This document summarizes a study on effectively grounding microstrip lines. The study measured the via hole inductance of microstrip lines on a GaAs substrate using a vector network analyzer. A test structure with a single via hole was fabricated to approximate a 50 ohm microstrip line. Via hole inductance measurements were taken from 1-5 GHz and the mean inductance was calculated to be 43.29 pH. The preliminary investigation provides useful information for designing microwave integrated circuits using microstrip lines with effective grounding.

1. International Journal of Electronics and Communication Engineering & Technology (IJECET),
INTERNATIONAL JOURNAL OF ELECTRONICS AND
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME
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ISSN 0976 – 6472(Online)
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IJECET
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Preliminary Investigation on Effective Grounding Measurement of
Microstrip Line
Satya Sai Srikant
Assistant Professor, SRM University, Modinagar Campus, 201204, India
satya.srikant@gmail.com
ABSTRACT: This paper is to find the RF measurement when microstrip is effectively grounded.
The manufacturing method is used for grounding measurement for VIA hole inductance
measurement. The available structure for the present investigation was fabricated on GaAs
substrate. In this paper, wafer probing measurement and mean value of VIA hole inductance is
measured with vector network analyzer (VNA) with proper calibration, when the package is
effectively grounded. Further studies are in progress.
KEYWORDS: Microstrip, VNA, Groundings, VIA Hole, RF probe, Calibration
I.
INTRODUCTION
The high frequency performance of monolithic microwave integrated circuits (MMIC) is highly
affected by the way in which package is grounded. Microstrip has not any topside ground
plane, so some means of achieving a low inductance ground must require. The manufacturing
method grounding is used; requires a topside metallization pattern near the periphery of the
wafer which can be connected to the chip ground. If the field effect transistor (FET) is located
at the edge of the chip in MMIC, the source grounding can be affected by multiple wire bounds
to the surrounding chip carrier. Practically, FET does not locate near the chip edge as
grounding consideration and its calculations due to continuous variations will be very
cumbersome task [1].
II.
MATERIAL AND METHODS
A. Raw Materials
Holes are chemically milled through the GaAs substrate (εr = 10.8) until the topside
metallization is reached. Such a hole is called as VIA hole groundings. Fig. 1 shows a simplified
cross section of substrate with VIA holes in which it contains one VIA hole; that pad out to two
terminals. The signal / ground structure approximates to a 50 Ω microstrip to the VIA hole and
is intended for wafer probing measurement. The layout minimizes the interconnecting
parasitic because the 50 Ω microstrip is maintained up to the edges of the VIA hole. Fig. 2
International Conference on Communication Systems (ICCS-2013)
B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India
October 18-20, 2013
Page 45

2. International Journal of Electronics and Communication Engineering & Technology (IJECET),
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME
shows the equivalent circuit of Signal / Ground RF probe. The parameters of 50 Ω microstrip
line segments are:
Zo(εr ) = 50 Ω, l = 2771µm, h = 200 µm, εr = 12.8, ϴ = 9 º / GHz, w = 100 µm
100 Ω Signal /
Ground
Signal Plane
One Via Hole
Ground
Plane
Fig. 1: Cross sectional view of microstrip with effective grounding
Fig. 2: Equivalent circuit of RF probe
B. Experimental Set up and Methods
The VIA grounding directly connect the signal conducting plane and ground plane of microstrip
that is to be measured for low valued inductance from vector network analyzer (VNA) with
manufacturing method [2]. Fig. 3 is the set up for measuring the VIA inductance. It is desired to
measure the mean value of VIA hole inductance by the manufacturing approach in the range of
1- 5 GHz. This helps in studying the effective dielectric constant and characteristic impedance
for microstrip with dispersion effect when the package is grounded.
Fig. 3: Set up for measuring the VIA inductance, Microstrip with VIA holes & Equivalent circuit
International Conference on Communication Systems (ICCS-2013)
B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India
October 18-20, 2013
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3. International Journal of Electronics and Communication Engineering & Technology (IJECET),
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME
III.
ANALYTICAL METHOD
The S parameter S11 of a 50 Ω microstrip line segment terminated by VIA hole and subsequent
de-embedding the line segment results in VIA inductance [1,3,4]. The S parameter (S11) is
measured with the help of vector network analyzer (VNA). With the help of S11, the input
impedance Zin can be found out by pressing Smith Chart menu in VNA. The load impedance Zl
for measured input impedance Zin can be evaluated by using Transmission line concept.
