A Ku band 4×1 linear slot array antenna design based on recently developed gap waveguide technology is presented. The complete antenna has been built using two parallel plates where the bottom metal plate has the guiding ridge and periodic pins and the top metal plate is smooth. The antenna feed network consists of power dividers has been realized on the bottom metal plate, and the radiating slots are placed on the top metal plate. Design and simulation results of the linear array show that it is possible to have a slot array antenna with 20 % bandwidth based on ridge gap waveguide technology

Kildal, Per-Simon

Zaman, Ashraf Uz

A Ku band 4
71 linear slot array antenna design based on recently developed gap waveguide technology is presented. The complete antenna has been built using two parallel plates where the bottom metal plate has the guiding ridge and periodic pins and the top metal plate is smooth. The antenna feed network consists of power dividers has been realized on the bottom metal plate, and the radiating slots are placed on the top metal plate. Design and simulation results of the linear array show that it is possible to have a slot array antenna with 20 % bandwidth based on ridge gap waveguide technology

Uz Zaman, Ashraf

Chalmers Research

Ku band linear slot-array in ridge gapwaveguide technology

Chalmers Publication Library

Chalmers Publication Library
Ku band linear slot-array in ridge gapwaveguide technology
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2013 7th European Conference on Antennas and Propagation, EuCAP 2013
Citation for the published paper:
Zaman, A. ; Kildal, P. (2013) "Ku band linear slot-array in ridge gapwaveguide technology".
2013 7th European Conference on Antennas and Propagation, EuCAP 2013 pp. 3078-3081.
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Ku Band Linear Slot-Array in Ridge Gapwaveguide 
Technology 
 
Ashraf Uz Zaman 
Department of Signals and System 
Chalmers University of Technology 
SE- 41296, Göteborg, Sweden 
zaman@chalmers.se 
Per-Simon Kildal 
Department of Signals and System 
Chalmers University of Technology 
SE-41296, Göteborg, Sweden 
per-simon.kildal@chalmers.se
 
 
Abstract— A Ku band 4×1 linear slot array antenna design based 
on recently developed gap waveguide technology is presented. 
The complete antenna has been built using two parallel plates 
where the bottom metal plate has the guiding ridge and periodic 
pins and the top metal plate is smooth. The antenna feed network 
consists of power dividers has been realized on the bottom metal 
plate, and the radiating slots are placed on the top metal plate. 
Design and simulation results of the linear array show that it is 
possible to have a slot array antenna with 20 % bandwidth based 
on ridge gap waveguide technology.   
Keywords- Slot array antenna, corporate-feed, T-junction, 
Ridge gapwaveguide, Artificial Magnetic Conductor (AMC). 
I.  INTRODUCTION  
Planer waveguide slot array antennas and microstrip patch 
array antennas have been used in many microwave 
applications since 1970s. Typical printed antennas can be 
compact and lightweight and offer low cost, but these types of 
antennas have low efficiency due to dielectric and conductive 
losses at high frequencies. Also, when a printed antenna array 
is built for high gain or multiple beam applications, the 
antenna efficiency decreases even more because of increased 
losses in the feeding network. The problems of unwanted 
surface waves are also associated with these type of printed 
antennas [1-2]. Rectangular waveguide slot array antennas do 
not suffer from the above disadvantages, and is therefore an 
attractive candidate for high frequency applications requiring 
high gain [2-4]. However, waveguide slot arrays have typically 
very complex feed networks under the radiating slots, and 
manufacturing costs are high at high frequency due to the 
requirements of electrically tight contacts between the slotted 
plate and the feed structure [5]. Apart from the cost of the 
waveguide array itself, the integration of high frequency 
MMIC with rectangular waveguide is very challenging at high 
frequencies [6-7].  
The recently proposed ridge gapwaveguide technology [8-9] 
can be a real solution to above mentioned problems and can be 
applied very successfully to design good performance 
antennas at high frequency. The gap waveguide is realized 
using the parallel plate cut-off condition between a PEC layer 
(perfect electric conductor) and PMC layer (perfect magnetic 
conductor). So, the waveguide has a smooth upper metal 
surface and a lower surface with a ridge surrounded by bed of 
nails. The air gap between upper metal surface and the lower 
metal ridge is kept smaller than λ/4. With the help of this new 
gapwaveguide concept, it is possible to excite the local quasi 
TEM wave between upper metal surface and the ridge in such 
a way that this mode exists over a larger bandwidth without 
the presence of global parallel plate modes.  
The low loss corporate feed network needed for an array 
can be built easily with the help of ridge gap waveguide 
concept with an inherent advantage of having no dielectric 
losses. Also the width of the line itself can be adjusted in a way 
that conductor losses can be reduced. The strip dimensions 
cannot be increased in normal microstrip feed lines because 
then the substrate supports surface waves, which is not present 
at all in gap waveguides. In addition, radiating slots can be 
placed conveniently on the top smooth metal plate of ridge gap- 
waveguide. There is also no requirement on good electric 
contact between the slotted plate and the feed structure. Thus, 
the ridge gapwaveguide slot antenna can be an attractive as 
well as cost effective solution for high gain and high efficiency 
applications. 
Till now, there have been very few papers on gap 
waveguide antennas, except for horn antennas [11], the initial 
works in single hard-wall waveguide slot arrays [12] and the 
single slot design in ridge gapwaveguide [13]. Also, a multi-
layer phase array antenna for automotive radar application has 
been presented in [14]. In the present paper we present a 4×1 
linear slot array excited by ridge gapwaveguide. We consider 
fully radiating slots corresponding to using fully branched 
distribution network, i.e. a corporate-feed network. The spacing 
between the slots is kept at 17mm corresponding to about 0.85λ 
to avoid grating lobes.  
II. ANALYSIS OF ISOLATION BETWEEN THE ELEMENTS 
The periodic pin structure need for realizing the artificial 
magnetic conductor (AMC) is designed first. The dimensions 
chosen for this work are based on the design curves in [15] and 
corresponding dispersion diagram showing the parallel-plate 
stop band is presented in fig.1. After that, two ridge gap- 
waveguide structures with two radiating slot elements 
presented in [13] are placed side by side with only one row of 
pins spaced between the elements in order to measure the 
achieved isolation between the adjacent elements in the ridge 
gapw
enou
adjac
Still,
than 
isola
 
