1

Bo Li and Yiming TangSchool of Electronic Science and Engineering

Nanjing University of Posts and TelecommunicationsNanjing, China 210003

Zhongxiang Shen*School of Electrical and Electronic Engineering

Nanyang Technological UniversitySingapore 639798

Email: ezxshen@ntu.ed.sg

3D Frequency Selective StructuresUsing Multilayer PCBs

Forum for Electromagnetic Research Methods and Application Technologies (FERMAT)

This use of this work is restricted solely for academic purposes. The author of this work owns the copyright and no reproduction in any form is permitted without written permission by the author. *

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Recently, a new class of frequency selective surfaces, named as 3D frequency selectivestructures (FSSs), are reported in order to achieve high performance, such as sharp roll-off and wide out-of-band rejection. In these 3D FSS designs, multiple resonators areconstructed, providing a number of transmission zeros/poles at finite frequencies. Highperformance can then be obtained by controlling locations of these transmissionzeros/poles. However, the major disadvantage of these 3D FSSs is their complicatedtopologies. Most of them require extra assembly process after fabrication, which willincrease undesirable errors and uncertainties.

In this talk, a number of 3D FSSs implemented by using multilayered PCB technologyare presented. These structures are full printed circuits, which can be fabricated withoutassembly, thus leading to higher fabrication accuracy and suitable for mass production. Itis therefore feasible for this type of FSS to be applied at high frequency applications, suchas millimeter-wave systems.

Keywords – 3D frequency selective structures, printed circuit board, spatial filters.

Abstract

3

Outline• Background

– Brief Introduction to Frequency Selective Surfaces– Typical Frequency Selective Surfaces and Their Shortcomings

• 3D Frequency Selective Structures (FSSs)– Concept– Existing 3D Designs– Our Previous Work

• 3D FSSs Using Multilayered PCBs– Double-Layer Bandstop Design– Miniaturized-Element Design– Dual-Polarized Design

• Future Work & Conclusions

• Definition: a surface construction designed as a “filter” for plane waves– Frequency/angular response– Bandpass and bandstop performances– Typically a two-dimensional periodic surface

• Design Parameters– Element spacing– Element shape– Element dimensions

• Applications– Radome– Sub-reflector– Lens

4

What is Frequency Selective Surface?

5

Two Typical Frequency Selective Surfaces

• Single-Layer Surfaces– Strip resonators

– Slot resonators

5 10 15-50

-40

-30

-20

-10

0

Frequency (GHz)

S-pa

ram

eter

s (d

B)

|S21|

|S11|

5 10 15-50

-40

-30

-20

-10

0

Frequency (GHz)

S-pa

ram

eter

s (d

B)

|S21|

|S11|

Disadvantages of Traditional Surfaces

• Limited bandwidth: based on one resonance• Large cell size: typically half a wavelength so that it can

resonate. This large cell size results in poor angular response.Munk [1] used two slabs to alleviate the angular sensitivity.Others used miniaturized elements [2].

• Poor filtering response: maximally flat or Butterworth-typefiltering response can be achieved.

6

3D Frequency Selective Structures (FSSs)

It is possible to include multiple mode resonances. N different paths can generate N reflection zeros. Increased coupling to multiple modes results in high performance.

Generalized Circuit ModelGeneralized Topology [3]

7

8

Existing 3D FSS Designs (1)• SIW Structure [4, 5]: • Cylindrical Ring Structure [6]:

9

Existing 3D FSS Designs (2)

• Apertured Cavity Structure [7]: • Crossed Dipole + Waveguide Structure [8]:

Microstrip-Line Based 3D FSSDescription of the Structure

– Two-dimensional periodic array of stacked microstrip lines

4 6 8 10 12 14 16-40

-30

-20

-10

0

Frequency (GHz)

|S21

| (dB

)

= 0o

= 20o

= 40o

= 60o

Full-waveanalysis

Measurement ( = 0o, 40o)

5 10 15-40

-30

-20

-10

0

Frequency (GHz)

|S21

| (dB

)

= 0o

= 20o

= 40o

= 60o

Measurement = 40o

Measurement = 0o

• Wide-Band Design [9] • Narrow-Band Design [9]

Dielectric constant. Strip width to horizontal period ratio t/b. Substrate height to vertical period ratio

d/h.

10

Miniaturized-Element Bandpass FSSDescription of the Structure

Region 2

Metallic plateMetallic rod

Printed copper

Substrate

z

y

x

Ey

Hk

Region 2Region 1

Met

allic

pla

te

Met

allic

pla

te

h

Ey kH

Sim. = 0o

Sim. = 40oMeas. = 0o

Meas. = 40o

5 10 15 20 25 30Frequency (GHz)

-60

-50

-40

-30

-20

-10

0

Mag

nitu

de (d

B)

|S11|

|S21|

1.5 3 4.5-40

-20

0

Frequency (GHz)

Mag

nitu

de (d

B)

0

Advantages [10]: The unit cell size and thickness of the single-polarized

bandpass FSS is 0.060 × 0.0450 × 0.0960 (0 isthe free-space wavelength at the center frequency).

