FiniteGapFeed

R2026b

Create a finite gap feed

Since R2026b

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    Description

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

    The FiniteGapFeed object represents a coplanar multi-ground edge feed across a physically finite gap between conductors. This feed excites the finite gap directly, modeling the structure more realistically. A delta-gap feed, by contrast, would require you to make the gap infinitesimally small by adding more metal, which can introduce undesirable parasitic effects.

    Creation

    Syntax

    f1 = FiniteGapFeed
    f1 = FiniteGapFeed(PropertyName=Value)

    Description

    f1 = FiniteGapFeed creates a default FiniteGapFeed object.

    f1 = FiniteGapFeed(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

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    Locations to apply positive excitation, specified as a N-by-2 matrix in meters. N is the number of excitation sites.

    The first and second columns correspond to the x- and Y-coordinates, receptively, in meters. Each location must lie on the edge of a metal layer.

    Example: [0.002,0]

    Data Types: double

    Locations to apply negative excitation, specified as a N-by-2 matrix in meters.N is the number of excitation sites.

    The first and second columns correspond to the x- and Y-coordinates, receptively, in meters. Each location must lie on the edge of a metal layer.

    Example: [-0.02,0]

    Data Types: double

    Layer index for positive and negative excitation site, specified as a positive integer scalar. SignalLayers is the layer index into the pcbStack layer stack.

    Example: 2

    Data Types: double

    Width of each excitation site, specified as an N-by-1 vector in meters. N is the number of excitation sites. The metal edges on which SignalLocations(n,:) and GroundLocations(n,:) lie must be at least as long as SignalWidths(n). Each negative excitation site has the same width as its corresponding positive excitation site.

    Example: 0.003

    Data Types: double

    Examples

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    Open Live Script

    The radiator is two collinear arms separated by a feed gap, etched on a dielectric substrate.

    Define the length and width of each arm, the feed gap between them, and the board and substrate dimensions.

    La = 0.030;
Wa = 0.004;
g  = 0.002;
Lb = 0.090;
Wb = 0.030;
sub = 1.6e-3;

    Define an FR4 substrate and set its thickness.

    d = dielectric("FR4");
d.Thickness = sub;

    Create the two arms as rectangles using the antenna.Rectangle object, positioned symmetrically about the origin and separated by the feed gap. Combine them using Boolean addition. One arm acts as the signal conductor and the other as the ground conductor of the differential feed.

    xL = -(g/2 + La/2);
xR =  (g/2 + La/2);
armSignal = antenna.Rectangle(Length=La, Width=Wa, Center=[xL 0]);
armGround = antenna.Rectangle(Length=La, Width=Wa, Center=[xR 0]);
top = armSignal + armGround;

    Create the pcbStack as a two-layer stack: the radiator over the substrate with no ground plane, so the structure remains balanced.

    p = pcbStack;
p.BoardShape = antenna.Rectangle(Length=Lb, Width=Wb);
p.BoardThickness = sub;
p.Layers = {top, d};

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

    p.FeedFormat = 'FeedDefinitions';

    Create the FiniteGapFeed object and orient across the gap between the arms. Use the SignalLocations property to set the signal side of the gap and the GroundLocations property to set the ground side, so the feed spans the physical gap. The SignalWidths property gives the feed its finite physical width, matching the arm width.

    f = FiniteGapFeed(SignalLocations=[-g/2 0], GroundLocations=[g/2 0], ...
    SignalWidths=Wa, SignalLayers=1);
p.FeedDefinitions = f;

    View the structure to confirm the two arms, the feed gap, and the substrate.

    figure
show(p)
title("Differentially Excited PCB Radiator with Finite-Gap Feed")

    Figure contains an axes object. The axes object with title Differentially Excited PCB Radiator with Finite-Gap Feed, xlabel x (mm), ylabel y (mm) contains 4 objects of type patch, surface. These objects represent PEC, feed, FR4.

    Compute and plot the reflection coefficient. The radiator resonates near 1.85 GHz with an input impedance close to 50 Ω, so the default 50 Ω reference gives a good match.

    s = sparameters(p, linspace(1e9, 4e9, 61));
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