The effect of a bespoke glass sintering aid, 0.3Bi(2)O(3)-0.3Nb(2)O(5)-0.3B(2)O(3)-0.1SiO(2) (BN1), developed from the base ceramic composition, BiNbO4 (BN), on the sinterability, microstructure, and microwave (MW) dielectric properties of BN ceramics has been investigated. Densities > 97% theoretical could be achieved at 1020 degrees C for samples with up to 15% BN1 additions. The resulting microstructure was composed of BN laths surrounded by a residual glass phase that contained small fibrous crystals. Some evidence of dissolution of BN crystals was observed. Optimum properties were exhibited for samples with 15 wt% of glass addition sintered for 4 h at 1020 degrees C with a relative permittivity epsilon(r)=38, a MW quality factor Q x f(0)=17 353 at 5.6 GHz, and a temperature coefficient of resonant frequency tau(f)=-10 ppm/degrees C. The high Q x f(0), epsilon(r), and low tau(f), coupled with a relatively low sintering temperature, suggest that the use of bespoke glass sintering aids of this type may have great potential for the fabrication of MW ceramics.