New Antenna Design - A Brief Analysis of Plasma Antenna Technology

Due to the unique physical properties of plasma, plasma antennas have an incalculable development potential in solving antenna stealth and mutual coupling, and are a major advancement in antenna technology today. Many large companies in the world are researching and developing plasma antennas. Based on the tracking and analysis of the development of plasma technology, based on the collected information and technical literature, the development of plasma antenna technology at home and abroad is reviewed, and some representative patents of plasma antennas abroad are introduced.

Plasma is a kind of material form prevalent in space. It is the fourth state (or plasma state) coexisting with the gaseous, liquid, and solid states of matter. Its size is larger than the unit length of the electric dipole moment. In fact, the plasma is a collection of a large number of positive ions and free electrons. It is macroscopically approximately electrically neutral, and the ionized ion density is quite high. Its motion is mainly dominated by the electromagnetic force and appears to be significant. Group behavior. In ordinary gas, even if only 0.1% of the gas is ionized, the ionized gas already has good plasma characteristics. If 1% of the gas is ionized, such a plasma becomes very conductive. High ideal electrical conductor.

Plasma has a great influence on the propagation of electromagnetic waves. Under certain conditions, the plasma can reflect electromagnetic waves; under another condition, it can absorb electromagnetic waves. When a magnetic field is present, the polarization direction of the electromagnetic wave propagating in the direction of the magnetic field in the plasma generates a Faraday rotation effect, so that the polarization direction of the echo received by the radar is inconsistent with the reflection time, causing polarization distortion. Plasma antennas are made by using plasma to exhibit good conductor characteristics for electromagnetic waves of a certain frequency.

Plasma stealth technology refers to a technology that uses plasma to interfere with enemy radar detection. It is a new way to realize radar stealth and is the latest development of radar stealth technology. The technology utilizes a plasma generator or radioisotope to provide energy in a manner that produces a medium that discharges, activates, and ionizes the gas to form a plasma shield that absorbs radar electromagnetic or infrared radiation energy. After reasonable design, the characteristic parameters of the plasma (such as energy, ionization degree, oscillation frequency and collision frequency) can meet specific requirements, so that part of the radar wave irradiated onto the plasma layer is absorbed, and the propagation direction of the other part is Change, so that the energy returned to the radar receiver is very small, the echo is greatly reduced, in order to achieve the purpose of stealth. The plasma stealth technology is easy to use and has good stealth effect. It does not need to use absorbing materials, and it does not need to change the structural shape of the stealth equipment, thus reducing manufacturing costs and maintenance costs.

There are various methods for generating plasma, such as thermal ionization, gas discharge, high-energy particle bombardment, and laser irradiation. Militaryly, nuclear explosions, radiation of radioisotopes, shock waves from high-altitude supersonic vehicles, jets of easily ionized components such as helium, potassium and sodium, and jets of jets can form weakly ionized plasmas. The plasma in a plasma antenna is typically obtained by adding an electrode to the gas column to ionize the plasma to produce a plasma, such as a voltage-driven fluorescent rod plasma antenna developed by the Australian National University; another method That is, a strong laser beam illuminates the gas to ionize the gas to generate a plasma; and another method is to generate a plasma by applying a radio frequency plasma surface wave excitation gas column at one end of the gas column [1].

In order for the plasma to absorb enough of the radar electromagnetic wave, or to make a plasma stealth antenna, the generated plasma must have a sufficient density, volume (or thickness), and the plasma has sufficient duration and uniformity. . In view of these requirements, the following methods for generating plasma are the most promising: dielectric barrier discharge and creeping discharge; arc discharge; ultraviolet radiation; radioisotope irradiation [2].

A plasma antenna is a low-radar cross-section antenna that differs greatly from conventional antenna structures. It utilizes the switchable characteristics of the plasma to switch the radiation and stealth state of the antenna; the magnetic field of the plasma and the controllability of the excitation electrode are used to realize the antenna scanning; the complete shielding, partial transmission and complete transmission of the plasma are selected according to actual needs. Wait for the state, and use its characteristics of rotation, reflection, absorption and other characteristics to achieve reduction control of the antenna radar cross section.

