Herbert M. Aumann

A low-cost harmonic radar for tracking very small tagged amphibians

A low-cost, hand-held harmonic radar is described for tracking tagged amphibians weighting less than a gram during a cryptic period of their life history. The radar is based on inexpensive, commercial 5.8 GHz wireless communications and 11.6 GHz satellite television technology. The performance of the system was accurately predicted from laboratory measurements by defining an appropriate harmonic tag conversion efficiency. The harmonic radar has a demonstrated maximum tag detection range of 20 ft. The best performance was achieved with an asymmetric, dielectric sleeved dipole with a 1:2 arm length ratio.

A wideband harmonic radar for tracking small wood frogs

A wideband harmonic radar for tracking very small wood frogs in a high clutter environment is described. The one watt peak power radar transmitted in the 5.8 GHz ISM band and received in the 12 GHz satellite TV band. By transmitting a 150 MHz bandwidth linear frequency modulated waveform and exploiting the frequency doubling property of the harmonic tag to increase the bandwidth to 300 MHz, a range resolution of 1.6 feet was demonstrated. Furthermore, by resolving transmitter leakage and multipath, and by coherently integrating the tag return, the wideband harmonic radar sensitivity was improved by 20 dB over a comparable CW harmonic radar.

An asymmetrical dipole tag with optimum harmonic conversion efficiency

Extremely small passive dipole tags have been used for tracking insects with a harmonic radar. It will be shown that by adjusting the dipole feed point location, the conversion efficiency, and hence the maximum detection range, can be optimized. Analysis, simulations and measurements on X-band tags confirm that the best tag efficiency is achieved with a half-wavelength dipole and asymmetric 1:2 dipole arm lengths.

A 5.8 GHz harmonic RF tag for tracking amphibians

The proposed printed circuit harmonic RF dipole tag on a ground plane with an appropriate impedance matching technique offer better sensitivity at low excitation levels when compared to a more conventional wire harmonic dipole tag. By exploiting existing Wi-Fi and satellite TV technology, it should be possible to build a capable, low cost harmonic radar.

The radar microphone: A new way of monitoring honey bee sounds

This paper describes a radar microphone for studying incidental and deliberate insect sounds. It was specifically designed to record the sounds coming from honey bees inside a beehive. The sensor is based on a Doppler radar measuring the vibrations of a high dielectric object, such as a bee. It is shown that if the vibrational amplitude is much less that the radar wavelength, the frequency of the mechanical vibration and the frequency of the phase modulation in the reflected radar signal are the same. The instrument was implemented safely and inexpensively with readily available 5.8 GHz wireless components. The output of the radar microphone is a signal no different from the signal that might be recorded with an acoustic microphone. As such the same data collection and processing techniques can be applied. Examples are given of vibrations and airborne sounds from bees inside an observation hive.

A rotating source polarization measurement technique using two circularly polarized antennas

This paper combines the standard two-antenna gain measurement technique with the rotating source method for measuring the polarization ratio and tilt angle of the polarization ellipse of a circularly polarized antenna. The technique is illustrated with two identical helical antennas, one for the source and one for the antenna-under-test (AUT), facing each other. Measurements of the voltage transfer ratio are made over one 360 degree on-axis rotation of the source while the AUT remains stationary. The rotation causes the phase of the electric field of the principal polarization to rotate in one direction and the phase of the cross polarization to rotate in the opposite direction. A Discrete Fourier Transform (DFT) of the data from a single rotation is insufficient to resolve the two polarization components. Leakage from the principal polarization will most likely cover up the low-level opposite polarization signal. However, the DFT resolution can be artificially increased by appending to the measured data, precisely M-1 copies of the data. Now the polarization components will be separated by 2M revolutions. Application of a heavy weighting function to the augmented data and a phase compensation to the DFT allows a clear determination of the amplitude and phase of the on-axis principal and cross polarization components. The technique was verified by electromagnetic simulations and by measurements in an anechoic chamber with two 6-turn 5.8 GHz helical antennas separated by 4 feet. There was very good agreement between the simulations and measurements of the polarization ellipse tilt angle and a −20 dB polarization ratio.

A constant beamwidth reflector antenna for a harmonic radar operating in the near-field

A dual-frequency constant beamwidth reflector antenna for use with a harmonic radar in the focused near-field is proposed. The technique matches reflector defocusing effects to the frequency dependent phase center displacement of a log-period dipole antenna feed by specifying the LPDA apex angle. The technique was verified by simulations and measurements.

Maximum directivity of a series-fed microstrip array antenna for wireless application

An omnidirectional colinear microstrip array antenna is modeled as a ladder network. A formula is derived for the maximum directivity of a series-fed colinear antenna with an infinite number of ladder sections. It is shown that the maximum directivity is asymptotically limited and depends upon the product of the series impedance and shunt admittance of the equivalent ladder network. The result is verified by simulation and experiment.

Polarization ratio determination with two identical linearly polarized antennas

This paper describes a method for determining the complex polarization ratio using two identical, linearly polarized antennas. By Fourier transform analysis of S21 measurements with one of the antennas rotating about its axis a circular polarization ratio is derived which can be transformed into an equivalent linear polarization ratio. A linearly polarized reference antenna is not required. The technique was verified by electromagnetic simulations and illustrated by measurements in an anechoic chamber with two 3.3 GHz square patch antennas.

Effect of axial rotation on mutual coupling between helical antennas in a doppler radar

Some amount of mutual coupling between the transmit and receive antennas is required for proper operation of a logarithmic square-law detector in a Doppler radar. The radar performance is shown to be optimized when the mutual coupling magnitude is reduced to equal the magnitude of the target return. If the transmit and receive antennas are same-sense axial mode helical antennas, the mutual coupling reduction can be accomplished by a mechanical rotation of one of the antennas about its axis. This result is verified by electromagnetic simulations and by measurements with a 5.8 GHz Doppler radar and a mechanical honeybee radar cross-section simulator.