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This brief introduces novel architectures of bandpass filters (BPFs) using a substrate integrated waveguide (SIW) cavity with a rectangular ring slot (RRS) for compact size, extensible order, and broad stopband responses. Two bandpass filters, which demonstrate a second-and a fourth-order Chebyshev response, respectively, are realized by employing identical cavities with RRS, without increasing the physical size of the circuit. A rectangular ring slot is etched along the perimeter and a metallic via is allocated towards the bottom edge of the cavity to realize the resonances. The resonant frequencies of different modes are controlled by introducing one or three slots, which enable the realization of the second and fourth-order BPFs with wide stopbands, respectively. The working principles of the filters are illustrated by applying the eigen-mode analysis, field distribution, and the coupling matrix. Finally, a second-order BPF centered at 0.87 GHz, and a fourth-order BPF centered at 0.92 GHz are synthesized, fabricated, and experimentally validated. As compared to the earlier works, the proposed fourth-order BPF offers competitive performance with a low insertion-loss of 0.7 dB, compact size of $0.036\mathbf {\lambda } ^{2}$ , and a wide passband of 22.1%. Additionally, the second- and the fourth-order BPFs achieve wide upper stopband responses of $3.86{f} _{0}$ at a level greater than 20dB and $3.98{f} _{0}$ at a level greater than 30dB, respectively. [ABSTRACT FROM AUTHOR]

In this communication a compact planar-fed substrate integrated waveguide (SIW)-based self-multiplexing (SM) antenna for hexa-band operation is proposed for the first time. Six different patches with planar $50~\Omega $ feed lines are designed and attached to the top side of the rectangular SIW cavity. The antenna operates at six different frequencies (5.33, 5.76, 6.31, 6.86, 7.34, and 7.8 GHz) simultaneously. The antenna attains 4.5, 4.94, 4.9, 5.12, 6.12, and 6.6 dBi peak gain at respective resonant frequencies. Port relocation, stepped patches, and additional vias are exploited to maintain isolation (>23 dB) between any two ports. The front-to-back ratios (FTBRs) are between 10 and 20 dB and Co-pol to Cross-pol ratios are between 10 and 29 dB. The design supports single-variable independent frequency tuning for all six patches and eligible for wide range of applications. The proposed design is fabricated and results are validated through measurement. The antenna is suitable for planar microwave devices. [ABSTRACT FROM AUTHOR]

In this letter, a shielded quarter-mode substrate integrated waveguide (S-QMSIW)-based self-diplexing antenna for closely spaced bands and high isolation is proposed. A ${\rm Y}$ -shaped slot is engraved on the top of the metal to enhance the extra capacitance of the QMSIW cavity resonator; thus, it helps to reduce its size as well as achieve dual-band characteristics. The S-QMSIW resonator is then excited by two orthogonal microstrip feed lines in the full-wave electromagnetic simulator (high-frequency structure simulator) to operate at two distinct frequencies (3.47 and 3.84 GHz). A transmission zero is generated at 3.56 GHz to provide port isolation better than 47 dB. In addition, a lumped circuit model is predicted to validate the antenna structure. To demonstrate the proposed concept, an S-QMSIW-based self-diplexing antenna is designed, fabricated, and tested. The recorded peak gains of the antenna are 4.8 and 5.7 dBi at 3.47 and 3.84 GHz, respectively. At each band, the antenna front-to-back ratio is greater than 20 dB. The circuit size of the proposed antenna is very compact (0.15 $\lambda _g^{2}$). [ABSTRACT FROM AUTHOR]

This letter presents the design of compact triple- and quad-band power dividers (PDs) based on substrate integrated waveguide (SIW) technology. The proposed PDs are designed as a rectangular cavity, one pair of unequal complementary split-ring resonators (CSRRs) and U-shaped slots (USSs). Initially, a dual-frequency SIW PD is implemented using unequal CSRRs on the top surface of the SIW cavity. This dual-frequency PD is converted into triple-band and quad-band operations by employing USSs on the bottom surface of the cavity. The center frequencies of the proposed PDs are controlled by varying the dimensions of CSRRs and USS. To demonstrate the proposed concept, triple- and quad-band PDs are designed, fabricated, and tested. The measured responses are very much consistent with the simulated one. The overall sizes of the proposed triple- and quad-band PDs are 0.03λg2 and 0.02λg2, respectively. The proposed PDs feature compact size, triple- and quad-band operation, good return loss, and isolation. [ABSTRACT FROM AUTHOR]

A novel and compact all planer-fed self-triplexing patch antenna is designed and demonstrated for triple-band operation simultaneously. The model is comprised of one substrate-integrated waveguide (SIW) cavity, three planar ports, and one modified I-shaped slot. The proposed antenna is designed in a simple three-step method to achieve improved self-triplexing property. In the first step, a rectangular slot is created and its position is altered to obtain initial isolation (>20 dB) between any two ports. Secondly, the same slot is modified to an I-shape, which creates three patches facing three different ports and radiates at three different frequencies (4.14, 6.1, and 8.32 GHz) with minimum isolations above 28.4 dB. In the third step, one input-port is off-centered to obtain port isolation tradeoff so that isolation between any two ports is better than 30.8 dB. Importantly, the proposed design also supports easy individual frequency tuning using single variable. For demonstration purpose, the antenna is fabricated and characterized. The proposed planar antenna is very simple, compact, and feasible for handheld microwave devices. [ABSTRACT FROM AUTHOR]

In this letter, a quad-band balun employing Pi-shaped and series connected coupled lines is proposed. The closed form design equations are derived analytically. Based on these equations, a quad-band balun operating at 1.8/3.6/5.8/7.8 GHz is designed, fabricated and tested. The measurement result shows that, the return loss and isolation are better than 18 dB and the bandwidth obtained is more than 150 MHz at each operating frequency band, which is feasible for most applications. Good agreement is found between the theoretical predictions and experimental results. [ABSTRACT FROM PUBLISHER]