458 Aharon Ben-Tal, Arkadi Nemirovski
the diagram
D(θ) =
40
j=1
x
j
D
κ
j
(θ)
is nearly uniform in the “angle of interest” 77
◦
≤ θ ≤ 90
◦
, specifically,
77
◦
≤ θ ≤ 90
◦
⇒ 0.9 ≤
40
j=1
x
j
D
κ
j
(θ) ≤ 1;
under this restriction, we want to minimize the “sidelobe attenuation level” max
0≤θ≤70
◦
|D(θ)|.
With discretization in θ, the problem can be modeled as a simple LP
min
τ,x
1
,...,x
40
τ :
0.9 ≤
40
j=1
x
j
D
κ
j
(θ) ≤ 1,θ∈
cns
−τ ≤
40
j=1
x
j
D
κ
j
(θ) ≤ τ, θ ∈
obj
(8)
where
cns
and
obj
are finite grids on the segments [77
◦
, 90
◦
] and [0
◦
, 70
◦
], respec-
tively.
Solving (8), one arrives at the nominal design with a nice diagram as follows:
0 10 20 30 40 50 60 70 80 90
−0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.81e−02
0.2
0.4
0.6
0.8
1
30
210
60
240
90
270
120
300
150
330
180
0
103
110
Dream: Nominal design, no implementation errors
Sidelobe attenuation level 0.018 (left diagram is in polar coordinates)
In reality, the optimal weights x
j
correspond to characteristics of certain physical devices
and as such cannot be implemented exactly. Thus, it is important to know what happens
if the actual weights are affected by “implementation errors”, e.g.
x
j
→ (1 +ξ
j
)x
j
,ξ
j
∼ Uniform[−, ] are independent. (9)
It turns out that even quite small implementation errors have a disastrous effect on the
designed antenna: