  The concept of self-mixing antenna arrays is presented and analyzed with
respect to its beneficial behavior of large gain over a wide angular range. The
large gain is attained by an antenna array with large element spacing, where
all array element signals are combined approximately coherently over the entire
angular receiving range. This functionality is achieved by the self-mixing
principle, where an exact description via an intermediate frequency (IF) array
factor is derived. For verification purposes, a 4 x 2 self-mixing array is
fabricated and measured in the frequency range from 34 GHz to 39 GHz. A
multiple-resonances millimeter-wave microstrip patch antenna has been
especially developed to achieve large bandwidth and a wide angular receiving
range. The broad beamwidth is achieved by two parasitic patches and suitable
radiation characteristics of the resonant modes. The self-mixing of the receive
signal is realized at each antenna element by a Schottky diode with an
optimized operating point. The down-converted array element signals are then
combined and measured at the IF. The receive power is increased significantly
over a large angular range as compared to conventional array feeding
techniques. The simulation results are verified by measurements, which show
very good agreement.
