Miniaturized microstrip window hairpin resonator with T-feeder coupling lines

In this paper, a new structure of planar hairpin resonator with T-feeder coupling lines was developed. Two symmetrical T-shaped feedlines mounted inside the side-by-side window structure behave as resonators, and they are responsible for maintaining the 50 Ω input/output impedance matching and transforming electrical energy into electromagnetic (EM) energy with the desired resonance characteristics. With varying widths for the X-axis and heights for the Y-axis of the window configuration of the hairpin resonator, corresponding changes in the resonant frequency and useable bandwidth can be observed. Hence, frequency tuning can be easily achieved by adjusting window dimensions of the proposed hairpin resonator. The dimensions of the proto-type resonator are approximately 0.24λg mm by 0.48λg. The measurement results showed that an acceptable return loss (S₁₁) equal to -22.6 dB and an insertion loss (S₂₁) of 0.95 dB are measured at a resonant frequency 5.8 GHz. The measurement results are quite matched with the simulation results.