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A magneto-electric dipole filtering antenna with slots and parasitic elements is proposed and verified in this letter. By utilizing the lower pass-band intrinsic radiation null of the magnetoelectric dipole antenna, a high radiation suppression level is achieved in the low-frequency band. Combining parasitic elements and etching slots on the electrical planes, radiation nulls are introduced in the high-frequency band. The measured |S11|<-10 dB bandwidth of the proposed antenna is 72.6% (1.71–3.66 GHz). The measured results show that the radiation suppression level in the high-frequency band and the low-frequency band is −25.3 dB and −16.8 dB, respectively. Moreover, the measured realized gain is about 7.2 dBi in the operating band. [ABSTRACT FROM AUTHOR]

A novel Ultra Wide-Band (UWB) frequency reconfigurable filtering antenna (or reconfiltenna) is presented in this research article. In the first step, a stepped-flower-shaped UWB antenna is optimized having a 3.5–14.1 GHz band. In the next step, a UWB filter with two stubs is designed to pass the frequency band from 3 GHz to 11.2 GHz having a stop band (notch) in between them from 5.9 GHz to 7.1 GHz. Then, the filter is merged with the feedline of the UWB antenna. The radiating patch is coupled at the output of the filter forming the filtering antenna or filtenna. This filtenna operates from 3.52 GHz to 10.1 GHz with a notch band of 5.42 GHz to 6.8 GHz. Finally, six PIN diodes are embedded in the stubs of the filter to vary the effective length of the stubs by switching ON/OFF the PIN diodes in different combinations. This variation, in turn, produces a controllable or trackable notch-band. The proposed reconfiltenna carries a small volume of 32 mm × 27 mm × 0.2 mm with a thin photo paper substrate. It produces a maximum gain and efficiency of around 7.54 dBi and 83% respectively. The simulated outcomes are cross-referenced and confirmed through comparison with experimental results. [ABSTRACT FROM AUTHOR]

This paper presents the design and characterization of a coplanar waveguide (CPW) fed, low-profile, and flexible arrow-shaped filtenna for ISM band applications at 2.45 GHz. The antenna design involves an innovative approach incorporating etching slots to achieve miniaturization by 34%, contrasting with a traditional quadrilateral-shaped antenna. After the attainment of desired miniaturization, the unwanted harmonics are also mitigated by deploying simple filtering methodology. A perpendicular rectangular stub is strategically introduced to the feedline, effectively minimizing harmonics across a broad frequency range of 3.3–11.0 GHz. Through simulations and measurements, the results indicate that the antenna's operational band spans from 2.276 to 2.75 GHz, encompassing the entire ISM band (2.4–2.5 GHz). Notably, the antenna demonstrates promising radiation characteristics, including omnidirectional gain of approximately 2.2 dBi and a radiation efficiency exceeding 95%. With a compact overall size of 0.24λ × 0.20λ × 0.0005λ (where λ is the free-space wavelength at 2.45 GHz), coupled with wide harmonic rejection property, the proposed arrow-shaped flitenna emerges as a compelling candidate for ISM band applications. [ABSTRACT FROM AUTHOR]

This paper investigates a thin low-pass filtering antenna array based on dual-polarized Vivaldi elements. The low-pass filtering in the antenna elements reduces the requirement for the front-end filtering between the antenna and the microwave electronics, resulting in improved overall out-of-band suppression, size reduction, and lower cost. The array employs a novel stacked-PCB structure, where simple two-sided PCBs are stacked on top of each other. The via-connected metal layers of all PCBs form a tapered slotline along the surface normal of the PCBs. The filtering effect is realized by corrugating the tapered slotlines, which provides effective, space-saving integration of the filters that fit into a half-wavelength lattice. According to unit-cell simulations, the proposed antenna array operates at 6–18.5 GHz, and the stopband extends from 21 GHz to 37 GHz. The antenna array provides a −10-dB active reflection coefficient (ARC) with beam-steering angles within ±60° in E- and D-planes, and −6 dB within ±55° in the H-plane. At stopband frequencies, the attenuation with respect to simulated total efficiency is at least 20 dB. The operation of the proposed antenna array is confirmed by measurements of an $11\times 12$ antenna array prototype, which show that the gain suppression level in the stopband is more than 30 dB up to 37 GHz, and more than 20 dB up to 40 GHz.

Narrowband bandpass filters (BPFs) are in great need in future terahertz (THz) technologies to suppress EM signals beyond the operating band. THz filters and antennas play a crucial role in controlling and transmitting THz signals for the application of high data rate (6G) communication, non-destructive sensing, imaging, switching, and filtering. The proposed filtenna is designed using a dual-band THz BPF with a complementary split ring resonator (CSRR) metamaterial (MM). This paper suggests the circle in the pentagon (CP) filtenna and the simulation results show the filtering characteristics of two pass bands with resonant frequency (fr) between 6.3 and 7 THz and between 8 and 9.8 THz with a squared ratio of 0.54. Also, the maximum 3-dB bandwidth (BW) of 1.3 THz, low return loss (RL) of −28.46 dB, and low insertion loss (IL) of almost 0 were attained. The proposed antenna radiates at the frequency of 6.8 THz with an RL of −27.72 dB. The proposed CP filtenna applies to various wireless communication, especially in drone-to-drone communication with excellent data rates. [ABSTRACT FROM AUTHOR]

