ITC254 Wireless Networks-Types of Antennas

nd Discone antennas are taken as VHF and UHF.

Super High Frequency (SHF) & Extremely High Frequency (EHF) antennas: This category includes antennas like Pyramidal, Fractal, Microstrip patch, Parabolic, and Discone monopoles, and dipoles antennas ("IEEE Transactions on Antennas and Propagation announces special issue on antennas and propagation for body-centric wireless communications", 2008).

Aperture

Antennas has aperture through which they transmit and receive energy and can be can be further classified. The examples of such antennas are Wire, Horn, Parabolic, and Casegrain Antenna

Radiation

The other classification of antennas is on the basis of radiation patterns like Isotropic, Omnidirectional, Hemispherical and Directional antenna.

Polarization

The polarization of electromagnetic waves is another classification of antennas that includes antennas like Circularly Polarized and Linearly that can be Vertical or Horizontal Polarized antenna.

Explanation of some Antennas used in wireless networks:

Directional Antennas: These antennas offer distance coverage are but don’t offer a wide coverage area. One of the examples of Directional Antennas is Flat Panel Antennas which can be used for directing a wifi signal (Khodier & Al-Aqil, 2010). They offer a wide angle of coverage. This in between 35 to 120 degrees and is suitable for directing a wifi signal in small area like a section in a building. Another example of directional Antenna is Yagi Antenna; these are used for covering medium distances. These antennas are very much similar to TV antenna and should be kept in right direction in order get maximum signals.

Omnidirectional Antennas: These antennas are used to get 360-degree coverage of wireless signals. The signal strength of these antennas is relatively low. These are used in homes and small offices (LIU & LI, 2013).

Horn Antennas: These antennas are used to improve the radiation efficiency. These are considered to be flared waveguide. The design of the flare angle decides the directivity making it a disadvantage. These are being used in satellites and microwaves.

V-Antennas: Generally used for commercial and radio communications, v- antennas are better version of long wire antennas (Lu, Wicker, Towsley, Xiong & Lio’, 2009). The frequency range of operation of V-antenna is around 3 to 30 MHz this antenna works in high frequency range. The major disadvantage of these is that they work for fixed frequency operations.

Lens Antennas: These Antennas are used for higher frequency applications. They use curved surface for both transmission and receiving the signals. These antennas are used as wide band antennas.

Parabolic Reflectors: The Cassegrain feed parabolic reflector is mainly used in satellite communications and are also used in wireless telecommunication systems. The frequency range used for the application of parabolic reflector antennas is above 1MHz (Nyberg, Kildal & Carlsson, 2010).

Analyzing the types of antenna and there working it’s clear that Parabolic Reflector Antennas will be one of the dominating players in future for medium and long distance wireless transmissions.  Apart from these Directional Antennas like Yagi Antennas is even one of the promising players.

Multiplexing is a process of enabling a single channel for multiple signals. There several techniques to do multiplexing, three basic types of division-based protocols that can used includes: FDMA also known as frequency division multiple access, CDMA OR code division multiple access and TDMA that can also be called as time division multiple access. Given below is the comparison between CDMA and FDMA technique:

Concept

CDMA is the acronym of Code Division Multiple Access, in this type of multiplexing various pseudorandom binary sequence is allocated to every person using it and the carrier is modulated, forming the spectrum’s waveform. A unique code pattern is provided to each of the user ("Diversity-Multiplexing Tradeoff for Opportunistic Access Systems", 2014). In FDMA one channel or bandwidth is divided into several individual bands. There is a need to accommodate the transmission’s signal spectra that are needed to be propagated. Therefore, the individual channels and bands formed are wide enough. Each subcarrier is modulated with the transmitted data and then these subcarriers are linearly mixed.

Usage

CDMA is being used in telephone systems with Ultra high frequency.  CDMA works by using the combination of spread spectrum technology together with analog to digital conversion (ADC) technique. The First step is to digitize the audio input into binary form and the next step will be the transmission of the frequency of the signal which is explained into unique pattern (Yi Jiang & Varanasi, 2008). In fiber optic communication systems FDMA is used, due to the enormous bandwidth of each fiber optic it can be divided into several smaller bandwidths. A different light frequency is assigned to different data or information sources for the purpose of the transmission.

Advantages

The benefit CDMA technique is that only the programmed receiver with the same frequency response and same unique code can intercept the transmitted signal hence making it secure. The channel for CDMA is normally 1.23 MHz wide. The signals per unit bandwidth capacity are much larger in CDMA technique due to the combination of digital and spread spectrum than the techniques which use analog. CDMA allows roaming nationally due to its compatibility with other cellular technologies ("Diversity-Multiplexing Tradeoff for Opportunistic Access Systems", 2014). The benefits of FDMA when not in use it sits idle; the channel bandwidth is also relatively low. It uses a very simple algorithm.

Disadvantages

As the number of user’s increases in CDMA the overall quality of the service decreases. It also faces the problem of self- jamming. In FDMA major issues are the presence of guard bands and that it does not significantly differ from analog system.

References

Diversity-Multiplexing Tradeoff for Opportunistic Access Systems. (2014). IEEE Wireless Communications Letters, 3(2), 185-188.

IEEE Transactions on Antennas and Propagation announces special issue on antennas and propagation for body-centric wireless communications. (2008). IEEE Antennas And Propagation Magazine, 50(1), 255-255.

Khodier, M., & Al-Aqil, M. (2010). Design and optimisation of Yagi-Uda antenna arrays. IET Microwaves, Antennas & Propagation, 4(4), 426.

LIU, Z., & LI, Y. (2013). Algorithms of neighbor discovery in wireless networks with directional antennas. Journal Of Computer Applications, 32(4), 917-919.

Lu, X., Wicker, F., Towsley, D., Xiong, Z., & Lio’, P. (2009). Detection Probability Estimation of Directional Antennas and Omni-Directional Antennas. Wireless Personal Communications, 55(1), 51-63.

Nyberg, D., Kildal, P., & Carlsson, J. (2010). Effects of intrinsic radiation Q on mismatch factor of three types of small antennas: single-resonance, gradual-transition and cascaded-resonance types. IET Microwaves, Antennas & Propagation, 4(1), 83.

Yi Jiang, & Varanasi, M. (2008). Spatial Multiplexing Architectures with Jointly Designed Rate-Tailoring and Ordered BLAST Decoding - Part I: Diversity-Multiplexing Tradeoff Analysis. IEEE Transactions On Wireless Communications, 7(8), 3252-3261.