WLL Micro Strip Antenna

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Abstract — A new design for single feed, WLL micro strip
antenna is presented and experimentally studied. The antenna
is 10.3mm × 17.2mm size, radiates an end fire beam and
operates on the (3.4-3.6 GHZ) standard WLL - rural
application - band. The antenna gain is better than 4.96dbi.
I. I NTRODUCTION
quick and economical way to implement communications
infrastructures that link these areas to the rest of the word. FWA is specifically designed to deliver quality, cost-
effective services in low density and scattered rural areas.
Global system for mobile communication (GSM) remains
the world’s leading mobile communications technology.
Recently, equipment vendors have encouraged GSM
operators to use fixed GSM (FGSM) technology to deliver
basic telephone service to low and medium density rural
areas that are not served by landline networks .
Although FGSM may appear to present opportunities for attracting new subscribers by leveraging existing GSM infrastructures, in reality, the advantages this technology
provides are limited to the high density and often narrow
corridors already covered by mobile networks. Extending such networks into the country side in low density regions is
not necessarily a cost effective solution as the per-subscriber cost of delivering basic telephony substantially increases.
Given the uncertainties of FGSM’s evolutionary path, and
indeed the lack of Support for a cost- effective solution for delivering toll-quality voice and functional Internet access to
low-density areas, network planners did carefully consider
Manuscript received November 20, 2005. This work was supported in
part by the EMI, Laboratoire De Recherche Eléchtronique ET System De
Telecommunications, Rabat, Morocco. By Antennes ET Hyperfréquences,
Institut d’Electronique ET de Télécommunications De Rennes, Rennes
France as a second part, and by the INPT, Propagation Micro-ondes et
optiques as a third one.S. Lebbar is the main author of this article. She was with the Electrical
Departement of FIT, FL, USA and is now within the EMI, Rabat, Morocco,
where she is preparing a PHD, in the Laboratoire De Recherche
Elechtronique Et System De Télécommunications, Rabat, Morocco. (e-
mail.: [email protected])
Z. Guennoun, is within the Department of Electrical engineering, in the
EMI, Rabat, Morocco.
M. Drissi. is the co-director of antenne et hyperfrequences, Intitut
d’electronique et de telecommunication de rennes, Renne, France. He is
with the Electrical Engineering Department, INSA engineering School,
France.
F. Riouch is within the INPT, Rabat, Morocco.
the use of wireless local loop (WLL), called also radio in the
loop(RITL), or fixed radio excess. Wireless local loop (WLL), sometimes called, radio in the
loop, or fixed-radio access (FRA), uses public switched
telephone Network (PSTN) to connect subscribers using radio signal instead of copper wire for all or part of the connection. In rural telephony WLL uses the 3.4 -3.6
frequency band. Micro strip antennas are small structures, used in external
public switched network (PSTN), to collect or radiate electromagnetic wave. Most people require an antenna that
can stand up to daily abuse and still keep reception whenconnected to the network. (3.4 -3.6 GHz) is the frequency band used in the WLL technology.
In this article, we will report a new one band micro strip
antenna structure working on the WLL band, the antenna is aimed to work in the (3.4-3.6 GHz) band. The compactness of this antenna was our huge premium. And this is especially
true when the designed antenna, needs to fit the conditions of having the needed gain. Furthermore, it was very difficult to achieve the required polarization performance, besides all
these challenges, the requirement of significant bandwidth. All of these factors make this antenna design and
development a daunting task and some practical engineering compromises needed to be made.
II. COMPACT MICROSTRIP ANTENNA DESIGN
Microstrip antenna can be designed using couple of methods, the most straight forward one has been finding the
antenna width and length for specific i) resonant frequency,
ii) substrate permittivity, and iii) substrate height. The formulas used in the rectangular forms have been
successively:
( ) 2
Rural Application
R

Such that εr the relative substrate permittivity, C the speed of light (3*108 m/s), L1 the antenna length, L2 the antenna width and fr the resonant frequency. Adding a via to the
rectangular patch, the resonant frequency can be increased to
)(**4 d W L
Where d is the via diameter, and α the compensation
coefficient, generally equal to 0.9.
Compactness of conventional resonating microstrip patch
antenna is accomplished by loading the dominant mode of
resonant structure. Loading can take place in various forms: i) use of dielectrics, ii) use of lumped or distributed element, and iii) perturbing the basic structure.
The use of high permittivity substrate is the most straight forward approach to reduce the antenna size, because
resonant length is proportional to 1/√εr . However, size
reduction is associated with reduction in bandwidth and radiation efficiency of the antenna. Indeed, the characters expected in size reduced antenna are large reactance
variation near resonance and low conductance. This results
in high Q value and hence small bandwidth. One of the most known techniques to solve this problem, is to create multiple resonance by i)adding parasitic patches in stacked or planar
geometry, ii) adding reactive loading by shaped slot , cuts or notch, iii) or increase the substrate thickness.
During this article we will be using Thick, high
permittivity, substrate. However, creating multiple resonance, by increasing the subtract thickness degrade
radiation efficiency. This poor radiation is due to the fact
that surface wave modes, which are guided waves propagating along the interface, increases the leakage power,
which becomes the main source of the poor radiation efficiency and also for the mutual coupling in the phased arrays. There exist many solutions to improve the antenna
radiation efficiency. This has been achieved through the suppression of surface wave propagation in the antenna structure. First approach is based on the cavity backed
antennas, in which electric walls are placed surrounding the patch to avoid the surface wave propagation. The second
approach is based on micro-machining technology, in which
part of the substrate beneath the radiating element is removed to realize a low effective dielectric constant substrate which in turn reduces the power leakage to surface
waves. The third approach relay on photonic crystals and in this case the substrate is periodically loaded so that the surface waves cannot propagate along the interface and
hence the power leakage to surface wave reduces.
III. NEW METHODOLOGY ANTENNA DESIGN
In its basic form, Microstrip antenna can be viewed as a
matrix with X variables and four unknown b. Such that A*X = b. (7)
The unknowns are resonant frequency, bandwidth, gain or efficiency, and polarization. And the variables X are resonant patch length and width, the subtract height, the
relative permittivity, and the feeding position, length and width, ect.
To illustrate this more and show the problem solution,
let’s take the most basic micro strip antenna structure (see figure 1)
Figure 1: Basic micro strip antenna
The variables are L1, L2, εr and H1 and the unknowns are resonant frequency, bandwidth, gain, and polarization. So
using neural network methodology, and numerical analysis software that helps make multitude of trials, one can solve
the four unknown with the four variables. But some variables are correlated, do the necessity of adding other variables. Those new variables could be in the form of
adding new slot, changing the resonant metal form, adding couple of substrate…ect. Also the problem solving can
depict some unphysical result, ex high L1, L2 or H1 do the need of looking into bibliography of some predefined results or the need of trying new ideas to solve the problem. (See Part 2 of this paper)
IV. METHODOLOGY APPLICATION
The WLL new microstrip antenna structure proposed in this paper (Fig.2) is an application of the antenna strategy
8/8/2019 WLL Micro Strip Antenna
described above. The antenna is working on the (3.4-3.6)
frequency band and is 17.2 mm long, has 10.3 mm width, and 9.4 mm height. The 9.4mm antenna’s thickness is designed using two stacked substrate, alumina and air with
relative permittivity (εr) 9.6 and 1 respectively. The

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WLL Micro Strip Antenna