A new two-port MIMO filtenna with center frequency and bandwidth tunability is introduced by integrating a tunable filter into the feeding section of a monopole antenna. The tunable filter is constructed by a dual-mode square loop resonator having four varactor diodes. One of the varactor diodes are separated from the other varactors, so that the tuning process is achieved by using two different bias voltages. Thus, the bandwidth can be tuned by the singly biased varactor diode, while the center frequency is tuned by controlling all varactors. The monopole antenna is developed by a slotted radiation patch to obtain high gain within the desired frequency band which must also cover the tuning range. A two-port tunable MIMO filtenna was fabricated and successfully tested for experimental validation. The 10-dB bandwidth of the designed MIMO filtenna can be tuned from 340 to 690 MHz at the highest center frequency, while the center frequency is tuned between 3.4 and 3.93 GHz. Within the tuning range, the maximum peak gain varies between 1.6 and 4 dBi in the electromagnetic (EM) simulations. Isolation between the outputs of the MIMO filtenna was measured as better than -20 dB and envelope correlation coefficient (EEC) was observed as less than 0.001. Diversity gain (DG) and mean effective gain (MEG) were obtained as close to 10 and less than 3 dB, respectively. Moreover, radiation efficiency of the proposed MIMO filtenna was obtained between 60% and 72%.

This paper introduces a novel filtering approach that employs integrated periodic structures with a conventional Vivaldi antenna to achieve a fully integrated bandpass filtering antenna. The approach results in a wide out-of-band suppression, high passband selectivity, adjustable operational bandwidth, and low insertion loss. The proposed filtering approach maintains the original size of the conventional Vivaldi antenna (base antenna) without requiring additional modifications. To validate the approach, we present two filtering Vivaldi antennas: filtering antenna I (center frequency: 18GHz, fractional bandwidth: 21%, insertion loss: 0.32dB) and filtering antenna II (center frequency: 6.5GHz, fractional bandwidth: 12%, insertion loss: 0.6dB). Their wide out-of-band gain suppression (typically $\geq 15$ dB) covers the conventional Vivaldi antenna’s frequency range (4-24GHz). A prototype of the filtering antenna I is manufactured. Its measurement results validate the proposed approach and show good agreement with the simulated reflection coefficient, realized gain, and radiation patterns. The features of the proposed filtering antenna approach, make it suitable for various applications requiring efficient frequency filtering.

The fifth generation (5G) mobile communication systems employ technologies such as massive MIMO, millimeter-wave (mmWave), and ultra-dense networks to support higher transmission data rate and lower latency, thereby enabling commercial deployment. Furthermore, the forthcoming sixth generation (6G) networks will integrate terrestrial and non-terrestrial networks, aiming to achieve full spectrum, full applications, and global coverage. Whether in the context of 5G or 6G networks, base transceiver stations (BTS) require a substantial number of radio frequency (RF) transceiver chains and antenna array, particularly in mmWave frequency bands. It is known that bandpass RF filters between antenna elements and transceivers are key components for suppressing out-of-band spurs and interference. The single board seamless integration of transceivers and antennas has become a growing trend. It means there is no extra room for a large number of filters at mmWave bands, leading to the emergence of integrated designs that combine filtering circuitry with antennas, known as filtenna or filtering antenna. With illustrated examples, the design methodologies, operational principles, and implementation strategies of filtennas are reviewed in this paper.

In this paper, methods for improving frequency selectivity in filter antennas by employing controllable radiation nulls (RN) are reviewed. Radiation nulls in the Gain graph help in improving the rejection of out-of-band frequencies. The majority of the designs reviewed in this paper use substrate-integrated waveguide (SIW) technology. Some of the methods of generating RNs include: loading filtenna with slots or shorting pins, using proper design of multi-signal path between source and load, employing electric and magnetic mixed-coupling, embedding filtering structures, parasitic elements, employing filtering action in the feed network. Certain designs achieve more than two radiation nulls which give even better selectivity.

This paper presents a novel broadband filtenna design for 5G applications. The filtenna structure comprise of a bow tie slot loaded path antenna with a four-pole lowpass filter structure on the feed-line. In addition, the defected ground structure method was applied to miniaturize the size and widen the operating frequency bandwidth. The proposed filtenna was designed and optimized with utilizing Keysight’s PathWave EM Design (EMPro) software. In addition, the filtenna design was analysed with utilizing four different substrates, which are Rogers RT5880, RO3003, RO4003 and RT6006, and the electromagnetic simulation results were presented. Moreover, the design was manufactured with utilizing Rogers RT5880 and the design was validated with the measurements. The developed filtenna operates at a centre frequency of 3.9 GHz and the operating frequency bandwidth of 2.86 to 4.89 GHz which yields a fractional bandwidth of 52%. Furthermore, the filtenna has a reflection coefficient better than -10 dB and the measured maximum antenna gain was 3.26 dBi. The filtenna has a compact size of 0.463λ_0×0.506λ_0 where λ_0 is the wavelength at the center frequency. The proposed filtenna can be utilized for 5G applications with its compact-size, low-cost and high-performance characteristics.

