Individual Patch Antenna and Antenna Patch Array for Wi-Fi Communication

Wireless communication (Wi-Fi) takes interest, because the wires are cumbersome and generate less free space. This type of communication is widely used among electronic equipments, mainly at home and industry. Patch antennas are very popular due to its characteristics. The aim of this work is to obtain an efficient and economical patch antenna prototype for indoor and outdoor uses. At first, the prototype of a rectangular patch antenna designed for Wi-Fi, with linear polarization, is presented. After, cuts and grooves were realized on it, in order to improve its gain. The proofs with the individual antenna with four cuts show the feasibility of its use for indoor use. Subsequently, an antenna array, on the base of the individual rectangular modified patch antenna, was also designed in order to obtain an improved prototype. Proofs demonstrate a good performance of the proposed antenna array for its use for indoors and outdoors as it was expected.


Problem description
The implementation of wireless networking, also called Wireless Fidelity (Wi-Fi) or 802.11 networking, is been expanded not only to large size places (airports, coffee shops, libraries or hotels), but also to small places like homes, due to the low-cost internet access provided by this technology, which also supply comfortable workplaces because of wires elimination.
The great demand of Wi-Fi networks has led to the constant search of connectivity improvements; among them has appeared the use of antennas to replace to the original routers antennas, in order to increase substantially the performance, the coverage and the data rate [1].
The gain is another characteristic to improve.The original router antennas of low cost, provide gains from 1,5 up to 2 dBi, in special cases.In fact, in order to increase the coverage some manufacturers of routers sell replacement antennas of high gain [2], for indoors and outdoors [3].In addition, to improve the quality and reliability of a wireless link (figure 1a) is necessary the use of antenna diversity, as it is shown in figure 1b.

Previous work
The design of patch antenna is realized in several areas, like GPS communication, cellular telephony, etc ( [9]).At commercial level, in the case of Wi-Fi networks, several variants have been implemented in routers, such as the use of patch antennas in antenna arrays (figure 2), or individual replacement patch antennas for indoors and outdoors (figure 3) [3].
The elimination of communication wires among computing devices is a critical step toward advanced communication in construction since the dynamics projects site make wires difficult to support [11].In particular, in the case of patch antennas design to operate at 2.4 GHz, or for multiband applications [9], research works and several patents are been developed [12].

Introduction
The   The microstrip antennas are relatively inexpensive at its manufacturing and design is not complex.They are frequently used in Ultra High Frequency (UHF) and higher frequencies as the size of an antenna is directly tied to the wavelength at the resonant frequency.
A single patch antenna provides a maximum gain directly from 6 to 9 dB.It is relatively easy to print an array of patches in a single substrate using lithography techniques.An arrangement patch provides much more than a simple patch gain for a small additional cost, and a bigger broadband [14].
The rectangular patch has a simple

Rectangular patch antenna design
The parameters to be considered in the design of a patch antenna are shown in  With these parameters, the patch dimensions can be calculated using the following equations [13,[16][17]: For the patch width: Individual Patch Antenna and Antenna Patch Array Where: c = Constant speed of light in vacuum,  r = Dielectric constant substrate and f 0 = Operating frequency.
The effective length is calculated using: where the effective dielectric constant,  eff , due to the influence of the metal patch, was obtained from: The two increments in the length, which are generated by the fringing fields, making electrical length lightly larger than the physical length of the patch: The patch length is given by: The length and width of ground plane (and the substrate), L g and W g , are [13]: To improve the performance of the rectangular patch, it is possible to make changes in its geometry, such as cuts and grooves.
Using 2.4 GHz as the operation frequency, and 1.6 mm as the width of FR-4 PCBs plates; the corresponding sizes of the rectangular patch antenna are presented in Table 1.The feed point location is (-0.005m, 0), considering the center of the patch as the coordinates origin.

Comparison of the rectangular geometries
The rectangular patch antenna designs were realized considering different geometries.Cuts and grooves on the rectangular patch were implemented in order to improve its performance, basically its gain.In figure 5, 4 antennas geometries are shown.grooves combined with cuts and rectangular with small cuts in the four patch corners.
Grooves and cuts performed on rectangular patch antenna geometry allow us to determine the electric and magnetic field operation modes and to increase the gain, respectively.When we make cuts, is necessary to be careful with its size and its number.The cuts not only increase our gain, they can also modify other parameters.The first parameter that is necessary to verify when we perform a cut is the central operation frequency, because when we increase the cut depth, the surface of the patch diminishes and the distribution of currents is modified.Then, it is necessary to relocate the feeding point.
Under critical cases, it is necessary to redesign all again.
In table 2, it is shown the corresponding gain values to each antenna.
As can be seen, the biggest gain was obtained with the rectangular geometry with cuts.For this reason, the prototype was realized using this geometry.The fabrication of rectangular patch antenna, with small cuts is easy to realize by means of PCBs templates.

Individual antenna design
The basic characteristics of final design of the modified rectangular patch antenna are:  6)  Beam width: 90 degrees (Figure 7)  The calculated characteristic impedance is of 7.72 Ω, using equation 8 [16], which is very near to the value obtained from simulation, 6.2 Ω, (figure 10), at the central frequency.
The simulated impedance considering a 50 Ω load is presented in figure 11.At 2.41 GHz, the impedance value is 60.51 Ω.

