Full H-band waveguide-to-coupled microstrip transition ...hompi.sogang.ac.kr/rfdesign/paper/170912.pdf · coupled microstrip transition using dipole antenna ... W. L. Stutzman and

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

a) [email protected]

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

http://dx.doi.org/10.1109/CSICS.2010.5619675




http://dx.doi.org/10.1109/TTHZ.2014.2387259





http://dx.doi.org/10.5515/JKIEES.2015.15.1.59










http://dx.doi.org/10.1109/IRMMW-THz.2014.6956402




http://dx.doi.org/10.1109/LMWC.2009.2020043




http://dx.doi.org/10.1109/22.809007

http://dx.doi.org/10.1109/22.809007

http://dx.doi.org/10.1109/22.809007

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].


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IEICE Electronics Express, Vol.14, No.13, 1–6

http://dx.doi.org/10.1109/APS.1988.94241




http://dx.doi.org/10.1109/APMC.2015.7413388





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


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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).


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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).


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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.


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