Microstrip antenna

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A microstrip antenna array for a satellite television receiver Feedingstrips.jpg
A microstrip antenna array for a satellite television receiver
Diagram of the feed structure of a microstrip antenna array Antenna flat panel.png
Diagram of the feed structure of a microstrip antenna array

In telecommunication, a microstrip antenna (also known as a printed antenna) usually is an antenna fabricated using photolithographic techniques on a printed circuit board (PCB). [1] It is a kind of internal antenna. They are mostly used at microwave frequencies. An individual microstrip antenna consists of a patch of metal foil of various shapes (a patch antenna) on the surface of a PCB, with a metal foil ground plane on the other side of the board. Most microstrip antennas consist of multiple patches in a two-dimensional array. The antenna is usually connected to the transmitter or receiver through foil microstrip transmission lines. The radio frequency current is applied (or in receiving antennas the received signal is produced) between the antenna and ground plane. Microstrip antennas have become very popular in recent decades due to their thin planar profile which can be incorporated into the surfaces of consumer products, aircraft and missiles; their ease of fabrication using printed circuit techniques; the ease of integrating the antenna on the same board with the rest of the circuit, and the possibility of adding active devices such as microwave integrated circuits to the antenna itself to make active antennas [2] Patch antenna. Based on its origin, microstrip consists of two words, namely micro (very thin/small) and is defined as a type of antenna that has a blade/piece shape and is very thin/small. [3]

Contents

The most common type of microstrip antenna is commonly known as patch antenna. Antennas using patches as constitutive elements in an array are also possible. A patch antenna is a narrowband, wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating dielectric substrate, such as a printed circuit board, with a continuous metal layer bonded to the opposite side of the substrate which forms a ground plane. Common microstrip antenna shapes are square, rectangular, circular and elliptical, but any continuous shape is possible. Some patch antennas do not use a dielectric substrate and instead are made of a metal patch mounted above a ground plane using dielectric spacers; the resulting structure is less rugged but has a wider bandwidth. Because such antennas have a very low profile, are mechanically rugged and can be shaped to conform to the curving skin of a vehicle, they are often mounted on the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications devices.

Advantages

Microstrip antennas are relatively inexpensive to manufacture and design because of the simple two-dimensional physical geometry. They are usually employed at UHF and higher frequencies because the size of the antenna is directly tied to the wavelength at the resonant frequency. A single patch antenna provides a maximum directive gain of around 6–9 dBi. It is relatively easy to print an array of patches on a single (large) substrate using lithographic techniques. Patch arrays can provide much higher gains than a single patch at little additional cost; matching and phase adjustment can be performed with printed microstrip feed structures, again in the same operations that form the radiating patches. The ability to create high gain arrays in a low-profile antenna is one reason that patch arrays are common on airplanes and in other military applications.

Such an array of patch antennas is an easy way to make a phased array of antennas with dynamic beamforming ability. [4]

An advantage inherent to patch antennas is the ability to have polarization diversity. Patch antennas can easily be designed to have vertical, horizontal, right hand circular (RHCP) or left hand circular (LHCP) polarizations, using multiple feed points, or a single feedpoint with asymmetric patch structures. [5] This unique property allows patch antennas to be used in many types of communications links that may have varied requirements.

Rectangular patch

The most commonly employed microstrip antenna is a rectangular patch which looks like a truncated microstrip transmission line. It is approximately of one-half wavelength long. When air is used as the dielectric substrate, the length of the rectangular microstrip antenna is approximately one-half of a free-space wavelength. As the antenna is loaded with a dielectric as its substrate, the length of the antenna decreases as the relative dielectric constant of the substrate increases. The resonant length of the antenna is slightly shorter because of the extended electric "fringing fields" which increase the electrical length of the antenna slightly. An early model of the microstrip antenna is a section of microstrip transmission line with equivalent loads on either end to represent the radiation loss.

Specifications

The dielectric loading of a microstrip antenna affects both its radiation pattern and impedance bandwidth. As the dielectric constant of the substrate increases, the antenna bandwidth decreases which increases the Q factor of the antenna and therefore decreases the impedance bandwidth. This relationship did not immediately follow when using the transmission line model of the antenna, but is apparent when using the cavity model which was introduced in 1973 by Itoh and Mittra [6] The radiation from a rectangular microstrip antenna may be understood as a pair of equivalent slots. These slots act as an array and have the highest directivity when the antenna has an air dielectric and decreases when it is replaced by a dielectric substrate with increasing relative permittivity.

The half-wave rectangular microstrip antenna has a virtual shorting plane along its center. This may be replaced with a physical shorting plane to create a quarter-wavelength microstrip antenna. This is sometimes called a half-patch. The antenna only has a single radiation edge (equivalent slot) which lowers the directivity/gain of the antenna. The impedance bandwidth is slightly lower than a half-wavelength full patch as the coupling between radiating edges has been eliminated.

