ARL-TN-0691 ● AUG 2015

US Army Research Laboratory

Simultaneous-Frequency Nonlinear Radar: 

Hardware Simulation

by Gregory J Mazzaro, Kenneth I Ranney, Kyle A Gallagher, 

Sean F McGowan, and Anthony F Martone

Approved for public release; distribution unlimited.
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ARL-TN-0691 ● AUG 2015

US Army Research Laboratory

Simultaneous-Frequency Nonlinear Radar: 

Hardware Simulation

by Gregory J Mazzaro, Kenneth I Ranney, Kyle A Gallagher, 

Sean F McGowan, and Anthony F Martone

Sensors and Electron Devices Directorate, ARL

Approved for public release; distribution unlimited.
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Aug 2015

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06/2015–08/2015

4. TITLE AND SUBTITLE

Simultaneous-Frequency Nonlinear Radar: Hardware Simulation

5a. CONTRACT NUMBER

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6. AUTHOR(S)

Gregory J Mazzaro, Kenneth I Ranney, Kyle A Gallagher, Sean F McGowan, 

and Anthony F Martone

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US Army Research Laboratory

ATTN: RDRL-SER-U

2800 Powder Mill Road

Adelphi, MD 20783-1138

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ARL-TN-0691

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Approved for public release; distribution unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT

A simultaneous-frequency nonlinear radar is presented for detecting radio frequency electronic targets of interest. The radar 

transmits 20 frequencies (“tones”) between 890 and 966 MHz, at approximately equal amplitudes and evenly spaced 

4 MHz apart. The radar transceiver and the target are connected by coaxial cabling as a hardware simulation of a wireless 

channel. The radar receives intermodulation produced by these 20 frequencies, in a 90-MHz band just below 890 MHz and 

another 90-MHz band just above 966 MHz. An inverse Fourier transform of this intermodulation demonstrates successful 

detection and ranging of each electronic target at a distance (i.e., cable length) of just over 50 ft.

15. SUBJECT TERMS

nonlinear radar, intermodulation products, stepped frequency radar

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Kenneth I Ranney

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(301) 394-0832

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iii

Contents

List of Figures iv

1. Introduction 1

2. Experiment and Data 1

3. Conclusions 8

4. References 9

Distribution List 10
iv

List of Figures

Fig. 1 A simultaneous-frequency radar that transmits at the frequencies f1 and 

f2 and receives the intermodulation frequencies 2f1 – f2 and 2f2 – f1......1

Fig. 2 Coaxial-line experiment to collect simultaneous-frequency data from 

nonlinear electronic targets of interest...................................................2

Fig. 3 Targets: FV300 (left), T4500 (center), and connector in place of 

antenna (right)........................................................................................2

Fig. 4 Time-domain Tx and Rx waveforms for multitone experiment: the 

received waveform shown is from the Motorola FV300 radio..............3

Fig. 5 Frequency-domain Tx and Rx waveforms: the received waveform is 

from the Motorola FV300 radio.............................................................4

Fig. 6 Received waveform from the FV300, filtered and processed via 

inverse FFT into the range profile waveform hIMD ................................5

Fig. 7 Time-domain Tx and Rx waveforms for multitone experiment: the 

received waveform shown is from the Motorola T4500 radio ..............5

Fig. 8 Frequency-domain Tx and Rx waveforms: the received waveform is 

from the Motorola T4500 radio .............................................................6

Fig. 9 Received waveform from the T4500, filtered and processed via inverse 

FFT into the range profile waveform hIMD.............................................6

Fig. 10 Time-domain Tx and Rx waveforms for multitone experiment: the 

received waveform shown is from an open circuit at the end of the 51-

ft cable....................................................................................................7

Fig. 11 Frequency-domain Tx and Rx waveforms: the received waveform is 

from the open circuit..............................................................................7

Fig. 12 Received waveform from the open circuit, filtered and processed via 

inverse FFT into the range profile waveform hIMD ................................8
1

1. Introduction

The nonlinear radar studied in this report transmits multiple simultaneous 

frequencies and receives intermodulation products in the vicinity of those same 

frequencies. This work is similar to that on intermodulation radar;1–4 however, the 

simultaneous-frequency radar is wideband and allows for the generation of a range 

profile of the nonlinear radar environment.5–9

A 2-tone simultaneous-frequency radar is shown in Fig. 1. The radar transmits 2 

frequencies, f1 and f2, at (approximately) the same amplitude. The radar receives at 

least 2 intermodulation frequencies, 2f1 – f2 and 2f2 – f1. Although not depicted in 

Fig. 1, the radar may also receive higher-order intermodulation frequencies such as 

3f1 – 2f2 and 3f2 – 2f1. The current experimental radar transmits 20 simultaneous 

frequencies and receives enough (higher-order) intermodulation products to 

adequately construct a range profile over more than 100 ft.

