This article presents compact, scalable Gysel power combiners (PCs) in a rectangular coaxial (rectax) guide for high-power applications. Compared to corporate and radial PCs, the proposed Gysel PCs achieve a compact footprint while ensuring reliable high-power operation and scalability to higher order configurations. The proposed concept is validated through two different implementations of Gysel PCs. The first implementation employs the conventional TEM mode of a coaxial guide, while the second employs the microstrip-like quasi-TEM mode in modified rectax. It further reduces fabrication and assembly effort by minimizing the number of individual components required and can improve thermal performance by increasing the core metal volume/surface area in the PCs. In the first implementation, a Gysel PC is designed, fabricated, and measured at 1.87 GHz with a fractional bandwidth of 42%. In the second implementation, two-, four-, and six-way Gysel PCs operating at 2.9, 3.37, and 3.18 GHz are developed, exhibiting fractional bandwidths of 15.5%, 16.3%, and 27.35%, respectively, thereby validating the proposed design concept. To the authors’ knowledge, this is the first implementation of the Gysel PCs in the rectax guide.

This letter presents the design and development of a compact two-way Gysel power divider for high frequency (HF), very high frequency (VHF), and ultra high frequency (UHF) receiver applications. The proposed Gysel power divider achieves the miniaturization by employing ferrite-core transformers and ensures the reliable wideband operation with 1000:1 bandwidth. To validate the proposed concept, a prototype is designed, fabricated, and measured over the frequency range from 1 to 1000 MHz. The fabricated prototype exhibits a measured return loss better than 16.3 dB and isolation exceeding 18 dB over the band. The peak insertion loss is 0.8 dB, resulting in a peak combining efficiency of 84%. The average combining efficiency is better than 74% over the HF, VHF, and UHF bands. The measured amplitude and phase imbalances (PIs) are better than 0.4 dB and 0.3 degrees, respectively, over the entire band of operation. Furthermore, no nonlinearity is observed upto an input drive of 20 dBm.

This letter presents a six-way Gysel power combiner (PC) in a rectangular coaxial guide (rectax) for high-power applications. Compared to corporate and radial PCs, the proposed Gysel PC achieves a compact footprint while ensuring reliable high-power operation and scalability to higher order configurations. To validate the proposed concept, a Gysel PC is designed, fabricated, and measured at 1.87 GHz with a fractional bandwidth of 42%. The measured return loss is better than 15 dB, and the isolation exceeds 23 dB across the entire bandwidth. The peak insertion loss is approximately 0.1 dB, and the average combining efficiency remains better than 90% over the operating band. To the authors’ knowledge, this is one of the first implementations of the Gysel PC in the rectax guide.

This article reviews the evolution of three-dimensional (3D) tunable microwave bandpass filters over the past decade, providing an outline of the tuning elements employed and their benefits and limitations. The major challenges of realizing 3D tunable filters with a minimum number of tuning elements over a wide tuning range, without compromising the filter performance are addressed. The development of 3D tunable filters has progressed through three stages: i) using tuning elements only for the resonators, ii) using a single tuning element for the entire filter, and iii) exploiting techniques to widen the tuning range while using a single element. The article summarizes the work reported in the literature over the past decade in these three stages.

This paper presents a continuously tunable delay line based on coupled transmission-line resonators whose resonant frequencies and coupling coefficients are controlled using BST (Barium Strontium Titanate) varactors. By independently tuning these parameters, the proposed architecture enables fully analog adjustment of both the operating center frequency and the achievable group delay, offering design flexibility. The reflection group delay produced by the two-resonator network is transformed into a transmission group delay using a circulator. The prototype operates with tunable center frequency over 3.4-3.7 GHz, covering one of the sub-6-GHz 5G frequency bands. This prototype achieves a continuously adjustable group delay from 1.5 ns to 7.5 ns while maintaining a flat response over a 20 MHz bandwidth. The measured results highlight the suitability of the proposed approach for applications such as self-interference cancellation, where large tuning range and fine resolution of group delay are simultaneously required.

In this work, we propose a method for designing an innovative H-plane filtering horn antenna (FHA) based on substrate-integrated waveguide (SIW) technology. The approach integrates a bandpass filter (BPF) directly into the flared section of the horn antenna, thus resulting in an efficient compact multifunctional filtering antenna. To demonstrate the concept, a third-order SIW H-plane FHA with an iris-coupled filtering structure is designed, fabricated, and tested at 5.8 GHz, achieving a 3% fractional bandwidth (FBW). The proposed approach significantly enhances the efficiency of conventional horn antenna from a modest 9.2% to 41.3%. The design concept is further extended to millimeter-wave (mm-wave) frequencies with an E-plane metal septum filtering structure, where a second-order H-plane FHA centered at 28 GHz is designed. Furthermore, the proposed design methodology is systematic and scalable to realize a higher-order FHA. Additionally, this approach offers substantial size and volume reductions, along with integrated multifunctionality, promoting overall system miniaturization.