This paper presents the design and characterization of a coplanar waveguide (CPW) fed, low-profile, and flexible arrow-shaped filtenna for ISM band applications at 2.45 GHz. The antenna design involves an innovative approach incorporating etching slots to achieve miniaturization by 34%, contrasting with a traditional quadrilateral-shaped antenna. After the attainment of desired miniaturization, the unwanted harmonics are also mitigated by deploying simple filtering methodology. A perpendicular rectangular stub is strategically introduced to the feedline, effectively minimizing harmonics across a broad frequency range of 3.3–11.0 GHz. Through simulations and measurements, the results indicate that the antenna’s operational band spans from 2.276 to 2.75 GHz, encompassing the entire ISM band (2.4–2.5 GHz). Notably, the antenna demonstrates promising radiation characteristics, including omnidirectional gain of approximately 2.2 dBi and a radiation efficiency exceeding 95%. With a compact overall size of 0.24λ × 0.20λ × 0.0005λ (where λ is the free-space wavelength at 2.45 GHz), coupled with wide harmonic rejection property, the proposed arrow-shaped flitenna emerges as a compelling candidate for ISM band applications.

Abstract This paper presents a novel design of a compact, wideband tunable microstrip filtenna system for effective spectrum sensing in cognitive radio (CR) applications. The proposed filtenna structure has a total bandwidth of $$1.63\,\text{GHz}$$ 1.63 GHz and flexible frequency scanning design throughout the frequency range from $$1.93\,\text{ to }\,3.56\,\text{ GHz}$$ 1.93 to 3.56 GHz with high selectivity and narrow bandwidths ranging from $$39.9\,\text{to}53\,\text{MHz}$$ 39.9 to 53 MHz . Frequency tuning is accomplished electrically via integrating a varactor diode into the filtenna construction. The filtenna is realized on a Rogers TMM4 substrate with $$h=1.52\,\text{mm}$$ h = 1.52 mm thickness and relative dielectric constant of $${\varepsilon }_{r}=4.5$$ ε r = 4.5 with dimensions of $$(25\times 35)\, {\text{mm}}^{2}$$ ( 25 × 35 ) mm 2 . The obtained gain and efficiency of the filtenna ranged from $$0.7$$ 0.7 to $$2.26\,\text{dBi}$$ 2.26 dBi and 49% to 60%, respectively, within the tuning range. Simple biasing circuitry, wideband operation, and compact planar structure are distinctive and appealing aspects of the design. For the manufactured prototypes, a significant level of agreement is found between the simulated and measured results in terms of scattering parameter $${\text{S}}_{11}$$ S 11 and radiation patterns at different operating frequencies.

Abstract A dual-port multiple-input multiple-output (MIMO) filtenna with minimal sizes of 80 × 45 mm2 is set up in this study. Each element in this MIMO filtenna is positioned orthogonally to the one next to it to improve isolation. For the MIMO element to achieve high-frequency selectivity and compact size, a frequency-reconfigurable filtenna that was created by fusing a band-pass filter and a monopole radiator was used. The suggested filtenna can switch between its C-band and X-band operating states with ease. On build the filtenna circuit, a band-pass filter based on defective microstrip structure is inserted to a circular monopole radiator. The developed filtenna operates in the C-band frequency range of 6.5–8 GHz and the X-band frequency range of 8–12 GHz. It is possible to use the X-band operating state for communication in a cognitive radio environment. Used as a decoupling structure, metamaterial structures can increase isolation to more than 40 dB across the bandwidth. The suggested MIMO filtenna system has an envelope correlation coefficient of 2.4e−6, a peak gain of 6 dBi, and an impedance bandwidth of 7.4–7.75 GHz. The MIMO filtenna is constructed and measured, and the findings of the measurement and simulation are in good agreement.

A filtenna (filtering antenna) for the fifth generation (5G) mobile communications in millimeter‐wave (mmWave) band is proposed in this paper. The filtenna is fed by a probe, and two radiation nulls are generated at the upper sideband based on the stacked‐patches structure. Then, two shorting pins loaded on the driven patch are introduced, which then result in the third radiation null. An "X‐character" shape radiation loop is added therefore, the fourth radiation null can be generated. Besides, the fifth radiation null at around 34 GHz is generated by adding four parasitic strips on the top radiation patch. The measured −10 dB impedance bandwidth of the filtenna is from 23.07 to 30.99 GHz. The average gain of the antenna is larger than 5.5 dBi, and the stopband suppression can reach 14 dB with a wide stopband. With the merits of low profile, wide stopband, and stable radiation, the proposed filtenna can be a good candidate for 5G mmWave applications. [ABSTRACT FROM AUTHOR]