Fig. 1 A simultaneous-frequency radar that transmits at the frequencies f1 and f2 and 

receives the intermodulation frequencies 2f1 – f2 and 2f2 – f1

2. Experiment and Data

The experiment used to collect simultaneous-frequency data is depicted in Fig. 2. 

The radar environment is currently simulated in hardware using 51 ft of Megaphase 

F130 cable to mimic transmission over the air from the radar to an electronic target 

and reflection over the air back to the radar. The target is a radio that has been 

connectorized (i.e., its antenna was removed and replaced with an SMA end-launch 

connector).
2

Fig. 2 Coaxial-line experiment to collect simultaneous-frequency data from nonlinear 

electronic targets of interest

The transmitted signal source is the Tektronix AWG7052 arbitrary waveform 

generator. The MiniCircuits ZHL-42W amplifies this signal by 38 dB before it is 

input to the Hewlett-Packard 778D dual-directional coupler. The output of the HP 

778D feeds into 51 ft of low-loss, low-distortion Megaphase F130 cable (three 

12-ft lengths plus one 15-ft length in cascade). At the end of the 51-ft cable is the 

connectorized target. Data was collected from 2 targets: the Motorola FV300 and 

the Motorola T4500 (handheld radios). Photos of these 2 targets and a zoomed-in 

view of the connectorized FV300 are given in Fig. 3.

 

Fig. 3 Targets: FV300 (left), T4500 (center), and connector in place of antenna (right)

The output from the AWG7052 contains N = 20 simultaneous frequencies.

10 The 

lowest frequency is fstart = 890 MHz. The highest frequency is fend = 966 MHz. The 

frequencies are evenly spaced by ∆f = 4 MHz. The output power is 

–54 dBm/frequency (–41 dBm total).

The voltage wave that reflects from the target is separated from the wave 

transmitted to the target by the directional coupler. The transmit (Tx) and receive

(Rx) waveforms are sampled at 20 dB down from their true amplitudes via the Txand Rx-coupled ports on the 778D. These sampled waveforms are captured by the 
3

Lecroy Wavemaster 8300A digitizing oscilloscope; channel 1 captures vtrans and 

channel 2 captures vrec. A fast Fourier transform (FFT) computed in Matlab is used 

to view the time-domain-captured waveforms in the frequency domain.

Figure 4 contains the time-domain transmitted and received waveforms for the 

Motorola FV300 as the target. Figure 5 contains the frequency-domain versions of 

these same waveforms. The transmit waveform contains a significant amount of 

intermodulation (below 890 MHz and above 966 MHz), which can be traced to the 

output from the AWG. For this wireline experiment, the current level of transmittergenerated intermodulation is not prohibitive. For a wireless experiment, this

intermodulation should be minimized using pre-distortion or feedforward 

cancellation (because the received intermodulation, which is expected to be much 

weaker in the wireless case, is likely to be masked by the transmitter-generated 

intermodulation).

Fig. 4 Time-domain Tx and Rx waveforms for multitone experiment: the received 

waveform shown is from the Motorola FV300 radio
4

Fig. 5 Frequency-domain Tx and Rx waveforms: the received waveform is from the 

Motorola FV300 radio

The received waveform contains intermodulation generated by the target 

(particularly in the ranges 800–886 and 970–1060 MHz, and relative to the power 

at the intended 20 transmit frequencies). In the upper part of Fig. 6, the targetgenerated intermodulation is isolated from target’s linear response by band-stop 

filtering vrec between 890 and 966 MHz. An inverse FFT6,8 of this filtered vrec, 

whose horizontal axis is scaled from time to distance by 2 p d ut = , is given in the 

lower part of Fig. 6 as hIMD. The propagation speed used for this calculation is that 

reported by the cable manufacturer: 1 1.27 ns ft p u = .

11

Figures 7–9 are the same as Figs. 4–6 but for the T4500 radio as the target instead 

of the FV300. Figures 10–12 are the corresponding data traces for an open circuit 

located at the end of the 51-ft cable instead of an actual target.