Using the conductivity of the plasma and the ability to reflect and absorb electromagnetic waves, the stealth design of the antenna can be achieved in three different ways [5]:

The plasma antenna is used as a vibrator unit of a glass tube filled with a thin and easily ionizable gas, and is used as an antenna when the gas is ionized. When it is not working, it is equivalent to an ordinary glass tube, and its radar reflecting surface is actively small. It is important for aircraft and ships that require stealth design. The plasma antenna has been designed in the United States and Australia.

The partially reflective antenna can be designed as a plasma antenna, which utilizes the ability of the plasma to reflect electromagnetic waves. To reduce power consumption and radiated interference, this plasma must also operate at low air pressure. Lowering the working pressure, reducing the collision frequency of the plasma, increasing the degree of ionization, and increasing the electron density, thereby increasing the applicable frequency. However, in this gas discharge mode, the electron density generally falls below 1020/m3, so the upper limit frequency of the antenna in this manner is about 10 GHz, which has limitations in use.

The use of plasma as a barrier to aircraft radar antennas allows for good stealth of the antenna. This mainly utilizes the absorption characteristics of electromagnetic waves by plasma. This plasma barrier has a wide electromagnetic wave absorption bandwidth. When the radar is working, the plasma barrier must be off. But in fact, airborne radars emit and receive electromagnetic waves for very short periods of time, and working hours are limited. The switching speed of the plasma barrier can be very high, so the plasma barrier is turned off at the moment the radar transmits and receives electromagnetic waves. Open, combined with the tactical use of the aircraft, can greatly improve the stealth effect of the aircraft. For reconnaissance early warning radars, the plasma barrier is equivalent to the absorbing material on the surface of the aircraft, and the airborne radar antenna can be shielded, and the stealth effect is very good. In this way, not only the working pressure can be low, the power is small, but also the adaptive frequency can be flexibly adjusted by controlling the discharge intensity.

Conventional antenna designs mostly use a certain size of metal conducting surface to radiate electromagnetic waves at a selected frequency, while plasma antennas use ionized gas as a vibrator to radiate electromagnetic waves. When the gas ionizes to form a plasma state, it can conduct electricity like a conductor, thereby functioning as an antenna for transmitting and receiving radio signals. When the ionization state is removed, it does not generate backscattered waves to the enemy detection radar, nor does it absorb high-power microwave radiation that can reduce the effectiveness of the electronic countermeasures, and has good stealth characteristics.

Compared to conventional metal antennas, plasmonic antennas have many advantages over metal antennas: first, they have a lower radar cross section, making it possible to form antennas. Secondly, it is not necessary to change the physical structure of the antenna. By changing the physical parameters such as the gas composition and electron concentration of the plasma, the parameters such as the frequency, bandwidth and directivity of the antenna can be dynamically reconstructed [3] [4], as needed. A plasma antenna array can be designed with relatively small weight and volume.

The basic components of a plasma antenna are a plasma reflector and a fixed feed. Its working mechanism is similar to that of a conventional metal antenna. The radio signal from the feed is emitted onto the plasma during transmission and is reflected off the thin layer of plasma. The transmission path of the radio signal at the time of reception is reversed. The thin plasma layer constituting the plasma reflector is generated by gas discharge between the two electrodes in the low pressure vessel. In the low-pressure vessel, the cathode and the anode are placed above and below, and the high-energy electrons emitted from the cathode ionize the gas in the low-pressure vessel, and the thickness of the plasma layer is effectively controlled by the magnetic field. The required electron density is calculated according to the operating frequency during design. The electron density is proportional to the square of the frequency. The higher the operating frequency, the higher the plasma electron density required.

