CoaxialFeed

R2026b

Create a coaxial feed

Since R2026b

expand all in page

    Description

    Use the CoaxialFeed object to specify the FeedDefinitions property in a parent pcbStack object.

    The CoaxialFeed object models a coaxial-style feed as a signal via excited across an annular antipad gap in a ground metal layer (higher-fidelity version of a probe feed).

    Creation

    Syntax

    f1 = CoaxialFeed
    f1 = CoaxialFeed(PropertyName=Value)

    Description

    f1 = CoaxialFeed creates a default CoaxialFeed object.

    f1 = CoaxialFeed(PropertyName=Value) sets object properties using one or more name-value arguments. PropertyName is the property name, and Value is the corresponding value. You can specify several name-value arguments in any order as PropertyName1=Value1,...,PropertyNameN=ValueN. Properties that you do not specify retain their default values.

    example

    Properties

    expand all

    Cross-sectional shape of the feed's via pad, specified as an antenna.Circle object. The pad forms the signal via of the coaxial feed. This shape must correspond exactly to a feature on the pcbStack metal layer specified by GroundLayers.

    PadShape and AntipadShape must have the same number of edges, and corresponding edges on each shape must be parallel.

    Example: c=antenna.Circle(Radius=0.002);PadShape=c

    Data Types: double

    Cross-sectional shape of the feed's via antipad, specified as an antenna.Circle object. The antipad is the outer ring removed from the metal layer specified by GroundLayers, and it typically surrounds the associated PadShape.

    AntipadShape and PadShape must have the same number of edges, and corresponding edges on each shape must be parallel.

    Note

    The size of the AntipadShape must be greater than the size of its associated PadShape.

    Example: c=antenna.Circle(Radius=0.004);

    Data Types: double

    Layer index for positive excitation site, specified as a positive integer scalar. SignalLayers is the layer index into the pcbStack layer stack identifying the layer that the feed via reaches from the GroundLayer layer. Only the via terminus lies on this layer, while the pad, antipad, and cross-gap excited edges lie on the GroundLayer layer.

    Example: 2

    Data Types: double

    Layer index for negative excitation site, specified as a positive integer scalar. GroundLayer is the layer index into the pcbStack layer stack. The entire feed structure consisting the AntipadShape, the PadShape, and the cross-gap excited edges must lie on this layer. Extrude a via from this layer up to the layer specified by the SignalLayers property.

    Example: 4

    Data Types: double

    Examples

    collapse all

    Open Live Script

    Define the radiating patch and the ground plane as two rectangles using the antenna.Rectangle object, with an air dielectric between them. Create the pcbStack object as a three-layer stack: the patch on the top layer, the dielectric in the middle, and the ground plane on the bottom layer.

    r1 = antenna.Rectangle(Length=0.075, Width=0.0357);
r2 = antenna.Rectangle(Length=0.150, Width=0.0750);
d  = dielectric("Air");
p = pcbStack;
p.BoardShape = r2;
p.BoardThickness = d.Thickness;
p.Layers = {r1, d, r2};

    To enable the FeedDefinitions property, set the FeedFormat property to FeedDefinitions.

    p.FeedFormat = 'FeedDefinitions';

    Create two concentric circles at the feed site using the antenna.Circle object. The smaller circle defines the pad, the conductor shape that connects the probe to the board. The larger circle defines the antipad, the clearance ring that isolates the probe from the ground plane.

    cPad = antenna.Circle(Center=[-0.0187 0], Radius=0.5e-3, NumPoints=16);
cAntipad = antenna.Circle(Center=[-0.0187 0], Radius=1.5e-3, NumPoints=16);

    Etch the antipad clearance into the ground plane by subtracting the antipad shape, then restore the pad conductor by adding the pad shape back in. The ground plane is the third layer of the stack.

    p.Layers{3} = p.Layers{3} - cAntipad + cPad;

    Create a CoaxialFeed object, using cPad and cAntipad for the PadShape and AntipadShape properties. The SignalLayers property connects the probe to the patch on layer 1, and the GroundLayers property references the ground plane on layer 3.

    f = CoaxialFeed(PadShape=cPad, AntipadShape=cAntipad, ...
    SignalLayers=1, GroundLayers=3);
p.FeedDefinitions = f;

    Display the structure to confirm the patch, the ground plane with its antipad gap, and the feed location.

    figure
show(p)
title("Coaxial-fed Microstrip Patch Antenna")

    Figure contains an axes object. The axes object with title Coaxial-fed Microstrip Patch Antenna, xlabel x (mm), ylabel y (mm) contains 7 objects of type patch, surface. These objects represent PEC, feed.

    Then calculate and plot the reflection coefficient over a 1 GHz to 5 GHz frequency band.

    s = sparameters(p, linspace(1e9, 5e9, 51));
figure
rfplot(s)

    Figure contains an axes object. The axes object with xlabel Frequency (GHz), ylabel Magnitude (dB) contains an object of type line. This object represents dB(S_{11}).

    Version History

    Introduced in R2026b

    See Also

    Objects