Advances in wireless technology have sparked interest in multiband reconfigurable antenna, an emerging technique that can shape the future of wireless technology. For various IoTs applications, it is desirable to have an efficient reconfigurable antenna in limited space. Configurability can be achieved by changing the physical parameters through electronic switches, optical switches, or metamaterials. This review paper comprehensively surveys recent cognitive radio antenna (CRA) advancements. The CRA is opportunistic spectrum accessibility (OSA) for "underutilized spectrum" feasible for utilizing resources and boosting licensed spectral occupancy. It significantly integrates two crucial concepts of spectrum sensing and communication. A thorough analysis of several interweave cognitive radio (CR) antennae is done. An explanation of filtering for hybrid CR approaches is also included, which offers a glimpse into the future. The ultra-wideband (UWB) / narrow band (NB) antenna's sensing and communication capabilities have been elaborated, which is best suited for CR. [ABSTRACT FROM AUTHOR]

In this letter, a compact circularly polarized (CP) microstrip patch filtenna designed by reusing dual‐mode substrate integrated waveguide (SIW) cavity is proposed. The dual‐mode SIW cavity, operating at its TE120 and TE210 modes, can be used not only as the first stage resonator of the filtering network but also feeds the four microstrip patches working at their TM10 and TM01 modes. A pair of asymmetric perturbed posts is inserted in the SIW cavity to perturb the electric field distributions of TE120 and TE210 modes so as to achieve one axial ratio (AR) minima. The other AR minima is realized by sequentially exciting the four orthogonal microstrip patches via the four rectangular slots that are etched on the top surface of the SIW cavity. In addition, four metal posts penetrated the SIW cavity is employed to improve the impedance matching. For verification, a CP filtenna prototype centered at 5.13 GHz is designed, manufactured, and tested. The measured results agree well with the simulated ones, demonstrating a fractional impedance bandwidth of 6.9% (4.95–5.3 GHz), a 3 dB AR bandwidth of 4.2% (5–5.21 GHz), and a maximum boresight realized gain of 8.4 dBic. [ABSTRACT FROM AUTHOR]

A dual-port multiple-input multiple-output (MIMO) filtenna with minimal sizes of 80 × 45 mm2 is set up in this study. Each element in this MIMO filtenna is positioned orthogonally to the one next to it to improve isolation. For the MIMO element to achieve high-frequency selectivity and compact size, a frequency-reconfigurable filtenna that was created by fusing a band-pass filter and a monopole radiator was used. The suggested filtenna can switch between its C-band and X-band operating states with ease. On build the filtenna circuit, a band-pass filter based on defective microstrip structure is inserted to a circular monopole radiator. The developed filtenna operates in the C-band frequency range of 6.5–8 GHz and the X-band frequency range of 8–12 GHz. It is possible to use the X-band operating state for communication in a cognitive radio environment. Used as a decoupling structure, metamaterial structures can increase isolation to more than 40 dB across the bandwidth. The suggested MIMO filtenna system has an envelope correlation coefficient of 2.4e−6, a peak gain of 6 dBi, and an impedance bandwidth of 7.4–7.75 GHz. The MIMO filtenna is constructed and measured, and the findings of the measurement and simulation are in good agreement. [ABSTRACT FROM AUTHOR]

This paper presents a novel design of a compact, wideband tunable microstrip filtenna system for effective spectrum sensing in cognitive radio (CR) applications. The proposed filtenna structure has a total bandwidth of 1.63 GHz and flexible frequency scanning design throughout the frequency range from 1.93 to 3.56 GHz with high selectivity and narrow bandwidths ranging from 39.9 to 53 MHz . Frequency tuning is accomplished electrically via integrating a varactor diode into the filtenna construction. The filtenna is realized on a Rogers TMM4 substrate with h = 1.52 mm thickness and relative dielectric constant of ε r = 4.5 with dimensions of (25 × 35) mm 2 . The obtained gain and efficiency of the filtenna ranged from 0.7 to 2.26 dBi and 49% to 60%, respectively, within the tuning range. Simple biasing circuitry, wideband operation, and compact planar structure are distinctive and appealing aspects of the design. For the manufactured prototypes, a significant level of agreement is found between the simulated and measured results in terms of scattering parameter S 11 and radiation patterns at different operating frequencies. [ABSTRACT FROM AUTHOR]

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External partial discharge (PD) sensors for the ultra-high frequency (UHF) method are widely used to detect the PD signals in high-voltage power equipment for ease of installation and maintenance. However, conventional external PD sensors detect not only PD signals but also LTE signals; thus, a microwave filter is usually employed. In this work, a UHF filtering antenna (filtenna) is proposed as the external PD sensor to detect PD signals and simultaneously block LTE-band signals. The proposed UHF filtenna is the printed monopole antenna with a built-in interdigital bandpass geometry, which is selected for its compact size. Measurement results show that the proposed UHF-printed monopole filtenna operates adequately in the frequency range of 1 GHz to 1.6 GHz and simultaneously blocks LTE signals significantly.

We propose a $2\times2$ patch array filtenna specifically designed for radio altimeter applications with significant suppression of unwanted adjacent 5G spectrum signals. The patch radiator is carefully selected to meet the radiation requirement of radio altimeters and the substrate integrated waveguide (SIW) feeding network is meticulously designed to provide shielding property and excellent suppression level for adjacent 5G spectrum through the evanescent mode characteristic. In specific, the proposed filtenna harnesses inherent suppression characteristic of low-band RF signals below a cutoff frequency in the SIW feeding network, eliminating the need for additional filtering geometries. The proposed filtenna is fabricated and measured, and experimental results confirm its effective operation in the radio altimeter band (4.2–4.4 GHz), exhibiting successful suppression of 5G spectrum (3.4–4 GHz) by 40.70-dB to 43.26-dB. Comparative analysis reveals that the proposed filtenna demonstrates superior suppression level for adjacent spectrums compared to previous planar array filtennas.

