Simulation of broadside impact on frequency-scan array antennas

Аuthors

Suchkov A. V.

Lianozovo Electromechanical Plant, 110, Dmitrovskoye shosse, Moscow, 127411, Russia

e-mail: avsu@bk.ru

Abstract

Frequency-scan array antennas (FSAA) are widely used in airspace surveillance radars and air traffic-control systems. In most cases, these antennas present a planar equidistant array of linear emitters connected to the traveling wave multichannel power divider (PD). PD is based on couplers, connected in series with sinuous delay line (DL). It is well known that sharp increasing of PD input voltage to standing-wave ratio (VSWR) on the frequency corresponding to beamforming near broadside is a significant disadvantage of such antennas. The reason for this is the in-phase addition of large quantity of even low reflections from periodic discontinuities: couplers and DL bends. This effect, which leads to a significant gain reduction and unacceptable distortions of directional pattern, is called a “broadside impact” in technical literature. Currently, to eliminate the broadside impact, the method, based on integer odd number of quarter-wavelength in DL shift between all of even and odd discontinuities was proposed.

This paper presents the simulation results obtained using the algorithm, realized in MathCAD. The algorithm was designed for FSAA PD input VSWR evaluation at a certain reflection level from periodic discontinuities and amplitude-phase distribution (APD) forming in frequency-scan plane. During the simulation it has been established that the aforementioned elimination method have a disadvantage, i. e. occurrence of broadside impact in the lower and upper operating frequency range when wide-angle scanning with pattern at a relative bandwidth of more than a few percent was implemented. Thus, the new method, which was designed for complete elimination of broadside impact, is proposed. It is based on automated iterative search procedure of electrical lines lengths connected between the couplers and DL bends. The iterative convergence condition search procedure is defined by PD input VSWR lowest possible value, which achieved in operating frequency range at a certain reflection level from discontinuities. Reasonability of transition from PD series circuit to series-parallel circuit with wide-angle scanning implementation in a relative bandwidth of more than 5% was analyzed. Thus, the main practical result of research concludes in FSAA broadside impact complete elimination possibility and, respectively, operating frequency range and scanning sector expansion without reducing the antenna gain requirements.

Keywords:

frequency-scan array antenna, frequency scanning, pattern, traveling wave power divider, broadside impact, simulation modeling

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