Design of a high isolation dual-polarized offset parabolic reflector

In some Ka-band interactive wireless applications, there is need for high isolation between transmit and receive signals at the customer site. If the isolation from the two polarizations at the antenna level is to exceed 50 dB, ordinary cost-effective ortho-mode transducers (OMT) used in conjunction with reflector geometries do not normally provide isolations of this magnitude in the whole range of the required bandwidth. This paper discusses the design of a dual-polarized reflector antenna with a gain of about 35 dBi, with side-lobe levels better than 20 dB, and with isolations between the vertical and horizontal polarizations greater than 50 dB. The transmit frequency was considered to be 29.1 GHz and the receive frequency was considered to be 28.5 GHz. Of the three design choices, namely, the front-fed configuration, the Cassegrain configuration, and the offset configuration, the last configuration in conjunction with a polarizer was chosen. The advantages of the offset configuration are reduced blockage, high efficiency and good return loss. The necessity of using a polarizer, which inevitably introduces some blockage makes the offset geometry the only viable option.