A Miniaturized Dual-Band SIW Filtering Antenna With Improved Out-of-Band Suppression

In this article, a dual-band substrate integrated waveguide (SIW) filtering antenna with improved out-of-band rejection is presented. It consists of two dual-mode rectangular cavity resonators integrated with the slot antenna. Four metal–insulator–metal (MIM) capacitors are designed in the first cavity to realize circuit miniaturization and wide upper stopband. The second slot-loaded cavity achieves a miniaturized dual-band radiation by cutting the currents of TE
₁₁₀
and TE
₂₁₀
modes. Three radiation nulls are obtained due to the multiple coupling paths between the resonating and spurious modes. The radiation nulls locations can also be adjusted by changing the feeding position. For verification, a SIW filtering antenna operating at 3.6/4.1 GHz (
$f_{1}/f_{2}$
) is designed and fabricated. The measured peak gain and 10 dB bandwidth at low band of 3.57 GHz (high band of 4.12 GHz) are 4.84 dBi (4.85 dBi) and 2.3% (1.6%), respectively. The measured >30 dB inner stopband suppression and 20 dB upper stopband suppression up to
$1.46f_{2}$
are achieved.