A bottom-feed omni-directional CP (circularly polarized) antenna array is proposed in this letter. The antenna array is composed of four elements (two printed ZPS (zero-phase-shift) line loops and two half-wavelength dipoles). The four elements are fed with the same phase and amplitude. The ZPS line loops provide the horizontal polarization while the dipoles provide the vertical polarization. Therefore, omni-directional circular polarization is formed in the far field. The feeding network consists of a 1–4 T-shaped power divider formed by parallel strip lines. In order to balance the amplitude of the feeding coaxial cable, the structure is used in the bottom to transfer parallel strip line to micro-strip line. Besides, the loops and the dipoles are placed on the different side of the network to guarantee the omni-directional radiation property. The measured impedance bandwidth of the fabricated antenna is 0.13 GHz (2.40–2.53 GHz) and the measured maximum CP gain at 2.45 GHz is 4.8 dBic.

In this paper, the design and control of an omni-directional mobile microrobot are described for micro-assembling in a micro-factory. A unique locomotion mechanism composed of three special castors units is proposed. The castor consists of two coaxial conventional wheels, connected to the chassis and connected with each other by a set micro-gears. The microrobot is approximately 8 mm in length, 6 mm in width and 6 mm in height. Its kinematics and characteristics are analyzed. Experimental results from a prototype of a microrobot are presented, which demonstrates the feasibility of building an omni-directional microrobot with micromotor and special castors.