In addition, with the development of microwave technology, many new problems have been brought to the design of the antenna system. In order to obtain a high power pulse source and a wider operating frequency band (10 MHz 10 GHz), the size and weight of the antenna radiating element are increasing. The power of the pulse signal radiated by the antenna is mainly determined by the input voltage of the antenna. Sometimes the input voltage needs to reach several megavolts, which easily leads to the direct destruction of the antenna and the feeder, and the power transmission performance of the output power of 10 MW is also poor. If a high-voltage pulsed plasma antenna is used, its volume and weight are not large, the mobility is good, the size and weight are easy to meet the requirements, and the high-voltage burning of the feeder and the antenna is avoided. The working principle of a high-voltage pulsed plasma antenna is to convert the energy generated by the explosion into electromagnetic energy. This generator produces voltages in excess of 30 kV, a volume of approximately 0.5 m3 and a weight of approximately 300 g.

The plasma antenna mainly includes a gas plasma antenna, a solid plasma antenna, and a liquid plasma antenna. A typical gas plasma antenna is a gas plasma antenna developed by Markland Technologies, Inc. [6]. Articles on solid plasma antennas are light-controlled solid plasma leaky wave antennas and solid plasma antennas [7] [8]. In the 2004 IEEE Antenna and Propagation Annual Conference paper, an article on the polarization frequency of liquid plasma antennas was included [9].

From another perspective, the plasma antenna can be further divided into a plasma dielectric antenna, a plasma horn antenna, and a plasma mirror antenna. The first two are active radiators, the latter being passive reflectors [10].

The earlier research work in the United States on the practical use of plasma antennas appeared in 1990. The US Naval Laboratory (NRL) has been conducting system research for 15 years since 1990. The main research objects are X-band shipborne antennas, 94GHz airborne antennas and 60GHz space-based antennas. The main idea is that The plasma plate is used to replace the traditional conductor reflection surface, and the magnetic field and the electrode are used to control the scanning beam direction of the antenna [11].

Since the mid-1990s, the University of Tennessee has conducted research on stealth plasma antennas, including plasma radiation windows, under the auspices of the US Air Force Scientific Research Service (AFOSR) and the Naval Research Service (ONR). Theoretical and related feasibility experiments for antennas, low-radar cross-section vibrator antennas and their arrays. The mechanism is to use the plasma discharge tube as an antenna element. When the discharge tube is energized, it becomes a conductor, which can transmit and receive radio signals; when it is powered off, it becomes an insulator and basically does not emit a signal.

In 1998, the US Navy commissioned the University of Tennessee to successfully develop a plasma antenna that was developed into a U-shaped discharge tube. The U-shaped discharge tube was filled with ionized inert gas, as shown in Figure 1. When the antenna is in operation, the electrodes ionize the gas therein by gas discharge to form a plasma. Since the plasma contains a large amount of free electrons, it can play a similar role as a common metal antenna, that is, when a radio signal enters the tube through the metal electrode, electromagnetic waves can be generated by causing free electrons in the plasma to oscillate, that is, The radio signal can be sent out, and it can also be used to receive radio signals. When it is not necessary or need to be concealed, as long as the metal electrode at the base of the antenna is turned off, the inert gas immediately returns to the normal state and becomes an insulator. At this time, the antenna becomes an ordinary dielectric material, and the enemy radar is difficult to find. The latest experimental results show that the antenna has the same effect as the same configuration of the metal antenna in 100MHz 1GHz, and the noise levels of both transmitting and receiving are equivalent.

The US Navy also recently revealed that it is working on a small plasma antenna that can be mounted on a periscope and can be quickly assembled and disassembled for use in receiving radio signals in the 145 GHz frequency range.

In recent years, Markland is studying gas plasma antenna technology, which is jointly funded by the US military and led by the company's top plasma physicist group. Figures 2 and 3 show a partial plasma antenna developed by the company. According to reports, a series of important results have been achieved. Research results have shown that plasma antennas have unique advantages over traditional metal antennas, including:

1) Stealth: When the ionization state is removed, the plasma antenna will not generate backscattered radar waves, nor will it absorb high-power microwave radiation that can reduce the effectiveness of electronic countermeasures;

2) Adapt to a variety of signals: Plasma antennas have dynamically reconfigurable characteristics such as bandwidth, frequency, gain, and directivity;

3) Easy to remotely arrange: the plasma antenna is lighter and smaller than the conventional antenna design;

4) Higher efficiency: The plasma antenna can greatly reduce the impact excitation effect, thereby improving the performance of the short pulse radar.

