диафрагмированные волноводные фильтры / 6ef797ec-a697-4e51-9356-08e9d150e4c1
.pdfTerahertz Devices with EMXT Structure Fabricated by MEMS
Shengjie Yang1, Hongda Lu2, Zhipeng Liu1, Yong Liu1, Bin Li1, Xin Lv1
1Beijing Key Laboratory of Millimeter Wave and Terahertz Techniques, Beijing Institute of Technology, Beijing, 100081 China, 2Information Science Academy of China Electronics Technology Group Corporation, Beijing, 100086 China
To verify the advantages ofMEMS, we fabricated 90° bend waveguides, bandpass filter and H-plane horn antenna. The experimental results agree well with the simulation results.
II. RESEARCH ON TERAHERTZ PASSIVE DEVICE
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A. 90°-bend waveguide |
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Fig. 1 shows the proposed terahertz 90°-bend waveguide |
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with EMXT structure. Periodic square-shaped rodsa×(a×h) |
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form this structure with the lattice constant P. The line defects |
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are |
used to transmit |
terahertz wave as waveguides |
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I. |
INTRODUCTION |
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removing three rows of rods which also form a chamfered |
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Terahertz communication system integrates the |
advantages |
bend. The width of waveguide is 4P-a. The side view of this |
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90°-bend waveguide is shown in Fig. 1. The final optimized |
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of |
microwave |
communication |
and |
optical |
communication,parameters are as follows: W = 1756 μm, H = 787 μm, a = 48 |
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such as small size, high security, precise position, high speed |
μm, h = 241 μm, P = 132 μm. |
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and large capacity for information [1]. Terahertz system has |
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broad application prospects in the future. As a part of terahertz |
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communication |
system, |
the |
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performance |
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of |
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terahertz |
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functional devices has an impact on the |
performance |
of |
4P-a |
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terahertz system. Its development can not be ignored. |
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With |
frequency |
increasing, |
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terahertz |
devices |
have |
a |
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minimum |
size of less than 1 |
millimeter. |
It’s |
extremely |
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difficult to fabricate terahertz device with |
conventional |
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technology, |
considering |
the |
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processing |
error, |
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surface |
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roughness, |
and |
energy |
loss. |
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Micro-Electro-Mechanical |
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W |
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Systems |
(MEMS) |
can |
solve |
thisproblem [2]. |
With |
bulk |
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silicon MEMS technology, some cavities can be etched on the |
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(a) |
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silicon wafers. The surfaces of ilicons wafers are coated with |
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sputtering |
gold. Silicon wafers |
finally |
are |
connected |
together |
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a |
h |
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with gold-gold thermo-compression bonding |
to |
form |
the |
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designed terahertz functional devices. |
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(b) |
(c) |
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High precision and deep etching are typical advantages of |
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P |
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bulk |
silicon |
MEMS |
technology to |
fabricated |
complex |
H |
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structure like electromagnetic crystal (EMXT, also called |
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photonic crystals at optical frequency |
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[3]. |
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For |
the |
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electromagnetic band gaps of EMXTs, they can also be used |
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to transmit electromagnetic waves. These structures consist of |
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periodical metallic or dielectric cells which can |
easily |
form |
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(d) |
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passive terahertz devices, such as waveguides, filters and |
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antennas. The |
EMXT size in |
the |
microwave |
band |
is on |
the |
Figure 1. Structure of proposed 90°-bend waveguide: (a) schematic diagram |
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order of centimeters and in the optical band is on the order of |
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(b) partial top view (c) partial side view (d) whole side view. |
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nanometers. It’s too large to integrate or too small to fabricate. |
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This waveguide operated from 0.365 THz to 0.578 THz |
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But |
it’s |
suitable |
in |
terahertz |
band. |
Bulk |
silicon |
MEMS |
45.2% relative bandwidth. The cross section |
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technology provides such means for terahertz |
circuit |
and |
with |
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corresponds to WR-1.9 standard rectangular waveguides. The |
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components fabrication. |
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S parameters of this 90°-bend waveguide is presented in Fig. 2. |
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by
size
978-1-5386-2416-6/18/$31.00 ©2018 IEEE
The insertion loss is around 0.2 dB in the operating frequency band which is very close to 0 dB. And the return loss is lower than -10 dB from 0.36 THz to 0.57 THz. S21 converted into energy transfer rate is 90%. 90% energy has been transmitted from one port to the other port. The maximum transmittance
of the conventional 90°-bend |
waveguide |
without |
EMXT |
structure can only reach up to |
80% by |
contrast |
[4]. This |
structure of terahertz 90°-bend waveguide has the advantages of low energy loss and high transmission efficiency.
