Analysis of Ultrawideband Trident Inset-Fed Monopole Antenna with Conical Ground

This example shows how to analyze the performance of a U-shaped monopole antenna designed on a PCB and mounted on a conical ground. You achieve low-frequency matching by inserting a trident inset feed. The conical ground with an elliptical shape at the base of the radiator outperforms traditional UWB monopole designs in impedance-matching bandwidth and radiation pattern omnidirectivity [1].

Create Conical Ground

Create a circle with a radius equal to the cone base radius. Extrude the circle in the positive z-direction to a height of 35 mm with a scaling factor of 0.25, thereby generating the cone with a top radius of 12.5 mm.

Reorient the cone in the negative z-direction so the top of the cone alligns with the xy-plane.

c = shape.Circle(Radius=50e-3);
outerBottom = extrudeLinear(c,35e-3,Direction=[0,0,1],Scale=0.25,caps=true);
[~] = translate(outerBottom,[0 0 -35e-3]);

The center of the ground does not have a clean edge for attaching the feed because of the diagonal edge. The top and bottom surfaces of the cone are closed.

show(outerBottom)
view([10 -8])
title("Extruded Cone with Closed Top and Bottom");

Use removeFaces to remove the bottom face from the cone. Alternatively, you can use removeFaces without specifying a face number through an interactive panel by selecting the relevant face.

removeFaces(outerBottom,3);
view([10 -8])
title("Cone with Removed Bottom Face");

Imprint Feed Edge

To make sure that the feed edge does not split in future operations, imprint a horizontal feed edge on top face of the cone. This imprint ensures a robust connection to the feed.

show(outerBottom)
view(2)
title("Top Face of Cone with Diagonal Edge");

imprintStrip = shape.Rectangle(Length=2e-3,Width=2e-3,Center=[1e-3 0]);
outerBottom = imprintShape(outerBottom,imprintStrip);
show(outerBottom)
view(2)
title("Cone with Vertical Edge Center of Top Face");

Rotate and reorient the cone.

[~] = rotateY(outerBottom,90);
d = 4.5e-3; % Gap between monopole and ground
l = 75e-3; % Length of monopole
[~] = translate(outerBottom,[-(0.5*l)-d 0 0]);

Create Trident Inset Feed

Create the trident feed geometry from defined parameters. The dimesions of feed are defined in [1]. Modify the values of r and q to match the created geometry. Complete geometry details are not available.

t = 16.7e-3; 
r = 1.25e-3;
q = 0.15e-3;
n = 1.5e-3;
m = 0.5*(t-(6*q)-(3*n));
rectW = r + (2*n);
rectL = t - (2*q);
rectF = shape.Rectangle(Length=rectW,Width=rectL,Center=[(0.5*r)-n 0]);
show(rectF)
title("Strip to Modify as Trident Feed");

Create rectangles to subtract for making holes.

holeW = r + n;
holeL = m + (2*q);
offset = 1e-3;
rectLH = shape.Rectangle(Length=holeW+(2*offset),Width=holeL,Center=[(0.5*(r-n))+offset q+0.5*(m+n)]);
rectRH = shape.Rectangle(Length=holeW+(2*offset),Width=holeL,Center=[(0.5*(r-n))+offset -q-0.5*(m+n)]);
hole = rectLH + rectRH;
rectF = subtract(rectF,hole);
show(rectF)
title("Rectangle with Cuts");

Create triangles to subtract for making mitred bends.

lc = shape.Polygon(Vertices=[(-2*n) (0.5*rectL)-n;-n (0.5*rectL);-(2*n) (0.5*rectL);]);
rc = shape.Polygon(Vertices=[(-2*n) (-0.5*rectL)+n;-n (-0.5*rectL);-(2*n) (-0.5*rectL);]);
cornerCuts = lc + rc;
rectF = subtract(rectF,cornerCuts);
show(rectF)
title("Rectangle with Mitred Bends");

Create rectangles to add for making fills.

fillL = m;
fillW = r;
fillLH = shape.Rectangle(Length=fillW,Width=fillL,Center=[0.5*r q+0.5*(m+n)]);
fillRH = shape.Rectangle(Length=fillW,Width=fillL,Center=[0.5*r -q-0.5*(m+n)]);
fill = add(fillLH,fillRH);
rectF = add(fill,rectF);
show(rectF)
title("Shape with Added Fills");

Create rectangle to add as the input line.

rectInp = shape.Rectangle(Length=n,Width=n,Center=[(-2.5*n) 0]);
rectF = add(rectF,rectInp);

Use the removeSlivers function to remove very small triangles.

rectF = removeSlivers(rectF,1e-6);
show(rectF);
title("Trident Feed");

Create U-shaped Monopole

Create a U-shaped monopole using the defined geometry parameters.

