REPUBLIC OF SERBIA

MINISTRY OF DEFENCE

www.mod.gov.rs

MINISTRY OF DEFENCE

Material Resources Sector

Defensive Technologies Department

Military Technical Institute

www.vti.mod.gov.rs

TWO-DIMENSIONAL PRINTED BROADBAND ANTENNA ARRAY WITH TAPERED DISTRIBUTION OPERATING IN 26-34 GHz RANGE

Zoran Mićić

IMTEL Komunikacije, Beograd, zoran@insimtel.com

Ivana Radnović

IMTEL Komunikacije, Beograd, ivana@insimtel.com

Aleksandar Nešić

IMTEL Komunikacije, Beograd, aca@insimtel.com

Marjan Stanković

IMTEL Komunikacije, Beograd, marjan@insimtel.com

Abstract: The paper presents two-dimensional printed broadband antenna array with 64 (8x8) radiating elements operating in the frequency range 26-34 GHz. The array is modeled and optimized using WIPL-D program package, and realized on the thin dielectric substrate. Radiating elements are pentagonal dipoles that operate on the second resonance and are characterized by slower impedance variation with frequency than conventional antennas with patches which are the basic and most commonly used type of printed antennas. High side lobe suppression is obtained by using balanced microstrip tapered feed network enabling diverse feeding of the central and the edge elements in the array. Benefit of using balanced microstrip lines is elimination of parasitic couplings between radiating elements and the feed network. Arrays with tapered distribution have somewhat lower gain as well as directivity than uniformly fed antenna arrays, regardless of technology in which they are realized. Thus, in case of uniform distribution simulated antenna gain would be 26.5 dBi at 30 GHz which is about 0.6 dB greater than simulated gain of the same antenna array with applied tapering (25.9 dBi) presented here. Measured gain of presented array in the operational frequency range is between 20.7 dBi and 22.3 dBi, while measured side lobe suppression is around 18 dB. In order to simplify WIPL-D modeling and thus save computational time, the simulation is performed on a free space antenna model that can be assumed as a fair approximation considering the broadbandness of pentagonal dipoles, and low dielectric permittivity and thickness (e_r=2.17, h=0.127 mm) as well as low losses (tg d=4´10^-4) of the material the array is printed on, which is verified on a number of previously realized models [1]. Due to lack of adequate connectors (K or 2.4mm) for Ka frequency range, we used SMA connector with thin center conductor in the realization. Discrepancies between simulated and measured results are due to losses in the dielectric and copper and poor electrical characteristics of SMA connectors above 21 GHz..

Key words: millimeter-wave printed antennas, broadband antennas, sidelobe suppression.