Compact Rotman Lens on Water Based Substrate for Low-Frequency Applications

The Rotman lens is an inexpensive, less complex, compact, wideband and easy to fabricate analog beam former used extensively for producing multiple beams in the sky for simultaneous observation over a wide field of view. It is expected to play a major role in low frequency applications where physical dimensions are not easily manageable because of large wavelength involved. We have developed a new methodology of making the Rotman lens compact by a factor of a little over 8 when compared to vacuum by designing it on an in-house developed water based composite dielectric medium which has an effective dielectric constant of about 26.8. A Rotman lens has been designed and developed on this dielectric medium to produce two beams at ~ ±30 deg. around zenith along with a beam at the centre in the frequency range of 100–200 MHz. A prototype has been constructed to demonstrate the concept with the help of a three element antenna array.