Design of a steerable reflect-array antenna with semiconductor tunable varactor diodes

The demonstrator of a steerable reflect-array antenna was designed as a system of dipoles loaded by varactor diodes. The microwave response of a dipole loaded by varactor has been simulated in closed form based on equivalent circuit approach. The circuit analytical model has been verified by the full-wave analysis. Change of the varactor capacitance in the range of 0.3-1.3pF was provided by biasing voltage 0-20V. The array consists of 20 dipoles structured as two parallel lines. The operational frequency is 11 GHz, the length of the dipole is 9.2mm, spacing between dipoles is 18mm. The double-side metallized PTFE with epsilon = 2.8 and thickness of 1 mm was used as a substrate. Dipole structure was manufactured by a photolithographic process and formed with surface mounted varactor diodes. The radiation pattern of the array is characterized by the width of the main beam approximate to 8 degrees, the side lobe level -(12 divided by 20) dB, the steering range +/- 15 degrees. Control voltage was set manually with variable resistors separately for each varactor. The fine alignment of the control voltage for each varactors turned out to be very important. Inherited data are used for correction of the operational principle of a varactor steerable antenna controller.