In this letter, a defected ground structure (DGS) is applied to design a compact microstrip rat-
race hybrid coupler. The proposed structure can achieve both a significant reduction of size
and harmonic signal. By embedding the DGS section, it is observed that the resonant
frequency of the hybrid coupler is significantly lowered, which can lead to a large amount of
size reduction for a fixed frequency operation. Besides, the third harmonic signal is
suppressed to-30 dB with respect to a conventional rat-race hybrid coupler. In this case, the …

In this paper, defected microstrip structure (DMS) is applied to design a compact microstrip
rat-race hybrid coupler. The proposed structure introduces both harmonic signal
suppression and a significant reduction of size because half of the ring is embedded in
upper section. By embedding the DMS, it is observed that the third harmonic signal is
suppressed to-25 dB with respect to a conventional rat-race hybrid coupler. Besides, this
structure also effectively reduces the occupied area to 25% of the conventional case. Finally …