COL 12(4), 040401(2014) CHINESE OPTICS LETTERS April 10, 2014
Compact waveguide bandpass filter employing
two-dimensional metallic photonic crystals for
millimeter to terahertz frequencies
Feng Lan (
)
1∗
, Ziqiang Yang (
)
1
, Limei Qi (
)
2
, and Zongjun Shi (
)
1
1
School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
2
College of Physics and Engineering, Qufu Normal University, Qufu 273165, China
∗
Corresponding author: lanf uestc@aliyun.com
Received December 5, 2013; accepted March 5, 2014; posted online April 4, 2014
Tw o-dimensional metallic photonic crystal slabs with square lattice are proposed to be used for the design
of waveguide bandpass filters operating in millimeter to terahertz region. Filter characteristics are studied
when rod radii and lattice constants are changed. Based on the frequency scaling technique, a series of
higher frequency filters has been designed. By using laser drilling and welding processing techniques, a
compact waveguide filter embedded in an EIA-WR10 waveguide with central frequency 145.5 GHz and
3-dB bandwidth of 5.26 GHz is fabricated and measured. The measurement data agree well with the
simulation prediction.
OCIS co des: 040.2235, 120.2440, 050.5298, 120.7000.
doi: 10.3788/COL201412.040401.
Millimeter to terahertz (THz) radiations
[1,2]
have at-
tracted much attention for their special properties
[3−5]
,
such as biomedical diagnostics, communications, imag-
ing, and spectroscopy. In recent years, many researches
on photonic crystals (PCs) have attracted much attention
for the remarkable feature of photonic band gap, which
offers a possibility to design new devices
[6−10]
. The pass
band filter is one of the most impor tant devices which
can manipulate THz radiations effectively. With the
development of THz communication technology, minia-
turization has become the new direction of development
of the waveguide filter. However, traditional technologies
targeting on microwave, infrared or visible light maybe
unsuitable or difficult to fabricate bandpass filter for
THz region. Metallic photonic crystal filters (MPC) are
promising alternatives, and have the advantages of be-
ing compact, robust, and inexpensive. Tunable metallic
photonic crystal filters composing of two orthogonal lin-
ear grids proposed and demonstrated
[11,12]
. A passband
filter which had a dual array structure of the same pe-
riod but different pillar dia meters was fabricated and
tested
[13]
. Recently, a passband filter utilizing the dis-
tinction between positive and negative refractions in a
metallic photonic crystal prism was studied by the finite
difference time domain (FDTD) method
[14]
.
In this letter, the filter characteristics of two-
dimensional (2D) metallic photonic crystals are analyzed
by varying the radii of metallic rods and lattice constants
using the FDTD method and a three-dimensional (3D)
full-wave electro-magnetic solver, ansoft HFSS
[15]
.A se-
ries of compact waveguide bandpass filters employing 2D
metallic photonic crystals for THz range are designed. A
prototype of MPC filter with a central frequency of 145.5
GHz and a 3-dB bandwidth of 5.26 GHz is simulated and
measured in the region of 100–150 GHz.
Band diagrams provide a quick overview of the most
important properties of photonic crystals. Figure 1(a)
shows the normalized band diagram of a square lattice
MPC obtained by FDTD. Only the first and second
TM modes are given along Γ − X direction with r and
a being the radius and lattice constant and rod ratio
t = r/a=0.26. It can be seen that the first mode shows
a passband characteristic, if selecting a=1.43 mm. The
passband frequency varies from 128 to 142 GHz.
The simulation model is symmetrical along the center
rods which are named as rod “1”, “2”, and “3”, with
rod ratios t
1
= t
2
= t
3
=0.26, resp ectively, as is shown
in Fig. 1(b). The number of rods of a single lattice is
expressed as N
y
,andN
y
=5. The box is defined as air
material with width L
x
= a,lengthL
y
=5a, and height
L
z
=0.5a. The rod is defined as perfect metal with ra-
dius r =0.26a. As for boundary conditions
[16]
,theyz
and xy planes on each side of the box are assumed to b e
perfect magnetic conductor (PMC) and perfect electric
conductor (PEC), respectively, and the xz planes are set
as waveports.
In order to achieve the fundamental structure of a
band pass filter with central frequency 145 GHz, opti-
mization of rod ratios and MPC periodicity N
y
toward
the transmission direction in a single slab is performed
Fig. 1. (a) Band diagram of the first and second modes along
Γ − X direction. (b) Simulation model for metallic TM pho-
tonic crystals.
1671-7694/2014/040401(4) 040401-1
c
2014 Chinese Optics Letters