(dB) |
0 |
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S-parameter |
-5 |
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Figure 4. Microscope image of proposed unbonded THz bandpass filter |
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-10 |
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Comparison of measurement and simulation is presented in |
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Fig. |
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5. |
The |
3dB |
bandwidth |
is |
30 |
GHz |
and |
the |
center |
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Simulated |
-15 |
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frequency of filter is 427 GHz. The simulation results shows |
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-20 |
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S11 |
1.3 |
dB insertion loss within the passband |
and |
return |
loss |
is |
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better |
than 14 |
dB. In the measured results, 3dB bandwidth |
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S21 |
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-25 |
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reaches up to 32 GHz. The insertion loss and return loss reach |
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0.4 |
0.5 |
0.6 |
up |
to |
2 |
dB |
and |
24 |
dB |
respectively. |
S11 |
and |
S21 |
show |
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0.3 |
expecting agreement between simulated and measured results. |
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Frequency (THz) |
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Figure 2. Simulated S-parameters of designed THz 90°-bend waveguide
B. |
Bandpass filter |
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(dB) |
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Fig.3 |
and Fig. |
4 present a |
325~350 |
GHz |
EMXT |
formed |
-20 |
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bandpass |
filter |
[5] |
fabricated |
by bulk |
silicon |
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MEMS |
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technology. |
Cylinder rods are arranged periodically |
as |
an |
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-40 |
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array. This bandpass filter is etched with deep reactive-ion |
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etching |
on |
the |
silicon |
wafers. |
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The |
standard |
thickness |
of |
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chosen silicon wafers is 400μm. Etching depth is 280μm for |
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parameterS- |
-60 |
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S11-simulated |
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the |
height |
of |
cylinder |
rods. |
Some |
rods are |
removed |
and |
-80 |
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S11-measured |
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S21-simulated |
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rearranged to form the cavity resonators. Two independent |
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S21-measured |
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TM110 |
modes |
can |
be |
generated |
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in |
these |
cavities. |
This |
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-100 |
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resonator |
offers |
a steeper side band response. |
WR-2.2 |
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325 350 375 400 425 450 475 500 |
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(560×280 μm) |
standard |
rectangular |
waveguides |
also |
match |
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Frequency (GHz) |
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well |
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with |
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this |
filter |
for |
the |
EMXT |
formed |
standard |
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waveguides |
design. Two filters have been fabricated. One |
Figure 5. Measured and simulated results of proposed THz bandpass filter |
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filter is unbonded shown in Fig. 4. The other is bonded for test. |
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With |
the |
full-wave simulation software |
high-frequencyC. H-plane horn antenna |
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structure simulator, the design parameters are optimized as |
The center |
frequency of this H-plane horn antenna is 0.5 |
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follows: r = 24 μm, P = 140 μm, d = 980 μm, R = 410 μm, α1 |
THz, |
which |
can be used with the |
proposed 90°-bend |
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= 120°, α2 = 60°, W1 = 310 μm, W2 |
= 410 μm, Lg |
= 420 μm, |
waveguide together [6]. Similarly, this EMXT structure is |
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Wg =560 μm, L = 2660 μm and W= 1960 μm. |
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consist of periodic square-shaped rods, some of which are |
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removed to form the gradually flared horn. Geometry of this |
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H-plane |
horn antenna is presented in Fig. 6. Logarithmic |
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curved taper is adopted to get low sidelobes in the H-plane. W |
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is |
the |
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1 |
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width of the waveguideL . is the length of the |
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waveguide. L2 and D are the length and aperture of this horn |
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antenna. The crystal lattice constant and dimensions of rods |
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Figure 3. Side view of proposed unbonded THz bandpass filter |
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are the same as the proposed 90°-bend waveguide. The |
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parameters with optimization of HFSS are as |
follows:W = |
483 μm, L2 = 3366 μm, D = 3348 μm, P = 132 μm, a = 48 μm, H = 241 μm.
D |
L2 |
W |
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L1 |
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(a) |
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P |
a |
H |
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III. CONCLUSION
Three kinds of terahertz device are fabricated with EMXT structures by bulk silicon MEMS technology and measured results showing expecting agreement with simulation. The fabricated 90°-bend waveguide shows 90% transmittance. The bandpass filter operates at a 426.5 GHz center frequency with 7.6% relative bandwidth. The insertion loss and return loss of
filter reach up to 2 dB |
and 24 |
dB |
respectively. Good |
normalized radiation patterns of |
H-plane |
horn |
antenna at the |
main beam are also demonstrated. For the high accuracy and fabrication flexibility, MEMS provides a feasible way to processing terahertz device. EMXT structure or other novel structures can be good choices to form terahertz passive devices for processing convenience.
ACKNOWLEDGMENT
(b) |
(c) |
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This work is supported by the Joint |
Research |
Fund in |
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Figure 6. Structure of proposed H-plane horn antenna: (a) schematic diagram |
Astronomy (U1631123) under cooperative agreement between |
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(b) partial top view (c) partial side view. |
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the National Natural Science Foundation of China (NSFC) and |
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Fig. 7 shows the E-plane and H-plane radiation patterns of |
Chinese Academy of Sciences (CAS). |
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this horn antenna. The 3dB beam width is 60° in the E-plane |
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REFERENCES |
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and 25° in the H-plane. The measured sidelobe in the H-plane |
[1] |
Christopher M. Snowden, "Prospects for |
terahertz |
technology", |
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is only -18.2dB. There is not clearly difference between the |
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Microwave and Millimetre-Wave Communications - the Wireless |
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curves of simulation and measurement at theta = 0°. The |
Revolution IEE Workshop on, pp. 7/1-7/6, 29 Nov 1995. |
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measured results show good consistence with the simulation |
[2] V. K. Varadan, K. J. Vinoy, and K. A. Jose, RF MEMS and Their |
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results. Normalized radiation pattern in the main beam (3dB |
[3] |
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beam width) shows little change between simulation and |
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measurement. It demonstrates the superior performance of |
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MEMS to fabricate the EMXT formed horn and waveguide. |
[4] |
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Normalized radiation pattern (dB)
0
-10
-20 |
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simulated E-plane |
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measured E-plane |
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-30 |
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simulated H-plane |
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measured H-plane |
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-90 |
-60 |
-30 |
0 |
30 |
60 |
90 |
Theta (deg)
[5]
[6]
Figure 7. Measured and simulated radiation pattern of proposed THz H-plane horn antenna.