In the early 1990s, Hughes Laboratories conducted a two-year, $650,000 experiment. The experiment shows that the plasma cross-sectional area of ​​a 13cm-long microwave reflector can be reduced by an average of 20dB in the frequency range of 4~14GHz, that is, the signal intensity of the radar acquisition echo is reduced to 1%. US naval scientists are still using ionized plasma to develop a radar system that is challenging for weapon design and military tactics. The US Naval Research Institute is implementing a research program called Agile Mirror, which aims to develop a new type of shipboard and airborne radar that can track at much faster speeds than existing radars. Attack missiles and make ships and aircraft more invisible.

Agile mirrors track multiple targets while continuously monitoring. Because it can be reoriented within lns (10-9s), conventional radar usually takes 1~10s, so the radar can be made very small and light, but the power generated is very large. The “Amazing Mirror” captures and tracks the target instantaneously, greatly improving the survivability of ships and fighters.

Plasma is a gas that can be considered almost no weight. There is enough free electrons in the structure of the plasma molecule, so it belongs to a kind of high temperature ionized superconducting gas. The superconducting properties of the plasma used in the "Amazing Mirror" are especially suitable for the reflection of radar microwaves, which can reflect radar electromagnetic waves like a mirror. In addition, the structure can be changed within 1 ns to transmit the radar beam in one direction. This shows that theoretically, 10 billion beams can be emitted simultaneously in 1 billion different directions within 1 s. Therefore, it can be said that the new system can theoretically provide a full range of coverage.

At present, the “Amazing Mirror” is still in the basic development stage, and the prototype has been completed using the existing model. If the radar system of the "Amazing Mirror" program is equipped on the fighter aircraft, the weight of the aircraft can be greatly reduced, enabling the aircraft to adopt more advanced guidance systems, avionics and new stealth materials.

The Australian National University has developed a unipolar surface-wave-driven plasma stealth antenna (shown in Figure 4) that has advantages that are not easily detected by enemy radars in special combat environments such as battlefields. The plasma antenna saves a large amount of metal material compared to a conventional antenna. Its appearance is a bit like a long fluorescent tube, and the inside of the tube is sealed with an inert gas. The tubular casing is made of a medium such as impact resistant glass, and is provided with a metal electrode at the bottom.

The propagation of the plasma surface wave is similar to the propagation of the wave on the metal antenna element, so the plasma column can be used as an antenna element like a metal bar. The Australian National University already has a corresponding plasma antenna patent [12], which is a plasma antenna for information transmission. The basic composition of the antenna is an electrodeless plasma tube and a power supply. The power source generates an effective electromagnetic field that causes the material in the tube to ionize, thereby forming a transmitting/receiving antenna.

Some Australian units also conduct research on the application of plasma antennas in communications and radar systems. Recent experiments have shown that good results can be obtained by transmitting HF and VHF signals with a plasma antenna. The radiation pattern can be preset and the baseband noise is not high.

In addition, the University of Canberra in Australia has also carried out theoretical and experimental research on plasma antennas under the auspices of the Australian Institute of Nuclear Science and Engineering (AINSE) and the Australian Research Council (ARC). The main target of the study is a communication antenna with a frequency below 500 MHz. In-depth theoretical analysis and experimental research on the excitation method and radiation efficiency of the plasma antenna, the conductive characteristics and noise of the plasma and its influence on the radiation performance of the antenna were carried out. These studies demonstrate the good potential of plasma antennas for scattering control [13].

The French Aerospace Research Institute has developed a fully stealth plasma radar antenna, which has a greater performance and resolution than conventional radar antennas. The radar antenna replaces conventional flat and parabolic antennas with plasma planar antennas. Figure 5 shows a schematic diagram of the working mechanism of a fully stealth plasma radar antenna. A plexiglass cylinder with a height and a diameter of 30 cm is filled with nitrogen gas, a linear hollow cathode is arranged on the top, and a metal anode is arranged on the bottom, and a plasma plane is generated by discharging the capacitor.