aveguide arr
gh room for
ent slot elem
 this one row
20dB betwe
tion results ar
 Fig. 1. Dispe
structur
Waveguid
port 1
Fig. 2. Tw
Fig. 3. Sim
ay. This is 
 more than 
ents to maint
 of pins prov
en the adja
e shown in fig
rsion diagram f
e;  a = 2 mm, h
e
Waveguide
port 2
o slot elements
ulated isolatio
shown in fig
one row of 
ain the spacin
ides an isolat
cent element
.3.  
or unit-cell of p
 = 1mm and d =
 separated by o
n between two
.2. There is
pins between
g of about 0
ion level of m
s. The simu
eriodic metal p
 6mm.  
Waveguide
port 3
ne row of pins
adjacent slots
 not 
 the 
.85λ. 
ore 
lated 
 
in 
 
 
 
The 
pres
T-se
The 
12-1
11.7
to m
of ro
this 
be s
desi
sam
on th
T
S
11
(d
B
)
    T
elem
III.
simple linear
ented in [13]
ction with th
single slot el
4GHz. The 
5 and 5.85 m
ake sharp cor
unded corne
frequency ba
o severe. A
gned in ridg
e frequency. 
e single T- ju
Bottom plate wit
Texture and Guiding
op Metal Plate with
2mm thickness
Fig. 4. 
S
11
  (
d
B
)
Fig. 5. S
he linear array
ent spacing c
LINEAR SL
 slot array d
. The single s
e ridge just 
ement is work
slot-length an
m respective
ners for each 
r is not consi
nd the effect 
lso, four-way
e gapwavegu
The four-way
nction 3dB p
h Pin 
 Ridge
 
