Aerospace and Electronic Systems Magazine December 2017 - 59

Frazer
Table 1.

Range, Bearing, and Azimuth with Respect to the TX
Array Location (Boresight 359.5° T)
Bearing
(° T)

Azimuth
(°)

863.0

345.0

-14.5

Elliott

1,514.0

350.5

-9.0

Tindal

1,864.0

348.2

-11.3

Hermannsburg

844.4

338.2

-21.3

Kings Canyon

867.2

329.4

-30.1

15.8

313.2

-46.3

Location
Mt. Everard

Glendambo

Range
(km)

mately 21°. Precise range, bearing and azimuth details for both
campaigns are given in Table 1.
In a preamble to MSE-II, we placed radar receivers on the
elements of the Coondambo transmit array and placed a radar
transmitter at the Elliott site to gather comparative single-input
multiple-output data to reproduce previously demonstrated mode
selectivity on receive that is relevant for the target to receiver
path in the two-way skywave OTHR scenario. We also placed
a broadband repeater transponder at a third location approximately 10 km from the Kings Canyon receiver site to support
some preliminary two-way point-scatterer backscatter investigations conducted at the end of MSE-II. An additional receiver site
was established at Glendambo approximately 16 km from the
Coondambo transmit location at a respective azimuth very different than the respective azimuth to all other down-range receiver
sites. With this system it was possible to measure point scatterer
backscatter-two-way-radar returns from the transponder for
the path: Coondambo transmitter to Kings Canyon transponder
to Glendambo receiver. Results from this measurement dataset
are not reported in this article.

In all MISO cases, the down-range systems were unattended
and operated remotely from the central control site at Coondambo.
Each receiver location recorded and processed both the transmitted
MISO waveform set as well as the wide-band OIS transmission
which provided information concerning the prevailing ionospheric
propagation conditions between the transmitter location and the
down-range locations. The OIS measurements also allowed an independent measure of the take-off elevation angles for the various
propagation modes and paths involved as a check for the elevation
directions-of-departure determined from the MISO transmit array.
Each down-range radar receiver incorporated computing, control, and communications equipment designed to provide local processing, remote control and display. The control and display was
remoted back to the central control location at the Coondambo
transmit facility. We used both satellite and 3G cell-phone systems
for the communications links. Local-to-the-receiver processing was
operated via the remote-control data links, permitting real-time
adaptive transmit beamforming to be applied to the received data
which we were able to observe in real-time at the central control
location. The performance of our mode selectivity approach at all
down-range sites could be viewed simultaneously. Transmit beamformer solutions generated at the receiver sites could be fixed and
held for subsequent received coherent measurement intervals in order to assess temporal stability. These solutions could be fed back
to the transmitter system and applied as a conventional transmit
beamformer to compare the energy budget between MISO and conventional single-input single-output (SISO) transmit beamforming.
Mode selection beamformer solutions determined at one location
could not be applied to other down-range locations in real-time but
this comparative analysis was undertaken post experiment.
The waveform set used comprised Kt = 12 time-staggered linear frequency modulated continuous wave (LFMCW) waveforms,
where the individual waveform set member start-time was uniformly dispersed in time throughout the waveform repetition interval. The choice of waveform set cardinality is based on the results
reported in [24], [39]. A spectrogram of the radiated waveform
set received at Mt. Everard is shown in Figure 5 where the time-

Figure 5.

Spectrogram showing time-frequency representation of the radiated waveform set. The units are time (s) on the horizontal axis and frequency (KHz) on
the vertical axis.

DECEMBER 2017

IEEE A&E SYSTEMS MAGAZINE

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine December 2017