A Circularly Polarized Multiple Radiating Mode Microstrip Antenna for Satellite Receive Applications

A beam peak and null steering multiple radiating mode based microstrip patch antenna is presented for satellite receive applications operating at L1 Global Positioning System (GPS) band. Two collocated microstrip patch antennas were designed to produce TM₁₁ and TM₂₁ radiating modes. These orthogonal and circularly polarized radiation patterns were combined enabling full hemispherical steering of a single beam peak and null. Using theoretical analysis and full-wave simulation, the multimode aperture was designed to operate over a 25 MHz bandwidth centered at 1.575 GHz, which covers the L1 GPS band. Impedance and radiation pattern measurements of the passive antenna aperture were in close agreement with the simulated data. Next, this antenna was integrated with an active feed network allowing full hemispherical control over the beam null position and limited beam peak scan in ≈ 5^° increments. Using a simple calibration scheme, the measured beam peak and null elevation angles were programmed to within <; 10° of the intended value based on simulation. Azimuthal positions were consistently offset by ≈ 20^° from the simulated value, which could be resolved in the board layout by phase matching the transmission lines and test point locations. The antenna maintained high total efficiency >68% and low axial ratio 3 dB over all steering angles.