log spiral arm truncation

[bacurrie45]

Hi there i have managed to design a log spiral antenna with the following parameters
but cant seem to get matlab to truncate each arm of my antenna

• a = 0.22
• N = two turns
• flow = 300Mhz
• fhigh = 1Ghz
• ro = 75mm

I have simulated my designs in matlab and i am getting a two arm log spiral but i want to truncate each arm in an arc does anyone know how to do this ?. I have attached my matlab code and a picture of my antenna any help would be appreciated thanks

>> clear all
alpha = 0.22;
delta = pi/2;
theta = 0:pi/60:4*pi*(2);
k = 0.075;
r1 = k*exp(alpha*theta);
r2 = k*exp(alpha*(theta-delta));
r3 = -k *exp (alpha*theta);
r4 = -k*exp(alpha*(theta-delta));
x = r1.*cos(theta); 	
y = r1.*sin(theta); 
 
 x1 = r1.*cos(theta);
 y1 = r1.*sin(theta);
 x2 =  r2.*cos(theta);
 y2 =  r2.*sin(theta);
 x3 = r3.*cos (theta);
 y3 = r3.*sin (theta);
 x4 = r4.*cos (theta);
 y4 = r4.*sin (theta);
 
plot (x,y, 'b','linewidth',3); hold on; grid on;
plot (x1,y1,x2,y2,x3,y3,x4,y4,'r','linewidth',3); hold on; grid on ;
z = [x,y];
z = [x1,y1,x2,y2,x3,y3,x4,y4];
axis('equal')
rotate3d on

 

[andre_luis]

I´m not very familiar with MATLAB syntax, but I presume you could insert a kind of constraint on code above like that:

\[{r}_{i}<= \sqrt{ {{x}_{i}}^{2} + {{y}_{i}}^{2}}\]

 

[bacurrie45]

thanks for the reply i even tried inserting the specific start and stop angles for each curve of the log spiral but that did not help either. I just need to truncate each armand i have a feeling it may have something to do with my angles