Effective Radar Cross Section in Close-Range Joint
Communication and Sensing Applications
Steve Blandino
(1)(2)
, Jelena Senic
(3)
, Neeraj Varshney
(1)(2)
, Jihoon Bang
(5)(6)
, Jack Chuang
(4)
, Samuel Berweger
(3)
, Jian
Wang
(4)
, Camillo Gentile
(4)
, and Nada Golmie
(4)
(1)
Associate, National Institute of Standards and Technology (NIST), Gaithersburg, MD
(2)
Prometheus Computing LLC, Bethesda, MD
(3)
National Institute of Standards and Technology (NIST), Boulder, CO
(4)
National Institute of Standards and Technology (NIST), Gaithersburg, MD
(5)
Associate, National Institute of Standards and Technology (NIST), Boulder, CO
(6)
University of Colorado, Boulder, CO
Abstract—Radar Cross Section (RCS) is traditionally mea-
sured under far-range conditions where targets are fully illumi-
nated by the antenna beam. However, in close-range scenarios,
such as those encountered in Joint Communication and Sensing
(JCAS) systems, the far-range assumption breaks down due to
partial target illumination. This leads to discrepancies between
the intrinsic RCS—the target’s inherent scattering—and the
effective RCS—the scattering measured under limited antenna
beam coverage. This paper develops a methodology and conducts
measurements to establish their relationship. Measurements are
conducted with a test metallic sphere and human targets to
demonstrate the relationship between effective RCS and distance,
highlighting the transition from partial to full illumination. By
accounting for the area defined by the beamwidth and the
target retrieved from geometrical modeling, the intrinsic RCS
is recovered. The proposed methodology enables the prediction
of effective RCS using intrinsic RCS values and vice versa,
facilitating the design and analysis of sensing systems in close-
range applications.
I. INTRODUCTION
Radar Cross Section (RCS) is a fundamental parameter
of sensing systems that quantifies the electromagnetic energy
scattered by a target to the receiver (RX), thereby determining
its visibility and influencing the design of sensing systems
[1]. Traditionally, RCS has been measured and modeled under
far-range conditions, where the target is sufficiently distant
from the radar [2]. In these scenarios, the antenna beam fully
illuminates the entire target. This assumption has been suitable
for conventional radar systems developed primarily for aircraft
and military applications, where targets are generally in the
far-range. However, sensing technology is increasingly ex-
panding into commercial applications, such as human sensing
for smart homes, automotive systems, and automated indoor
factories. This trend has been further accelerated by the next
generation of communication systems, which aim to integrate
sensing and communication functions using shared hardware,
including smartphones, base stations, and networks such as
WLAN or cellular systems [3]–[6]. In these scenarios, targets
like humans are often in close proximity to the sensing radio,
leading to close-range conditions where traditional far-range
assumptions no longer apply. Moreover, in 5G and upcoming
6G systems, the problem becomes even more relevant because
they use highly directional antennas with narrow beamwidths,
Fig. 1: Partial vs. full illumination as a target moves away
from the antenna.
unlike previous generations, which used omnidirectional an-
tennas. As a result, the target may only be partially illuminated
by the narrow beam. As a result, relying on far-range RCS
values during system design may lead to inaccuracies, such as
overestimating the target’s visibility and predicting erroneous
sensing performance, since the far-range RCS values do not
account for the effects of partial illumination that occur in
close-range scenarios.
For close-range applications, antenna beams may only
partially illuminate the target, resulting in a reduced RCS,
referred to as the effective RCS, compared to the intrinsic
RCS observed under full illumination conditions. Despite its
significance, the effect of partial target illumination on RCS in
close-range conditions remains underexplored in current litera-
ture. To address the above-mentioned gap, this paper develops
a methodology to establish the relationship between intrinsic
RCS and effective RCS. As in conventional surface clutter
analysis for Synthetic Aperture Radar (SAR) [1], the presented
methodology relies on the illuminated area as a key factor,
calculating the RCS contribution based on the overlap between
the radar beam and the illuminated surface, while accounting
for the effects of beam geometry and distance on the scattered
power. Experimental measurements are conducted to confirm
the validity of the proposed model.
II. GEOMETRIC MODEL OF EFFECTIVE RCS
In close-range scenarios, the finite beamwidth of the antenna
limits the illuminated portion of the target. Fig. 1 illustrates
