Design of an Ultrawideband Directional Antenna Based on a Bidirectional Radiator and a Multilayer Pyramid Absorber

An antenna with a unidirectional radiation pattern for level sensing in a storage tank is presented. The proposed antenna configuration consists of a bidirectional radiator and a multilayer absorber. The frequency of operation ranges from 300 to over 1500 MHz with a reflection coefficient of less than -10 dB. By placing the multilayer absorber behind the bidirectional radiator, a stable unidirectional radiation pattern over the frequency range from 300 MHz to 900 MHz can be achieved. The absorber with 3 layers forms a pyramidal shape to absorb the signal at 3 difference frequency ranges namely around 300 MHz, 600 MHz and 900 MHz. This multilayer absorber is used to improve radiation pattern of the slot antenna by absorbing and reflecting the back lobe over the frequency of interest. The front to back ratio has a maximum value of 9.8 dB at 800 MHz.