The radar pulse (for example generated by a commercial 9.4 GHz radar transceiver, Raytheon Marine GmbH, Kiel, NSC 2525/7 XU) is emitted by a parabolic antenna providing approx. 44 dBi (Fig. 22A). The pulse is received by a transponder fixed to the thorax of the bee (see section 10.1.1.2.) and emits the second harmonic component of the signal (18.8 GHz). The receiving unit consists of a 18.8 GHz parabolic antenna, with a low-noise pre-amplifier, directly coupled to a mixer (18.8 GHz oscillator), a preamplifier with low noise and a downstream amplifier with a 90 MHz ZF-Filter. A 60 MHz ZF-Signal is used for signal recognition. The two antennae are mounted on a common vertical pole which rotates the two antennae in synchrony (Fig. 22A).
Fig. 22A. The harmonic radar unit is mounted on a small trailer and accurately aligned horizontally. The lower larger antenna radiates off the main radar pulse, the higher smaller antenna received the harmonic signal. Both antennae are attached to the vertical rotating pole. Notice the displacement between the two antennae, which requires calibration of the transponders localization by a side-wise correction. B. A honey bee carrying a transponder. Notice the two number tags glued together with a double sticky tape. (Photo B: Dr Christoph Grüter).