Other types

Another type of patch antenna is the planar inverted-F antenna (PIFA). The PIFA is common in cellular phones (mobile phones) as a built-in structure. [7] [8] These antennas are derived from a quarter-wave half-patch antenna. The shorting plane of the half-patch is reduced in length which decreases the resonance frequency. [9] It offers a low profile and also with acceptable SAR properties. This antenna resembles an inverted F, which explains the PIFA name. It is popular as a compact antenna with an omnidirectional pattern. [10]

Often PIFA antennas have multiple branches to resonate at the various cellular bands. On some phones, grounded parasitic elements are used to enhance the radiation bandwidth characteristics.

The folded inverted conformal antenna (FICA) [11] has some advantages with respect to the PIFA, because it allows better volume reuse.

Defected Ground Structure (DGS)-integrated microstrip patch has been popular for multiple purposes. This technique introduces a limited number of small-sized slots, termed as 'defects' on the ground plane beneath the patch, and is potentially capable of improving its far-field as well as near-field properties. This was conceived and introduced in 2005 by Guha [12] to control the cross-polarized radiations without involving any extra component, volume, weight, or cost. The technique is advanced enough to reduce cross-polarized radiations even over the diagonal-planes of a microstrip patch. DGS-technique is equally effective in reducing the mutual coupling in large microstrip arrays and hence mitigating the scan blindness issue of the radar beams. [13] [14] The DGS technique is found to be highly attractive in air-borne applications.

See also

Related Research Articles

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<span class="mw-page-title-main">Microstrip</span> Conductor–ground plane electrical transmission line

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<span class="mw-page-title-main">Patch antenna</span> Type of antenna with a low profile

A patch antenna is a type of antenna with a low profile, which can be mounted on a surface. It means that it is printed on the dielectric material. It consists of a planar rectangular, circular, triangular, or any geometrical sheet or "patch" of metal, mounted over a larger sheet of metal called a ground plane. They are the original type of microstrip antenna described by Howell in 1972.

<span class="mw-page-title-main">Unbalanced line</span>

In telecommunications and electrical engineering in general, an unbalanced line is a pair of conductors intended to carry electrical signals, which have unequal impedances along their lengths and to ground and other circuits. Examples of unbalanced lines are coaxial cable or the historic earth return system invented for the telegraph, but rarely used today. Unbalanced lines are to be contrasted with balanced lines, such as twin-lead or twisted pair which use two identical conductors to maintain impedance balance throughout the line. Balanced and unbalanced lines can be interfaced using a device called a balun.

The spurline is a type of radio-frequency and microwave distributed element filter with band-stop (notch) characteristics, most commonly used with microstrip transmission lines. Spurlines usually exhibit moderate to narrow-band rejection, at about 10% around the central frequency.

<span class="mw-page-title-main">Stripline</span> Early electronic transmission line medium

In electronics, stripline is a transverse electromagnetic (TEM) transmission line medium invented by Robert M. Barrett of the Air Force Cambridge Research Centre in the 1950s. Stripline is the earliest form of planar transmission line.

A dielectric resonator antenna (DRA) is a radio antenna mostly used at microwave frequencies and higher, that consists of a block of ceramic material of various shapes, the dielectric resonator, mounted on a metal surface, a ground plane. Radio waves are introduced into the inside of the resonator material from the transmitter circuit and bounce back and forth between the resonator walls, forming standing waves. The walls of the resonator are partially transparent to radio waves, allowing the radio power to radiate into space.

<span class="mw-page-title-main">Metamaterial antenna</span>

Metamaterial antennas are a class of antennas which use metamaterials to increase performance of miniaturized antenna systems. Their purpose, as with any electromagnetic antenna, is to launch energy into free space. However, this class of antenna incorporates metamaterials, which are materials engineered with novel, often microscopic, structures to produce unusual physical properties. Antenna designs incorporating metamaterials can step-up the antenna's radiated power.

<span class="mw-page-title-main">Tunable metamaterial</span>

A tunable metamaterial is a metamaterial with a variable response to an incident electromagnetic wave. This includes remotely controlling how an incident electromagnetic wave interacts with a metamaterial. This translates into the capability to determine whether the EM wave is transmitted, reflected, or absorbed. In general, the lattice structure of the tunable metamaterial is adjustable in real time, making it possible to reconfigure a metamaterial device during operation. It encompasses developments beyond the bandwidth limitations in left-handed materials by constructing various types of metamaterials. The ongoing research in this domain includes electromagnetic band gap metamaterials (EBG), also known as photonic band gap (PBG), and negative refractive index material (NIM).

<span class="mw-page-title-main">Waveguide filter</span> Electronic filter that is constructed with waveguide technology

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<span class="mw-page-title-main">Substrate-integrated waveguide</span> Waveguide formed by posts inserted in a dielectric substrate

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A via fence, also called a picket fence, is a structure used in planar electronic circuit technologies to improve isolation between components which would otherwise be coupled by electromagnetic fields. It consists of a row of via holes which, if spaced close enough together, form a barrier to electromagnetic wave propagation of slab modes in the substrate. Additionally if radiation in the air above the board is also to be suppressed, then a strip pad with via fence allows a shielding can to be electrically attached to the top side, but electrically behave as if it continued through the PCB.