A broadband high‐efficiency high‐gain empty substrate integrated waveguide cavity‐backed filtenna with dual beams is proposed. The antenna is vertically stacked by three cavities. Two rectangular slots are etched above the uppermost cavity to realize the radiation function. Since the interior of the cavity is covered with metal, the characteristics of the antenna are independent of the used dielectric substrate. The fractional bandwidth of the proposed filtenna is 21.1%, and the efficiency can reach more than 90% in the operational band. The antenna has good frequency selection properties, and the ratio of the −10 dB impedance bandwidth to the −3 dB impedance bandwidth is 0.88. Good gain flatness is obtained, the maximum gain of the filtenna within the operational band is 8 dBi. The proposed dual‐beam filtenna can realize broadband and filtering simultaneously, with low cost and high efficiency. It can be used in wireless communication systems. [ABSTRACT FROM AUTHOR]

In order to simplify the complex wireless communication system while maintaining good electrical performance and reducing the cost, a new compact design has been developed that combines two essential components of the wireless communication chain, the filter and the antenna, into a single multifunctional device capable of radiating and filtering. This filtering antenna, also known as a filtenna, was designed and manufactured for use in 5G sub-6 GHz and wireless applications at the n77-band (3.3–4.2 GHz). The structure consists of a hairpin filter made up of three folded U-shaped resonators integrated with a monopole antenna having a diamond-shaped radiating element. The strength of our work is that we were able to create a compact, small, and low-cost design while achieving good electrical performance. The simulated and measured results are compatible, the reflection coefficient showed a good impedance matching for both resonance frequencies 3.57 GHz and 4.10 GHz (|S11|≤ − 10 dB), as well as a voltage standing wave ratio less than 2. Several other results will be presented and discussed later in this article. The software used for the simulation is High-Frequency Structure Simulator (ANSYS HFSS) which employs the finite element approach. A prototype of the filtenna (filtering Antenna) was fabricated and measured using the vector network analyzer 3656D. [ABSTRACT FROM AUTHOR]

A gain enhanced dual-band filtenna operating at frequency bands of 3.5 and 5.3 GHz for 5G sub-6 GHz applications is presented in this article. A dual-band antenna is integrated with a filter to improve selectivity. The antenna uses printed monopoles as the radiating element, and the filtering response is achieved using a modified feedline. The designed filtenna is 50 × 38 × 1.63 mm3 in size with a maximum gain of 2.5 dBi. The novel filtenna design is equipped with an artificial magnetic conductor (AMC) for the first time to enhance the performance. A unit cell for the AMC is designed that offers zero phase shift in the desired frequencies. A four by four AMC array is designed using this unit cell, which is used as a reflective surface to improve the radiation characteristics of the filtenna. The gain of the filtenna is improved three times up to 7.5 dBi in both bands. The proposed design's overall planar dimensions are 80 × 80 mm2. Using AMC, the gain has improved with a very minute or no change in the other characteristics. The measured results are congruent with the simulated ones, illustrating that the filtenna has good impedance matching and excellent gain in both bands. [ABSTRACT FROM AUTHOR]

In this work, a dual dielectric resonator antenna (DRA) oriented in opposite directions is designed and analyzed. The unique feature of the proposed antenna is to provide dual-band filtering characteristics with a quasi-isotropic radiation pattern. The upper cylindrical ceramic is fed by the combination of a conformal strip and a circular patch, while the lower one is fed by a circular aperture. The proposed feeding mechanism produces HEM11δ and HEM12δ modes inside the ceramic material at 2.8 GHz and 5.4 GHz, respectively, providing a dual-band response. The proposed radiator has two main features: (i) the arrangement of the ceramic-based radiator creates radiation nulls at 5.8 GHz, 4.8 GHz, 3.5 GHz and 2 GHz, which provides the filtering response, and (ii) the opposite orientation of the dual ceramic produces quasi-isotropic radiation features. Experimental measurements confirm its operation in the frequency ranges of 2.48–3.3 GHz and 5.21–5.48 GHz. Maximum rejection is about −20 dBi in both frequency bands, while the passband gain is about 5.0 dBi. These radiation characteristics make the proposed antenna suitable for the WLAN (2.5 GHz/5.15 GHz) frequency band. [ABSTRACT FROM AUTHOR]

A reconfigurable wideband monopole antenna is introduced in this paper for cognitive radio and wireless applications. The reconfigurability was achieved by four varactor diodes embedded in the band pass filter (BPF) structure which was integrated with the suggested antenna through its feed line. The simulated impedance characteristics coped with the measured ones after fabricating the suggested model with/without the reconfigurable BPF. Furthermore, the model achieved the desired radiation characteristics in terms of radiation pattern with acceptable gain values at the selected frequencies within the achieved frequency range (1.3–3 GHz). [ABSTRACT FROM AUTHOR]