This article presents an interactive application for the design of a pyramidal horn antenna using rectangular waveguide technology. The application is targeted specifically at students to understand the design process of a pyramidal horn antenna and visualize the 2-dimensional and 3-dimensional radiation patterns. Commercial proprietary software which enables understanding are often expensive and are not easily accessible to students worldwide. The interactive application presented in this paper is available for free of cost and is easy to use without requiring sophisticated computational resources. The results of the application are compared with a commercial electro-magnetic simulator and a good correlation between the results from the application and simulator is seen. The statistical study shows an improvement of 58.8% in the learning scores after using the application among the postgraduate students. The mean of before scores and after scores is 4.66 and 7.4, respectively.

A single-layer substrate integrated waveguide (SIW) filtering power divider (FPD) using a modified coupling matrix is presented in this paper. By employing four SIW resonator cavities with an iris structure for inter-resonator coupling and tapering for input/output coupling, a fourth-order FPD is designed, simulated, and fabricated using RT/Duroid5880 substrate (30 mils thickness) at 3.5 GHz with 150 MHz bandwidth. The functional integration of band pass filter (BPF) and power divider into a single multifunctional component has resulted in better in-band performance and component miniaturization. The design has provided the measured return loss better than 15 dB over the band. The measured amplitude and phase imbalances are within 0.04 dB and 1 degree respectively. To the best of the author's knowledge, this is the first coupling matrix-based FPD implemented in SIW technology, in which the design strategy is scalable to produce higher-order FPD systematically. In addition, any of the filter synthesis techniques can be adopted for designing the proposed FPD.

This paper presents a novel multifunctional filtering leaky wave antenna implemented in substrate integrated waveguide technology. In-addition to filtering response, the proposed antenna exhibits a beam scanning range of 60 degrees from broadside to end-fire direction over a frequency range from 3.4 GHz to 3.6 GHz. The proposed filtering antenna basically incorporates periodic longitudinal slots on the broad wall of each resonator in an iris coupled bandpass filter. Transition to microstrip technology is adopted at the input and output ports. To verify the proposed concept, a filtering leaky wave antenna is designed, simulated and fabricated at a center frequency of 3.5 GHz. The measured return loss is better than 15 dB in the entire frequency range with a peak realized gain of 7.5 dBi. The scanning rate of the proposed filtering leaky wave antenna is 10.5 degree per percentage which is considerably higher than conventional SIW based leaky wave antenna.

This paper presents a dual band cavity backed patch antenna in substrate integrated waveguide technology. A square substrate integrated waveguide cavity is designed using a single layer substrate with a square shaped patch on the top layer which serves as a radiating element and is fed using coax probe. The dual band antenna produces the two types of radiation pattern due to the square slot dual resonance. The prototype is simulated, fabricated and measured for return loss, and radiation pattern, where two operational bands with omnidirectional and directional radiation along the broadside direction are realized at 2.23 GHz and 4.45 GHz with fractional bandwidth of 1.34% and 3.37%. The antenna offers multifunctionality with two independent operating bands having different radiation patterns.

In this paper, we have presented a novel filtering leaky wave antenna using radiative band-pass filter concept in rectangular waveguide technology. The design methodology achieves radiation by utilizing slots in each of the resonator cavities of an iris coupled band-pass filter. For proof of concept, an 8th order filtering leaky wave antenna is designed, fabricated, and tested at a center frequency of 9.7 GHz with a fractional bandwidth of 4.6 %. Furthermore, the radiation pattern of the filtering leaky wave antenna exhibits beam scanning 30 degrees in the entire operating band with a peak realized gain of 13.3 dBi. The beam scanning rate of the proposed filtering antenna is 6.5 degree per fractional bandwidth. The proposed methodology is scalable to realize high gain leaky wave antennas with higher order filtering response. Furthermore, it offers multifunctionality within the same size of the waveguide band-pass filter, thereby contributing to the overall system miniaturization.

In this letter, we have presented a novel multifunctional E-plane metal septum-based filtering horn antenna in rectangular waveguide technology. The proposed design methodology is systematic and scalable to realize higher-order filtering responses. For the validation of the concept, a 4th-order filtering E-plane horn antenna is designed, fabricated and tested at 10 GHz with a fractional bandwidth of 2% and a realized gain of 11 dBi. The realized gain of the filtering horn antenna is identical to that of the conventional horn antenna. The proposed design leads to significant savings in mass and volume and hence contributes to system miniaturization especially beneficial in aerospace applications.

