Design of a Waveguide Slot Antenna

O.Nell, K. Solbach, J. Dreier: Rundumstrahlende Hohlleiter-Schlitzantenne für Horizontalpolarisation
UKW-Berichte 1/91 und 2/91

In [49]:
f0 = 5760 # [MHz] Frequency
N = 10 # Number of slots

Z_F0=120.0*pi
c0=2.997831e8
lambda_0= C0/f0/1e6

print 'Freespace wavelength in: %6.2f mm' % (lambda_0*1e3)
print 'Cutoff value for a: %6.2f mm' % (lambda_0*1e3/2)
print 'Optimum width for a: %6.2f mm' % (lambda_0*sqrt(3.)*1e3/2)

Freespace wavelength in:  52.05 mm
Cutoff value for a:  26.02 mm
Optimum width for a:  45.07 mm

In [48]:
a = 43.8 # [mm] waveguide width
b = 23.9 # [mm] waveguide height

lambda_c=2.0*a/1e3
lambda_h= lambda_0 / sqrt(1.0 - (lambda_0/lambda_c)**2)

print 'lambda_h: %3.2f mm' % lambda_h

g= 10*log10(N * lambda_h/lambda_0)
print 'Approximate antenna gain: %3.1f dBi' % g

dtheta=50.7 * lambda_0 / N / lambda_h * 2.0
print 'Beamwidth: %3.1f deg' % dtheta

# calculate offset from center
x = 1e-3 * a/pi*arcsin(sqrt(lambda_0*b/(N*3.5*lambda_h*a*cos(pi*lambda_0/2.0/lambda_h)**2)))
print 'slot offset from center: %6.2f mm' % (x*1e3)

# slot width
sb = lambda_h / 30
print 'slot width: %6.2f mm' % (sb*1e3)

# compute slot length
# use figure 7 and interpolate
x_23cm = f0/1270 * x
sx=[ 0,    8.6,   10,    20,   29 ] # x in mm
sl=[ .475, .491,  .494,  .519,  .55] # L/lambda_0

L = interp(x_23cm*1e3,sx,sl)
print 'slot length: %6.2f mm' % (L*1e3*lambda_0)

# calculate slots
print ''
print '   Slot No    Distance'
print '----------------------------------------'
for i in range(N-1):
print '      %d       %6.2f mm' % ( i+1 ,1e3*(lambda_h/4+lambda_h/2*i) )

lambda_h: 0.07 mm
Approximate antenna gain: 11.0 dBi
Beamwidth: 8.1 deg
slot offset from center:   5.08 mm
slot width:   2.21 mm
slot length:  27.50 mm

Slot No    Distance
----------------------------------------
1        16.58 mm
2        49.73 mm
3        82.89 mm
4       116.05 mm
5       149.20 mm
6       182.36 mm
7       215.51 mm
8       248.67 mm
9       281.83 mm