RFID Antenna
Design

The radiation pattern is a graph showing the angular variation of the antenna strength (the intensity of the electromagnetic field) at a constant distance in the far field of the antenna. The antenna radiation pattern is three-dimensional, but in practice, it is usually drawn as two-dimensional cross-sections in horizontal and vertical planes. When working as an antenna receiver or transmitter, the radiation pattern is the same. The size of the radiation pattern does not matter. What matters is the relative distance from the antenna position to the points forming the radiation pattern. The radiation pattern of an antenna is obtained by measuring the intensity of the electromagnetic field in the far-field region of the antenna. The area near the antenna or any radiating element is defined as the near field, while the far field is defined as the far field. The near field is the area where the electric and magnetic field components do not show the plane wave character. The far field is the region where plane wave approach can be done. The definitions of the near and far fields are determined by parameters such as frequency, antenna dimensions, and antenna type and interactivity. The power density is measured in the far field E field (electric field) sensor or H field (magnetic field) sensor. It is difficult to measure the power density in the near field. Communication is achieved by using the far field component of the antennas. The simplest radiation pattern is the radiation pattern of an isotropic antenna, which is defined as a theoretical antenna (not implemented in practice). The radiation pattern of the isotropic antenna is a beam with an isotropic antenna at its center. In the radiation pattern of the antenna, there are 3 different radiation types as main lobe, back lobe and side lobes

The direction of the antenna is the ratio of the power density at the far end of the antenna to the maximum power at which the same power isotropic antenna is at the same distance.

Beam is the direction the antenna sends or receives maximum power from. The beamwidth of a directional antenna is the angle between the directions in which the maximum radiant power falls on the beam in the beam diagram. In these directions, where the power falls halfway, the power level is 3 dB below maximum power. The beamwidth is given in terms of half power beamwidth or 3-dB beamwidth.

Antenna efficiency is related to the spreading of the power applied to the antenna by the antenna or the expenditure within the antenna. Also known as radiation efficiency, is the ratio of the electrical power applied to the antenna to the radiated power of the antenna. If this power applied to an antenna input can radiate away is called a high efficiency antenna; a low efficiency antenna does not spread away but absorbs a large of it. Antenna efficiency varies with the selection of the antenna transmission line for incompatible impedance values. In short, antenna efficiency is a measure of antenna losses and is between 0 and 1.

Antenna gain is equal to antenna efficiency multiplied by directionality. The gain of a lossless antenna is equal to the gain of the antenna. Antenna gain is commonly given in dB. It can also be expressed in terms of dBi to indicate that it is relative to the isotropic antenna. Antenna gain is the directing of the antenna output power in a certain direction rather than obtaining a larger output power than the power applied to the antenna. That is, the radiation power is reduced to some direction, and it is replicated in one direction.

The polarization of the antenna is named according to the type of the electric field vector that is emitted from the antenna. There are three types of antenna polarizations, linear, circular and elliptical. Linear polarization; If the electric field is horizontal, it is called horizontal polarization. If the electric field is vertical, it is called vertical polarization. Circular polarization is called right-hand or left-hand polarized according to the direction of rotation of the electromagnetic waveguide and the circular rotation of the vector of the electric field. The elliptic polarization is called the right-hand or left-hand polarized according to the orientation of the electromagnetic wave and the direction in which the electric field vector is drawn by ellipsis. Nonconsequential to the polarity, the electric and magnetic field vectors are perpendicular to each other and are located in a plane perpendicular to the direction of propagation of the electromagnetic waveguide. This is called a plane wave. These two vectors, rotating perpendicular to each other at a certain angular velocity, form an electromagnetic field traveling in the direction of travel of a screw relative to the direction of rotation of the electric field vector.

The input impedance of the antenna is the flux rate of the voltage at the feed ends of the antenna. In order to minimize the losses on the antenna resistance and thus increase the antenna efficiency, the characteristic impedance of the transmission line feeding the antenna must be chosen as the conjugate of the antenna impedance. This process is called impedance matching.

The bandwidth of the antenna is the frequency range in which the antenna’s significant performance parameters are within acceptable limits. In general, the bandwidth of the antenna is considered to be between the points where the s-parameters reach -10 dB.

The bandwidth of the antenna is the frequency range in which the antenna’s significant performance parameters are within acceptable limits. In general, the bandwidth of the antenna is considered to be between the points where the s-parameters reach -10 dB.