Hybrid non‐uniform‐ Q lossy filters with substrate integrated waveguide and microstrip resonators

Abstract

Three lossy filters with flat passband are proposed with substrate integrated waveguide (SIW) and microstrip resonators, designed with the non‐uniform‐Q method. By properly selecting the lower‐Q‐to‐higher‐Q ratio, the 0.2 dB bandwidth of the first filter is obtained to be 215 MHz (17% improvement), which is equivalent to a uniform unloaded Q‐factor of 820 at the cost of additional in‐band insertion loss (IL) of 0.5 dB, when compared with the full‐SIW filters. Further, two techniques are utilised to adjust the Q‐factor ratio. One method is implemented by mounting a resistor on each microstrip resonator to reduce its unloaded Q‐factor. Then, the 0.2 dB passband of 243 MHz is achieved for the second filter, equivalent to a uniform unloaded Q‐factor of 1420. The other method is realised by adjusting the Q‐factor due to radiation loss of microstrip resonators. By changing the input/output feeding structures, the 0.2 dB bandwidth of the third filter is enhanced by 32%, at the cost of minimum IL increased by 0.9 dB. The occupied area of the proposed planar hybrid filters is reduced by 15–21% and the passband flatness is much better than that of the uniform‐Q filter counterparts, as demonstrated by the simulated and measured results.

Bandpass filter with flat passband and transmission zeros using parallel-connected resistor loaded hairpin-shaped resonators

“…Although the center frequency shifts to the lower side at about 4 MHz, it is found that the measured S-parameters are in good agreement with those from EM simulation. It is found that the advantages of the proposed BPF are flexibly controllable unloaded quality factor and good flatness in the passband compared with other references [14,15,16,21,26,27,28,29,30,31,32].…”

A Parallel Connected Hybrid Microstrip-Substrate Integrated Waveguide Bandstop Filter

“…For this SIWbased high-pass filter, the cut-off wavelength (λ c , hpf ) is found by ( 1) and (2) as 28.61 mm. The cut-off frequency and wavelength of the substrate integrated waveguide [14]:…”

Compact hybrid eighth‐mode substrate integrated waveguide and microstrip line filters with mixed electric and magnetic coupling

“…Besides, sub-mode SIW resonators are not as flexible and convenient as the MSL ones in developing higher-order BPFs. In this event, some researchers have proposed the hybrid SIW and MSL BPFs with outstanding performance [19][20][21][22][23][24][25][26]. In Ref.…”

“…In Ref. [22], a series of fourth-order non-uniform-Q lossy BPFs with SIW and microstrip structures are proposed to achieve improved passband flatness and compact physical footprint. In Refs [23][24][25][26], quarter-wavelength (λ/4) short-circuited MSLs are connected to the normal full-mode SIW or sub-mode SIW cavities directly.…”