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A 2-layer 45° -Slant-Polarised Phased Array Antenna with Baffles Based on Gap Waveguide Technology for mmWave 5G Systems



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A 2-layer 45-Slant-Polarised Phased Array
Antenna with Baffles Based on Gap Waveguide
Technology for mmWave 5G Systems
Gerolf Meulman1, Alireza Bagheri1,2, Andr´
es Alay´
on Glazunov1,3
1University of Twente, Enschede, Netherlands
2Gapwaves AB, Gothenburg, Sweden
3Chalmers University of Technology, Gothenburg, Sweden
Corresponding author,
Abstract—A 45slant-polarised gap waveguide phased array
antenna designed with focus on mmWave 5G is presented.
Baffles are used to reduce grating lobes. The total efficiency of
the array is greater than 0.7dB, and the average broadside
gain is 24.2dBi in the band from 26.529.5GHz.
Keywords—Gap-waveguide, Phased array, mmWaves, 5G
The 5th generation (5G) communication systems will also
operate on millimeter Wave (mmWave) frequency bands
in order to satisfy the demands for higher data rates. For
example, the 26.529.5GHz band will be used in several
countries, e.g., the USA, Japan and South-Korea. On one
hand, the number of antenna elements required to direct
energy to a user is large, while on the other hand the
array antennas need to have a small form-factor and a low
manufacturing complexity in order to keep costs low.
Slotted waveguide array antennas are well-known to pro-
vide high-gain, high-efficiency and low-profile antennas.
Their flat structure, low weight and the possibility to use
electronic steering to rapidly change the main beam direction
make these antennas attractive for many applications [1]. An
important issue with slotted waveguide antennas at mmWave
frequencies is the complex manufacturing process. This may
result in very high costs and to leakage if the gaps between
different parts are not fully sealed. One proposed solution is
to use a substrate integrated waveguide (SIW) [2]. One of the
drawbacks of a SIW antenna is the increased dielectric loss
due to the substrate. A way to remedy the leakage without
using a substrate is the gap waveguide technology. The gap
waveguide technology has emerged as an excellent candidate
to provide a fair trade-off between cost and manufacturing
complexity [3].
To reduce manufacturing complexity the antenna is de-
signed with only two layers. Fig. 1 shows the gap-waveguide
distribution and the radiation layers. The distribution layer
is fed from the middle, which functions as a H-type T-
junction, and includes a wedge. There is no cavity layer,
Fig. 1: Exploded view of (a) an element and (b) the array
so the radiation layer with slots is placed directly on the
distribution layer. The slots are slanted 45to enable the
easy addition of an orthogonal polarization when necessary.
To increase the azimuth field-of-view and the spatial
selectivity, a phased array comprising eight similar elements
is proposed. To prevent grating lobes, the maximum distance
between the elements is limited. For a scan angle of θ= 45
a maximum distance of 0.58λis allowed. In a horizontally-
oriented gap-waveguide this is not possible since the width
of the waveguide plus the width of the pins is already ex-
ceeding this value. Therefore, a vertical polarized waveguide
-80 -60 -40 -20 0 20 40 60 80
Gain [dBi]
Fig. 2: Radiation pattern of the array antenna in azimuth
plane for different scanning angles at 28 GHz.
26 26.5 27 27.5 28 28.5 29 29.5 30
Freq [GHz]
Gain [dBi]
Total efficiency
AZ 20°
AZ 40°
Fig. 3: Co-polar gain and total efficiency vs. frequency.
will be used. It is possible to create vertical gap-waveguide
structures by using a groove-gap waveguide [4]. In this case,
slots can only be placed on the waveguide every at a distance
of λfrom each other instead of 0.5λ. The former will result
in grating lobes in the elevation plane. To avoid this, a shift
of 0.5λis added to every other element. Furthermore, baffles
are used to reduce grating lobes in the D-plane [5].
The designed array antenna is simulated and optimized
using the CST MWS software. Fig. 2 shows the realized co-
polar gain patterns in the azimuth plane for different steering
angles. For the 0steering angle, the average realized gain
is 24.2dBi. Increasing the steering angle reduces the gain,
e.g., a 3dB gain drop occurs at 35. Fig. 3 shows the total
efficiency for different steering angles, which remains equal
to 0.7dB within the frequency range of interest. The effect
of using baffles can be seen in Fig. 4. A 5dB reduction,
from 6dB to 11 dB, of the unwanted grating lobe levels
relative the main lobe can be observed by comparing Fig.
4a and Fig. 4b showing the radiation patterns without and
with baffles, respectively, when scanning to a 10angle in
the azimuth plane.
A45-slant-polarised phased array antenna based on the
gap waveguide technology is proposed. The array has only
-1 0 1
-1 0 1
Fig. 4: UV-plane array radiation pattern when scanning to
10, (a) without baffles, and (b) with baffles.
two layers, the feed distribution layer, and the radiating layer
with 8elements and 6slots each. The average gain of the
array is 24.2dBi with a per-element gain of 15.2dBi in the
broadside direction, and the total efficiency is above 0.7
dB. Performance is maintained from 26.529.5GHz, which
makes it suitable for mmWave 5G applications.
Financial support was received from the WAVECOMBE
project with GA No.766231-WAVECOMBE-H2020-MSCA-
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[2] J. Puskely, Y. Aslan, A. Roederer, and A. Yarovoy. “SIW
based antenna array with power equalization in elevation
plane for 5G base stations”. In: 12th European Conference
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In: Antennas and Propagation Society Symposium 1991 Di-
gest. 1991, 1156–1159 vol.2.
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