The performance of the plasma plane in the cylinder depends on the frequency band of the radar. The thickness of the plasma plane can be controlled by the magnetic field of the coil. The magnetic field of about 170 mm can obtain a plasma plane with a thickness of 26 mm thick. The magnetic field of 50 Gauss can obtain a thickness of 50 mm. Plasma plane. This plasma planar reflector opens up new avenues to improve radar antenna performance and adopt a novel working mechanism. The plasma planar antenna can be formed within 10 μs of the radar start-up, which is much faster than the conventional diode phase shifter type planar antenna.

At present, the plasma radar antenna has an optimal working range of 815 GHz and can be extended to a wider frequency band, which can be extended to longer wavelengths on decimeter waves and to 100 GHz on millimeter waves. Density can be maximized.

When using a single-base radar, the plasma radar antenna has a transmitting and receiving distance of approximately 300 km. According to the surveyor of the institute, for a short pulse, when using a multi-base radar, such a plasma planar antenna can also be used, and the receiver does not need to be oriented, because the plasma plane reflector is coded with an electromagnetic wave emission direction. .

This kind of plasma planar antenna is the first to be applied to the warning and tracking radar of the anti-missile defense system. The French Navy used it for defense against long-range supersonic anti-ship missiles. From the current display of the plasma stealth antenna, the structure is quite compact, and the next step will be to replace the current magnetic coil with the electronic device on the azimuth and elevation scan of the plasma planar transmitter, and then the structure of the antenna. It will be more compact and can be used not only for remote detection and surveillance of aircraft, but also for small military aircraft.

The Russian Kerdes Research Center has developed a new aircraft plasma stealth technology. This new technology can reduce the probability of aircraft being detected by radar by more than 99% without changing the shape of the aircraft, almost close to zero, reaching the full The purpose of stealth design. The working mechanism of this technology is completely different from the stealth technology of "reducing the target recognition feature" in the United States, which can ensure the stealth of the protected target and the cost is low. The new stealth technology is to form a special plasma cloud around the aircraft, without changing the shape design of aircraft and other equipment, without affecting flight performance, and even reduce flight resistance by more than 30%.

According to reports (Editor's note: the credibility of media reports, please consider the discretion), in early 1999, the Russian Kerdes Research Center has developed the first and second generation plasma generators, and tested on the aircraft Got a success. It is reported that its first generation product is a plasma generating sheet with a thickness of 0.50.7 mm, which is attached to the strong scattering portion of the aircraft, and plasma can be generated by ionizing the air. The second generation of products is a plasma generator. The ionized gas is added to the plasma generator. After the "pulse corona", the gas changes from high temperature to low temperature, and the plasma cloud layer can be generated. It has been proved by flight tests that it can not only weaken the radar's reflected signal, but also achieve stealth by changing the frequency of the transmitted signal.

The research center is currently developing a third-generation more effective stealth device based on the new physical mechanism. According to reports, the third-generation stealth device can use the electrostatic energy around the aircraft to reduce the radar cross-sectional area of ​​the aircraft. The Russian MiGer 1.44 (also known as MF-1) fighter aircraft, which can compete with the US F-22 fighter, is said to have adopted the new stealth device. The existing first and second generation stealth devices have been listed as approved Russian defense products.

In addition, Russia recently introduced a new method of using plasma weapons to intercept missiles. The main feature of the law is to change the flight condition of the flying body, that is, to use the high-power electromagnetic energy beam or beam that crosses each other to change the flight environment of the missile, so that the missile in flight deviates from the direction and loses the fighting effect. Plasma weapon refers to the use of a plasma generator and antenna mounted on the ground to emit ultra-high frequency electromagnetic energy beams or laser beams to focus in the atmosphere and form a cloud of high ionized air, ie, plasma clouds, density and ionization. The larger gas ionosphere is 1 to 100,000 times higher. This kind of plasmoid can be projected to the front and sides of the target, just like an "electromagnetic foot" to the target, which produces a rotational moment, deviates from the predetermined flight orbit, and under the influence of huge overweight differential pressure and inertia. Destroyed by itself, the entire interception process takes only 1/10s.

