Prodrugs of 6-\u03b2-hydroxymethylpenicillanic acid sulfone having the structurewherein R is H or methyl, and solvates thereof, are disclosed. The sample hold circuit includes a sample unit, a direct current voltage elimination unit, and a hold unit. To minimise interference caused by the presence of non-orthogonal signals, signals to a single secondary station may be transmitted as a plurality of parts encoded with different scrambling codes. Instead of balancing the currents, temperature can also be balanced with the intelligent gate driver units. The vehicle rear monitoring method comprises displaying a vehicle on one side of a monitor and displaying a rear image of the vehicle on an opposite side of the monitor, and displaying the vehicle on the opposite side of the monitor and displaying the rear image of the vehicle on the one side of the monitor, and switching from said one display to said other display on the monitor. A planar antenna array includes an array of planar radiator elements interconnected through a feed line network of planar coplanar transmission lines that enable high-efficiency operation, at millimeter wave operating frequencies.