A balanced substrate integrated waveguide (SIW) filter is proposed by etching transverse slots on the top surface. The SIW structures between each two adjacent slots are resonators operating at TE 20δ mode for differential-mode (DM) operation and at TE 10δ and TE 30δ modes for common-mode (CM) operation. The proposed TE 20δ-mode resonator is much shorter than the traditional TE 201-mode resonator, which causes the whole design to be compact and low loss. Furthermore, the strong electric coupling formed by slots make it have wider bandwidth when compared with the state-of-the-arts. A prototype is designed at 3.5 GHz with the size of 1.2λ d × 0.83λ d (λ d is the wavelength in dielectric at the center frequency), the minimum insertion loss of 0.91 dB, the 3-dB fractional bandwidth (FBW) of 16%, and the FBW for 20 dB CM suppression of 79%. INDEX TERMS Balanced filter, compact, low loss, substrate integrated waveguide (SIW), TE 20δ mode.
A compact single‐layer balanced bandpass filter using just one half‐mode substrate‐integrated waveguide (HMSIW) multimode resonator with slots is proposed. The pair of microstrip direct‐feed lines with space about 0.5λg (λg is the guide wavelength of HMSIW at the centre frequency f0) makes TEHM 103, TEHM 104 and TEHM 105 modes of the HMSIW multimode resonator operate in differential mode and TEHM 102 and TEHM 106 modes operate in common mode (CM). As a result, the features of wide bandwidth and low insertion loss (IL) can be achieved when compared with the state‐of‐art substrate‐integrated waveguide balanced filters. Furthermore, the etched slots can be slightly tuned to make up for the performance deviations caused by the manufacturing error. A prototype is designed with a total size of 1.2λ0 × 0.14λ0 (λ0 is the wavelength in free space at f0), the 3 dB fractional bandwidth (FBW) of 28% at the centre frequency of 6 GHz, the minimum IL of 0.86 dB, and the bandwidth of 20 dB CM suppression of 0.25f0.
A single-layer balanced phase shifter with uniform reference line is proposed to achieve the advantages of compact size and wide bandwidth compared with state-of-art single-layer balanced phase shifters. The odd-mode equivalent circuit with one quarter-wavelength coupled line and two quarterwavelength short-ended stubs makes wideband differential-mode (DM) impedance matching and phase shift. The even-mode equivalent circuit with two transmission paths provides wideband common-mode (CM) suppression without affecting the DM responses. The prototype of 45 • (90 •) phase shifter is designed with the operating bandwidth of 81% (82%), with the phase deviation of ±2.3 • (±4.7 •), with the minimum insertion loss of 0.29 dB (0.31 dB), and with the size of 0.27 λ 2 g (0.35 λ 2 g , λ g is the guided wavelength at the center frequency f 0).
A wideband balanced microstrip‐to‐microstrip vertical transition is proposed. This vertical transition is based on the back‐to‐back hexagonal microstrip lines with a slot on the common ground. The etched slot is used to achieve the vertical transmission of differential‐mode signal and the suppression of common‐mode (CM) signal. The back‐to‐back hexagonal microstrip lines enable the transition to obtain wide bandwidth. One prototype shows the fractional bandwidth (|Sdd11| ≤ −15 dB) of 63%, the minimum (maximum) insertion loss of 0.7 dB (1.9 dB), and the minimum CM suppression inside passband of 27 dB.
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