According to reports, Russia has developed a test-type plasma weapon, which consists of a UHF electromagnetic wave generator, a directional antenna, a strong power supply and a control system, and adopts a container-type module structure. The test set successfully shot down the shells. According to reports, the practical plasma weapon will be composed of the above system modules, each module can oscillate and output super-power (several billion watts) microwave beam propagating at the speed of light. The radar system for detecting the target is combined with the electromagnetic beam transmitting system that generates the plasma cloud. It integrates the functions of searching, detecting and striking the target, without taking time to identify the true or false target or the orientation of the target. You need to detect the target to shoot it down. Plasma weapons will greatly enhance the operational effectiveness of Russia's existing Moscow anti-missile defense system.

China has also begun its plasma exploratory research work. In 2002, China listed plasma stealth technology research as one of the major research projects of the country and one of the major projects of the National Natural Science Foundation of China.

The Institute of Environmental Engineering of Dalian Maritime University has carried out research on the strong ionization non-equilibrium plasma stealth method for aircraft [14], focusing on the reflection, absorption and reflection of electromagnetic waves by parameters such as plasma critical electron density and electron plasma frequency. influences. A strong electric field ionization discharge method is used to generate high-density, high-energy electrons in the discharge gap, which is sufficient to ionize nitrogen, oxygen and other gases, and form a high-density plasma layer with a certain gradient on the surface of the aircraft, capable of absorbing and refracting electromagnetic waves. The attenuation radar has an area of ​​more than a thousand times. The plasma device is a very thin assembly that weighs more than a hundred grams and can be attached to the electromagnetic wave scattering portion and the inlet wall. The method has the characteristics of absorption frequency bandwidth and high absorption rate, and is expected to become an airborne micro plasma generating device.

Under the auspices of the National Natural Science Foundation of the University of Electronic Science and Technology of China, the University of Electronic Science and Technology of China has developed a basic research facility for microwave plasma applications. It has developed a multi-functional, multi-purpose, computer-controlled large-scale microwave plasma application and diagnostic equipment. It is suitable for the composite diagnosis of non-equilibrium plasma, and does not carry out the mechanism of microwave plasma generation, and the in-depth study of the interaction mechanism between microwave plasma and matter provides an extremely important means [15].

Using the open cavity theory, combined with the needs of practical applications, the open microwave reaction chamber in the microwave plasma system was studied [16], and the plasma density and plasma collision frequency were calculated and analyzed. , phase and reflection coefficient effects. The numerical results show that under a certain plasma density, as the plasma collision frequency increases, the absorption of the microwave field by the plasma increases. This open structure can effectively form a microwave plasma in the cavity. The resulting standing wave field.

The University of Information Engineering, under the auspices of the National 863 Program, is studying plasma active lens antennas [17]. The so-called plasma active antenna is based on the atmospheric breakdown theory, and uses the multi-beam synthesis technology to control the ground HPM array to form an atmospheric ionization cloud of a specific structural shape in space, so that it has many antenna-like characteristics and functions.

The working principle of the plasma active lens antenna is to use a sufficiently high HPM pump wave energy and the nonlinear action of the atmosphere to focus in a specific region of the open atmosphere, so that the atmosphere in the focus region is excited to generate a high-intensity ionization reaction and form A relatively stable plasma having a specific structure and shape constitutes a lens antenna.

In the process of atmospheric ionization cloud formation, high-power microwave energy is the energy source for generating and maintaining a stable ionization cloud, while free electrons in the atmosphere act as catalysts in the process of ionization cloud formation, after the stable formation of ionization clouds The role of the transducer is to convert the pump wave energy into a bundled microwave energy, so it is called an active antenna.

The researchers proposed a plasma active lens antenna with HPM as its energy source, and discussed its working characteristics and applications. It can bunch HPM working waves as needed, or it can be sent back to the original HPM wave. In addition, it can also form devices such as spatial active filtering. The significant difference between this type of antenna and conventional active antennas is that it is strongly dependent on the pump-wave HPM pump source; because it is in space and the forming device does not have to be moved, the size and shape of the antenna are generally unrestricted; It has a short existence time and strong maneuverability; it is more convenient to form a large high-gain antenna.

