In this letter, a wideband three-section branch-line hybrid with harmonic suppression is designed using a novel transmission line model. The proposed topology is constructed using a coupled line, two series transmission lines, and open-ended stubs. The required design equations are obtained by applying even- and odd-mode analysis. To support these equations, a three-section branch-line hybrid working at 0.9 GHz is fabricated and tested. The physical area of the prototype is reduced by 87.7% of the conventional hybrid and the fractional bandwidth is greater than 52%. In addition, the proposed technique can eliminate second harmonic by a level better than 15 dB.

Sidelobes in the two-way radiation pattern are of serious concern in a radar array. Several techniques have evolved to mitigate the problem, which include amplitude tapering, Genetic Algorithm (GA) optimization, thinning transceiver aperture, and two-weight amplitude distribution. With such optimization schemes, the sidelobes can be considerably suppressed but at the cost of a reduction in directivity or taper efficiency. Further, such amplitude tapers require a complex feeding network design. This work alleviates such design restrictions and proposes a systematic approach to lower the sidelobes in radar two-way shared aperture arrays. The proposed methodology can achieve a sidelobe level (SLL) of below -52 dB in both linear and planar arrays, which is about 18 dB enhancement in SLL compared with uniform transmit and thinned receive arrays. In addition, as a result of the equal transceiver array size in the proposed design, an improvement of approximately 0.44 dB and 0.68 dB in directivity is achieved in linear and planar arrays, respectively. A novel feeding architecture is also illustrated to reduce the cost and complexity of the overall feeding network. A set of full-wave simulations have also been performed to validate the theoretical results.

In this paper, a novel multi-mode resonator-based ultra-wideband bandpass filter topology is proposed, analyzed, and experimentally validated. The filter comprises a short shunt-stepped impedance resonator and shunt-open stubs. Thus, it can be easily implemented using microstrip technology, offering a simple and cost-effective alternative to multilayer and high-temperature superconductor thin-film-based bandpass filters. S-parameter expressions for the proposed filter are derived using even- and odd-mode methods. To validate theoretical results, a filter prototype operating at the center frequency ($f_o$) of 6.85 GHz is designed, fabricated, and experimentally tested. The measured 3 dB fractional bandwidth (FBW) of the filter exceeds 176%, and the selectivity factor (SF) reaches 0.87. Additionally, the filter outperforms most existing designs in the literature in terms of insertion loss (IL) and return loss (RL). Finally, a figure of merit (FoM) is proposed to measure the trade-off among key performance parameters (i.e., FBW, IL, RL, SF, $f_o$, and group delay flatness), and confirms that the proposed bandpass filter exhibits the best FoM compared to the state of the art.

The presence of side-lobes which are adjacent to main-lobe are serious concern in radar systems. The amplitude distributions across the array aperture improves the side-lobe performance at the cost of directivity and hence aperture efficiency. The current two-way array pattern optimization techniques reveals that if the receive pattern nulls are placed along transmit pattern side-lobe peaks and by using two weight amplitude distribution, side-lobe levels (SLL) can be suppressed up to −50dB. In this work, these techniques are further investigated using three weight amplitude excitation to achieve the best design of a radar array resulting in SLL less than −57dB. These solutions has been validated by parametric optimization and supported by two case studies.

This article presents a highly miniaturized frequency reconfigurable self-triplexing antenna with high isolation. The proposed antenna is constructed using two half-mode and one full-mode substrate-integrated cavities (SICs). The cavities are excited through microstrip feed lines loaded with slots to produce three fixed operating frequencies. Two methods are utilized to adjust these frequency bands. The initial approach involves adjusting the slot dimensions to fine-tune the individual frequency bands. This method provides frequency tuning ranges of 2.75–3.55 GHz, 4.3–6.3 GHz, and 5.42–8.05 GHz at lower, middle and upper-bands, respectively. Nonetheless, with each alteration in slot dimension, the proposed antenna must undergo fabrication and experimental validation, which is time consuming and costly. To address this issue, the frequency bands are reconfigured by utilizing microfluidic channels at the bottom of the cavities, which are filled with dielectric liquids. This technique provides frequency tuning ranges of 2.55–2.86 GHz for the lower band, 3.99–4.6 GHz for the middle band, and 5.2–5.89 GHz for the upper band, respectively. This technique also eliminates the need for additional fabrication. Using slot-loaded half-mode cavities and the channels offers a highly miniaturized footprint and high isolation. An equivalent circuit is developed to analyze the proposed antenna. To validate the design, an antenna prototype is fabricated and experimentally demonstrated. The antenna occupies a small area of 0.079λ_g² with high isolation of 33.2 dB. Furthermore, it exhibits frequency tuning within the ranges 2.55–2.86 GHz, 3.99–4.6 GHz, and 5.2–5.89 GHz using both the techniques with realized gain varying from 2.4 dBi to 5.65 dBi. Good alignment is observed between full-wave simulation and measurements.

The radar systems specify the peak sidelobe levels (SLLs) of the two-way antenna array pattern, which is the product of the patterns of the transmit and receive antenna arrays. The presence of high sidelobes near the main beam of the two-way array pattern can cause interference and ground clutter of the radar system, thereby degrading overall performance. This paper presents a novel technique for synthesizing a two-way phased array antenna pattern that utilizes a uniform transmit and a thinned receive array. Specifically, we propose a centerdominant sparse edge receive array architecture, where all elements in the central region remain continuously active, while only a few elements are activated at both edges of the array to achieve thinning. The proposed antenna array has a peak SLL of $-39.36 \mathrm{~ d B}$, representing a $12.84 \mathrm{~ d B}$ improvement at the cost of a $1.18 \mathrm{~ d B}$ reduction in directivity compared to conventional arrays, where the peak SLL achieved is $-26.52 \mathrm{d B}$. Furthermore, the proposed array shows an improvement of $7.36 \mathrm{~ d B}$ and $0.22 \mathrm{~ d B}$ in SLL and directivity, respectively, compared to the state-of-the-art solutions.