RF MODULE

Model Definition
The patch antenna is fabricated on a printed circuit board (PCB) with a relative
dielectric constant of 5.23 (Ref. 1). The entire backside is covered with copper, and
the front side has the pattern of the drawing shown in Figure 3-34 below.
Figure 3-34: The printed pattern of the patch antenna shown as a top view. The large
square is 10 mm by 10 mm, the smaller rectangles are 5.2 mm by 3.8 mm, the thicker lines
are 0.6 mm wide, and the thinner lines are 0.2 mm wide and 5.2 mm long. The entire pcb
is 50 mm by 50 mm and 0.7 mm thick.
The coaxial cables have an outer conductor with an inner diameter of 4 mm and a
center conductor with a diameter of 1 mm. The gap between the conductors is filled
with a material with a dielectric constant of 2.07 (teflon). This gives an impedance of
the cables close to 58 Ω. There are two coaxial cables feeding the patch antenna from
two sides, resulting in a balanced feed. The shape of the field at the outer boundary of
the cables are known TEM modes, which can be specified with analytical formulas
expressed in the local cylindrical coordinate system of each cable. With the port
boundary condition you can automatically calculate the coaxial TEM mode, and
specify a power level and a phase shift for each defined port. In this model, the signals
in the cables have the same magnitude but are shifted 180 degrees in phase.
The entire antenna is modeled in 3D, using the electric field as solution variable. The
time-harmonic nature of the signals makes it possible to solve the Vector-Helmholtz
equation for the electric field everywhere in the geometry,
where k 0 is the wave number for free space and is defined as
184 | CHAPTER 3: RF AND MICROWAVE MODELS
2 εr E
∇ µ 1 – × ( ∇ × E)
– k0 =
0