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Full H-band waveguide-to-coupled microstrip transitionusing dipole antenna withdirectors
Wonseok Choe, Jungsik Kim, and Jinho Jeonga)
Department of Electronic Engineering, Sogang University, Korea
Abstract: In this paper, we propose low-loss and broadband terahertz
(THz) waveguide-to-coupled microstrip transitions using dipole antenna with
directors. The simulation and measurement show that insertion/return loss
and bandwidth of the waveguide transition can be improved by adding
two directors to the basic dipole antenna. The fabricated transition with
two directors on a 50µm-thick quartz substrate exhibits a back-to-back
insertion loss of 1.5 dB and return loss better than 15.0 dB across full H-
band (220–325GHz). This belongs to the excellent performance compared
with the reported H-band waveguide transitions using dipole antenna.
Keywords: terahertz, waveguide transitions, dipole antenna
Classification: Microwave and millimeter-wave devices, circuits, and
modules
References
[1] M. Urteaga, et al.: “InP HBT integrated circuit technology for terahertzfrequencies,” 2010 IEEE Compound Semiconductor Integrated CircuitSymposium (2010) 1 (DOI: 10.1109/CSICS.2010.5619675).
[2] J. Kim, et al.: “H-band power amplifier integrated circuits using 250-nm InPHBT technology,” IEEE Trans. THz Sci. Technol. 5 (2015) 215 (DOI: 10.1109/TTHZ.2014.2387259).
[3] D. Yoon, et al.: “A wideband H-band image detector based on SiGe HBTtechnology,” J. Electromagn. Eng. Sci. 15 (2015) 59 (DOI: 10.5515/JKIEES.2015.15.1.59).
[4] L. A. Samoska: “An overview of solid-state integrated circuit amplifiers in thesubmillimetre-wave and THz regime,” IEEE Trans. THz Sci. Technol. 1 (2011)9 (DOI: 10.1109/TTHZ.2011.2159558).
[5] A. Zamora, et al.: “A 170–280GHz InP HEMT low noise amplifier,” 201439th Int. Conf. on Infrared, Millimeter, and Terahertz waves (2014) 1 (DOI: 10.1109/IRMMW-THz.2014.6956402).
[6] K. M. K. H. Leong, et al.: “A 340–380GHz integrated CB-CPW-to-waveguidetransition for sub millimetre-wave MMIC packaging,” IEEE Microw. WirelessCompon. Lett. 19 (2009) 413 (DOI: 10.1109/LMWC.2009.2020043).
[7] N. Kaneda, et al.: “A broad-band microstrip-to-waveguide transition usingquasi-Yagi antenna,” IEEE Trans. Microw. Theory Techn. 47 (1999) 2562(DOI: 10.1109/22.809007).
[8] W. L. Stutzman and G. A. Thiele: Antenna Theory and Design (Wiley, New
© IEICE 2017DOI: 10.1587/elex.14.20170487Received May 10, 2017Accepted May 31, 2017Publicized June 14, 2017Copyedited July 10, 2017
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LETTER IEICE Electronics Express, Vol.14, No.13, 1–6
York, 2012) 3rd ed. 168.[9] C. Tsao, et al.: “Aperture-coupled patch antennas with wide-bandwidth and
dual-polarization capabilities,” IEEE AP-S Int. Symposium Digest (1988) 936(DOI: 10.1109/APS.1988.94241).
[10] L. Xu, et al.: “Compact broadband waveguide-to-GPWG transition operatingaround 300GHz,” 2015 Asia-Pacific Microw. Conf. (2015) 1 (DOI: 10.1109/APMC.2015.7413388).
1 Introduction
Recently, integrated circuits (ICs) operating in terahertz (THz) frequencies such as
amplifiers, mixers, oscillators, and detectors have been successfully reported using
heterojunction transistors (HBTs) or high-electron mobility transistors (HEMTs)
[1, 2, 3]. THz ICs are generally fabricated using planar transmission lines such as
microstrip lines or grounded coplanar waveguides (GCPWs). Therefore, low-loss
and broadband transitions from waveguide-to-microstrip or GCPWs are essential to
package THz ICs in the waveguides for module and system applications.
Several THz waveguide-to-microstrip transitions have been proposed using
E-plane probes, dipole antenna, and fin-lines [4]. The transitions using dipole
antenna have shown low-loss and wideband performance in THz frequencies with
a compact size and input/output ports aligned in the waveguide direction. In [5]
and [6], low noise amplifier (LNA) modules were reported at 170–280GHz and
340–380GHz using the dipole transition on 50µm-thick InP substrate. Insertion
loss per single transition was 0.8 and 1.0 dB, respectively, with relatively narrow
bandwidth of return loss. Although this result is good enough for LNA module
fabrication, it can be further optimized to achieve better performance for other
applications requiring lower loss and wider bandwidth.
In this work, we introduce directors to improve insertion/return loss and
bandwidth of waveguide-to-coupled microstrip transitions using dipole antenna.
We design and compare the performance of the transitions by increasing the
number of directors. Finally, we present the optimized waveguide-to-coupled
microstrip transition with two directors operating at full H-band (220–325GHz).
2 Design of the transitions
Fig. 1(a) shows the waveguide-to-coupled microstrip transitions using dipole
antenna without directors in [5, 6]. As shown in this figure, the substrate with
dipole antenna is placed in the central E-plane of waveguide to transform TE10
mode of waveguide to the mode of coupled line. This study focuses on the effect of
directors on the transition performance, so is not included the transition from
coupled lines to microstrip lines or CPWs which can be easily designed using balun
or half-wave long lines as demonstrated in [5, 7]. More importantly, coupled lines
can be directly used in the design of differential or balanced THz circuits without
requiring transitions or baluns. The ground plane of the substrate, which lies on the
metallic pedestal, serves as a reflector in the dipole antenna, improving radiation
pattern [8].
© IEICE 2017DOI: 10.1587/elex.14.20170487Received May 10, 2017Accepted May 31, 2017Publicized June 14, 2017Copyedited July 10, 2017
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IEICE Electronics Express, Vol.14, No.13, 1–6
In order to improve the performance of the dipole transitions, we introduce
directors which is able to increase directivity and bandwidth of dipole antenna [9].
We designed and optimized dipole transitions using 50µm-thick quartz substrate
with dielectric constant of 3.78 as the number of directors increases. The full-wave
simulation was performed to optimize the dimensions and find the performance
of transitions depending on the number of the directors. It is found from this
simulation that the performance in terms of insertion and return losses can be
gradually improved by increasing the number of directors up to two. More than two
directors rather degrades the performance. Therefore, the optimum number of
directors is determined to be two. Fig. 1(b) shows the dimensions of the optimized
transitions with two directors.
Fig. 2 shows the simulated S-parameters of the transitions with no and two
directors. Insertion loss (�20 log jS21j) is reduced from 1.06 to 0.93 dB in full H-
band by adding two directors. Note that the loss is an average value across H-band
(220–325GHz) and the graph displays the data from 220–330GHz. In addition, the
ripple in insertion loss is reduced from 2.08 to 1.43 dB. Return loss (�20 log jS11j)is also greatly improved as shown in Fig. 2(b). Bandwidth of 15-dB return loss
is improved from 43.0 to 82.5GHz. Fig. 2(c) shows the simulated electric field
distribution of the back-to-back transition with two directors in the E- and H-planes
at 270GHz. They illustrate that the designed transition enables the electromagnetic
wave to propagate from waveguide to coupled line and vice versa. Note that the
field on the substrate is concentrated on the dipole and coupled lines.
3 Experimental results
To verify the proposed idea, two transitions (one with no director and the other with
two directors) were designed and fabricated as shown in Fig. 3(a) and (b). Fig. 3(c)
demonstrates the transition with two directors mounted in the waveguide. It sits on
the metallic pedestal as illustrated in Fig. 1(a). The waveguide split-blocks were
manufactured in using aluminium by standard machining technique. The size of the
waveguide blocks is 3 cm � 3 cm � 3 cm as shown in Fig. 3(d). For the compar-
ison, standard WR-03 straight waveguide with the length of 3 cm were also
(a) (b)
Fig. 1. H-band waveguide-to-coupled microstrip transition using di-pole antenna
© IEICE 2017DOI: 10.1587/elex.14.20170487Received May 10, 2017Accepted May 31, 2017Publicized June 14, 2017Copyedited July 10, 2017
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IEICE Electronics Express, Vol.14, No.13, 1–6
manufactured. The performance of the fabricated waveguide transitions was
measured at H-band after through-reflect-line (TRL) calibration using WR-03
waveguide short and through sections.
