The new microstrip gap waveguide supports a quasi-TEM mode in the air by the use of artificial magnetic conductors which force the field to travel in the air rather than in the substrate. This paper presents an evaluation of losses by measuring the Q-factor of a resonator made in this technology, made using a mushroom-type EBG surface. Losses are crucial when using printed circuits to feed slot antennas, thereby motivating this work. Comparisons with standard microstrip lines will be provided, showing promising results

Kildal, Per-Simon

Pucci, Elena

Rajo-Iglesias, Eva

Rajo, Eva

Chalmers Research

Evaluation of losses in microstrip gap waveguide for slot antennas applications

Chalmers Publication Library

Chalmers Publication Library
Evaluation of losses in microstrip gap waveguide for slot antennas applications
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2012 IEEE International Symposium on Antennas and Propagation, Chicago, USA, July 8-
14, 2012 (ISSN: 1522-3965)
Citation for the published paper:
Pucci, E. ; Rajo-Iglesias, E. ; Kildal, P. (2012) "Evaluation of losses in microstrip gap
waveguide for slot antennas applications". 2012 IEEE International Symposium on Antennas
and Propagation, Chicago, USA, July 8-14, 2012 pp. 1-2.
http://dx.doi.org/10.1109/APS.2012.6348596
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(article starts on next page)
Evaluation of Los
for Slot
Elena Pucci and Per-Simon Kild
Department of Signals and System
Chalmers University of Technolog
Gothenburg, Sweden 
elena.pucci @ chalmers.se, per-simon.ki
chalmers.se 
 
 
Abstract—The new microstrip gap waveguide s
TEM mode in the air by the use of artificial ma
which force the field to travel in the air ra
substrate. This paper presents an evaluatio
measuring the Q-factor of a resonator made in
made using a mushroom-type EBG surface. L
when using printed circuits to feed slot a
motivating this work. Comparisons with stan
lines will be provided, showing promising results
I. INTRODUCTION 
Printed slot antennas are of large intere
radar and communication systems due to their
low cost and easy manufacturing. In additi
directly adapted to the fabrication of monol
integrated circuits (MMIC) [1]. However
microstrip feeding network are often the 
limitations in antenna arrays [2]. Furthermor
appear when packaging those circuits. The re
ridge gap waveguide technology has demo
potential for applications at high frequency be
loss [3-5]. Its printed version, called microstrip
has been lately presented for packaging
components [6] and it is now considered as p
for slot arrays applications. A parametric
mushroom dimensions on the parallel-plate 
found in [7]. Therefore, this paper will go th
study, by calculating the attenuation from t
factor of a resonator made in this technology
this gap waveguide version, shown in Fig
propagation in the air, thanks to the use 
magnetic conductor, such as a mushroom-typ
which surrounds the microstrip line, forcing t
in the air gap between the strip line and upp
The idea is that this solution can be used to fe
located in the upper metal lid. 
Figure 1.  General sketch of a microstrip gap waveguide. 
ses in Microstrip Gap W
 Antennas Applications 
al 
s 
y 
ldal @ 
Eva Rajo-Igles
Department of Signal Theory an
University Carlos III o
Madrid, Spain
eva @ tsc.uc3m
upports a quasi-
gnetic conductors 
ther than in the 
n of losses by 
 this technology, 
osses are crucial 
ntennas, thereby 
dard microstrip 
. 
st nowadays for 
 compact profile, 
on, they can be 
ithic microwave 
, losses in the 
cause of gain 
e, cavity modes 
cently proposed 
nstrated a good 
cause of its low 
 gap waveguide, 
 of microstrip 
ossible candidate 
 study of the 
stopband can be 
rough the losses 
he measured Q-
. The design of 
. 1, permits the 
of an artificial 
e EBG surface, 
he field to travel 
er ground plane. 
ed slot antennas, 
 
