)
Frequency (GHz)
MagOSL MagTRL MagLRL
-150
-100
-50
0
50
100
150
Phase(S
21 ) (Deg)
PhOSL PhTRL PhLRL
(a) (b)Fig 2 (a) S
21 (Real-Imaginary), (b) S
21 (Magnitude-Phase) of waveguide attenuator measured using SOLT, TRL and LRL
References:[1] R.A. Hackborn, An automatic network analyzer system, Microwave Journal, 11(1968) 45-52.[2] G.F. Engen, C.A. Hoer and R.A. Speciale, The application of ‘Thru-Short –Delay’ to the calibration of the dual six-port, IEEE MTT-S Int.Symp. Dig. , (1978) 184-185. [3] G.F. Engen and C.A. Hoer, Thru-reflect-line: An improved technique for calibrating the dual six-port automatic network analyzer, IEEE Trans. Microwave Theory tech., 27(1979) 987-993. [4] R.B. Marks, A multiline method of Network analyzer calibration, IEEE Trans Microwave Theory tech., 39 (1991) 1205-1215.[5] J.A. Reynoso-Hernandez, E. Inzunza-Gonzalez, Comparison of lrl (m), trm, trrm and tar calibration techniques using the straightforward de-embedding method, ARFTG Conference Digest, Spring (2002) 93-98[6] David K. Walker and Dylan F. Williams, Comparison of SOLR and TRL calibrations, NIST Publications[7] U. Stumper, Influence of nonideal LRL or TRL calibration elements on VNA S-parameter measurements, Advances in Radio Science, 3 (2005) 51-58.[8] U. Stumper, Uncertainity of VNA S-parameter measurement due to Non-ideal TRL calibration items, IEEE Trans. Instru. Meas., 54(2005) 51-58.