Fig. 4(a) shows the simulation and measurement results of the 3 cm-long
standard WR-03 straight waveguide. The measured insertion loss was 0.75 dB on
(a) (b)
(c)
Fig. 2. Simulation results of the designed transitions: (a) insertion loss(S21), (b) return loss (S11), and (c) electric field distribution ofthe back-to-back transition with two directors at 270GHz.
(a) (b)
(c) (d)
Fig. 3. Photographs of the fabricated transitions: (a) dipole transitionwith no director, (b) dipole transition with two directors,(c) dipole transition mounted in WR-03 waveguide, and (d)fabricated transition jig (bottom).
© IEICE 2017DOI: 10.1587/elex.14.20170487Received May 10, 2017Accepted May 31, 2017Publicized June 14, 2017Copyedited July 10, 2017
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IEICE Electronics Express, Vol.14, No.13, 1–6
average in H-band which is close to the simulation result of 0.52 dB. Fig. 4(b) show
the performance of the transition jig itself without the transition substrate mounted.
Note that there is a metallic pedestal in the middle of the 3 cm-long waveguide.
The insertion loss was greater than 10 dB with very poor return loss thanks to the
metallic pedestal which prevents the electromagnetic wave from directly propagat-
ing through the waveguide as shown in Fig. 4(c).
Fig. 5 shows the comparison of the measured S-parameters of the transitions.
As shown in Fig. 5(a), the average insertion loss across full H-band was decreased
from 1.90 to 1.51 dB with the reduced ripple from 0.99 to 0.73 dB by adopting two
directors. Furthermore, the transition with two directors exhibits return loss better
than 15.0 dB across full H-band as shown in Fig. 5(b), which is much better than
the conventional transition. The bandwidth of 10-dB return loss is increased from
(a) (b)
(c)
Fig. 4. Simulation and measurement results of the fabricated 3 cm-longwaveguide jigs: (a) standard straight waveguide, (b) transitionjig without the transition substrate, and (c) electric fielddistribution of transition jig in H-plane at 270GHz.
(a) (b)
Fig. 5. Measurement results of the fabricated transition: (a) insertionloss (S21) and (b) return loss (S11).
© IEICE 2017DOI: 10.1587/elex.14.20170487Received May 10, 2017Accepted May 31, 2017Publicized June 14, 2017Copyedited July 10, 2017
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IEICE Electronics Express, Vol.14, No.13, 1–6
98 to 110GHz. This result demonstrates that the insertion/return loss and band-
width can be improved by adding two directors as in the simulation.
Table I compares the performance of the reported transitions using dipole
antenna. The optimized transition with two directors exhibits the measured in-
sertion loss of 0.38 dB per transition across full H-band. It also exhibits excellent
bandwidth of 15-dB return loss broader than 115GHz (full H-band).
4 Conclusion
In this letter, low-loss and broadband waveguide-to-coupled microstrip transition
was developed using dipole antenna. The simulation and measurement proved that
adding two directors can greatly improve the loss and bandwidth performance of
the dipole transitions. It showed low-loss flat insertion loss and excellent return loss
across full H-band. Therefore, it can be applied to design various differential planar
THz circuits with waveguide input and output, which can be useful for the
implementation of low-cost and high-performance THz modules and systems.
Acknowledgments
This research was supported by a grant to Terahertz Electronic Device Research
Laboratory funded by Defense Acquisition Program Administration, and by
Agency for Defense Development (UD150043RD).
Table I. Reported dipole antenna transitions around H-band.
Frequency(GHz)
Substrate/thickness
Loss per transition(dB)
Bandwidth�
(GHz)
[5] 170–280 InP/50 µm 0.8 38
[6] 340–380 InP/45 µm 1.0 < 10
[10] 270–330 InP/50 µm 1.5 < 10
This work 220–325 Quartz/50 µm 0.38�� > 115
�for 15-dB return loss��The loss of the 3 cm-long straight waveguide was subtracted.
© IEICE 2017DOI: 10.1587/elex.14.20170487Received May 10, 2017Accepted May 31, 2017Publicized June 14, 2017Copyedited July 10, 2017
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IEICE Electronics Express, Vol.14, No.13, 1–6