The waveforms hIMD in Figs. 6 and 9 display a maximum at d = 53 ft, corresponding 

to the length of the cascaded Megaphase cables, plus an extra 2 ft due to the length 

of the 778D coupler and each cable between the coupler and the oscilloscope.

Compared to the “no-target case,” i.e., the open-circuit data in Fig. 12, the presence 

of a well-defined peak indicates successful detection of each nonlinear target. The 

location of the peak at a distance d corresponding to the physical length of the 

coaxial line between the radar transceiver and the target indicates successful 

ranging of each nonlinear target. Simultaneous-frequency radar, for 20 tones and 

transmit frequencies between 890 and 966 MHz, has been successfully 
5

demonstrated via wireline. A follow-up experiment will replace the “simulated 

radar environment” of Fig. 2 by a fully wireless transmit/receive channel.

Fig. 6 Received waveform from the FV300, filtered and processed via inverse FFT into the 

range profile waveform hIMD

Fig. 7 Time-domain Tx and Rx waveforms for multitone experiment: the received 

waveform shown is from the Motorola T4500 radio
6

Fig. 8 Frequency-domain Tx and Rx waveforms: the received waveform is from the 

Motorola T4500 radio

Fig. 9 Received waveform from the T4500, filtered and processed via inverse FFT into the 

range profile waveform hIMD
7

Fig. 10 Time-domain Tx and Rx waveforms for multitone experiment: the received 

waveform shown is from an open circuit at the end of the 51-ft cable

Fig. 11 Frequency-domain Tx and Rx waveforms: the received waveform is from the open 

circuit
8

Fig. 12 Received waveform from the open circuit, filtered and processed via inverse FFT 

into the range profile waveform hIMD

3. Conclusions

Simultaneous-frequency nonlinear radar was successfully demonstrated for 20 

transmitted tones, evenly spaced between 890 and 966 MHz, for 2 electronic targets

of interest, at a distance of just over 50 ft, by receiving and processing 

intermodulation generated by each target. The wireline experiment implies that the 

results may be extended to a well-controlled (high transmit power, low noise, shortrange) wireless test. True standoff radar operation must be confirmed by replacing 

the wireline channel (coaxial line) with a fully wireless channel (over the air).
9

4. References

1. Saebboe J, et al. Harmonic automotive radar for VRU classification.

Proceedings of the International Radar Conference; pp. 1–5, Oct. 2009.

2. Martone AF, Delp EJ. Characterization of RF devices using two-tone probe 

signals. Proceedings of the 14th Workshop on Statistical Signal Processing, pp. 

161–165, Aug. 2007.

3. Lyons RG. Signal and interference output of a bandpass nonlinearity. IEEE 

Transactions on Communication, 1979 June;27(6):888–891.

4. Walker AL, Buff PM. Method and apparatus for remote detection of radiofrequency devices. US Patent 8,131,239, Mar. 6, 2012.

5. Phelan BR, Ressler MA, Mazzaro GJ, Sherbondy KD, Narayanan RM. Design 

of spectrally versatile forward-looking ground-penetrating radar for detection 

of concealed targets. Proceedings of the SPIE. 2013 May;8714:87140B(1–10).

6. Mazzaro GJ, Gallagher KA, Martone AF, Narayanan RM. Stepped-frequency 

nonlinear radar simulation. Proceedings of the SPIE 2014 

May;9077:90770U(1–10).

7. Gallagher KA, Mazzaro GJ, Ranney KI, Nguyen Lam H, Sherbondy KD,

Narayanan RM. Nonlinear synthetic aperture radar imaging using a harmonic 

radar. Proceedings of the SPIE. 2015 Apr;9461:946109(1–11).

8. Mazzaro GJ, Gallagher KA, Martone AF, Sherbondy KD, Narayanan RM. 

Short-range harmonic radar: Chirp waveform, electronic targets. Proceedings 

of the SPIE. 2015 Apr;9461:946108(1–12).

9. Gallagher KA, Narayanan RM, Mazzaro GJ, Ranney KI, Martone AF, 

Sherbondy KD. Moving target indication with non-linear radar. Proceedings 

of the IEEE Radar Conference. 2015 May:1428–1433.

10. Ranney K, Gallagher K, Martone A, Mazzaro G, Sherbondy K, Nanrayanan 

R. Instantaneous, stepped-frequency nonlinear radar. Proceedings of the SPIE.

2015 Apr;9461:946122(1–8).

11. “GrooveTube cables: Time delay: 1 & 2 Series,” Megaphase product 

datasheet, www.megaphase.com, 2011.
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