The New world of Plasma Antennas

The New world of Plasma Antennas..

 The future of high-frequency, high-speed wireless communications could very well be plasma antennas capable of transmitting focused radio waves that would quickly dissipate using conventional antennas..

 

Transmission and reception of electromagnetic waves have become an integral part of the present day civilisation. Antenna is an essential device for this process. It is a transducer that transmits or receives electromagnetic waves. In other words, antennas convert electromagnetic radiation into electric current, or vice versa. Antennas are used in systems such as radio and television broadcasting, point-to-point radio communication, wireless LAN, cellphones, radar, and spacecraft communication. Antennas are most commonly employed in air or outer space, but can also be operated underwater or even through soil and  rock at certain frequencies for short distances.

 


Growing need for speed of communication network along with data handling capacity are the major forces helping to explore new vistas of transmission and reception. With the wireless generations moving from 2G to 3G, 4G, 5G and so on, the real benefit of upgrading the Wi-Fi networks is to get them to run faster. Wi-Fi usually can manage 54 megabits of data per second. The fancied Wi-Fig (a graphical user interface for configuring wirless connection) would handle up to 7 gigabits per second. This would mean downloading a TV show in a matter of seconds. Advances in antenna technology are expected to play a great role in the desired speed and capacity-handling capabilities of communication networks.

Antenna technology
Physically, an antenna is an arrangement of one or more conductors, usually called elements. In transmission, an alternating current is created in the elements by applying a voltage at the antenna terminals, causing the elements to radiate an electromagnetic field. In reception, the inverse occurs. An electromagnetic field from another source induces an alternating current in the elements and a corresponding voltage at the antenna’s terminals. Some receiving antennas (such as parabolic and horn types) incorporate shaped reflective sufaces to collect the radio waves striking them, and direct these waves onto the actual conductive elements.

 

Some of the firstrudimentary antennas were built in 1888 by Heinrich Hertz (1857-1894) in his pioneering experiments to prove the existence of electromagnetic waves predicted by the theory of James Clerk Maxwell. Hertz placed the emitter dipole at the focal point of a parabolic reflector.

The words antenna (plural: antennas) and aerial are used interchangeably, but usually a rigid metallic structure is termed an antenna and a wire format is called an aerial. The origin of the word antenna relative to wireless apparatus is attributed to Guglielmo Marconi. In 1895, while testing early radio apparatuses Marconi experimented with early wireless equipment. A 2.5-metre long pole along which a wire was carried, was used as a radiating and receiving aerial element. In Italian a tent pole is known as l’antenna centrale, and the pole with a wire along side it used as an aerial was simply called l’antenna. Until then wireless radiating, transmitting and receiving elements were known simply as aerials or terminals. Marconi’s use of the word antenna (Italian for pole) became a popular term for what today is uniformly known as the antenna.

Since the discovery of radio frequency (RF) transmission, antenna design has been an integral part of virtually every communication and radar application. Technology has advanced to provide unique antenna designs for applications ranging from general broadcast of radio frequency signals for public use to complex weapon systems. In its most common form, an antenna represents a conducting metal surface that is sized to emit radiations at one or more selected frequencies. Antennas must be efficient so the maximum amount of signal strength is expended in the propagated wave and not wasted in antenna reflection.
 


There is a long list of antenna designs with their suitability, advantages and limitations.  There are many antenna types and many ways of categorising them. Antenna types can be used to differentiate antennas for radios, televisions and radar systems. Because antennas can be built for transmission of different frequencies, another way to categorise antenna types is by their frequency. For radio antennas, it’s important to know whether these are built for, say, frequency modulation (FM) broad-casting at 88-108 MHz or amplitude modulation (AM) broadcasting at 535-1605 kHz . For television antennas, one distinguishes between ultra-high frequency (UHF) antennas and very-high frequency (VHF) antennas, or antennas that pick up both. 

Traditional telecom antenna

Stores that sell antennas categorise various types on terms of customers’ needs. The range of antennas can be categorised as short, medium or long. For customers buying a television antenna, the decision is dependent on how close they are to the transmitting towers that they wish to pick up a signal from. If the range is well-matched to the distance, it will help avoid the antenna picking up unwanted signals.

Location is another way of looking at antenna type. Antennas can be made for indoor, outdoor or attic installation. Indoor antennas are easy to install but usually do not have the elevation to provide the best signal, particularly for customers who are far from the transmission. Outdoor antennas were primarily made for rooftops, but now more are being designed to mount on the side of a house, on a pole or deck. The attic can be a useful installation point for those who do not want their antenna inside or outside for aesthetic or other reasons.

Another set of antenna types is differentiated by style. Style can mean the antenna’s appearance in terms of design. It can also address whether the antenna is directional and gathers signals from a central location or whether it is multi-directional—seeking signals from towers transmitting from different locations. The latest version of antenna, i.e., plasma antenna employs ionised gas enclosed in a tube (or other enclosure) as the conducting element of the antenna. 

Plasma antennas
The different states of matter generally found on earth are solid, liquid and gas. Sir William Crookes, an English physicist, identified a fourth state of matter, now called plasma, in 1879. Plasma is by far the most common form of matter. Plasma in the stars and in the tenuous space between them makes up over 99 per cent of the visible universe and perhaps most of what is not visible. 

Important to antenna technology, plasmas are conductive assemblies of charged and neutral particles and fields that exhibit collective effects. Plasmas carry electrical currents and generate magnetic fields.

