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Millimetre-Wave Intelligent Antennas for Wireless Systems
Qi Luo*, Zhang Long*, Steven Gao*
*School of Engineering and Digital Arts, University of Kent (q.luo@kent.ac.uk; s.gao@kent.ac.uk)
Introduction
Millimetre-wave intelligent antennas attract increasing interests for their applications in wireless systems
including satellite and mobile broadband communications [1, 2]. For an intelligent antenna system, a high
efficiency array antenna with beam steering or switching capability is always desirable. Several
millimetre-wave array antennas have been reported for the application of intelligent antenna, including
direct radiating beam-steering array using millimetre-Wave Radio over Fibre [3], multi-layered reflectarray
[4], antenna system based on substrate integrated waveguide (SIW) technology [5] and etc.
In this paper, two millimetre-wave array antennas that are suitable for the intelligent antenna systems are
presented. One is a beam-steering folded reflectarray (FRA) and the other one is a beam switching
array-fed reflector (AFR).
Beam-steering folded reflectarray with large scan angles
Fig.1 presents the configuration of the beam-steering FRA and the layout of the array unit cell [4]. The
array element is a dual-polarized slot antenna with multi-layered PCB structure and the FRA is designed
to operate at 29.5-30.8GHz band for both transmitting and receiving with single linear polarization. The
objective of this work is to design a reflectarray that is capable of scanning its beam within large angle
range and continuous beam steering can be obtained after the FRA is integrated with the monolithic
microwave integrated circuit (MMIC) and phase shifters. To realize the wide scan angle, Vias are
introduced on the antenna elements in order to to suppress the surface wave propagation and reduce the
mutual coupling between adjacent array elements spaced by 0.5λ30GHz. The measured radiation pattern
of the passive demonstrators consisting of 116 elements are shown in Fig.1.The experimental results
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show that the presented reflectarray is capable of steering the beam up to ±60 in both E- and H-planes.
2.4mm
E
Polarizer
Vias
E
Back
drilling
holes
5mm
1.9mm
Printed
reflectarray
Feed
Stripli
nes
4.6mm
E
MMIC
Slot
antenna
E
Phase
shifter
MMIC
Fig.1: The configuration of the beam-steering folded reflectarray, the layout of the unit cell and measured radiation patterns with
different beam scanning angles
Beam-switching array-fed reflector with an interleaved feeding array antenna
Fig.2 presents the configuration of the interleaved array antenna for a beam-switching AFR. The feeding
array is designed to operate at dual frequency band within K band with circular polarizations. Equilateral
triangular patches of two different sizes are grouped into a subarray with Hexagonal configuration: three
for higher band and three for lower band. Shielding vias were introduced to increase the isolation
between adjacent subarrays. Then, seven subarrays forms a feeding cluster in a septet configuration as
demonstrated in Fig.2.
The single patch is fed by two microstrip lines connected to the outputs of the branch line coupler which
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provides the desired 90 phase shift to excite the CP waves [6]. To evaluate the beam-switching
performance of the AFR, the radiation pattern of the feeding cluster was used as the feeding source of a
reflector with diameter of 300mm. The simulated beam-switching performance of the AFR in symmetry
plane at 20.1GHz by de-focusing the feed array is given in Fig.2. As can be seen, the beam can be
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switched to ±15 with small gain variation. With the subarray concept, the number of the RF chain
required can be reduced by a factor of three.
Vias
3
Antenna
for band 2
1
6
4
2
7
5
Be
am
f or
mi
ng
net
wo
rk
Antenna
for band 1
Fig.2: The layout of the feeding array for a beam-switching AFR and simulated radiation patterns of the AFR with different
beam scanning angles
Conclusion
In this paper, some recent developments in millimetre-wave intelligent antennas for the advanced
wireless system have been presented. Two array antennas, including one linearly polarized Ka-band
folded reflectarray with wide-angle beam steering capabilities for and one K-band circularly polarized
beam-switching array-fed reflector are described. Both of these two array antennas show promising
radiation performance with reduced system complexity compared to the conventional direct radiating
arrays.
Acknowledgement
The authors acknowledge the financial support through EC FP7 program under the FLEXWIN (contract
number 257335) and GANSAT (contract number 606981) project.
References
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2
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3
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(MWP), pp. 130-133, 2013.
4
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5
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6
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