IEEE - Aerospace and Electronic Systems - February 2020 - 30

Feature Article:

DOI. No. 10.1109/MAES.2019.2961215

GnuRadar: An Open-Source Software-Deﬁned Radio
Receiver Platform for Radar Applications
Ryan Seal, Harvest, AL, USA
Julio Urbina, School of Electrical Engineering and Computer Science,
The Pennsylvania State University, State College, PA, USA

INTRODUCTION
This article intends to provide researchers with a complete,
cost-effective radar system, suitable for many areas of
research; providing access to budget-limited researchers
across the globe. The receiver described in this article is a
modified version of the original [1] receiver, providing
8 MHz of instantaneous bandwidth distributed amongst 1, 2,
or 4 receive channels; resulting in a maximum data rate of
32 Mb/s using 32-b complex samples. Since the completion
of this work, the original USRP1 is no longer available for
purchase, however, the firmware used in this project is
generic and directly transferrable to any FPGA device. Additionally, software dependencies [2], [3] used to implement
the radar system's back-end software are still considered
state-of-the-art at the time of this writing. The complete
design, including both firmware and software, is freely available as an open-source project [4]. We begin with a brief,
high-level overview of the system, followed by sections
detailing the receiver and software modifications required to
make the system suitable for pulsed-radar data acquisition.
The final section will validate system performance and stability through analysis of a continuous, 13-h data collection.

SYSTEM OVERVIEW
The Rock Springs radar system at Penn State comprises a
30-kW transmitter operating at 50 MHz (i.e., 6-m VHF
Authors' current address: Ryan Seal, Harvest, AL 35749
USA. E-mail: (ryanseal@zoho.com). Julio Urbina,
School of Electrical Engineering and Computer
Science, The Pennsylvania State University, PA 16802
USA. E-mail: (jvu1@psu.edu).
Manuscript received January 13, 2019, revised August
14, 2019; accepted May 11, 2019, and ready for
publication December 18, 2019.
Review handled by Daniel W. O'Hagan.
0885-8985/20/$26.00 ß 2020 IEEE
30

band), paired with Yagi antennas [5] in a monostatic configuration. Synchronization of transmit and receive lines
are configured and controlled digitally using reconfigurable
hardware instrumentation [6], [7] targeted specifically for
coherent radar systems. Received signals from the antenna
array are conditioned through a series of filters and lownoise amplifiers; followed by sampling, down conversion,
and filtering by the modified SDR receiver. Processed samples are streamed via USB 2.0 connection from the receiver
to a general-purpose computer (GPC) where real-time software performs a series of tasks including: 1) data alignment, 2) data formatting, 3) image display, and 4) storage
to disk. An overview of the system and its components are
depicted in Figure 1. The system stores I/Q data samples
for postprocessing purposes and provides real-time display
of radar time intensity (RTI) images as a means to validate
proper system operation. Interpretation of RTI images produced by the system are beyond the scope of this article
and interested readers are referred to [8] for a comprehensive overview of such techniques.

RADAR RECEIVER
The Universal Software Radio Peripheral (USRP) [9],
designed by Matt Ettus and Eric Blossom, provides a lowcost, open-source platform, from which typical applications
in SDR can be realized. Several versions of the device exist,
varying widely in capabilities and cost. The design described
in this article utilizes the original version of the device,
referred to as the USRP1, providing up to 8 MHz of instantaneous bandwidth. The modified system described in this article will be referred to as the GnuRadar system [4], which
encompasses both hardware modifications in the USRP1 as
well as data collection software used to capture, format,
and store incoming data from the receiver. The USRP1 utilizes a small, consumer-grade field-programmable gate
array (FPGA) and peripherals making it suitable for applications requiring limited signal bandwidth. Although the
device was intended for radio applications, modifications

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