3172 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 66, NO. 6, JUNE 2018
Communication
Novel W-Band Millimeter-Wave Transition From Microstrip Line to Groove
Gap Waveguide for MMIC Integration and Antenna Application
Yongrong Shi , Junzhi Zhang, Sheng Zeng, and Ming Zhou
Abstract— For monolithic microwave integrated circuit integration and
antenna application, a novel W-band millimeter-wave transition from
microstrip line to groove gap waveguide (GWG) is proposed in this com-
munication. The transition is achieved by a modified planar triangular-
microstrip patch resonator with an inner shorting via. To give a physical
insight, E-field analysis is presented, and its working mechanism is
similar to that of the passband filter based on coupled resonators.
The proposed transition may contribute to a potential groove GWG
application in the W-band radar and communication system. Finally,
a back-to-back transition prototype is fabricated and assembled for
measurement. To improve S
11
of the prototype, a modified CPW probe
pad is applied. Moreover, the influences on S
11
and S
21
of the conductor
losses are given. The measured results show that there is an excellent
transition passband from 90 to 99.5 GHz, in which frequency band, S
11
is almost below −12 dB.
Index Terms—Field coupling, groove gap waveguide (GWG),
microstrip line (MSL), modified planar triangular-microstrip patch
resonator, W -band transition.
I. INTRODUCTION
Recently, W-band has many applications in various fields, such as
automotive radar [1], point to point backhaul for 5G networks [2],
synthetic aperture radar for security [3], and frequency-modulated
continuous-wave missile fuze for defense. Traditionally, W -band
antenna, circuit module, and system construct from the machined
WR-10 waveguide as interconnection. Unfortunately, the traditional
W-band waveguide system (including antenna, filter, coupler, and
divider) is too bulk and heavy for monolithic microwave inte-
grated circuit (MMIC) integration in a compact space. Meanwhile,
the assembling of the fineline or microstrip line (MSL) probe
transition from MMIC to the waveguide is challenging. This limits
the extensive use of the conventional W-band waveguide systems.
In order to overcome those limitations, gap waveguide (GWG)
technology is provided as an attractive solution [4].
The concept of the GWG was, first, proposed by Kildal et al.[5],
Rajo-Iglesias et al. [6], [8], Zaman et al. [7], and Shi et al. [9] to the
area of the microwave circuit packaging. Then, the GWG technology
was introduced to guide the electromagnetic wave for microwave
circuit designs including filter, divider, and antenna array [10]–[13].
The GWG is a modified parallel-plate waveguide in which one
plate is smooth while the other is a textured surface. In the GWG,
the electromagnetic wave is forced to propagate along the desired
path by means of a conducting ridge, groove, or microstrip in the
textured surface [9].
Manuscript received December 1, 2017; revised January 26, 2018; accepted
March 20, 2018. Date of publication March 26, 2018; date of current
version May 31, 2018. This work was supported by the National Natural
Science Foundation of China under Grant 61601421. (Corresponding author:
Yongrong Shi.)
The authors are with the Microwave Circuit Module Department,
Nanjing Electronic Devices Institute, Nanjing 210016, China (e-mail:
yongrongshi@hotmail.com).
Color versions of one or more of the figures in this communication are
available online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TAP.2018.2819902
In addition to these GWG passive components and antennas, it is
important to integrate active components with the GWG for practical
applications [14]. For example, a low noise amplifier MMIC is
usually used in the active antenna in the radar receiver front end.
For this purpose, the transitions between the planar transmission
line and the GWG were proposed for different frequency band
applications. For Ku-band, a novel wideband MSL to ridge GWG
transition was reported by using defected ground slot [15]. Another
Ka-band microstrip-to-ridge GWG with simple impedance matching
part was proposed in [16]. A novel V -band transition from MSL to
groove GWG was also presented for MMIC packaging and antenna
integration [4] based on the resonant cavity which efficiently helps
to couple the field from the MSL to the GWG. Moreover, a novel
F-band transition from MSL to ridge GWG was designed in [17]
by using the coupling microstrip patch. However, there is a lack
of W-band transitions from the MSL to the GWG for some certain
applications described earlier.
In this communication, a novel transition between the MSL and
the groove GWG is proposed in W-band. In this transition, the
field is coupled between the MSL and the groove GWG by the
modified planar triangular-microstrip patch resonator with an inner
shorting via. This shorting via is added for changing the resonance
frequency to W-band and it can also help couple the matched field
mode. Besides, three steps with different lengths in the groove
GWG are designed for impedance matching. The novel transition
consists of the GWG fabricated by the machining and the microstrip
circuit fabricated by thin-film technology on the quartz substrate.
Finally, a back-to-back transition prototype is designed, fabricated,
and measured. Good agreement is achieved between the simulation
results and the measured ones. The measured results show that there
is a transition passband from 90 to 99.5 GHz for the back-to-back
prototype at least. The measured insertion loss of one transition is
about 2 dB at average.
II. P
ROPOSED W-BAND TRANSITION
Fig. 1(a) shows the explosion view of the proposed transition
structure. Fig. 1(b) and (c) shows its top view and 3-D view,
respectively. As depicted in Fig. 1, the groove GWG is located on the
left, and the side view of the unit cell of the rod in the groove GWG
is also inserted in Fig. 1(b) for clarity. The period of the unit cell is p,
the height of the groove GWG is h
2
, the width of the rod is d,and
the height of the rod is h
1
. The 50 MSL with the width w
2
and
the length a
6
is located on the right. A modified planar triangular-
microstrip patch resonator with a shorting via is introduced between
the groove GWG and the MSL. The length and width of its left
rectangle terminal are l
3
and a
7
. The length and width of the right part
of the modified triangular-microstrip patch are w
1
and a
4
. The radius
of the shorting via is r. The shorting via is located at the symmetrical
plane, and the distance between the shorting via and the left side
is a
8
. The modified planar triangular-microstrip patch resonator is
fabricated on the quartz substrate (ε
r
= 3.824 and tan δ = 0.000015)
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