In this paper Substrate Integrated Waveguide-based filtenna operating at Ku band is proposed. The model is designed on a low loss dielectric substrate having a thickness of 0.508 mm and comprises of shorting vias along two edges of the substrate walls. To realize a bandpass filter, secondary shorting vias are placed close to primary shorting vias. The dimension and position of the vias are carefully analyzed for Ku band frequencies. The model is fabricated on Roger RT/duroid 5880 and the performance characteristics are measured. The proposed model achieves significant impedance characteristics with wider bandwidth in the Ku band. The model also achieves a maximum gain of 7.46 dBi in the operating band thus making it suitable for Ku-band applications. Substrate Integrated Waveguide (SIW) Structures possess most of the advantages over conventional radiofrequency waveguides since they have high power management capacity with self-consistent electrical shielding. The most noteworthy advantage of SIW, it can able to integrate all the components on the same substrate, both passive and active components. [ABSTRACT FROM AUTHOR]

A quad-port multiple-input multiple-output (MIMO) filtenna with compact dimensions of $50\times50$ mm2 is arranged. In this MIMO filtenna, each element is placed orthogonal to its adjacent one to enhance the isolation. The MIMO element is configured based on the novel COVID-19 virus shape with a co-planar waveguide (CPW) feeding structure and dimensions of $17\times22$ mm2. The element bandwidth ranges from 3.3 GHz to more than 60 GHz. Three frequency notches are designed at 3.5 GHz for WiMAX, 5.5 GHz for WLAN, and 8.5 GHz for X-band applications. A bandpass filter (BPF) with high out-of-band rejection is used as a decoupling structure (DS) to improve the isolation to more than 30 dB across most of the bandwidth. The BPF is designed based on LC lumped elements, and then implemented using planar strip lines. The proposed MIMO filtenna system provides an impedance bandwidth of 2.4–18 GHz, a peak gain of 5 dBi, and an envelope correlation coefficient (ECC) less than 0.00021. In turn, channel capacity loss does not exceed 0.2. The MIMO filtenna is fabricated and measured showing a good agreement between the measured and simulated results.

In this article, a dual-functional microwave system with a single input port that can simultaneously be used for antenna and sensor applications is presented. The dual-functional ability of the proposed system is achieved by integrating a two-port microwave sensor and a Wi-Fi antenna with a novel frequency-selective multipath filter (FSMF). The FSMF ensures efficient system operation by not affecting the operational bandwidth of the communicating antenna in the presence of different sensed materials under test (MUTs) on top of the sensor. The proposed microwave sensor also has a unique capability of measuring one more sensing parameter in addition to the often used reflection and transmission coefficients. The additional parameter is the frequency distance of two closely spaced resonance frequencies of the microwave sensor in the presence of an MUT. Compared to existing state-of-the-art techniques, the additional sensing parameter (as done in this work) can be used as an alternative to transmission coefficient for characterization of different MUTs or as an additional parameter giving more degree of freedom. The entire system is designed in a single substrate with a common input source. The performance of the dual-functional system was tested using different MUTs and showed a good agreement with the measurement results. [ABSTRACT FROM AUTHOR]

This article presents a millimeter-wave (mmWave) dual-band dual-polarized filtenna, which can achieve desirable out-of-band rejection for 5G applications. The dual-band dual-polarized antenna element consists of two fully-shielded quarter-mode substrate integrated waveguide (FSD-QMSIW) cavities and a dual-band stacked ring antenna. Two parts are coupled through the slot on the ground. The cavities are completely enclosed by the metal holes and copper cover to eliminate radiation loss. The loaded slots can tune the frequencies of the first two modes in the FSD-QMSIW cavity for dual-band operation. The inherent transmission null between the dual modes is generated to improve the stopband attenuation. To verify the proposed method, a dual-band dual-polarized filtenna with a three-order filtering function and four radiation nulls is designed and fabricated. The −10 dB impedance bandwidth can effectively cover 5G n258 (24.25–27.5 GHz) and n260 (37–40 GHz) bands in the measurement. The gains of two polarizations drop over 20 dB between the two bands. A four-element filtenna array is constructed to test its beam-scanning ability and further integrated with active beamformer integrated circuits (ICs). The measured results show that the fabricated filtenna array maintains satisfactory out-of-band rejection performance and can be one of the most promising 5G communication candidates. [ABSTRACT FROM AUTHOR]

A new method for frequency selective surface (FSS) with high selectivity, namely, filtenna–filtenna (FA-FA)-based technique, is proposed, which consists of two filtering antennas and impedance matching network. Based on the reciprocity theorem, the radiation null of filtenna can provide a stopband of the proposed FSS. In this work, it is validated by using a periodic array of back-to-back magnetoelectronic (ME)-dipole antennas with split-ring resonators (SRRs), and a slotted GND plane is used to connect the two ME-dipole antennas for impedance matching. Bandpass response of the proposed FSS is realized by the intrinsic high-pass characteristic of ME-dipole antennas and the bandstop characteristic of SRRs. Four transmission zeros (TZs) and three transmission poles (TPs) are generated, exhibiting a high-order filtering response. TZs and TPs are analyzed by equivalent circuit model and current distributions. The 3 dB fractional bandwidth (${\mathrm {FBW}}_{\mathrm {3\,dB}}$) of 38.5% in the passband and the 20 dB fractional bandwidths $({\mathrm {FBW}}_{\mathrm {20\,dB}})$ of 8.7% in the lower rejection band and 13.8% in upper rejection band are obtained in this design. Finally, a prototype is fabricated and measured to further validate the proposed FA-FA-based technique. Simulated and measured results show that the proposed FA-FA-based FSS is with the distinct advantages, including wide passband, low profile, tunable TZs, and dual-polarized application, which verifies the proposed method of FSSs. [ABSTRACT FROM AUTHOR]