Individual antenna prototype
The final prototype was realized including a female BNC connector.The first step is to make the silkscreen on the PCBs plate, on both sides.On the used board is possible to obtain 9 antennas.The serigraphy technique produce that not all antennas have a good quality.Better results are obtained with commercial printing, but the costs are increased.
After removed the cooper excess, we cut each antenna and accomplish the drilling for the connection of their corresponding feeding points.In figure 12, two individual antennas are shown with its corresponding feed point welded to the BNC connector.This type of connector was chosen for compatibility with the laboratory equipment.A detailed analysis of materials selection was considered.Their frequency response and availability were also taken into account.

Experimental results
After, the prototype fabrication, the The tests were realized by using a signal generator and a spectrum analyzer, with antenna prototypes coupled by means of coaxial cables to their exit and entrance, respectively (see Figure 14).The distance between the antennas was of 6 cm.replaced its antennas with our prototypes (figure 17). Figure 18 shows the received power inside and outside of the CIICAp building, using a laptop as reference.
The signal "ciicap" is the name of the router with the commercial antennas and "alecita", the router with the antenna prototypes.As can be seen, outside the CIICAp building, the transmission/reception is better using "ciicap", but inside, the signal is stronger with "alecita".Therefore, it can be concluded that this individual prototype shows an excellent performance for indoors.After, finished the first part of this work, we also designed an antenna array, in order to increase the obtained gain, and to obtain a prototype for outdoors.This approximation is presented in the following sections.

Antenna array
In order to improve the reception outside of the building, we design an antenna array connected by microstrip lines.The length of the microstrip lines corresponds to  g /8 (figure 19), that is, 8 mm and a width of 2 mm.The impedance of the microstrip, obtained from tables [16] is approximately 60 Ω.
The maximum gain is 4.4 dB (figure 20).The beamwidth was reduced to 80 degrees (figure 20), as it was expected, while, the directivity is increased from 3.44, for the case of individual antenna, to 4.47 for the array (figure 22).The corresponding prototype is shown in figure 23.As can be seen, with the antenna array prototypes we obtained a very good response not only inside, but also an acceptable robustness outside of the CIICAp building, which was the aim of this design.
In order to compare the performance of the router used to replace the antennas, against its performance considering its original antennas, see "alecita" signal figure 27.As can be appreciated from figures 26 and 27, the router with the antenna prototypes has better reception in both cases, inside and outside of the building, compared with its performance using its commercial integrated antennas.

Economic profit
The high range routers, with antenna pounds [20] (see figure 28).In the case of the antenna array the cost would be substantially increase due to the ABS cover, not for the substrate cost, then other material cover alternative must be analyze.
The prices can be drastically reduced if a great scale fabrication is considered.In the case of the antenna arranges, the prices would be lightly increased, specially, due to the cover costs.

Conclusions
The best response for the two cases
geometry.When the air is the substrate of the antenna, the length of the rectangular microstrip is approximately half of the wavelength in the free space.As the antenna is loaded with a dielectric substrate, the length of the antenna decreases, while the relative dielectric constant of the substrate increases.An inherent advantage of the patch antennas is the ability to have diversity of polarization.They can be easily designed to have Vertical, Horizontal, Circular Right Hand (RHCP) or circular Left Hand (LHCP) polarizations, by means of using of multiple feed points or a single one.This property allows patch antennas to be used in several communication areas, such as in the design of personal communication equipment [15].In this work, we presented the design and fabrication of prototypes of an individual rectangular antenna and of antenna array for 2.4 GHz.The tests for sending-receiving signals using the patch antenna prototypes are realized in order to know their performance.

Figure 4 ,
Figure 4, they are:  Operation frequency (f o ). Dielectric constant of the substrate (ε r ). Height, h (or thickness, t) of substrate.

Fig. 5 .
Fig. 5. Implemented geometries: rectangular, rectangular with 2 and 4grooves combined with cuts and rectangular with small cuts in the four patch corners.

Fig. 12 .
Fig. 12. Patch antenna coupled to the spectrum analyzer.In order to verify the operation frequency range, a sweeping of frequency from 250 MHz up to 10 GHz was made.

Figure 15 ,
Figure 15, shows the obtained values of the received power.As can be seen, the highest received power occurs in the frequency range from 2 to 3 GHz.An enlargement corresponding to the frequency range from 2.2 to 2.8 GHz is presented in figure 16.As can be seen, the peak frequency corresponds to the range from 2.4 to 2.45 GHz, in accordance with the corresponding design requirement and simulation (see figure 9).

Fig. 26 .
Fig. 26.Commercial external patch antenna.In this work, without considering the costs of the used equipment, the devoted time, and the profit margin, the fabrication net cost of individual antenna prototypes is approximately of $150 Mexican pesos for each required antenna, considering also the acrylonitrile butadiene styrene ABS cover, which is suggested for commercial presentation of our prototype.

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Photonics lab (outside of the main building)

Table 1 .
Dimensions of the rectangular patch antenna.

Table 2 .
Geometries and theirs corresponding gains.