198 Design of CMOS Millimeter-Wave and Terahertz Integrated Circuits
(CRLH) transmission-line (T-line) structure with broadside radiation under a
zero phase propagation condition. Moreover, stacking a high-resistivity dielec-
tric layer is deployed to improve efficiency. A 13-cell on-chip CRLH T-line is
fabricated in the 65nm CMOS process and is characterized from 220 GHz to
325 GHz. The corresponding 1D and 2D LWA array design shows a broadside
radiation pattern, 65% efficiency and 5.1-dBi gain at 280 GHz.
In the second par t of this chapter, one wide -band 280-GHz on-chip circu-
larly polarized SIW antenna is designed in the CMOS process with compact
area. By creating corner slots in SIW structure, the size of the proposed SIW
antenna is reduced by 15% when compared to the co nventional de signs. As
verified by the EM simulation, the proposed antenna has -0.5-dBi antenna
gain and 32.1-GHz bandwidth centered at 268 GHz.
8.2 CRLH T-Line-B ased Leaky Wave A ntenna
The r ecently explored left-handed metamaterial can provide neg ative phase
with a nonlinear phase-and-length dependence, which can realize a zero-phase
EM-wave propagation or radiation with compact area on chip [232], ideally
for a broadside radiation antenna design. In this section, the CRLH T-line is
studied for leaky wave antenna (LWA) design at THz with broadside radiation
under a ze ro phase propagation condition.
CRLH T-line is a well-known metamaterial structure that can achieve
positive, negative and zero phase propagation. A CRLH T-line consists of
a number of periodic unit-cells. The traveling wave can be generated in the
CRLH T-line-based LWA with
φ(y, z) = φ
0
e
−jk
y
y
e
−γz
(8.1)
where γ = α − jβ is the propaga tion constant of the traveling wave in the
CRLH T-line; k
y
=
p
k
2
0
− |β|
2
is the wave factor of radiated power along the
y axial; and k
0
is the wave number in free space.
When the signal travels along the antenna surface (z axis) as shown in
Figure 8.1, the energy leak-out is confined in parallel with k
0
. If the phase
velocity is slower than tha t of light, or |β| > |k
0
|, the signal is attenuated
exponentially along the y axial. In this case the antenna works in slow-wave
region. On the other hand, if |β| < |k
0
|, the antenna is in the fast-wave mode
with a real k
y
, which is a de sired condition for LWA to operate. Note that the
main beam radiation angle can be described by
θ
MB
= arcsin(|β|/|k
0
|). (8.2)
Therefore, the ra diation pattern becomes broadside when |β| equals zero,
and beam steering can be observed along broadside radiation with high direc-
tivity for THz communication.
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