This work presents an innovative, compact phase shifter integrated variable coupler in substrate-integrated waveguide (SIW) technology for millimeter-wave beam-forming applications. The phase-shifting mechanism leverages rectangular slots on the top and bottom walls of the SIW, enabling a precise and tunable phase shift of +/- 60 degrees. This phase shifter is functionally embedded into a cruciform directional coupler to realize variable coupling with arbitrary phase shift, combining functionality in a single, unified component. To validate this concept, seven prototypes are fabricated, each operating at a center frequency of 37 GHz, and offering variable coupling and phase-shift configurations (3 dB, 1 dB, 5 dB, +/- 60 degrees, and +/- 30 degrees). Characterization of these prototypes confirms the effectiveness and flexibility of the design, marking a significant advancement in compact, multi-functional millimeter-wave components. The proposed integrated design functions as a single component, ideal for advanced beam-forming networks, including Generalized Joined Coupler Matrix (GJC) architectures.

A systematic design approach to realize a multi-functional filtering power divider (FPD) in microstrip technology is demonstrated in this paper. The coupling matrix of the coupled resonator-based band-pass filter (BPF) is exploited to design the FPD. The FPD integrates the features of a BPF and a power divider (PD) into a multi-functional component. This enhances system performance by mitigating additional losses like cascaded mismatch loss. In-addition, it leads to reduced form factor due to functional integration. The proposed design methodology can be utilized to design the higher-order FPDs.

In this paper, we present a circularly polarized filtering conical horn antenna for aero-space communication applications. This filtering antenna basically includes the functionality of a band pass filter and a circularly polarized conical horn antenna within a single component. This not only leads to a small form factor (reduced size due to functional integration) but also eliminates additional losses like cascaded mismatch loss and hence enhancing the performance of the transceiver system. The proposed 4th order filtering antenna is realized at 11.2 GHz with a bandwidth of 350 MHz and realized gain of 8.1 dBi.

This article presents a novel method for extending the applicability range of neural network models (NNMs) developed within a specific, narrow range. This technique is particularly useful for applications where creating the NNM requires access to a large number of accurate data points, obtained through either electromagnetic (EM) simulations or experimental results. The proposed approach employs a double-mapping (DM) technique to expand the NNM’s range without generating many EM data points. Initially, the NNM is constructed using training data from the fine model (FM) within a defined range. The DM strategy is then used to generate additional data points, extending the NNM’s applicability without relying on time-consuming RF simulations or additional experimental measurements. To demonstrate the effectiveness of this approach, it is applied to NNM of a four-pole dielectric resonator (DR) filter and a patch antenna, successfully extending their original training range. The performance of the extended NNM is evaluated using the mean squared error (MSE), showing a significant improvement in prediction accuracy. It provides an efficient way to extend the validity range of the NNM without requiring many RF simulations.

RF sources are vital components in numerous scientific and engineering pursuits related to wireless communication and sensing applications. However, state-of-the-art RF sources like analog signal generators and vector signal generators are expensive for educational purposes. This article describes a low-cost electronically tunable S- and X-Band continuous wave RF source for a microwave laboratory at the undergraduate and post-graduate levels. RF signals in the unlicensed industrial, scientific and medical (ISM) band (2.4 to 2.525 GHz) are generated directly using an inexpensive commercially available nRF24L01 transceiver module. The module is configured using an Arduino Uno microcontroller through a serial peripheral interface (SPI) protocol. Active frequency multiplication (by a factor of 4) is achieved using a HMC443LP4ETR MMIC chip from Analog Devices to convert the output to X-Band.

In this paper, we present a novel multifunctional filtering power divider (FPD) which is realized in coaxial technology for power combining applications. This FPD basically includes the functionality of a band pass filter and a power divider within a single component. This not only leads to a small form factor (reduced size due to functional integration) but also eliminates additional losses like cascaded mismatch loss thus enhancing the system performance. The proposed FPD is realized at 3.5 GHz with a fractional bandwidth of 4.3 %.

This paper presents the design and development of a compact E-plane sectoral waveguide power combiner at Ku-band operating from 13.6 GHz to 15.6 GHz. The proposed 4-way in-phase power combiner involves only 2 design parameters and achieves a measured return loss better than 15 dB. The measured amplitude imbalance and phase imbalance are within 0.65 dB and 6 degrees respectively. The total power combining efficiency is better than 82.5 % over the entire band of operation. The E-plane power combiner is proposed to be used in Ku-band satellite communication applications.