Polarized Slot Antenna

ABSTRACT This paper presents a novel design of a circular polarized antenna for ultra-wideb and (UWB) applications. A simple narrowband patch antenna is optimized to the geometry of the UWB an tenna. A partial ground plane, a couple of cross slots, and additional slots were designed and optimized using CST Mic rowave Studio. Horizontally polarized and dual polarized antennas are described herein. In some examples, a horizontally polarized and dual polarized antenna may be mounted or operated with the physical vertical axis of the antenna being substantially perpendicular to a plane defined by the surface of the earth, and emanate an electric field that is parallel. A slot antenna consists of a metal surface, usually a flat plate, with one or more holes or slots cut out. When the plate is driven as an antenna by an applied radio frequency current, the slot radiates electromagnetic waves in a way similar to a dipole antenna.

Circularly polarized single-layer U-slot microstrip patch antenna has been proposed. The suggested asymmetrical U-slot can generate the two orthogonal modes for circular polarization without chamfering any corner of the probe-fed square patch microstrip antenna. Polarized antennas than for the linearly polarized antenna A. Comparing the real part of the input impedance versus the ARB instead of the slot width it can be seen that for a given substrate and ARB the real part of the input impedance of the different antennas is similar except for antenna C. Contrary to the linearly polarized antenna.

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Electronic Theses and Dissertations, 2004-2019

Title

Author

Keywords

Wideband, Dual-Polarized, Differential, SIW, Cavity Backed, Slot, Antenna, Double-Resonant, Circular Polarization, Array

Abstract

A new technique for designing wideband dual-polarized cavity-backed slot antennas is presented. The structure is in the form of a double-resonant, dual-polarized slot antenna backed by a shallow substrate integrated cavity with a depth of approximately one tenth the free space wavelength. The presence of the cavity behind the slot enhances the antenna's directivity and reduces the possibility of surface wave propagation in the antenna substrate when the element is used in an array environment. Moreover, the dual-polarized nature of this radiating element may be exploited to synthesize any desired polarization (vertical, horizontal, RHCP, or LHCP). The double-resonant behavior observed in this substrate-integrated cavity-backed slot antenna (SICBSA) is utilized to enhance its bandwidth compared to a typical cavity-backed slot antenna. A prototype of the proposed antenna is fabricated and tested. Measurement results indicate that a bandwidth of 19%, an average gain of 5.3 dB, and a wideband differential isolation of 30 dB can be achieved using this technique. The principles of operation along with the measurement results of the fabricated prototype are presented and discussed in this dissertation. The SICBSA is investigated as a candidate for use as an array element. A uniform two element phased array is demonstrated to locate the main beam from boresight to thirty degrees. The potential effects of mutual coupling and surface wave propagation are considered and analyzed.

Notes

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Circularly Polarized U-slot Antenna

Graduation Date

2010

Advisor

Wahid, Parveen

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Polarized Slot Antenna

Electrical Engineering and Computer Science

Degree Program

Electrical Engineering

Format

application/pdf

Identifier

CFE0003066

URL

http://purl.fcla.edu/fcla/etd/CFE0003066

Language

English

Release Date

May 2010

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

STARS Citation

Paryani, Rajesh, 'Design Of A Wideband Dual-polarized Cavity Backed Slot Antenna' (2010). Electronic Theses and Dissertations, 2004-2019. 4226.
https://stars.library.ucf.edu/etd/4226

Included in

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Antenna Basic Theory Tutorial Includes:
Basic antenna theoryPolarisationResonance & bandwidthGain & directivityFeed impedance

Antenna polarisation is an important factor when designing and erecting radio antennas or even incorporating them into small wireless or mobile communications systems. Some antennas are vertically polarised, others horizontal, and yet other antenna types have different forms of polarisation.

When designing an antenna, deciding on a particular form of antenna, it is important to understand which way it needs to be polarised. Radio antennas with a particular polarisation will not be effective receiving electromagnetic wave signals with a different polarisation.

That said, many wireless and mobile phone systems may rely on the fact that there are likely to be many reflections between the transmitter and the receiver and these will tend to mean that a signal will have a particular polarisation when it reaches the receiver. Nevertheless, the polarisation of the antenna is still important.

Antenna polarisation basics

For the electromagnetic wave the polarization is effectively the plane in which the electric wave vibrates. This is important when looking at antennas because they are sensitive to polarisation, and generally only receive or transmit a signal with a particular polarization.

For most antennas it is very easy to determine the polarization. It is simply in the same plane as the elements of the antenna. So a vertical antenna (i.e. one with vertical elements) will receive vertically polarised signals best and similarly a horizontal antenna will receive horizontally polarised signals.

It is important to match the polarization of the RF antenna to that of the incoming signal. In this way the maximum signal is obtained. If the RF antenna polarization does not match that of the signal there is a corresponding decrease in the level of the signal. It is reduced by a factor of cosine of the angle between the polarisation of the RF antenna and the signal.

Accordingly the polarisation of the antennas located in free space is very important, and obviously they should be in exactly the same plane to provide the optimum signal. If they were at right angles to one another (i.e. cross-polarised) then in theory no signal would be received.

For terrestrial radio communications applications it is found that once a signal has been transmitted then its polarisation will remain broadly the same. However reflections from objects in the path can change the polarisation. As the received signal is the sum of the direct signal plus a number of reflected signals the overall polarisation of the signal can change slightly although it remains broadly the same.

Polarisation categories

Different types of electromagnetic wave polarisation propagate in slightly different ways under some circumstances.

