[Legacy Report] IEEE seminar by Prof. Krishna Naishadham on "Multi-Band Array Design"

#Expert #Lecture

Antenna size is the dominant limiting factor in miniaturizing electronics and RF
front ends.  Optimizing the antenna aperture in moderately small physical space is a
challenge facing the design of antenna arrays for wireless and satellite
communications.  For example, there is a significant interest in packing diversity
and MIMO arrays in base station antennas covering several frequency bands. There is
an increasing trend in achieving multiple functions such as communication in
different wireless bands, video streaming, geolocation, etc. using antenna elements
and arrays within a small footprint dictated by package size, weight and power
constraints. This seminar reviews some of the challenges behind antenna design and
integration under these constraints, and discusses a solution involving the design
of planar multi-band arrays by stacking the feed circuitry and antenna elements
vertically in multiple layers of a substrate, a concept known as shared aperture
[e.g., Pozar et al., IEEE AP Trans. Feb. 2001].  This concept was originally
developed in early 1980s for multi-band synthetic aperture radar on satellites, but
has recently gained interest for mobile wireless communications, especially for base
station antenna miniaturization. A major problem with vertical integration of
antenna elements into tightly packed substrates is to ensure adequate isolation
between the antennas in different bands.  Designing the feed layers such that the
feed lines will have minimal adverse impact on the radiation pattern (e.g.,
interference and cross-polarization) is another design challenge. First, the
problems of antenna integration in a shared aperture are highlighted in the seminar,
and then using simple configurations such as patches, slots and printed dipoles, we
describe design strategies to minimize channel interference (e.g., scalability,
elements with low cross-polarization, geometrical symmetries to reduce mutual
coupling, etc.). Using these design concepts, we demonstrate how one can proactively
design the antenna elements for low inter-channel isolation and improve the array
performance.  Pitfalls and limitations of this approach are discussed and potential
solutions are proposed.  We present a novel design for a dual-band array, comprising
interleaved printed dipoles spaced to avoid grating lobes in each band. The folded
dipoles are designed to be resonant at octave-separated frequency bands (1 GHz and 2
GHz), and each dipole is gap-fed by voltage induced electromagnetically from a
microstrip line on the other side of the substrate. This nested element
configuration shows excellent corroboration between simulated and measured data,
with 10-dB return loss bandwidth of at least 5% for each band and mutual coupling
lower than -15 dB.  Measurements on the array reveal broadside gain of 12 to 17 dBi
in each band with low cross-polarization.

• Date: 02 Jan 2015
• Time: 04:30 AM UTC to 05:45 AM UTC
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• Kanpur, Uttar Pradesh
• India

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• Co-sponsored by Yogesh Singh Chauhan