Novel Varactor-Loaded Phasing Line for Reflectarray Unit Cell with Large Reconfigurability Frequency Range - New Contributions in Information Systems and Technologies - page 4

2.1 Radial Stub Properties

The input impedance of a radial stub typically shows a smoother behavior with respect
to an equivalent linear stub, so it is usually adopted in the design of broadband
matching circuits [10, 11]. In order to demonstrate the above assertion, the input
reactance of some radial stubs is computed with a full-wave code as a function of
frequency. The simulated stubs are printed on a substrate with ʵ r =6 and a thickness

equal to 0.762 mm. For simplicity, they are designed to obtain a zero value impedance
at 11.5 GHz. Fig. 2 shows the reactance of each radial stub compared with the input
impedance of an equivalent linear stub. A smoother frequency behavior in the case of
radial stub samples is obtained with respect to the standard linear stub. Furthermore, it
can be observed that the slope of the reactance curve decreases when the stub aperture
angle increases.

In this work, the radial stub properties are fruitful exploited to synthesize a phase
tuning line having the capability to actively control the reflection response of an
aperture coupled reflectarray cell within a large frequency band.

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Fig. 2. Simulated input reactance vs. frequency for different stubs ( input port width w g =1.6mm )

2.2 Unit Cell Performances

The layout in Fig. 1 is adopted to design a unit cell operating at 11.5 GHz. In order to
better appreciate the improvement introduced by the new phasing line geometry with
respect to the previous unit cell configuration [9], both the array grid size as well as the
element stratification are set to the values adopted in [9], therefore ʔ x× ʔ y is fixed to

0.46 ʻ 0 at 11.5 GHz and the layers stratification of the antenna is that reported

in Table 1. By adopting the design procedure described in [8], the unit cell is
synthesized to give a quite full phase range at 11.5 GHz, obtaining the following
dimensions (Fig. 1(a)): L= 7.75 mm, W= 7.75 mm, L a = 5.7 mm, W a = 0.5 mm, r 1 = 3.8
mm, r 2 = 3.9 mm,

ʻ 0 ×0.46

=90°. It is important to note that the only difference between the
new element and the unit cell designed in [9] lies in the phasing line, while the patch
and the slot sizes result to be identical in both considered cases.
Parametric full wave simulations of the unit cell are performed, by adopting the
infinite array approach and assuming a normally incident plane wave. As it can be

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