dual ban rectangular patch antenna

8/9/2019 Dual Ban Rectangular Patch Antenna

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Dual-band bent slot-loaded pin-fedrectangular patch

Quick Summary

Background

Patch antennas are popular for their well-known attractive features, such as low profile, light weight and compatibility with MMICs. Their main

disadvantage is an intrinsic limitation in bandwidth, which is due to the resonant nature of the patch structure.

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: 2 - 2 - 2 0 1 5 , C o n t e n t C o p y r i g h t M a g u s P t y ( L t d )

Quantity Typical Minimum Maximum

Polarisation Dual-linear - -

Radiation pattern Single broadside lobe - -

Gain 6 dbi 4 dBi 8 dbi

Performance bandwidth 0.2 % - -

Complexity Moderate - -

Impedance 50 Ω

Balun None Required - -

Ratio betweenoperating frequencybands

1.5 1.2 1.9


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Dual-band bent slot-loaded pin-fed rectangular patch 2

Modern communication systems (GPS, vehicular, WLAN, etc.), however, often require antennas with compactness and low-cost, thus rendering

planar technology useful and sometimes unavoidable.

Dual-frequency patch antennas provide an alternative to wideband planar antennas in applications where a wide bandwidth is used for operation at

two separate transmit-receive bands.

Dual-frequency operation is achieved by modifying the natural modes of a rectangular patch through slot-loading and feed placement.

The coupled-slot technique employed by this design can reduce the patch area by up to about 30%.

Physical Description

Microstrip antennas are simple and inexpensive to manufacture using modern printed circuit technology (etching), except at the lower frequencies,

where a pair of scissors, knife, some copper tape and a low relative permittivity substrate may be sufficient.

Feed Method

Pin-fed patches are usually fed from underneath the ground plane with a coaxial cable.

Operation Mechanism

A conventional rectangular patch has the feed situated along the centre of the patch width at a certain inset from the patch edge (point A in the

figure below). This mode of operation is the TM01 mode. By placing the feed along the centre of the patch length at a certain inset from the patch

edge, the TM10 mode is achieved (point B in the figure below). By combining the above mentioned into a single feed position, both modes of

operation can be achieved (point C in the figure below).

Feed position for dual-frequency operation: point A for TM01 excitation only, point B for TM10 excitation only and point C for dual-

frequency operation

The introduction of the slots achieves dual-band operation, where both upper and lower frequency bands are lower in frequency than the centre

frequency of the same sized patch used in single-band operation mode. This technique results in significant miniaturization with area reduction by

up to 32% reported [Wong and Yang].

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Performance

Impedance Characteristics

The two important resonant frequencies occur at the TM01 (lower frequency) and the TM10 mode (upper frequency). The frequency ratio between

the upper and lower frequencies is mainly controlled by the length to width ratio (aspect ratio) of the patch.

The x-axes of the figures below are normalised to the first resonant frequency (TM01 mode). The second resonant frequency (TM10 mode) occurs at

1.33.

Typical input impedance versus frequency

Typical reflection coefficient versus frequency

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Radiation Characteristics

The patterns at the two relevant frequencies are similar in shape but rotated by 90° about the vertical axis with respect to one another. The

patterns are broad with a maximum direction normal to the plane of the antenna.

The figure below shows the radiation patterns of the first two resonant modes of operation (TM 01 and TM10 mode respectively). Their 90° rotation is

evident, with both gain maxima in the direction of the vertical axis through the patch surface.

The polarisation of the models are linear but in the orthogonal planes since their E-planes are rotated by 90°.

Typical total gain pattern at the lower (left) and upper (right) operating frequency

Typical normalised gain patterns at the lower and upper frequencies

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Typical total on-axis gain versus frequency

References

J.S. Chen and K.L. Wong, “A single-layer dual-frequency rectangular microstrip patch antenna using a single probe feed”, Microwave Optical

Technology Letters, vol. 11, no. 2, 5 February 1996, pp. 83-84.

K.L. Wong and K.P. Yang, “Compact dual-frequency microstrip antenna with a pair of bent slots”, Electronic Letters, vol. 34, no. 3, 5 February 1998,

pp. 225-226.

Model Information (FEKO)

Model 1

An infinite ground plane model using the MoM solution.

The infinite ground plane model should be used when simulation speed is more important than physical model accuracy

Model Information (CST MICROWAVE STUDIO)

Model 1

PEC cylinder model using a coaxial waveguide feed and a finite ground plane

The antenna is fed with a waveguide port at the end of a short piece of 50ohm air-filled coaxial line. The port reference plane is de-embedded to

the top of the metal ground plane.

This model is to be solved using the Frequency domain solver.

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Model Information (AWR DESIGN ENVIRONMENT)

Model 1

An infinite ground plane model.

The model uses an infinite dielectric substrate with an infinite perfect conducting ground plane.

Model Validation

The models were validated against measurements of a dual-frequency microstrip antenna with a pair of bent slots [Wong and Chen].

Each export model has been validated to give the expected results for several parameter variations in the design space.

Magus Analysis

The internal performance estimation is expected to be similar to a full 3D-EM analysis. The effects of finite ground planes are not considered, and

results may therefore differ for electrically small ground planes. Expect:

Small frequency offsets (-5% to +5%)

Possibly inaccurate reflection coefficients below -15 dB

Design Guidelines

The input impedance of this patch design is extremely sensitive to the feed position. It may, therefore, be necessary to optimise the exact position

of the feed, in order to achieve a specific desired impedance value. Below are some general guidelines which may help in achieving the desired

performance:

To increase (decrease) the lower resonant frequency, decrease (increase) the patch length.

To increase (decrease) the upper resonant frequency, decrease (increase) the patch width.

The operating bands can be increased (decreased) by decreasing (increasing) the slot length.

To increase bandwidth, increase the substrate height and/or decrease the substrate permittivity (this will also affect resonant frequency and the

impedance).

To increase (decrease) the input impedance at the lower frequency, decrease (increase) pin inset 2.

To increase (decrease) the input impedance at the upper frequency, decrease (increase) pin inset 1.

Note: Antennas on very thin substrates have high copper-losses, while thicker and higher permittivity substrates may lead to performance

degradation due to surface waves. The effect of surface waves and substrate size are described in the Magus article: “Planar antennas and surface

waves.”

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dual ban rectangular patch antenna

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