Coplanar waveguide structures and design structures for radiofrequency and microwave integrated circuits. The coplanar waveguide structure includes a signal conductor and ground conductors generally coplanar with the signal conductor. The signal conductor is disposed between upper and lower arrays of substantially parallel shield conductors. Conductive bridges, which are electrically isolated from the signal conductor, are located laterally between the signal conductor and each of the ground conductors. Pairs of the conductive bridges connect one of the shield conductors in the first array with one of the shield conductors in the second array to define closed loops encircling the signal line.