The FSS exhibits an excellent upper stopbandsuppression of 2f0 to 6f0 harmonics.

b

l

11

x

y

z k

Dual-Polarized Bandpass FSSDescription of the Structure

Metallic plate

Rod

Horizontal DSPSL

Vertical DSPSL

Via hole

Stub

Stub

4 6 8 10 12 14 16 18-40

-30

-20

-10

0

Frequency (GHz)

Mag

nitu

de (d

B) |S21|

|S11|

TE Polarization

4 6 8 10 12 14 16 18-40

-30

-20

-10

0

Frequency (GHz)

Mag

nitu

de (d

B)

|S21|

|S11|

TM Polarization

Measured = 0oMeasured = 20oSimulated = 0o

Measured = 40o

Printed strip

y

xz

k

Metallic plate

Via hole

12

Advantages [11]: The designed FSS has a relative 3dB passband bandwidth of 18.4% and a

bandwidth of about 78.4% for the out-of-band rejection better than 20dB. Dual-polarization is realized.

Problems & Solution

Problems:

Not all printed structures

Assembly procedures are needed

Large thickness

Solution: Multilayered printed circuits

Double-layer bandstop design

Miniaturized-element design

Dual-polarized design

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Double-Layer Bandstop DesignSimulated Result:

6 8 10 12 14-40

-30

-20

-10

0

Frequency (GHz)

Mag

nitu

de(d

B)

|S21||S11|

f1 f2 f3 f4

z

xTop layer

Bottom layerSubstrateVia hole

Side View

z

x y

k

f

Substrate

Via holes

Cross dipole array

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Advantages: Wideband bandstop filtering response

with sharp roll-off. Full printed circuits.

Description of the Structure

Miniaturized-Element Design

*B. Li and Z. Shen, IEEE Antennas Wireless Propag. Lett. vol. 13, pp. 145-148, 2014.

Original Structure (A Unit Cell) Multilayer Structure (A Unit Cell)

z

y

x

Ey

H k

Layer ALayer B

Layer C

d2

d1 Substrates 2 and 3Via holes

Layer B'

Printed copper

d1

d2

Substrates 1 and 4

Layer A'

kx

y

z

Ey

H

(a) Layer A and A' (b) Layer Cr2 r1

D

h1

h2

x

y

(c) Layer B and B'

x

y

x

y

Metallic plateMetallic rodPrinted patch

Printed patch

Metallic plate

Metallic rod

Via holes

Layer B and B′

Layer C

εr1εr2

εr2

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Odd-mode Excitation

(f2)

1

Z2 Z1

1

Z2 Z1

2LEven-mode Excitation

(f1)

L

Z2 Z1 Z1 Z2

1 2

Stepped-Impedance Resonators

Operating Principle

1 2

zy

Layer B′Layer C

Layer BLayer A Layer A′

1 2

Layer B Layer B′Layer CLayer A Layer A′

zy

E-field distributions at f1 and f2

5 10 15 20 25 30 35Frequency (GHz)

Mag

nitu

de (d

B)

0-50

-40

-30

-20

-10

0

|S21||S11|

f1 f2

16

5 10 15 20 25 30 35Frequency (GHz)

Mag

nitu

de (d

B)

0-50

-40

-30

-20

-10

0

θ =60°

θ =0°θ =30°

S21S11

f1

f2

Simulated Results

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Advantages:

▪ The unit cell size and thickness of the bandpass FSS is 0.070 × 0.050 × 0.10 (0 is thefree-space wavelength at the center frequency).

▪ The FSS exhibits an upper stopband suppression of 2f0 to 6f0 harmonics.▪ Full printed circuits.

εr1 =2.2, εr2 = 3.55, d1 = 1.016mm, d2 =2.078mm, h1 = 3mm, h2 = 4.2mm, r1 = 0.3mm,r2 = 0.3mm, D = 0.3mm, w = 0.85mm

Original Structure (A Unit Cell)

Dual-Polarized Design

y

xz

k

d1

Layer A

Layer B

Layer CLayer B′

Layer A′

Printed copper

Via holesSubstrates

d2

d3

d4

Multilayer Structure (A Unit Cell)

*B. Li and Z. Shen, IEEE Trans. Antennas Propag., vol. 62, no. 1, pp. 130-137, 2014.

y

xz

k

w1t5

D

xy

w2

xy

pl1

t1 t2 t3 t4

xy

(a) Layer A and A' (c)Layer C(b) Layer B and B'

Printed strip

Metallic plate

Via holes

Via holes

Layer B and B′

Layer C

Metallic plate

Via hole

Printed strip

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Current Distributions

8 10 12 14 16 18 20-50

-40

-30

-20

-10

0

Frequency (GHz)

Mag

nitu

de (d

B)

= 0o

= 30o

= 60o

|S21|

|S11|

f1

f2

f3f4

TE Polarization

8 10 12 14 16 18 20-50

-40

-30

-20

-10

0

Frequency (GHz)

Mag

nitu

de (d

B)

= 0o

= 30o

= 60o|S21|

|S11|

f1

f2

f3f4

TM Polarization

yz

E

kH

yz

E

kH

Layer A Layer BLayer C

Layer B′ Layer A′

yz

E

kH

yz

E

kH

Current Distributions:

At f1: At f2:

At f3: At f4:

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r = 3.55, d1 = 1.93mm, d2 = 0.813mm, d3 = 0.406mm, d4 =2.337mm, p = 5mm, t1 = 0.25mm, t2 = 0.35mm, t3 = 0.5mm, t4 =1.83mm, t5 = 0.6mm, w1 = 4.3mm, w2 = 1.7mm, l1 = 2.93mm, D= 0.3mm.

Layer A Layer BLayer C

Layer B′ Layer A′

Measurement

8 10 12 14 16 18-40

-30

-20

-10

0

Frequency (GHz)

|S21

|(dB

)

= 0o

= 30o

= 45o

8 10 12 14 16 18-40

-30

-20

-10

0

Frequency (GHz)

|S21

|(dB

)

= 0o

= 30o

= 45o

TE Polarization

TM Polarization

Photo:f1 f2

f3 f4

f1 f2

f3 f4

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Advantages:

▪ Dual-polarization.▪ Full printed circuits.

Future Work

Design of other multilayered 3D FSSs (dual-band ormulti-band response, dual-polarized bandpass andbandstop structures).

Thickness reduction by using Low Temperature Co-fired Ceramic (LTCC).

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Conclusions

A number of 3D bandpass FSSs based on multilayered PCBtechnology have been presented.

Compared with the previous microstrip-line based 3D FSSs, thistype of FSS can be fabricated without assembly, thus leading tohigher fabrication accuracy.

It is also easier for this type of FSS to be scaled to high frequencyapplications, such as millimeter-wave systems.

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References[1] B. A. Munk, Frequency Selective Surfaces: Theory and Design. John Wiley & Sons Inc., 2000.[2] K. Sarabandi and N. Behdad, “A frequency selective surface with miniaturized elements,” IEEE Trans.

Antennas Propag., vol. 55, no. 5, pp. 1239-1245, 2007.[3] A. K. Rashid, B. Li, and Z. Shen, “An overview of three-dimensional frequency selective structures,”

IEEE Antennas and Propagation Magazine, vol. 56, no. 3, pp. 43-67, 2014.[4] G. Q. Luo, et al., “High performance frequency selective surface using cascading substrate integrated

waveguide cavities," IEEE Microwave and Wireless Components Letters, vol.16, pp. 648-50, 2006.[5] G. Q. Luo, et al., “Design and experimental verification of compact frequency-selective surface with

quasi-elliptic bandpass response," IEEE Trans. Microwave Theory Tech., vol. 55, pp. 2481-2487, 2007.[6] S. N. Azemi, K. Ghorbani, and W. S. T. Rowe, “A reconfigurable FSS using a spring resonator element,”

IEEE Antennas Wireless Propog., vol. 12, pp.781–784, 2013.[7] X. Huang, C. Yang, Z. Lu, and P. Liu, “A novel frequency selective structure with quasi-elliptic bandpass

response,” IEEE Antennas and Wireless Propag. Lett., vol. 11, pp. 1497-1500, 2012.[8] C. Pelletti, G. Bianconi, R. Mittra, and Z. Shen, “Frequency selective surface with wideband quasi-

elliptic bandpass response,” Electron. Lett., vol. 49, no. 17, pp. 1052-1053, 2013.[9] A. K. Rashid and Z. Shen, “A novel band-reject frequency selective surface with pseudo-elliptic

response,” IEEE Trans. Antennas Propag., vol. 58, no. 4, pp. 1220-1226, 2010.[10] B. Li and Z. Shen, “Bandpass frequency selective structure with wideband spurious-rejection,” IEEE

Antennas Wireless Propag. Lett. vol. 13, pp. 145-148, 2014.[11] B. Li and Z. Shen, “Three-dimensional dual-polarized bandpass frequency selective structures with

wide out-of-band rejection,” IEEE Trans. Antennas Propag., vol. 62, no. 1, pp. 130-137, 2014.

Thank you very much!