In this letter, the optimum center-to-center separation between vias in the conductor-backed coplanar waveguide (CBCPW) is presented for leakage suppression in the dielectric region. Leakage mechanism at high frequencies associated with surface wave or parallel-plate mode were widely studied in the past. In this work, antenna arrays have been used to compare leakage in CPW and CBCPW feed network at S-band. By using identical antenna elements, CPW-fed slot dipole antenna array has been compared against CBCPW-fed slot dipole antenna array with a ground via fence. Instead of using shorting pins with minimum nonzero gap, optimum center-to-center separation distance between vias has been derived from the bandgap phenomenon. Approximately 20% of total loss across the frequency range of interest in CPW feed network obtained from the comparison of the CPW-fed antenna array against the CBCPW-fed antenna array can be attributed to unwanted leakage in the dielectric substrate.
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