ITC513 Wireless Networking Concepts of Antennas

Directional antenna: Yagi antennas – these antennas are mostly used in systems that require high gains and directivity, for instance in television sets. Its design facilitates better levels of signal to noise ratio (SNL) which focuses power in one region (Reckeweg, 2011).

Pros: 

• They have high gains which facilitate the transmission of low signals
• Their high levels of directivity minimise signal interferences.
• Simple and straightforward construction based on simple elements.
• Finally, they are easy to use as their design is easy to mount.

Cons:

• To accommodate high gain levels, the antennas must be long in size.
• Yagi antennas are limited to small gains i.e. 20dB(radio-electronics, 2017).

Horn antenna – another common example of directional antennas, however, this antenna consists of a flare-like aperture that focuses the beams in a given direction. Now, the energy of the transferred beam is usually slowly transferred into a radiation which reduces the losses. In the industry, this antenna is referred to as a ‘flared out wave guide’ as its design facilitates higher directivity which reduces signal diffraction.

Pros:

• Its propagation pattern consists of very few minor lobes (signal loss lobes).
• It has a high impedance matching scheme.
• Due to its shape and design, it has better directivity.
• Moreover, it has narrower signal width.
• Finally, it has minimal standing waves.

Cons:

• Complex design (Reckeweg, 2011).

Cellular antennas – a good example of Omni-directional antennas which are commonly used in mobile devices, from cell-phones to home appliances and even vehicles. They have the benefit of receiving signals in all directions but with minimal signal strengths.

Pros:

• They are easy to install.
• Can amplify signals from multiple sources.
• Good signal boosting capabilities.

Cons:

• Minimal transmission distance.
• Poor for low power signals(Carr, 2012)

Future applications

Directional antennas such as Horn and Yagi will always have the transmission advantage to their design that has better directivity properties. In fact, their application is only halted by their size. On the other hand, omnidirectional antennas e.g. cellular antennas are limited in terms of distance and directivity but are preferred in mobile systems due to their size. The future will most defiantly combine the two resulting in smart antennas that will have the flexibility of Omni-directional antennas but with the power of the directional antennas.

2. Multiplexing techniques in wireless networking

To meet the demands made by customers, the telecommunication industry has tried to develop efficient communication protocols that maximise the resources transferred. Now, bandwidth as a communication resource has always been a major problem for telecommunication which has led to the various variations highlighted below. In both instances, multiplexing, a facility that enables the multiple access of signals is used.

Frequency Division Multiple Access (FDMA) a protocol that uses the frequency parameter to assign channels for communication, through the same principle of multiple signal access. In essence, a communication channel is defined by a frequency. Now, in wireless networking, each communication channel is assigned a single user at any given time. On the other hand, Code Division Multiple Access (CDMA), uses a unique pseudorandom number (binary sequence) to regulate the transmission of multiple signals via a single carrier (channel). Therefore, a unique encoding key is used for each signal and this key is used to separate the signals at the destination (corps, 2000).

References

Carr, J. (2012). Directional or Omnidirectional antenna? Joe Carr's Radio Tech-notes, Retrieved 14 August, 2017, from: https://www.dxing.com/tnotes/tnote01.pdf.

corps, W. a. (2000). FDMA vs. TDMA vs. CDMA. Connecting Wireless, Retrieved 14 August, 2017, from: https://wirelessapplications.com/pdf/lf/FD_TD_CDMA.pdf.

radio-electronics. (2017). Yagi Antenna / Yagi-Uda Antenna. Antennas and propagation, Retrieved 14 August, 2017, from: https://www.radio-electronics.com/info/antennas/yagi/yagi.php.

Reckeweg, M. (2011). Antenna basic. Rhode & Schwarz, Retrieved 14 August, 2017, from: https://home.zhaw.ch/kunr/NTM1/literatur/Rhode_Schwarz_Antenna_Basics.pdf.