+
+
=
=
+
=
=
=
+
+
) ⁄[ (
(
=
(
=
)
+
) + (
+
−
) ]
+
⁄[ (
) + (
+
) ]
⁄2
=
The calibration of RF probe and VNA must be needed before the measurement of VIA
inductance. The measurement of VIA inductance requires a one port calibration, so LRM (Line
– Reflect – Match) is the most convenient calibration. It means that in LRM technique, the short
calibration is not used.
IV.
RESULT AND DISCUSSION
The measurement of VIA inductance in preliminary investigation on considering the effective
groundings of 50 Ω microstrip line is shown in Table 1. This grounding includes the effect of
pad inductance. The investigation satisfies the estimated inductance of a VIA Hole is
approximation 25 – 100 pH /mm of substrate thickness. However in practical case, the value of
the mean VIA hole inductance is approximation 40 – 55 pH for 200 µm substrate thickness.
Frequency
(GHz)
1
1.2
1.6
2
2.4
2.8
3.2
3.6
4
4.4
4.8
5
Measured
Re(Zin) in Ω
0.679
0.661
0.739
0.890
1.122
1.388
1.558
1.606
1.631
1.894
2.116
2.303
Measured
Im(Zin) in Ω
8.818
10.616
14.166
18.028
21.830
25.675
29.726
33.965
38.659
43.743
49.295
52.312
LVIA
(pH)
54.510
54.270
52.961
51.880
49.528
46.278
43.640
39.810
36.360
32.897
29.498
27.847
Table 1: Calculation of VIA Inductance (LVIA) {Mean LVIA = 43.29 pH}
International Conference on Communication Systems (ICCS-2013)
B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India
October 18-20, 2013
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4. International Journal of Electronics and Communication Engineering & Technology (IJECET),
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME
V.
CONCLUSION
The preliminary studies of effective grounding of microstrip are investigated with vector
network analyzer which shows the presence of impedance (VIA inductance) even though the
microstrip is effectively grounded. The value of VIA resistance measured from VNA shows that
it is almost zero. This shows that the high frequency performance of monolithic microwave
integrated circuits (MMIC) like microstrip with grounded is highly affected with VIA
inductance. This study is very useful in designing the filters, amplifiers, oscillators, antennas,
resonators, feeder, planner loads.
ACKNOWLEDGEMENT
I am thankful to Prof. Manoj Kumar Pandey, Director of SRM University, Modinagar for
encouraging me to perform the research work in the field of RF and Microwave electronics.
Thanks are also due to some of the scientists and research faculites of various laboratories for
their invaluable suggestions on this subject.
REFERENCES
[1] Snow, Philip and Wilson Terry "Two techniques for characterizing MMIC VIA holes"
Microwaves and RF Jr, vol. 27, Sept. 1988, pp 98-101.
[2] R Pucel “Design consideration for MMIC” IEEE Transactions on Microwave Theory and
Techniques, June 1991,vol 29 (6), pp 513 – 534.
[3] R Faraji Dana and Y L Chow, “The ac resistance of a microstripline and its ground plane,” in
IEEE MTT-S Int. Microwave Symposium Digest, June 1989, Long Beach, CA.
[4] M Goldfarb and R Pucel, “Modeling VIA hole grounds in microstrip,” IEEE Microwave
Guided Wave Letter, vol. 1 (6) , June 1991, pp 135-137.
BIOGRAPHY
Satya Sai Srikant was born 1974 at Dhanbad, Jharkhand, India. He
received his M.Tech degree in Microwave Electronics from University of
Delhi, India in 2002. From 2002-2009, he worked as research area with
different position in various R & D Organizations, India in the field of RF
and applications of microwaves in Minerals and Materials Technology.
From 2009 onwards, he is working as Assistant Professor, in Department of
Electronics and Communication Engineering, SRM University, Modinagar,
India. The author has recently submitted his PhD thesis in Microwave area
at ITER Bhubaneswar, Odisha, India. His current research interests focus on
Microwave circuits, antennas, application of Microwave energy in Minerals and Materials
Technology and system interfacing with Microwaves.
International Conference on Communication Systems (ICCS-2013)
B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India
October 18-20, 2013
Page 48