Reconfigurable Small-Aperture Evanescent Waveguide Antenna

We present a reconfigurable small-aperture evanescent wave guide antenna. Tuning and waveguide matching to free space are simultaneously achieved by placing a printed iris with a shunt varactor diode connected across the aperture of a below-cutoff waveguide. A design approach using the Imaginary Smith Chart is used to synthesize the antenna. The maximum dimension of the antenna is 0.36λ at 2.49 GHz and it operates over an operating frequency range of 2.05-2.49 GHz with maximum realized gain of 5 dBi. The antenna-due to its small size and compact feed arrangement-can be used in phased array/cognitive radio applications. Also its tuneable return loss characteristics enable it to act as an electro magnetic switch (shutter), or variable RCS aperture.