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 0o to nearly 360o. 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
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 0o to 360o. 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 Z0 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 Cmin
= 0,18 pF up to Cmax = 0,9
pF. The series resistance in the equivalent circuit of the varactor was R = 2,7 Ohm. The dimensions of the
dipole were 2l = 8 mm, w = 3.5 mm. The substrate had
the thickness H = 1 mm and dielectric
permittivity ed =
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.