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<span class="mw-page-title-main">Reconfigurable antenna</span> Antenna capable of modifying its frequency and radiation properties dynamically

A reconfigurable antenna is an antenna capable of modifying its frequency and radiation properties dynamically, in a controlled and reversible manner. In order to provide a dynamic response, reconfigurable antennas integrate an inner mechanism that enable the intentional redistribution of the RF currents over the antenna surface and produce reversible modifications of its properties. Reconfigurable antennas differ from smart antennas because the reconfiguration mechanism lies inside the antenna, rather than in an external beamforming network. The reconfiguration capability of reconfigurable antennas is used to maximize the antenna performance in a changing scenario or to satisfy changing operating requirements.

<span class="mw-page-title-main">Inverted-F antenna</span> Antenna used in wireless communication

An inverted-F antenna is a type of antenna used in wireless communication, mainly at UHF and microwave frequencies. It consists of a monopole antenna running parallel to a ground plane and grounded at one end. The antenna is fed from an intermediate point a distance from the grounded end. The design has two advantages over a simple monopole: the antenna is shorter and more compact, allowing it to be contained within the case of the mobile device, and it can be impedance matched to the feed circuit by the designer, allowing it to radiate power efficiently, without the need for extraneous matching components.

Debatosh Guha is an Indian researcher and educator. He is a Professor at the Institute of Radio Physics and Electronics at the Rajabazar Science College, University of Calcutta. He is an Adjunct faculty at the National Institute of Technology Jaipur and had also served Indian Institute of Technology Kharagpur as HAL Chair Professor for a period during 2015-2016.

Air stripline is a form of electrical planar transmission line whereby a conductor in the form of a thin metal strip is suspended between two ground planes. The idea is to make the dielectric essentially air. Mechanical support of the line may be a thin substrate, periodical insulated supports, or the device connectors and other electrical items.

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In radio systems, many different antenna types are used whose properties are especially crafted for particular applications.

A defected ground structure (DGS) is a purposefully created defect on the ground plane of a printed microstrip board. It is typically created in the form of an etched-out pattern on the ground plane. DGS is a simplified form of Electromagnetic Band Gap (EBG) structure. This EBG is a periodic pattern featuring a band-stop property in microstrip transmission line and circuit applications, but the DGS comprises a single defect or a very limited number of defects with periodic/aperiodic configurations.

References

  1. Lee, Kai Fong; Luk, Kwai Man (2017). Microstrip Patch Antennas. World Scientific. pp. 8–12. ISBN   978-981-3208-61-2.
  2. Pandey, Anil (2019). Practical Microstrip and Printed Antenna Design. Bostan: Artech House. p. 443. ISBN   978-1-63081-668-1.
  3. Rahman, Dzul (2023-01-02). "APA ITU ANTENA MICROSTRIP ?". bte-jkt.telkomuniversity.ac.id. Retrieved 2023-01-02.
  4. "Welcome to antennas 101" by Louis E. Frenzel, "Electronic Design" 2008
  5. Bancroft, R. Microstrip and Printed Antenna Design Noble Publishing 2004, chapter 2-3
  6. Tatsuo Itoh, and Raj Mittra "Analysis of microstrip disk resonator," Arch. Eleck. Ubertagung, vol. 21, Nov. 1973 pp. 456-458.
  7. "PIFA - The Planar Inverted-F Antenna".
  8. Iulian Rosu. "PIFA – Planar Inverted F Antenna".
  9. "Inverted-F Antenna (IFA)" at antenna-theory.com1
  10. Taga, T. Tsunekawa, K. and Saski, A., "Antennas for Detachable Mobile Radio Units," Review of the ECL, NTT, Japan, Vol. 35, No.1, January 1987, pp. 59-65.
  11. Di Nallo, C.; Faraone, A., "Multiband internal antenna for mobile phones," Electronics Letters, vol.41, no.9, pp. 514-515, 28 April 2005
  12. Guha, D.; Biswas, M.; Antar, Y. (2005), "Microstrip patch antenna with defected ground structure for cross polarization suppression", IEEE Antennas and Wireless Propagation Letters, 4 (1): 455–458, Bibcode:2005IAWPL...4..455G, doi:10.1109/LAWP.2005.860211, S2CID   27170050
  13. Hou, D.-B.; et, al. (2009), "Elimination of scan blindness with compact defected ground structures in microstrip phased array", IET Microwaves, Antennas & Propagation, 3 (2): 269–275, doi:10.1049/iet-map:20080037
  14. Guha, D.; Biswas, S.; Antar, Y. (2011), "Defected Ground Structure for Microstrip Antennas", in Guha, Debatosh; Antar, Yahia M. M (eds.), Microstrip and Printed Antennas, John Wiley & Sons, pp. UK, doi:10.1002/9780470973370, ISBN   9780470681923, S2CID   106449287