A plasma antenna is a type of antenna in which the metal-conducting elements of a conventional antenna are replaced by plasma. These are radio frequency antennas that employ plasma as the guiding medium for electromagnetic radiation. The plasma antennas are essentially a cluster of thousands of diodes on a silicon chip that produces a tiny cloud of electrons when charged. These tiny, dense clouds can reflect high-frequency waves like mirrors, focusing the beams by selectively activating particular diodes. The ‘beam-forming’ capability could allow ultra-fast transmission of high data loads—like those needed to seamlessly stream a TV show to an untethered tablet—creating an attractive option for the next generation of supercharged wireless transmitters. 

Many types of plasma antennas can be constructed, including dipole, loop and reflector antennas. Plasma antennas are interpreted as various devices in which plasma with electric conductivity serves as an emitting element. In gas plasma antenna the concept is to use plasma discharge tubes as the antenna elements. When the tubes are energised, these turn into conductors, and can transmit and receive radio signals. When de-energised, these revert to non-conducting elements and do not reflect probing radio signals.

The fact that the emitting element is formed over the interval needed for the emission of an electromagnetic pulse is an important advantage of plasma antennas. In the passive state (in the absence of plasma in the discharge tube), such a device does not exhibit electric conductivity.

A plasma stream flowing from a jet into the ambient space, the plasma trace of a body moving at an ultrasonic velocity in the atmosphere, and alternative plasma objects have been studied as possible antenna elements. Solid-state plasma antenna uses beam-forming technology and the same manufacturing process that is currently used for silicon chips. That makes it small enough to fit into smartphones.

Higher frequencies mean shorter wavelengths and hence smaller antennas. The antenna actually becomes cheaper with the smaller size because it needs less silicon. There is a gas plasma alternative but it’s not solid-state, so it is bigger and contains moving parts—making it more of a pain to manufacture. That leaves the door open for solid-state plasma antenna to be used for next generation Wi-Gig (its version 1.0 was announced in December 2009) that can reach up to 7Gbps bandwidth over frequencies up to 60 GHz. 

Development progress
Initial investigations were related to the feasibility of plasma antennas as low-radar cross-section radiating elements with further development and future commercialisation of this technology. The plasma antenna R&D project has proceeded to develop a new antenna solution that minimises antenna-detectability by radar at the first instance. But since then an investigation of the wider technical issues of existing antenna systems has revealed areas where plasma antennas might be useful.

A significant progress has been made in developing plasma antennas. Present plasma antennas have been operating in the region of 1 to 10 GHz.  Field trials have shown that an energised plasma refector is essentially as effective as a metal reflector. However, when de-energised, the reflecte signal drops by over 20 dB. Still some technicalities related to plasma antennas like increasing the operating plasma density without overloading the plasma discharge tubes, reducing the power required and the plasma noise caused by the ionising power supply, etc, have to be looked into in order to make them the useful technologies for wireless communication in near future. 

The future of high-frequency, high-speed wireless communications could very well be plasma antennas capable of transmitting focused radio waves that would quickly dissipate using conventional antennas. Thus, plasma antennas might be able to revolutionise not just high-speed wireless communications but also radar arrays and directed energy weapons. The good news is that plasma antennas will be on-the-shelf in the next couple of years. The bad news is that some military powers can use it to create a more advanced version of its existing pain beam. 

Advantages of  plasma antennas
1. An important advantage of plasma antenna over a conventional antenna is that the former is much lighter. Based on a set of patented beam-forming technologies, these high-performance electronically-steerable antennas are extremely lightweight and compact.

2. Free from mechanical parts, these maintenance-free plasma antennas are ideally suited for a wide range of wireless communications and sensing applications.

3. Plasma antennas have a number of potential advantages for antenna design. These are reconfigurable. Whe one plasma antenna is de-energised, the antenna reverts to a dielectric tube, and a second antenna can transmit through it. This allows using several large antennas stacked over each other instead of several small antennas placed next to each other. This results in better sensitivity and directivity.

4. When a plasma element is not energised it is difficult to detect it by radar. Even when it is energised, it is transparent to the transmissions above the plasma frequency, which falls in the microwave region. 

5. Plasma elements can be energised and de-energised in seconds, which prevents signal degradation.

6. When a particular plasma element is not energised, its radiation does not affect nearby elements.

7. Plasma antenna can focus high-frequency radio waves that would dissipate quickly if beamed by conventional arrays. 

8. Plasma antennas boost wireless speeds. Such antennas could enable next-generation Wi-Fi that allows for super-fast wireless data transfers. 

9. Solid-state plasma antennas deliver gigabit-bandwidth, and high-frequency plasma antenna could hold the key for economically viable super-fast wireless networking. 

10. Plasma antennas might also be used to create low-cost radar arrays that could be mounted on cars to help them navigate in low-visibility conditions, or used to make directed, more focused and less bulky energy weapons. 

11. Plasma antennas have developed an innovative range of selectable multi-beam antennas that meet the demands in today’s wireless communication, defense and homeland security markets.

Limitations
1. The current hardware uses a wider range of frequencies so it’s impractically massive to be used for mobile environments.

2. Plasma antennas are expensive and hard to manufacture.

3. High-frequency signals mean that antennas operating at higher frequencies couldn’t penetrate walls like conventional Wi-Fi, so signals would have to be refected throughout the buildings.

Plasma antennas could theoretically solve some of these problems because these can operate at a wider range of frequencies, but gas antennas are also more complex (and likely more expensive) than their silicon-diode counterparts, which are small enough to fit inside a cell phone.

With plasma antenna technology, there are kinks to iron out, but researchers and engineers are optimistic to make this promising technology commercially available in few years.