 Linear array in
Frequ
imulated return
 is designed f
an be kept 0
OT ARRAY  DE
esign starts w
lot design is 
below the r
ing within th
d slot-width
ly. It is pract
slot. But, at t
dered and it 
of the round
 equal split 
ide technolog
 power divid
ower divider 
4
 gap waveguid
ency (GHz)
 loss for the lin
 
or a fixed bea
.85λ to avoid
SIGN 
ith the single
based on add
adiating struc
e frequency r
are chosen 
ically not pos
his point the e
is expected th
ed corner wi
power divid
y to work a
er design is b
presented in [
 way Power Divider
4 Radiating Slo
e technology 
ear array 
m in mind. S
 grating lobe
 slot 
ing a 
ture.  
ange 
to be 
sible 
ffect 
at at 
ll not 
er is 
t the 
ased 
13].  
ts
 
 
o, the 
s and 
all the slot elements are excited with equal amplitude and 
phase. The complete array is shown in fig.4 and it is designed 
to operate in 12-14GHz frequency range. As shown in fig.4, the 
bottom plate with ridge and texture pin structure holds the 
feeding network for the array. On top is placed a smooth metal 
plate with four radiating slots at a distance of 1 mm from the 
bottom plate. It is important to mention that- no electrical 
contact between the radiating layer and bottom feed layer is 
needed in this ridge gapwaveguide array which is a significant 
advantage of this technology. The simulated reflection 
coefficient for the linear array is shown in fig. 5 and simulated 
radiation patterns are shown in figure 6(a) and 6(b). 
 
 
Fig. 6 (a). Simulated H-plane pattern of the linear array at 13GHz 
 
Fig. 6 (b). Simulated E-plane pattern of the linear array at 13GHz 
The simulated S-parameter value in fig.5 shows good 
impedance bandwidth from 11.5-14.5 GHz with a relative 
bandwidth of more than 20% around the center frequency of 
13GHz. The simulated radiation patterns shown in fig.6 are 
also quite acceptable. As expected, the array has more directive 
beam and symmetric pattern in H-plane. In H-plane, the first 
side-lobe is 12.8 dB lower from the beam peak value which is 
also common for uniform arrays. On the other hand, in E plane 
the beam is wider and is not really symmetric as the slots are 
close to the edge on one side. In E-plane, there is a possibility 
of back radiation as the slots are close to the edge. This is 
shown in the 3D far field pattern in fig.7.  But the level of back 
radiation can be improved by adding 2 or 3 corrugations being 
quarter wavelength deep at the lowest frequency of operation. 
These corrugations are not included in this work but will be 
incorporated in the final design. The simulated directivity value 
is 12.4 dBi and the simulated total efficiency is -0.12 dB at the 
center frequency of 13GHz. The radiation efficiency and total 
efficiency for the antenna over the band of interest are plotted 
in fig.8. It is needed also a transition from ridge gapwaveguide 
to the standard coaxial SMA connector for measurement of the 
entire antenna. This transition can be a simple interface 
consisting of steps in ridge which allows the Quasi TEM mode 
to convert to a groove gapwaveguide mode (similar to that of 
standard rectangular waveguide mode). Then we can connect 
easily with a SMA connector with an extended center 
conductor.  
  
Fig. 7. Simulated 3D radiation pattern and possible back radiation 
at 13GHz. 
 
Fig. 8. Simulated radiation efficiency and total efficiency for the 
linear array. 
11 12 13 14 15
-3
-2.5
-2
-1.5
-1
-0.5
0
Frequency ( GHz)
 E
ffi
ci
en
cy
  (
dB
) 
 
 
radiation efficiency
total efficiency
IV. CONCLUSION 
We have presented a linear slot array antenna based on 
ridge gap waveguide technology. The low-loss corporate feed 
network is designed on the bottom metal plate with guiding 
ridge and periodic pins, and above the ridges there are radiating 
slots in the top metal plate. These two parts of the ridge 
gapwaveguide antenna can be manufactured separately and 
there is no need for an electrical contact between these two 
parts, thus making it much simple and lower cost to 
manufacture. The simulated S-parameters and radiation 
patterns show promising results for the linear array at Ku-band 
from 11.5-14.5 GHz.  Though presented at Ku band, ridge 
gapwaveguide technology is very suitable for this type of single 
layered corporate feed array antenna even at millimeter-wave 
frequency range. Measured results for the designed linear array 
will be presented at the conference. 
 
Acknowledgment 
This work has been supported by the Swedish Research 
Council VR and by the Swedish Governmental Agency for 
Innovation Systems (VINNOVA) within the VINN Excellence 
Center Chase. 
 
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Ku band linear slot-array in ridge gapwaveguide technology

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