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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.

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.

A (1 × 2) filtenna array inspired by an inter-digital-based bandpass filter is presented in this paper for simultaneous radiation and filtration. The feed line of the proposed antenna array resonating at 14 GHz with fractional bandwidth of 5.72% is modified in such a way that it acts like an inter-digital-based bandpass filter. The equivalent lumped circuit model of the proposed structure is analysed and detail synthesis procedure is presented. To study the impact of dimensional variations on the performance of proposed filtenna array, various parametric studies of filtenna and corresponding antenna array are performed and compared. The design strategy involves (N-1) filter circuits for realising a (1 × N) element filtenna array. The proposed array exhibits advantageous features such as low circuit complexity, compact size and low operational power over other reported filtenna arrays. The presented filtenna possesses fractional bandwidth and peak gain of 3.85% and 8.14 dB respectively at resonating frequency of 14 GHz, which covers the standards of Ku-band. The physical size of the filtenna array in terms of free space wave length is 1.96λ0 × 1.96λ0 × 0.073λ0 at 14 GHz. The radiation patterns are omni-directional in E-plane and nearly omni-directional in nature at H-plane at resonance frequency of 14 GHz. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Filtering antennas or filtennas realize both antennas and filter functions in a single structure with the sole purpose of reducing losses and size in the design of a radio system. This article presents a comprehensive view of various filtennas design techniques and their types, satisfying the requirements of different wireless communication standards. The codesign and synthesis approaches and multilayer structure, slot/slit, and parasitic elements are the frequently used techniques reported in the literature to date for the filtennas design. The codesign and synthesis approaches need an extra filter in the filtenna's design, thus making it more complex. Whereas multilayer, slot, and parasitic elements do not require additional filters, and help the radio design become compact in size. The individual elements, that is, filter and antenna used in the filtenna are designed by cutting slots, stacking, resonators, or metamaterial structures. There are two broad categories of filtennas, namely, planar and nonplanar. Most of the papers covered in this article are planar, whereas, under the nonplanar category, horn filtennas are analyzed. Performance in each case is compared in terms of size, complexity, and cost. Considering filtennas frequency of operation, they are classified as a single band, multiband, ultra‐wideband, and their MIMO configurations are analyzed to improve the reliability of the wireless radio system. Finally, various types of filtennas are compared, and the design guidelines are elaborated, mainly focusing on their application aspect to achieve more compact radio design solutions. The different techniques related to designing filtennas have been compared, and their glance details are provided for a more realistic assessment of individual techniques used till date. Thus, the authors believe that this review article presents a helpful guiding platform for researchers working on filtenna design. [ABSTRACT FROM AUTHOR]

A compact and low cost butterfly shaped UWB filtenna with a pair of parasitic elements and a pair of slits is proposed in this work. The filtenna is supposed to be designed on a common and low-cost FR4 substrate with overall dimensions of 26mm*20mm*1.6mm .By inserting a pair of λg/2 (where λg is waveguide wavelength) D-shaped parasitic elements around the antenna feed line, the radiation of the 5 GHz WLAN applications is canceled to eliminated the interference. Furthermore, the rejection of the X-band satellite downlink is achieved by engraving a pair of λg/4 J-shaped slits on the ground plane. The simulation results exhibits the perfect coverage of the proposedfiltenna for the UWB frequency band as well as the elimination of the undesired radiation within the filtenna operating band. [ABSTRACT FROM AUTHOR]

Implementation and parametric analysis of single and dual band planar filtering antennas suitable for WLAN applications are described in this paper. The single band filtering antenna is designed using the filter synthesis approach in which the last resonator of the 5th order Chebyshev stub loaded bandpass filter is replaced by a monopole antenna. The dual band filtering antenna is designed by adding Electromagnetic Band Gap structures in the ground plane of stub fed patch antenna. The parameters of the two filtering antennas are analyzed and provide validation of the merits and demerits of the two design techniques used in the implementation of filtering antennas. Single band filtering antenna is designed at a center frequency of 2.4 GHz and has a gain of 3.1 dBi with less than − 16 dB reflection coefficient. The filter selectivity at the band edges is found to be 75/86 dB/GHz. The size of the single band filtering antenna is 0.68 λ0 × 0.216 λ0 (λ0 is the operating wavelength) and the structure is suitable for WLAN applications. Dual band filtering antenna is designed to have two operating bands at center frequency 1.875 GHz and 2.4 GHz. The reflection coefficient at the two operating bands is found to be less than – 20 dB and produces radiation nulls on either side of the two operating bands. The proposed dual band filtering antenna has dimension 0.57 λ0 × 0.714 λ0 and is suitable for LTE and WLAN applications as it has a gain of 5.8 dBi and 4.08 dBi at 1.875 GHz and 2.4 GHz respectively. [ABSTRACT FROM AUTHOR]

