This feed was published at EME2002, in Prague, by OK1DFC. It is a design that has been in use by various OK stations, on a number of microwave bands from 23cm to 3cm, for some time.
The design claims better than 1.1dB cicularity, with around 27dB isolation between Tx and Rx ports, without the use of polarizing or matching screws (c/f VE4MA circular and N7ART diagonal waveguide feeds).
I have constructed models, to the dimensions given by Zdenek, OK1DFC, in the presentation. The photos below show various stages in the construction - construction notes for the versions shown can be found here .
Using 6mm dia monopoles, and 15mm tuning discs, a Return Loss of better than 30dB can be achieved on each port (= SWR<1.07:1)
Summary Measurements obtained:
Tx port RL - -34dB
Rx port RL - -33dB
Cicularity: V/H +/- 0.1dB
Max cicularity Error: +/- 0.5dB
Transmission Loss: <0.1dB13 cm
Initial measurements at Martlesham Microwave Round Table, 2003, gave:
Tx port RL - >-20dB across 2250 - 2450MHz, with a dip at frequency selected by probe resonance
Rx port RL - >-20dB across band as above - also dip at probe resonance
no other measurements were taken on this occasion, but these will be added later.see the Construction Notes for more detailed information on measurements.
Page created: 16.10.2002 Last updated: 30.11.2003