From the existing public information, plasma antenna technology has attracted extensive attention from industry experts such as domestic electronic countermeasures, aircraft stealth, radar and antenna design, focusing on the stealth application of plasma antennas. In order to introduce the theoretical and experimental research of foreign plasma antenna technology, tracking the development and application status and feasibility analysis of foreign countries.

It can be seen from the above development overview that many large companies in the world are researching and developing plasma antennas, and some have entered the practical stage and applied for patents. Here are some representative plasma antenna patents, the patent holders in parentheses:

• Multi-tube plasma antenna [4] (US Naval Administration). This is a broadband, compact plasmon antenna for high frequency or ultra high frequency communication. The ionizing gas or plasma is used to propagate the high frequency or ultra high frequency electromagnetic signal, and the electrode is pressurized to ionize the gas. The plasma is restricted in the non-metallic coaxial tube in the non-metal pressure vessel, and the plasma is changed by the electric field gradient. The shape and density of the antenna affect the gain and directivity of the antenna. The plasma inner tube is used as a radiation source, and the outer tube is used for changing the radiation of the inner tube and reflecting the radiation signal, measuring the density of the plasma by an instrument, providing a method for measuring the incident signal and adjusting the radiation frequency;

• A plasma antenna that uses a reverse photon beam to generate current (US Naval Administration). A plasma antenna with a plasma column for low frequency and ultra low frequency communication. The laser emits a laser beam through the plasma in an alternating, reversed manner. When the laser is activated, its laser beam produces a photoelectric collision that transfers kinetic energy to the electrons in the plasma. The lasers alternately operate in the plasma to generate alternating currents, thereby radiating the electromagnetic field;

• Standing wave plasma antenna with a plasma reflector (US Naval Administration). The invention is applicable to underwater broadband communications. The ionizer produces an ionized beam in a plasma column that is elongated along a vertical axis. The modulated signal is applied to a photocell for modulating the ionized beam. The result of the change is the formation of a plasma gradient that causes ions and electrons to The vertical channel oscillates to form an oscillating current containing a modulation frequency. These currents produce an amplitude, phase, and frequency modulated electromagnetic field that is radiated from the plasma column;

• Reconfigurable plasma antenna (ASI Technologies, USA) [3]. The invention is a fully reconfigurable plasma antenna comprising a method of effecting a plasma antenna and reconstructing a plasma antenna radiation pattern. The main component of the antenna is: a closed chamber; the enclosed chamber contains a device for generating plasma; at least three excitation points connected to the device are used to generate electromagnetic waves; and an energy source coupled to the three excitation points is in the closed chamber. At least one plasma conduction path is created. The improved mechanism can be used to reconstruct the conduction path;

• Plasma controlled antenna (Raytheon, USA). It is an improved plasma controlled millimeter wave or microwave scanning antenna. An electron plasma zone and via are illuminated onto a photoconductive wafer. Using a special distribution of the plasma and a reflective surface behind the lens, the antenna can be formed at low light intensities, with a 180° phase shift applied to the selected millimeter wave/microwave;

• Solid plasma antenna (US Patent by Harper, RE). This is a solid electronically controlled antenna for high frequency communication (eg 1 GHz). A solid electronically controlled antenna is formed by creating a localized plasma region on a piece of semiconductor material. In this plasma region, a carrier can be injected or a carrier can be generated. The patent also describes a method of fabricating a sheet of semiconductor material (silicon wafer) used;

• Plasma antenna (Australian National University). The invention is a surface wave driven plasma stealth antenna. The foregoing has been introduced.

In addition, the Malibu Institute of the United States applied for a plasma phased array electronic scanning antenna. Waveband Technologies applied for an antenna with a plasma grid.

The magical function of the plasma, especially its obvious military application potential, has long been the focus of the world's military powers. Authorities say that the next high-tech commanding point in the military field is plasma technology.

The plasma antenna is an update of the traditional antenna structure, which expands the scientific attraction and engineering application ability of the plasma, and because of the unique physical properties of the plasma, it has an incalculable development potential in solving the mutual coupling and stealth of the antenna. A big step forward in today's antenna technology will finally show its tenacious vitality.