Single Slot Antenna With Multiple Radiation Modes Using a Parasitic Loop Pair

In order to increase radiation modes for slot antennas, a new method of loading a parasitic loop pair is proposed. By adding switches to control the open- or closed-state of each loop, the loop pair works at four states, generating multiple radiation modes. Consequently, besides the original bidirectional broadside mode, two additional directional radiation modes are generated, radiating to endfire. As a result, a simple slot antenna could work in multiple radiation modes with the proposed method; meanwhile, no much-increased size or complicated structure is needed. Thus, a single slot antenna can be employed to meet the requirement for multifunction and multienvironment applications. To demonstrate this design concept of using the parasitic loop pair, an antenna structure is designed and fabricated. One parasitic loop is formed by connecting two printed metallic strips with copper shorting pins; p-i-n diode switches and bias circuits are inserted to control the state of the two loops with dc signals. Both measured and simulated results indicate that the proposed parasitic loop pair is effective in providing multiple radiation modes for slot antennas.