Advantages of Utilizing Higher-order Response for a Harmonic Radar

In nonlinear radars, fundamental tone(s) are sent out to the environment. Clutters that are generally linear in behavior reflect these tone(s) towards the radar. However, the target has a tag containing antenna(s) and a nonlinear device such as a diode, a transistor, or a mixer. This nonlinear device then generates a series of nonlinear responses such as harmonic and intermodulation tones based on the incident fundamental signal. The radar's receiver is designed to accept these nonlinear responses and reject fundamental tone(s) for target identification and clutter rejection purposes. Traditionally, harmonic radars exploited 2nd-order harmonic response for clutter rejection and target identification. Since the 2nd-order harmonic and fundamental tones are relatively close to each other, these radars rely on high-quality filters to attenuate the 2nd-order harmonic from getting radiated from the transmitter and prevent fundamental responses from leaking into the receiver, which avoids any false detection. Hence expensive diplexers and cascaded reflectionless filters were used to achieve necessary attenuation of undesired clutter responses. This cascaded structure leads to complex and bulky radar systems. To solve this issue, the authors are proposing to exploit higher-order harmonics to achieve desired performance without using expensive, bulky diplexers and filters, thus making the system portable and easy to operate. In this paper a 2nd-order based and a 3rd-order based harmonic radar are compared and their performance is evaluated to decide the tradeoff of utilizing higher-order harmonics compared to the traditional 2nd-order harmonic response.