## A Phase Shifter with One Tunable Component for a Reflectarray Antenna (IEEE Antennas and Propagation Magazine, Aug '08).

**Phase
Shifter with one Tunable Component for**

** Reflect-Array Antenna**

# O. G. Vendik

Saint-Petersburg Electrotechnical University, Russia, E-mail: OGVendik@mail.eltech.ru

M. Parnes

MPA, Israel,* *E-mail: Michael@mpa.co.il

**Abstract**

Combination of a dipole and a tunable varactor forms the
phase shifter with one tunable component, which provides the phase shift in a
wide range from 0^{o} to nearly 360^{o}. The dipole loaded with
the tunable varactor is used as a patch component of a low profile reflect-array
antenna. Economic assessment shows that the production
price of the suggested phase shifter with one tunable component is more than 10
times smaller than the price of the traditional phase shifter based on *p-i-n* diode components. The design of
such a phase shifter is the goal of this paper. Simulation of the
phase shift and loss of the reflected wave as a function of control voltage
applied to the varactor were used on basis of an analytical
model verified by the full wave analysis. The result of simulations is in
agreement with measurements. The fast and correct simulation of the reflection
coefficient from the dipole loaded with the tunable varactor can be used for a
design and optimization of a low profile steerable reflect-array antenna.

A list of keywords:

Antenna arrays, Beam steering, Electromagnetic reflection, Microstrip antennas, Microstrip arrays, Microwave antenna arrays, Millimeter wave antennas, Phase shifters, Phased arrays, Planar arrays, Radar antennas, Reflector antennas, Scanning antennas, Varactor tuners

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**1. Introduction**

A low profile reflect-array antenna consists of rectangular microstrip patch radiators. The patch radiators form a set of reflectors, which converts a spherical wave radiated by a primary radiator into the plane wave . For conversion of the spherical wave into the plane wave, the phase shifts of the waves reflected by different radiators were specified. In order to exclude the large phase incursion, the principle of the Fresnel mirror is used.

There is a large experience in designing the low profile reflect-array antennas. A tunable reflect-array is formed by a set of dipoles loaded with tunable varactors, which can be realized as semiconductor or ferroelectric devices. The dipole loaded with the varactor is shown schematically in one can see a fragment of the reflect-array surface covered by the set of dipoles loaded with the tunable varactor diodes. A set of versions of tunable antenna structures based on RF MEMS switches, semiconductor or ferroelectric tunable components have been described.

A combination of the dipole and the tunable varactor
forms the phase shifter with one tunable component, which provides the phase
shift in a wide range from 0^{o} to 360^{o}. The design of such
a phase shifter is the goal of this paper. The characterization of any type of
phase shifter is given by the Figure of Merit (FM) of the phase shifter. The
numerical value of the Figure of Merit is determined by the Commutation Quality
Factor (CQF) of the tunable component (varactor) . The general relation between FM and CQF was
discussed earlier on the example of the phase shifter with the ferroelectric
tunable component. Such a procedure of the phase shifter characterization
will be used for the phase shifter with one tunable component, which this paper
is dedicated to.

The design of antenna array is based on the modeling of elementary equivalent waveguide cell containing a patch radiator at the interface between the free space and the grounded substrate layer. The fundamental task of the problem discussed is to develop a procedure for calculation of the reflection coefficient of linearly polarized wave, which is normally incident upon the patch radiator. An analytical model approach to the problem has been developed on the basis of the solution to the telegraph equations applied to the dipole loaded with the tunable varactor diode. The full wave analysis simulation was used to verify adequacy of the analytical model.

**2. Fundamentals of the phase
shifter with one tunable component.**

Parallel and series versions of the resonance
circuit can be considered with an equitable correctness. An ideal impedance
transformer can be included between a transmission line with characteristic
impedance *Z*_{0} and the
resonance circuit. The theory applied for the series circuit will be
considered. In order to transform formulas for the parallel resonance circuit
into formulas for the series resonance circuit, the duality principle should be
used.

** 3.
Experimental investigation of the reflection type phase shifter with one
tunable component.**

The measurements were performed at the frequencies 11.8 and 12
GHz. The MACOM varactor of the trademark MA46H120 was used. The capacitance of
the varactor was changed from *C*_{min}
= 0,18 pF up to *C*_{max} = 0,9
pF. The series resistance in the equivalent circuit of the varactor was *R* = 2,7 Ohm. The dimensions of the
dipole were 2*l* = 8 mm, w = 3.5 mm. The substrate had
the thickness *H* = 1 mm and dielectric
permittivity e_{d} =
2,8.** **

**4.
Conclusion**

The designing procedure and practical examining of the reflection type phase shifter with one tunable component has been described. Such phase shifters is promising to be used, as basic components of a low cost steerable reflect array antenna. The known parameters of the available varactors and practice in the phase shifter design make possible to conclude that the realization of such low profile steerable reflect-array antenna can be performed in the frequency range from 5 up to 35 GHz.

One should take into account that designing an electronically tunable reflect-array is a computerized procedure including two parts: 1) designing a unit-cell consisting of radiating dipole or patch and 2) optimization of the array structure aimed to obtain small side lobe level and high directivity in the all scanning range. For tailoring the optimization code one needs to use a fast and correct simulator of a tunable unit-cell.

The analytical model of the combination of the dipole and the phase shifter presented in this paper is a basis for realization of a very fast code for simulation of the unit-cell response. The realization of such a code and design of an optimized tunable reflect-array is the next promising steps in simulation and design of electronically tunable reflect-arrays suitable for a wide commercial application.

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