etchWidth = 1.2e-3; % Thickness of monopole etched from the edges
w = 61.2e-3; % Width of the monopole
weff = w-(2*etchWidth); % Effective width of the monopole after etching
a = 16.9e-3; % Major axis of elliptical curve on the bottom side of monopole
b = 12e-3; % Minor axis of elliptical curve on the bottom side of monopole
angl = 90:5:180; % Input angles to generate points for leftside curve
l1 = (-0.5*l) + b*(cosd(angl)+1); % Parametric coordinate notation of ellipse
l2 = (0.5*weff) + (a*(sind(angl)-1)); % Parametric coordinate notation of ellipse
angl = 180:5:270; % Input angles to generate points for rightside curve
r1 = (-0.5*l) + b*(cosd(angl)+1); % Parametric coordinate notation of ellipse
r2 = (-0.5*weff) + (a*(sind(angl)+1)); % Parametric coordinate notation of ellipse

Create a polygon using the generated vertices and visualize the U-shaped structure.

s = shape.Polygon(Vertices=[[0.5*l l1 r1 0.5*l]',[0.5*weff l2 r2 -0.5*weff]']);
show(s)
title("U-shaped Monopole");

Add Trident Feed to U-shaped Monopole

Create a rectangle to remove from the monopole for placing the feed. Make a hole in the monopole and add the trident to the resulting shape.

feedCut = shape.Rectangle(Length=r,Width=t,Center=[-0.5*(l-r) 0]);
[~] = translate(rectF,[(-0.5*l) 0 0]);
s = subtract(s,feedCut);
show(s)
title("Monopole with Feed Slot");

s = add(rectF,s);

Use the removeSlivers function to remove very small triangles.

s=removeSlivers(s,1e-6);
show(s)
title("Monopole with Trident Feed");

Add Conical Ground to U-shaped Monopole

Add conical ground to the U-shaped monopole and visualize the resulting structure.

tmetal = add(s,outerBottom);
show(tmetal)
title("Monopole with Trident Feed and Conical Ground");

Add Substrate to U-shaped Monopole with Ground

Create and add a substrate to the U-shaped monopole with a ground structure.

Create a box for assigning the substrate. Create a bounding box of air to contain the substrate and the U-shaped monopole with a ground. Defining this box is necessary because the mesher requires closed mesh as input.

box = shape.Box(Length=l+d,Width=w,Height=0.8e-3,Center=[-0.48*d 0 -0.4e-3],Dielectric="FR4",Color="g");
closedBox = shape.Box(Length=160e-3,Width=120e-3,Height=120e-3,Dielectric="Air",Color="b",Transparency=0.1);

Add a substrate in the air bounding box.

mbox = box + closedBox;
show(mbox,EnableIndividualColors=true)
title("Air Bounding Box with Added Dielectric");

Pass the substrate with the air box to the addSubstrate function to enclose the substrate with a metal box.

sb = addSubstrate(tmetal,mbox);
show(sb,EnableIndividualColors=true)
title("Metal Box Enclosure for Dielectric Substrate");

Create U-shaped Monopole Antenna with Conical Ground

Use the customAntenna object to convert the U-shaped monopole structure with a ground to an antenna. Create the feed, assign it to the antenna, and visualize the result.

ca = customAntenna(Shape=sb);
[~] = createFeed(ca,[-0.0445 0 0],1);
show(ca)

Manually Mesh Antenna

Manually mesh the antenna with an maximum edge length of 0.007 m.

mesh(ca,MaxEdgeLength=0.007);

Analyze U-shaped Monopole Antenna

Calculate and plot the reflection coefficient, radiation pattern, and gain against frequency.

Plot Reflection Coefficient

Plot the reflection coefficient for this antenna over a frequency band of 0.5 GHz to 8 GHz and a reference impedance of 50 ohms.

sparam = sparameters(ca,linspace(0.5e9,8e9,60));
figure
rfplot(sparam)
title("Return Loss of Monopole Antenna with Conical Ground");

Plot Radiation Pattern

Plot the radiation pattern for this antenna at center frequency of 4 GHz.

pattern(ca,4e9);
view([-90 -90]);
title("Radiation Pattern at 4 GHz");

Plot Gain Against Frequency

The gradual increment of gain with frequency in UWB antennas is due to the increase of ground size to radiator ratio as the frequency increases. The variation in this design is low as compared to traditional designs [1].

fr = 0.5e9:0.15e9:8e9; % Frequency sweep
h = zeros(size(fr));

Calculate gain at each frequecy.

for i = 1:length(fr)
    p = pattern(ca,fr(i));
    h(i) = max(max(p));
end
plot(fr,h)
ylim([0 8]);
grid on;
title("Gain of UWB Monopole Antenna");

Conclusion

In this example, you build and analyze the basic structure of the Trident inset-fed UWB antenna. The results closely match the reference. The minor deviation in results is likely due to missing geometry information.

References

[1] Dzagbletey, Philip Ayiku, Jin-Young Jeong, and Jae-Young Chung. “Ultra-Wideband Trident Inset-Fed Monopole Antenna With a 3-D Conical Ground.” IEEE Access 9 (2021): 2592–2601. https://doi.org/10.1109/ACCESS.2020.3047424.