Antenna Project TEL512E

Istanbul Technical University TEL 516E - Microwave Antennas Spring Semester 2013/2014

!Project Report: Design a Dual-Band WLAN Antenna by James Foot ! Abstract: At the beginning of this spring semester, a project was proposed, it consisted of designing a dual-band Wireless Local Area Network (WLAN) antenna. A dual band WLAN antenna is an antenna that operates mainly in the frequencies of specified by IEEE for the 802.11a/b/g protocols, these frequencies are 2.4 GHz and 5 GHz. The other condition that was given to us an the beginning of this project, was that the input impedance Zin would be 50 ohm. !1. Antenna Requirements ! Lets break down the introduction, and analyse everything in detail. A dual-band antenna is an antenna designed to operate in two frequency ranges. For this project I have to design a WLAN antenna that operated in the frequency ranges specified by the IEEE protocols 802.11a, 802.11b and 802.11g. IEEE 802.11a operates at the frequency of 5 GHz, with a bandwidth of 20 MHz. IEEE 802.11b and IEEE 802.11g operate at the frequency of 2.4 GHz, with a bandwidth of 20 MHz, the main difference is that 802.11g has a higher data rate. So this means that the WLAN antenna that i have to design has got to operate at 2.4 GHz and at 5 GHz. Its is also important to note that the antenna should be design only to operate at these frequencies, so as to avoid causing interference in the other frequencies. As mentioned above, the desired input impedance is 50 ohm. The peak Effective Isotropic Radiated Power (EIRP) should be less than 10 dBm. This number is a function of the conducted power (for WiFi its usually 15 dBm), the WIFI antenna efficiency, and the directivity of the antenna. Peak gain is basically equal to Conducted Power (dBm) plus the Antenna Efficiency (dB) plus the Directivity (dB). For instance, if the conducted power is 15 dBm, the antenna efficiency is -3 dB, and the directivity is 5 dB, then the peak gain would be 17 dBm. If the specifications for peak gain was 14 dBm, we could get there by dropping the conducted power to 13 dBm (a drop of 3 dB). A WLAN antenna efficiencies for handheld mobile devices is typically on the order of -6 dB to -2 dB. !2. Similar Antenna Solutions ! Depending on the desired functionality of the WLAN antenna, there are a some types you can choose from. Lets start with the two basic types, Omnidirectional or Directional. Omnidirectional antenna is one that radiates its power uniformly in all directions in one plane, this gives the antenna good coverage but a sort range. A directional antenna is one that focuses its main radiation beam in one direction, meaning that it will have a better range but a poor coverage. So depending for what case you need the antenna for, it will be one of these types. If I want to design an antenna for a home wireless access point, a dipole antenna would be good because its omnidirectional, and in this case coverage is more important than range. On the other microstrip antennas found in cell phones and laptops are mainly directional antennas, because of their limited size and to avoid interfering with the other components.

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3. Antenna Model ! For this project I choose a design based on a microstrip antenna model from a paper. This microstrip antenna covers an area of 28 x 32 mm2. On the top side, we have a radiator metallic plate that covers an area of 12 x 16 mm2, and is located in the centre of the microstrip antenna. On the bottom side we have a ground plate that covers the whole area of the antenna. Sandwiched in between the ground and the radiator plates, we have the substrate. It is an FR4 substrate with a thickness of 1.6 mm and a dielectric constant of 4.7. Also located on the bottom side is a SMA port used as the wave port for this antenna. The antenna was design using HFSS v. 13. Figure 1 is representation of the antenna design for this project. It uses the following dimensions L1 = 12mm, L2 = 16mm, s1-s4 = 0.5mm x 0.5mm, w1 = w2 = 3mm, w3 = g= 1mm and h = 1.6mm. The fed port is located near the split of one of the outer rings. !4. Results and Discussion ! Although most of the dimensions for the microstrip antenna where given in the paper [1], some of them, like the location of the fed port where not specified, and had to be figured out. Figure 2 shows the antenna designed in HFSS, the box located over the antenna is the radiation box, it has the same with and length as the microstrip antenna, and its 50 mm high.

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Figure 1 - Proposed microstrip antenna.

Figure 2 - The proposed microstrip antenna designed in HFSS, with the radiation box above it.


Figure 3 shows the return loss characteristics of this antenna, the different plots on that figure represents the change in the position of the SMA port, after analysing this graph I noticed that the best position for the SMA port is centred with y coordinate being 17.5mm and x coordinate 18mm from the reference centre (located at the lower right corner in figure 1). We can also observe on figure 3 that the proposed WLAN antenna radiates mainly at the 2.4 GHz and the 5 GHz, as it was intended to be. Figure 4 shows the radiation pattern at the 2.4 GHz. For some reason I couldn't find a way to show the radiation pattern at 5 GHz. !!!!


Figure 3 - Show the Return loss (S 11 ) characteristics of the WLAN.

Figure 4 - Show the radiation pattern of the proposed WLAN antenna.


5. References ![1] S. Basaran, “Compact dual-band split-ring antenna for 2.4/5.2 GHz WLAN applications,” Turk J Elec Eng & Comp Sci, Vol.20, No.3, 2012. [2] Antenna Theory. Available at http://www.antenna-theory.com. [3] Warren L. Stutzman and Gary A. Thiele , “Antenna Theory and Design,” Wiley, 2012. [4] C. Balanis, “Antenna Theory,” Wiley, 2005 !!!!


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Antenna Project TEL512E