Abstract: A tunable or dual-band antenna includes a ground plane, top plane, a cage structure, first and second half-loops, and a hybrid phase shifter. The cage structure is attached to the ground plane and the top plane that includes four leg structures in electrically-conductive contact with the top plane. The top plane is one of a cross-element with four equilateral elements, a cross-element with eight equilateral elements, or a disc element. The first and second half-loops are independent from each other, located diagonally to each other within the cage structure, and support transmitting and receiving an electromagnetic field orthogonal to each other. The hybrid phase shifter shifts a frequency of the first and second half-loops to 90° from each other. The ground plane has an inner ground plane with two or more capacitors embedded therein.