In this letter, an alumina ceramic-based multi-input multi-output antenna is designed and examined. The proposed feeding structure provides filtering characteristics as well as creates circularly polarized waves between 2.12 and 2.35 GHz. Filtering is achieved by creating radiation null at 1.75 GHz and 2.65 GHz. The introduction of the polarization diversity concept improves the isolation level by 35 dB. Experimental testing of the fabricated antenna confirms that it works from 2.05 to 2.55 GHz. The broadside radiation pattern along with the good value of diversity makes it appropriate for wireless LAN (2.5 GHz) application. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a compact and planar reconfigurable filtenna for application in Wireless systems. The filtenna is composed of a UWB circular antenna and a filter with two trapezoidal resonators. The filter is integrated on the antenna feed line and has a band-pass frequency response. The filtenna frequency response reconfiguration is achieved by changing the capacitance of a varactor diode, placed between filter resonators; the capacitance varies continuously from 1.32 pF to 4.09 pF according to an applied bias voltage. The varactor capacitance analog variation defines the filtenna frequency of operation, which can be varied from 2.2 GHz to 3.4 GHz with an average bandwidth of 200 MHz, while maintaining the radiation characteristics of the UWB antenna. Simulated and measured filtenna results are shown according to varactor diode bias, demonstrating multiband operation using a compact planar design.

This paper presents the design and realization of a flexible and frequency-reconfigurable antenna with harmonic suppression for multiple wireless applications. The antenna structure is derived from a quarter-wave monopole by etching slots. Afterward, the high-order unwanted harmonics are eliminated by adding a filtering stub to the feedline to avoid signal interference. Lastly, frequency reconfigurability is achieved using pin diodes by connecting and disconnecting the stubs and the rectangular patch. The antenna is fabricated on the commercially available thin (0.254 mm) conformal substrate of Rogers RT5880. The proposed antenna resonates (|S11| < –10 dB) at five different reconfigurable bands of 3.5 GHz (3.17–3.82 GHz), 2.45 GHz (2.27–2.64 GHz), 2.1 GHz (2.02–2.29 GHz), 1.9 GHz (1.81–2.05 GHz), and 1.8 GHz (1.66–1.93 GHz), which are globally used for 5G sub-6 GHz in industrial, medical, and scientific (ISM) bands, 4G long-term evolution (LTE) bands, and global system for mobile communication (GSM) bands. The simulated and measured results show that the antenna offers excellent performance in terms of good impedance matching with controllable resonant bands, high gain (>2 dBi), stable radiation patterns, and efficiency (>87%). Moreover, the conformal analysis shows that the antenna retains its performance both in flat and bending conditions, making it suitable for flexible electronics. In addition, the antenna is compared with the state-of-the-art works for similar applications to show its potential for the targeted band spectrums. [ABSTRACT FROM AUTHOR]

In this communication, a dual polarized (DP) stacked patch filtenna (filtering antenna) with a wide stopband is developed for tile array applications. The bandpass filtering property is realized by improving the feeding network and patch without adding extra bandpass circuit or size. An elaborate feeding structure with complementary pair of a short-circuited stub and an open-circuited stub (CSSOS) is developed, which generates two transmission nulls effectively enhancing the selectivity and suppressing the harmonic. Moreover, CSSOS has a small size and broadens the impedance bandwidth apparently by introducing an in-band resonance. By properly etching four U-shaped slots on the driven patch, a radiation null in the upper stopband is also generated. The nulls generated by the two approaches can be adjusted independently in wide ranges. For further harmonic suppression, bandstop striplines (BSSs) with ultralow insertion loss are developed. Measured results show that the filtenna performs a wide operating band (3.10–3.95 GHz) and a wide stopband up to 8 GHz with a rejection level higher than 16 dB. Besides, a 32-element tile phased array employing the filtennas is also fabricated and measured. A compact configuration, high selectivity, and good beam steering capacity are exhibited. [ABSTRACT FROM AUTHOR]

This study designed a wide-beamwidth pixelated dielectric resonator antenna (DRA) combined with a low-pass filter (LPF) to suppress harmonics. The DRA was designed to create a wide-beam pattern with a pixelated structure. The pixelated DRA was optimized by a genetic-learning particle swarm optimization algorithm. To prevent significant higher-mode radiation and harmonics from occurring in the DRA, an LPF was included in its feeding line. The filter had a seventh-order Chebyshev design, and a hybrid step-impedance filter was proposed by modifying the step-impedance filter for use in narrow spaces behind the ground. [ABSTRACT FROM AUTHOR]

