A continuously beam-steerable patch array using variable reactive reflection load

Summary form only given. Beam-steerable antennas/arrays have typically been realized by inserting phase shifters into the feeding network, but the higher losses and costs of phase shifters have been a major disadvantage. Another approach that has emerged recently is the electrically steerable passive array radiator (ESPAR) (H. Kawakami and T. Ohira, IEEE Antennas Propag. Mag., vol. 47, no. 2, pp. 43-50, Apr. 2005). An H-plane patch-type ESPAR antenna formed by a linear array of 3 patches arranged along its H-plane was proposed in (Y. Yusuf and X. Gong, IEEE AWPL, vol. 7, pp.81-84, 2008). Its angular range of beam-steering is within ±20°, which is not large enough, and more importantly, extending the array along its E-plane is another story because of the different coupling level and presence of microstrip line sections in between patch elements. Therefore, an E-plane patch-type ESPAR antenna is proposed in this work, and a variable reactive reflection load for the parasitic patches that can enlarge the steerable angular range in both the E- and Hplane ESPAR designs is presented. Our proposed E-plane patch-type ESPAR antenna, similar to its H-plane counterpart, is formed by 3 identical microstripedgefed rectangular patches. The microstrip feed line of the center (or driven) patch is connected via a coaxial-to-microstrip transition to the generator. The two side (or parasitic) patches are passively excited through mutual coupling from the center one. Each side patch i (i = 2 or 3) is loaded with a voltage-controlled reactance Zi = jXi, which is realized by a specially designed shunt connection of two varactors. The variable reactive reflection load is used to control the coupling coefficient, which is crucial in shaping the array factor. Continuous beam-steering of the proposed E-plane patch-type ESPAR antenna can thus be achieved. Note that the associated design principles, which will be presented in the conference, are also applicable to the H-plane- design. Besides, the general considerations applicable to both E- and H-planes patch-type ESPAR antennas will also be discussed. A planar patch array capable of two-dimensional (2D) beam-steering can thus be realized by incorporating the E- and H-plane array designs.