This means that for some forms of broadcasting, radio communications or for some wireless systems, different forms of polarisation may be used.

Circularly Polarized Square Slot Antenna

Antenna

In general the advantages and disadvantages of the various forms of polarisation are relatively subtle, but form some forms of broadcasting, wireless links of for radio communications or mobile communications systems these small differences can make a large difference.

Dual Polarized Slot Antenna

There are several categories of polarisation, and within each type there are several sub categories. Along with this the relevant antennas have corresponding polarisations.

  • Linear polarisation: Linear polarisation is the most common form of antenna polarisation. It is characterised by the fact that all of the radiation is in one plane - hence the term linear:
    • Horizontal polarisation: This form of antenna polarisation has horizontal elements. It picks up and radiates horizontally polarised signals, i.e. electromagnetic waves with the electric field in the horizontal plane.
    • Vertical polarisation: This form of antenna is typified by the vertical elements within the antenna. It could be a single vertical element. One of the reasons for using vertical polarisation is that antennas comprising of a single vertical element can radiate equally around it in the horizontal plane. Typically vertically polarised antennas have what is termed a low angle of radiation enabling a large proportion of their power to be radiated at an angle close to the earth’s surface. Vertically polarised antennas are also very convenient for use with automobiles.
    • Slant polarisation: This is a form of radio antenna polarisation that is at an angle to the horizontal or vertical planes. In this way both vertical and horizontally polarised antennas are able to receive the signal.
  • Circular polarisation: This has a number of benefits for areas such as satellite applications where it helps overcome the effects of propagation anomalies, ground reflections and the effects of the spin that occur on many satellites. Circular polarisation is a little more difficult to visualise than linear polarisation. However it can be imagined by visualising a signal propagating from an RF antenna that is rotating. The tip of the electric field vector will then be seen to trace out a helix or corkscrew as it travels away from the antenna.
    • Right hand circular polarisation: In this form of polarisation the vector rotates in a right handed fashion.
    • Left hand circular polarisation : In this form of polarisation the vector rotates in a left handed fashion, i.e. opposite to right handed.
  • Mixed polarisation: Another form of polarisation is known as elliptical polarisation. It occurs when there is a mix of linear and circular polarisation. This can be visualised as before by the tip of the electric field vector tracing out an elliptically shaped corkscrew.

It is possible for linearly polarised antennas to receive circularly polarised signals and vice versa. The strength will be equal whether the linearly polarised antenna is mounted vertically, horizontally or in any other plane but directed towards the arriving signal.

There will be some degradation because the signal level will be 3 dB less than if a circularly polarised antenna of the same sense was used. The same situation exists when a circularly polarised antenna receives a linearly polarised signal.

Applications for different types of antenna polarization

Different types of polarisation are used in different applications to enable their advantages to be used. Accordingly different forms of polarisation are used for different applications:

Polarized Slot Antenna Tuner

  • General radio communications: Linear polarization is by far the most widely used for most radio communications applications as the radio antennas are generally simpler and more straightforward.
  • Mobile phones and short range wireless communications: In recent years there has been a phenomenal amount of growth in the use of mobile phone and short range wireless communications. Everything from cellular communications to Wi-Fi and a host of other standards that enable short range wireless communications to be achieved.
    Normally linear polarisation is used for these devices because linearly polarised antennas are easier to fabricate in these devices, and hence the base stations need to have a similar polarisation. Although vertical polarisation is often used, many items like Wi-Fi routers have adjustable antennas. Also the fact that these communications often have signal paths that may reflect from a variety of surfaces, the polarisation that reaches the receiver can be relatively random, and therefore it can be less of an issue.
  • Mobile two way radio communications: There are many traditional mobile two way radio communication systems still in use for everything from the emergency services to a host of private mobile radio applications where radio transceivers are located in vehicles.
    Vertical polarisation is often used for these mobile two way radio communications. This is because many vertically polarised radio antenna designs have an omni-directional radiation pattern and it means that the antennas do not have to be re-orientated as positions as always happens for mobile radio communications as the vehicle moves.
  • Long distance HF ionospheric communications: Both vertical and horizontal polarisation are used:
    • Horizontal polarisation: Wire antennas are widely used for HF communications. These tend to be more easily erected using two poles leaving he wire antenna to be suspended between the two. In this way the antenna is horizontally polarised.
      For large multi-element antenna arrays, mechanical constraints mean that they can be mounted in a horizontal plane more easily than in the vertical plane. This is because the RF antenna elements are at right angles to the vertical tower of pole on which they are mounted and therefore by using an antenna with horizontal elements there is less physical and electrical interference between the two.
    • Vertical polarisation: Antennas consisting of a single vertical element are widely used. The vertically polarised antenna provides a low angle of radiation which enables it to provide good long distance transmission and reception.
  • Medium wave broadcasting: Medium wave broadcast stations generally use vertical polarisation because ground wave propagation over the earth is considerably better using vertical polarization, whereas horizontal polarization shows a marginal improvement for long distance communications using the ionosphere. A vertically polarised antenna has the advantage that it will radiate equally in all directions parallel to the Earth and this has advantages for coverage. Additionally a vertical antenna only requires the vertical element - a horizontally polarised antenna would need two supports.
  • Satellite communications: Circular polarisation is sometimes used for satellite radio communications as there are some advantages in terms of propagation and in overcoming the fading caused if the satellite is changing its orientation.

As can be seen, each form of radio antenna polarisation has its own advantages which can be utilised to effect in particular instances. Selecting the right form of polarisation can provide some advantages, and therefore can be quite important.

Circularly Polarized Slot Antenna

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