II. LOSSES 
The losses study is done conside
[6] and shown in Fig. 2. The st
mushrooms-type EBG, sharing the 
also short circuited to the ground 
leakage of field in to the dielectric, 
in Fig. 3. It can be seen that witho
normal microstrip mode can be exc
the lower ground plane, increasing l
Figure 2.  Front view of the microstrip gap
EBG surface. 
Figure 3.  2D color plots of the absolute vale
strip (first plot) and with vias added also in th
Losses are determined by first ca
factor of the resonator. Then, the 
extracted by using the known form
being the propagation consta
manufactured and shown in Fig. 4.
length three times λ/2, is printed at t
it is surrounded by mushrooms-t
surrounding the line by mushroom
suppress any possible leakage of e
the joints of the circuit, thus measu
certain precision. The dielectric use
2.2 and tan δ= 0.0009, and the meta
measured S21 are presented in Figu
be calculated using the following eq
aveguide  
ias 
d Communication  
f Madrid  
 
.es
STUDY 
ring the design presented in 
rip line is surrounded by 
same substrate. The line is 
plane with vias, to avoid 
as shown in the color plots 
ut vias on the strip line, a 
ited, between the strip and 
osses. 
 
 waveguide on a mushroom-type 
 
 of the E-field with no vias in the 
e strip (second plot). 
lculating the unloaded Q-
attenuation can be directly 
ula [5] α = β\2QU (with β 
nt). A resonator was 
 The strip line, of resonant 
he center of the circuit and 
ype EBG. The choice of 
s in all directions is to 
nergy which can occur at 
ring the unloaded Q with a 
d is Duroid 5880, with r = 
l is copper. Simulated and 
re 5. The unloaded Q can 
uation [8], 
 
211
L
U
QQ
S
=
−
, 
where QL can be directly determined from 
taking the ratio between the resonant frequen
power bandwidth.  Using (1) the unloaded Q-f
be 974 (at fo = 9.743 GHz) from the simulate
(at fo = 9.919) from the measured result. The r
= 0.9 dB/m for the simulation and α = 1.1
measurement. The discrepancy between 
simulated Qs could be due to the sur
mechanical tolerances and impurities of the
Also, the difference between simulated and m
frequencies is because the strip was realize
whereas in simulation the vias are totally fil
affect the resonant lengths.  For comparison
transmission line of thickness t = 0.787 
materials and resonant frequency used in th
easily calculated by analytical formula [5]
dB/m, proving how this new solution is less l
microstrip lines. 
III. CONCLUSIONS 
This paper presented a study of microstrip
made with a mushrooms-type EBG surface in
The structure has low loss due to its propagati
it does not generate cavity modes when pack
to standard microstrip lines, becoming a prom
to feed slot antenna arrays. Fig. 5 shows a 
design, with the slot located on top of the met
be considered as next step of this work. 
ACKNOWLEDGEMENT 
This work has been supported by the Sw
Council VR and by the Spanish project TEC2
01. 
Figure 4.  Microstrip gap waveguide resonator prototype. 
 
(1) 
the |S21| peaks, 
cy and the 3 dB 
actor is found to 
d result and 765 
esulting loss is α 
8 dB/m for the 
measured and 
face roughness, 
 materials used. 
easured resonant 
d by via holes, 
led and this can 
s, the loss of a 
mm, with same 
is paper, can be 
, obtaining 2.76 
ossy than typical 
 gap waveguide 
 terms of losses. 
on in the air and 
aged, compared 
ising candidate 
possible antenna 
al lid, which will 
edish Research 
009-14525-C02-
 
Figure 5.  Simulated and measured |S21| for
gap waveguide.        
 
. 
 
Figure 6.  Sketch of a slot antenna fed by the 
REFERENC
[1] K.-L. Wong, Compact and broadband 
York, 2002. 
[2] G. R. James, P. S. Hall, and C. Wood,
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10.5
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Measured
Simulated


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