This letter presents a dual-polarized, band-pass filtering antenna, or “filtenna” with a steep roll-off rate and a compact size. To simultaneously support multiple communication standards in a shared aperture, base station antenna arrays need to operate in multiple closely-spaced frequency bands. However, each filtenna has a limited space in the aperture-shared array; therefore, it is challenging to achieve a high roll-off rate. To resolve this problem, we proposed a filtenna that consists of four stacked X-shaped patches, of which the second from the bottom is the driven patch and the rest are parasitic ones. These closely coupled parasitic patches switch rapidly from resonance to antiresonance; however, their radiations change because they together cancel one another and create a very steep roll-off rate. The aperture dimension of the proposed antenna is $0.2 \, \lambda _{0} \times 0.2 \, \lambda _{0} \times 0.14 \, \lambda _{0}$ , where $\lambda _{0}$ is the wavelength in free space at the center frequency. The measurement results demonstrate a very steep roll-off rate up to 1795 dBi/GHz at the lower cutoff frequency of 1.8 GHz. The measured average gain was 8 dBi over the operating frequency band of 1.805–1.88 GHz, which makes the proposed filtenna a good candidate for multiband and multistandard base stations. [ABSTRACT FROM AUTHOR]

In this letter, a millimeter-wave (mmW) substrate integrated waveguide (SIW) filtering power divider (FPD) with differential outputs is proposed and used as a feeding network for bidirectional endfire filtenna array. By using theoretical design rule based on coupling coefficient and external quality factor (Qe), the proposed FPD combines multiple functions such as filtering, power divider, and unbalanced-to-balanced (balun) conversion into one single circuit. Meanwhile, the FPD is insensitive to the load impedance so that it can be seamlessly connected to the back-to-back quasi-Yagi antenna array for bidirectional radiation. For demonstration, an mmW bidirectional endfire filtenna array centered at 27.5 GHz fed by three-order FPD is designed and fabricated. The measured results exhibit that the proposed filtenna array owns an impedance bandwidth (|S11| < −10 dB) of 3.4%, flat passband gain with a peak gain of 5.4 dBi, and good selectivity (the stopband gain roll-off is up to 25 dB/GHz. Good agreement is observed between the simulated and measured results. [ABSTRACT FROM AUTHOR]

In this letter, a multilayer self-packaged suspended coplanar waveguide (SCPW) leaf-shaped wide slot wideband filtenna is proposed by using leaf-shaped feeding source and three-line couplings. The filtenna is designed working at 3.2 GHz with a fractional bandwidth of 52.3% and a gain of 4.02 dBi, and a pair of gain zeros which are used for improving frequency selectivity and suppressing the out-of-band spurious harmonics have been realized because of the introduced filtering circuit. The proposed filtenna has been fabricated and measured, and the experimental results approach to the predictions, while the advantages of wide bandwidth, high gain flatness, high frequency selectivity, and stable radiation pattern have been demonstrated. [ABSTRACT FROM AUTHOR]

This paper discusses the design of a high gain right-hand circularly polarized millimeter-wave frequency reconfigurable antenna array. The 16-element antenna array is designed to reconfigure its operating frequency over both K- and Ka-bands. More specifically, the reconfigurability is ensured through the integration of a modified ring resonator along with the array’s sequentially rotated stacked feeding network. The ring resonator is designed to reconfigure its operating frequency over four distinct bands with center frequencies at 25 GHz, 26 GHz, 27.75 GHz and 29 GHz, respectively. Such integration enables the proposed millimeter-wave antenna array to exhibit unique radiation characteristics by maintaining circular polarization with an Axial Ratio (AR) < 1 dB in a fractional bandwidth of 37.5% between 21.2 GHz and 31 GHz. A Figure of Merit that takes into account the array’s axial ratio, sidelobe levels and fractional bandwidth is developed to highlight the unique performance of the presented millimeter-wave circularly polarized array in comparison to available work in the literature. The fabricated antenna array shows good agreement with the simulated data where it is found that the measured realized gain exceeds 12 dBic with sidelobe levels of less than −17.5 dB over the various frequency bands of the frequency reconfigurable antenna array.

Linear-array of circular split ring resonators (C-SRR) integrated wideband notched filtering horn antenna with very strong rejection-band is proposed in this article. The linear C-SRR array, consisting of 3-sub arrays each having 4 identical C-SRR-elements, is printed on a dielectric substrate and is integrated into the throat or waveguide-section of the standard X-band horn (Narada 641). Staggered arrangement of the multiple C-SRRs based in-line filter contributes to the wideband notch filtering response with measured rejection band (S11 < 3-dB) of 315 MHz in proposed horn-filtenna. The realized horn-filtenna yields co- and cross- polar peak gain suppression of 35.42 dB and 24.6 dB at and around the centre of notch-band (9.8 GHz) while at the pass band of the C-SRR filter, the proposed antenna inherits the impedance and radiation characteristics of the standalone horn antenna. The proposed technique is simple, easy to integrate and can be used to eliminate adjacent band noise/interference for faithful reception of data without using any additional filter section.