Design Wideband Cellular Basestation antenna with Parasitic Elements

Since R2025a

This example shows how to design a custom antenna with parasitic elements for cellular base station applications. Specifically, it shows how to create a model of a dipole antenna with additional parasitic elements to enhance its directivity and bandwidth. This example is particularly useful for engineers and researchers working on antenna design and looking to explore the effects of parasitic elements on antenna performance.

Define Antenna Dimensions

Initialize the dimensions of the dipole antenna and the parasitic elements. These dimensions are crucial for determining the antenna's operational frequency and characteristics.

% Antenna dimensions
l = 72e-3; % length of dipole
h = 45e-3; % vertical length
t = 0.814e-3; % thickness of vertical substrate
dip_wid = 2e-3; % dipole width
len_wid = 150e-3; % ground length and width

Create Dipole and Parasitic Elements

Use the dimensions defined above to create the geometry of the dipole antenna and the parasitic elements. The shape.Rectangle function allows you to define rectangular shapes, which we then manipulate to create the desired antenna structure.

Creat main dipole elements

rec1 = shape.Rectangle(Center=[6e-3 0],Length=10e-3,Width=45e-3);
[~] = translate(rec1,[0 0 -t/2]); 
[~] = rotateX(rec1,90);

dipole1 = shape.Rectangle(Center=[23.5e-3 11.5e-3],Length=25e-3,Width=2e-3);
[~] = translate(dipole1,[0 0 -t/2]);
[~] = rotateX(dipole1,90);

Repeat for the second set of dipole elements

rec2 = shape.Rectangle(Center=[-6e-3 0],Length=10e-3,Width=45e-3);
[~] = translate(rec2,[0 0 -t/2]); 
[~] = rotateX(rec2,90);

dipole2 = shape.Rectangle(Center=[-23.5e-3 11.5e-3],Length=25e-3,Width=2e-3);
[~] = translate(dipole2,[0 0 -t/2]); 
[~] = rotateX(dipole2,90);

shape1 = rec1 + dipole1 + rec2 + dipole2;

Create parasitic elements

para_h = 33e-3;  % parasitic length
para_w = 2e-3;    % parasitic width
x1 = l/2; 
x2 = (l/2) - 2e-3; % position of parasitic

y = -(h/2) + 1e-3;   % lower coordinate
k = y + para_h;      % upper coordinate
x_cen = (x1 + x2)/2; % xcoord of centre
y_cen = (y + k)/2;   % y coord of centre


parasitic1 = shape.Rectangle(Center=[x_cen y_cen],Length=para_w,Width=para_h);
[~] = translate(parasitic1,[0 0 t/2]); 
[~] = rotateX(parasitic1,90);

parasitic2 = shape.Rectangle(Center=[-x_cen y_cen],Length=para_w,Width=para_h);
[~] = translate(parasitic2,[0 0 t/2]);
[~] = rotateX(parasitic2,90);
para = parasitic1 + parasitic2;

Create Feed line

Define feed line dimensions

feed_h1 = 18.27e-3; % vertical length
feed_h2 = 8.25e-3; % second vertical len
feed_l = 15.9e-3;  % horizontal length
f_w = 1.8e-3;  % feedline width
mid_wid = 0.5e-3;  % midline width

Use shape.Rectangle to create feed line

f1 = shape.Rectangle(Center=[(-8.8e-3-8.8e-3+f_w)/2 (-h/2-h/2+feed_h1)/2],Length=1.8e-3,Width=18.27e-3);
[~] = translate(f1,[0 0 t/2]); 
[~] = rotateX(f1,90);

f2 = shape.Rectangle(Center=[(-8.8e-3+feed_l-8.8e-3+feed_l-2e-3)/2 (-h/2+feed_h1-h/2+feed_h1-feed_h2)/2],Length=2e-3,Width=8.25e-3);
[~] = translate(f2,[0 0 t/2]); 
[~] = rotateX(f2,90);

f3 = shape.Rectangle(Center=[(-8.8e-3-8.8e-3+feed_l)/2 (-h/2+feed_h1-h/2+feed_h1+2e-3)/2],Length=15.9e-3,Width=2e-3);
[~] = translate(f3,[0 0 t/2]); 
[~] = rotateX(f3,90);

feedline = f1 + f2 + f3;

Create Antenna

Combine the individual elements using boolean addition to create the antenna structure. This involves adding the dipole and parasitic elements together.

shape1 = shape1 + feedline + para;

Define Ground Plane, Substrate and Bounding box

A ground plane and substrate are essential for the antenna's performance. Define a ground plane, substrate and bounding box for the antenna.

gnd = shape.Rectangle(Length=len_wid,Width=len_wid);
[~] = rotateZ(gnd,90);

[~] = translate(gnd,[0 0 round((-h/2)-(l/6000),4)]);
gnd_shape = add(gnd,shape1);

Create substrate shape

substrate1 = shape.Box(Length=85e-3,Width=47e-3,Height=t,Dielectric="FR4",Color="r");
[~] = translate(substrate1,[0 1e-3 0]);

Create a bounding box of air to enclose the antenna. Defining this box is necessary because the mesher requires closed mesh as input.

Boundbox = shape.Box(Length=250e-3,Width=250e-3,Height=150e-3,Dielectric="Air",Color="b",Transparency=0.1);
sub1 = substrate1;
[~] = rotateX(sub1,90);
sub1 = sub1 + Boundbox;
gnd_diele_shape = addSubstrate(gnd_shape,sub1);

Visualize Antenna

Use createFeed function to add the feed. With the antenna structure defined, visualize it using the show function. This helps verify the geometry before proceeding with the analysis.

ant = customAntenna(Shape=gnd_diele_shape);
[~] = createFeed(ant,[-7.9e-3,-t/2,(-h/2)],1);
figure
show(ant)
title("Wideband Cellular Basestation Antenna")

Analyze Antenna

Finally, analyze the antenna's performance by meshing it and calculating its radiation pattern and S-parameters over a specified frequency range.

Mesh the antenna

mesh(ant,MaxEdgeLength=0.01)

Plot the pattern

pattern(ant,2.1e9)

Calculate the s-parameters

S = sparameters(ant,1.5e9:0.02e9:2.5e9);
rfplot(S)

Use bandwidth function to calculate the bandwidth below -10dB

bandwidth(ant,1.5e9:0.02e9:2.5e9);

Conclusion

The addition of two vertical parasitic elements base station antenna significantly improves the bandwidth upto 350MHz. The designed antenna has a maximum gain of around 5.5 dB.The antenna is a promising candidate for compact base station communication system.

References

[1]Luo, Yu & Chu, Qing-Xin & Bornemann, Jens. (2017). Enhancing Cross-Polarization Discrimination or Axial Ratio Beamwidth of Diagonally Dual or Circularly Polarized Base Station Antennas by Using Vertical Parasitic Elements. IET Microwaves, Antennas & Propagation. 11. 10.1049/iet-map.2016.0928.