Arbitrary-Angle Squint-Free Beamforming in Series-Fed Antenna Arrays Using Non-Foster Elements Synthesized by Negative-Group-Delay Networks

Abstract

Beamforming in series-fed antenna arrays can inherently suffer from beam-squinting. To overcome the beamsquinting problem, low-dispersion, fast-wave transmission lines can be employed. Such transmission lines can be designed by loading a regular transmission line with non-Foster reactive elements (e.g. negative capacitors and inductors). As a result of a recent development, these non-Foster reactive elements can be implemented using loss-compensated negative-groupdelay (NGD) networks, providing a solution to the stability issues associated with conventional non-Foster networks. In this work, transmission lines augmented by loss-compensated NGD networks, representing the non-Foster reactive-element loading, are employed for designing wideband fast-wave, lowdispersion transmission lines. This work consolidates this non-Foster reactive element loading method with earlier efforts where NGD networks were used to implement zero-degree phase shifters for beamforming at the broadside direction, and generalizes these methods for arbitrary-angle beamforming from backfire to endfire including the broadside direction. Experimental results are presented for a wideband linear four-element transmitting array feed network for beamforming at 30 o with respect to the broadside direction in the frequency range of 1 to 1.5 GHz. By connecting this feed network to four wideband taperedslot antennas, the beamforming performance is experimentally verified inside an anechoic chamber. Moreover, the antenna array is experimentally tested for transmission of a narrow pulse, where low distortion is observed at the beamforming angle over the entire operating bandwidth. The physical length of the feed network is realistic and is 0.96 wavelengths long at the center of this frequency range. In addition, switched-line phase shifters are employed for squint-free beamforming in three other angles, namely-60 o , 0 o and -30 o .Index Terms-Non-Foster reactances, linear antenna arrays, antenna feeds, negative group delay (NGD), negative group velocity (NGV), dispersion engineering. 0018-926X (c)

Negative Group Delay Phenomenon Analysis Using Finite Unloaded Quality Factor Resonators

“…Therefore, conventional approaches to realize the NGD circuits are based on bandstop structures using either series or shunt RLC resonators [4][5][6][7][8][9][10][11]. The NGD circuits have been used in various practical applications in communication systems, such as shortening or reducing delay lines [11], enhancing the efficiency of feedforward linear amplifiers [12,13], designing broadband and constant phase shifters [14], realization of non-Foster reactive elements [15], and minimizing beam-squint in series-fed antenna arrays [16].…”

A Broadband Switch-Less Bi-Directional Amplifier with Negative-Group-Delay Matching Circuits

“…In order to improve the matching bandwidth of the amplifier, non-Foster elements are needed. In recent years, non-Foster elements implemented by NGD circuits were proposed in References [20,21]. Figure 2a,b gives the traditional configurations of NGD circuits.…”

Influence Analysis of Transmission Lines on a Stable Non-Foster-Loaded Electrically Small Dipole

“…NFCs are also employed in electrically small antennas (ESAs) to reduce their Q value and broaden their bandwidth [4][5][6]. In addition, NFCs are loaded in a waveguide and microstrip for broadband fast-wave propagation and squint-free beamforming of antenna arrays [7][8][9][10].…”