Novel Varactor-Loaded Phasing Line for Reflectarray Unit Cell with Large Reconfigurability Frequency Range - New Contributions in Information Systems and Technologies - page 5

observed in Fig. 3, by changing the diode capacitance C v from 0.2 pF up to 2 pF, a
phase variation range of about 330° is obtained at the design frequency f 0 =11.5 GHz.
Furthermore, as demonstrated by the simulated phase curves reported in the same
figure, the element reflection phase can be almost completely tuned also at other
neighboring frequencies ranging from 11.25 GHz up to 12.6 GHz ( f= 1.35 GHz). As

a matter of fact, each phase curve lying in this frequency span covers a phase range
greater than 290°, thus offering the capabilities to effectively reconfigure the antenna
radiation features. As illustrated in Fig. 4, the reconfigurability frequency range
obtained for the unit cell tuned by a simple linear phasing line [9] is smaller and results
to be limited between 11.4GHz and 11.8 GHz (

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f= 0.4 GHz). Consequently it is
possible to affirm that the proposed radial phasing line highly improves the frequency
performances of the antenna, allowing to increase about 3.4 times the frequency span
within which the unit cell phase shift can be actively tuned. The above results are
substantially determined by the slower phase shift variations introduced by the radial
phasing lines with respect to the frequency. At this purpose, the reflection phase curves
computed for different diode capacitances are plotted in Fig. 5 versus frequency, both
for the case of the radial line as well as the linear line tuned cells. A smoother behavior
can be observed in the case of the cell driven by the radial line, which results in a
widespread sensitivity to diode capacitance variations, appreciable within a wider
frequency range.

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Table 1. Element stratification

Layer Material Thickness

Patch Copper

35 μm

Diclad870
(ʵ r1 =2.33)

t= 0.762 mm

Antenna substrate

Air d= 0.762 mm

Ground plane with slot Copper 35 μ m

AR600
(ʵ r2 =6)

Phasing line substrate h= 0.762 mm

Phasing line Copper

35 μm

Fig. 3. Simulated phase curves vs. diode capacitance for different frequencies