IEEE Microwave Magazine - May 2017 - 116

copper foil as radiating elements and feed lines [53].
A three-step fabrication procedure for the antenna is
shown in Figure 7. The copper foil is laser micromachined using optimized laser parameters. In addition
to bending and crumpling assessments, the influence
of human body proximity was experimentally investigated using a semisolid phantom emulating the dielectric properties of human skin.

Antenna-to-Transmitter/Receiver Front-End
Integration Technologies
It is difficult to achieve flexible integration of printedcircuit devices with clothing using standard printed
circuit boards (PCBs) because the porosity and high
surface roughness of textiles make efficient and reliable
printing of electronics on them extremely challenging.
An option to overcome this has been proposed in [63]
using an interface layer known as "doctor blading,"
which preserves the natural elasticity of the clothing.
This results in a complete localization of the circuit
and antenna. The interface layer method is suitable

(1)
Textile (εr , tanδ )

Flexible
Copper Foil
Shieldlt

(2) Laser Ablation

Removing

(3)

for production of smart fabrics from any textile material using manual screen printing. Stencils made of
0.3-mm-thick polyethylene terephthalate (PET) film
are used for the screen printing. The PET stencil is
placed on top of the fabric textile and CM116-20 dielectric paste is poured onto the stencil. The resulting
device was field tested on a human body and showed
a communication range of up to 55 m and a localization accuracy of up to 8 m.
A single-chip solution by means of component integration onto wearable devices is proposed using 0.18-μm
complementary-metal-oxide-semiconductor RFIC-onchip antenna technology [64]. This technique realizes a
printed meander-line loop antenna for 1.575 and 2.4 GHz
wireless communication for a wristwatch application.
The antenna is 970 x 750 nm 2 and integrated into a
chip of 1.21 mm2 (1.1 mm x 1.1 mm). A transmit/receive
switch is also connected to the low-noise amplifier and
power amplifier, respectively. This solution indicated a
linear measured phase distribution and a quasi-omnidirectional H-plane pattern.
In addition, feed-structure modifications for a patch
antenna may enable ease of integration with other
components within the communication system. One
example of this is the integration of a magnetically coupled antenna into active circuitry using a transformerbased feeding topology [40], as shown in Figure 8. Its
primary and secondary windings can be implemented
directly onto the wearable antenna while avoiding
galvanic contacts between the antenna and the active
circuitry. Such design maximizes the power transfer
between the antenna and the load connected to the
secondary winding.

mmW Antennas for 5G Applications
Figure 7. The main steps in manufacturing printed
circuits and antennas on textiles in the V-band [53].

Black Foam
Flectron
Patch Antenna
Flectron
Ground Layer
Primary Winding
(a)

(b)
(c)

(e)

(d)

Pyralux with
Secondary
Winding and
U.FL Connector
Windings
Assembled
with Tape
Bi-Adhesive
Tape

Figure 8. Prototypes of an antenna-transformer: the (a) front,
(b) back, (c) top, and (d) bottom views using Pyralux with a
secondary winding and U.FL connector; and (e) an assembled
prototype using bi-adhesive tape [40].

116

Despite their increased fabrication complexity, multielement antennas such as Yagi-Uda and arrays are
envisioned for off-body communication in 5G, especially in the mmW bands. An example of such arrays
is the small textile Yagi-Uda antenna proposed in [29]
with an end-fire pattern for 6- GHz band operation. In
addition, an end-fire wearable Yagi-Uda antenna operating at 57-64 GHz was characterized in free space, on
a phantom, and under bending conditions [50]. This
antenna consists of a driven dipole and ten directors
printed on top of a cotton substrate. Its propagation
was studied in a realistic communication scenario
where the antenna was placed on a human hand along
with an off-body antenna, and satisfactory performance was maintained under bending and in planar
conditions. The antenna's reflection and radiation performance were measured in free space and on a skinequivalent phantom. Besides this, a slotted antenna
array featuring switched-beam operation at 28.5 GHz
was designed and presented in [41]. This antenna consists of two main parts: the beamforming network
and the planar array, as shown in Figure 9. The Butler

May 2017

Table of Contents for the Digital Edition of IEEE Microwave Magazine - May 2017