Relationship between axial ratio and cross polarization theory

Improved Measurement Method of Circularly-Polarized Antennas Based on Linear-Component Amplitudes

relationship between axial ratio and cross polarization theory

Antenna Theory. Share . 2. radiation pattern co polar and cross polar, and if you able to look at your E field it will rotate on antenna structure. 3. The axial ratio of circular polarized antenna is 3 dB or higher and linear polarized antenna is very large. What is the difference between co-polarization and cross polarization?. axial-ratio beam of simple circularly-polarized antennas. It is shown, that by cross polarization. As the reflections Theoretical background. Let us investigate difference at the dipole feeds Δph is up to ±6° distorted from. 90° (i.e. for Δph. Antennas With Axial Asymmetry: Theoretical Proof and Experimental (for the case of the SFP LWA) that the axial ratio is controlled and minimized by the the shunt radiation was cross-polarized, whereas no consider- ation was an intrinsic quadrature phase relationship between series radia- tion and.

The measured results are in agreement with the simulated results, which prove this method is correct, effective and practical. Introduction Circularly-polarized CP antennas have many advantages such as insensitivity to polarization locations, elimination of the signal Faraday rotation effect caused by the ionosphere, and strong anti-interference ability.

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Therefore, they are wi- dely used in satellite communication, radar, GPS and other systems. It is very important to measure their characteristics of axial ratio ARrotation sense, pattern and so on. By means of the measurement based on circular components, it is easy to measure CP antennas [1]. However, the auxiliary CP antennas with high polarization purity are rare in reality, so the uncertainty of this method is relatively large. Two methods about measuring ARs of CP antennas based on linear components are discussed in [2].

The first method is to measure one set of orthogonal LP amplitudes and phases by utilizing linearly-polarized auxiliary antennas.

relationship between axial ratio and cross polarization theory

Another method is to measure only two sets of orthogonal LP amplitudes without phase measurement. ARs and patterns are separately obtained in [3] [4] [5] by using the first method.

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However, the phase measurement is limited by measuring equipment and the error is relatively large in fact. The characteristics of ARs are got by utilizing the second method in [6] and [7]. It is not necessary to measure phase information, while amplitudes can be measured accurately. As a result, the measuring accuracy of AR is improved. But this method also has a problem that the rotation sense of the co-polarization cannot be determined due to the absence of the phase information.

There is no analysis about this problem in the related records.

relationship between axial ratio and cross polarization theory

An improved measurement method of CP antennas based on linear-compo- nent amplitudes is proposed in this paper. It is the first time to point out the problem that the rotation sense of the co-polarization cannot be determined. And a solution is presented to determine the rotation sense by using common CP auxiliary antennas. In addition, some particular cases with large errors occur in practical measurement, here revises and improvements are given.

Finally, co- polarization and cross-polarization patterns are further obtained from AR results. To verify this improved method, a self-developed CP microstrip array was measured repeatedly. The measured results are in agreement with the simulated results, which prove the correction method is correct, effective and practical. Measurement Based on Linear-Component Amplitudes and Phases The polarization state of the electromagnetic wave is distinguished by the orientation of its electric field vector.

However, this is seldom a problem unless there is noise or strong signals nearby. Typical Applications Vertical polarization is most often used when it is desired to radiate a radio signal in all directions such as widely distributed mobile units.

Vertical polarization also works well in the suburbs or out in the country, especially where hills are present. As a result, nowadays most two-way Earth to Earth communications in the frequency range above 30 MHz use vertical polarization. Horizontal polarization is used to broadcast television in the USA. Some say that horizontal polarization was originally chosen because there was an advantage to not have TV reception interfered with by vertically polarized stations such as mobile radio.

Also, man made radio noise is predominantly vertically polarized and the use of horizontal polarization would provide some discrimination against interference from noise. In the early days of FM radio in the MHz spectrum, the radio stations broadcasted horizontal polarization.

However, in the 's, FM radios became popular in automobiles which used vertical polarized receiving whip antennas. As a result, the FCC modified Part 73 of the rules and regulations to allow FM stations to broadcast RHC or elliptical polarization to improve reception to vertical receiving antennas as long as the horizontal component was dominant.

Circular polarization is most often use on satellite communications. This is particularly desired since the polarization of a linear polarized radio wave may be rotated as the signal passes through any anomalies such as Faraday rotation in the ionosphere. Furthermore, due to the position of the Earth with respect to the satellite, geometric differences may vary especially if the satellite appears to move with respect to the fixed Earth bound station.

Circular polarization will keep the signal constant regardless of these anomalies.

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  • axial ratio cross polarization

What is Available As stated earlier, for best performance, it is desirable to use an antenna with the same polarization on both ends of a communications path.

If a system is already in place, all that is required is to find out what polarization is presently being used and match it. Most base station antenna providers will supply either vertical or horizontal polarized antennas.

Antenna Axial Ratio to CP X-pol, circular polarization, antenna design

They are the most economical types. Furthermore, vertically polarized antennas seem to be the most popular for two way communications, as stated above, while horizontal polarization is most predominant in broadcast communications such as TV and FM. Circularly polarized antennas are normally more costly than linear polarized types since true circular polarization is difficult to attain.

An example of a true circularly polarized antenna is the helix. However, the most common circularly polarized antenna uses crossed Yagis for "near circular" or elliptical polarization. Elliptical polarization can be generated by placing two identical linear polarized Yagis at right angles 90 degree phase differential to each other and then feeding them with equal power and a phasing network.

Other Considerations If your antenna is to be located on an existing tower or building with other antennas in the vicinity, try to separate the antennas as far as possible from each other. In the UHF range, increasing separation even a few extra feet may significantly improve performance from problems such as desensitization.

When setting up your own exclusive communications link, it may be wise to first test the link with vertical and then horizontal polarization to see which yields the best performance if any. If there are any reflections in the area, especially from structures or towers, one polarization may outperform the other. Furthermore, if there are other RF signals in an area, using a polarization opposite the predominant high level signals will give some isolation as discussed earlier.

On another note, when radio waves strike a smooth reflective surface, they may incur a degree phase shift, a phenomenon known as specular or mirror image reflection.

relationship between axial ratio and cross polarization theory

The reflected signal may then destructively or constructively affect the direct LOS signal. Circular polarization has been used to an advantage in these situations since the reflected wave would have a different sense than the direct wave and block the fading from these reflections.

Diversity Reception Even if the polarizations are matched, other factors may affect the strength of the signal. The most common are long and short term fading.

Long term fading results from changes in the weather such as barometric pressure or precipitation or when a mobile station moves behind hills or buildings. Short term fading is often referred to as "multipath" fading since it results from reflected signals interfering with the LOS signal. Some of these fading phenomenon can be decreased by the use of diversity reception. This type of system usually employs dual antennas and receivers with some kind of "voting" system to choose the busiest signal.

However, for best results, the antennas should be at least 20 wavelengths apart so that the signals are no longer correlated. This would be feet at MHz, quite a structural problem. Nowadays we are inundated with mobile radios and cellular telephones.

relationship between axial ratio and cross polarization theory

The polarization on handheld units is often random depending on how they are held by the user. This has led to new studies which have found that polarization diversity can be an advantage.