This manuscript proposes a triple band filtering antenna operating in the frequency range of 2.4 to 2.484 GHz, 4.2 to 4.5 GHz, and 5.15 to 5.825 GHz for possible application in WLAN and aeronautical radio navigation. Initially, a conventional square shaped monopole antenna is designed at 4 GHz, in which staircases are introduced at the edges to enhance bandwidth. Later, a triangle shape is carved out of square patch and cascaded at the junction to generate the proposed sunflower shaped fractal filtenna. Also, the ground plane is modified to further enlarge the bandwidth. By inserting C shaped complimentary split ring resonator slot on the feed line, a stop band is created at 3.5 GHz. Within the proposed frequency band of operation, the filtenna depicts omni‐directional radiation pattern, good selectivity, and low insertion loss. Also, the VSWR observed is less than 2 and peak antenna gain is 3.5 dBi. A good uniformity is achieved between the simulation and the experimental. [ABSTRACT FROM AUTHOR]

This manuscript proposes a Filtenna operating in the frequency range of 5.15-5.35 GHz for possible application in wireless local area network (WLAN). Initially, a monopole antenna consisting of a square loop radiating patch is designed at 5.2 GHz and is integrated into a bandpass filter (BPF) with centre frequency of 5.2 GHz. Within the proposed frequency band of operation, the filtenna exhibits omni-directional radiation pattern, good selectivity and low reflection loss. Also, the VSWR observed is less than 2 and peak antenna gain is approximately 2.5 dBi within the frequency range. A consistency is obtained between the simulation and the experiment. [ABSTRACT FROM AUTHOR]

This paper demonstrates that it is possible to find an ideal filter response (Chebyshew, Butterworth,..) considering the antenna as the last resonator of a filter under certain circumstances related with the antenna performance and the bandwidth of the filtenna device. If these circumstances are not accomplished, we can achieve excellent performance as well, by means of an iterative process the goal of which is defined by either a filter mask or a classical filter function itself. The methodology is based on the conventional coupling matrix technique for filter design and has been validated by fabricating a microstrip prototype using hairpin resonators and a rectangular patch antenna.

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An integrated module with filtering and radiation performance realized by covering substrate integrated waveguide (SIW) cavity frequency selective surface (FSS) at aperture of horn antenna has been investigated in this paper. The module has functions of bandpass filter and horn antenna, so it is called a ‘filtering antenna’ (filtenna). It is very suitable for applications in military platforms where FSS is used for antennas and radars' radar cross section (RCS) reduction. The filtenna is simulated and optimized with CST software and its performance is verified by experiments. From simulated and measured results it can be found that the proposed structure keeps characteristics of return loss, radiation pattern and gain of the horn antenna within desired frequency band, meanwhile presents effective reflection to interference signals at out-band. Using this structure the volume and cost of communication systems in military platforms can be effectively reduced. [ABSTRACT FROM AUTHOR]

Reconfigurable and tunable radio frequency (RF) and microwave (MW) components have become exciting topics for many researchers and design engineers in recent years. Reconfigurable microstrip filter–antenna combinations have been studied in the literature to handle multifunctional tasks for wireless communication systems. Using such devices can reduce the need for many RF components and minimize the cost of the whole wireless system, since the changes in the performance of these applications are achieved using electronic tuning techniques. However, with the rapid development of current fourth-generation (4G) and fifth-generation (5G) applications, compact and reconfigurable structures with a wide tuning range are in high demand. However, meeting these requirements comes with some challenges, namely the increased design complexity and system size. Accordingly, this paper aims to discuss these challenges and review the recent developments in the design techniques used for reconfigurable filters and antennas, as well as their integration. Various designs for different applications are studied and investigated in terms of their geometrical structures and operational performance. This paper begins with an introduction to microstrip filters, antennas, and filtering antennas (filtennas). Then, performance comparisons between the key and essential structures for these aspects are presented and discussed. Furthermore, a comparison between several RF reconfiguration techniques, current challenges, and future developments is presented and discussed in this review. Among several reconfigurable structures, the most efficient designs with the best attractive features are addressed and highlighted in this paper to improve the performance of RF and MW front end systems. [ABSTRACT FROM AUTHOR]

In recent year, various filtenna circuits have been developed satisfying the objectives and prerequisites of wireless communication. Some of these developed designs are new or some are the improved version of previous works whereas the others are the combination of conventional methods. This article presents the review of filtenna circuits starting from the beginning to the improvements until date. This article starts with brief overview of various filters with their design strategies and ends in its implementation in filtenna designs followed by discussion on several filtenna designs in term of size and overall performances. Among various designs, bandpass, and bandstop filters are extensively used in filtenna realization as it provides a better selectivity in desired band. Various planar filtenna circuits, based on either defected ground structure (DGS) or resonator or SIW filters are reviewed and presented. Besides, planar filtennas, these filters are also integrated to the aperture of horn antennas for the realization of horn filtennas, applicable for high frequency operations. It is observed that SIW based filtennas exhibited narrow impedance bandwidth. This feature can be improved by doubling substrate layer as well as the number of metallic ways. Whereas, resonator based filtennas use resonator based filters along with DGSs to enhance impedance bandwidth as well as minimize mutual coupling and cross‐polar radiation. Apart from single element filtenna, filtenna arrays, and reconfigurable filtennas (including planar and horn reconfigurable filtennas) are presented. This review article may be helpful for beginners working on filtenna circuits and also such a review process is not available in the open literature to the best of author's knowledge. [ABSTRACT FROM AUTHOR]