Second-order Bandpass Response Research Articles

A broadband second-order bandpass frequency selective surface for microwave and millimeter wave application.

This paper presents a frequency selective surface (FSS) with a wideband second-order bandpass response in the dual-band of microwave and millimeter wave. The overall structure consists of three layers of metal pattern and two layers of thin dielectric substrate. The top and bottom metal layers have capacitive patches with integrated curled Jerusalem cross slot resonators, while the intermediate metal layer has an inductive grid structure with cross-shaped slot resonators. The incorporated slot resonators play a pivotal role in achieving the desired transmission poles or zeros, which enable a wideband second-order filtering response in the dual-band and a quick roll-off at the passband edges, increasing the efficacy of electromagnetic shielding. To fully investigate the structure's frequency response, an equivalent circuit model of the structure is created, spanning the complete frequency range of 5-50 GHz. Physical samples are created and measured to confirm the suggested approach's efficacy. The passband center frequencies of the FSS are found at f1 = 19.42 GHz and f2 = 42.78 GHz, and the - 3dB bandwidth is 4.34 GHz (17.25-21.59 GHz) and 8.54 GHz (38.51-47.05 GHz), respectively. The simulation results align well with the experimental data. The transmission response rapidly transitions from the passband to the stopband at the passband boundaries.

Low-Profile Higher-Order Narrowband Bandpass Miniaturized-Element Frequency-Selective Surface

We present a low-profile miniaturized-element frequency-selective surface (MEFSS) with narrowband, second-order bandpass response. The miniaturized-element unit cell comprises a capacitively loaded parallel LC unit cell resulting in a narrowband bandpass response. A higher-order filtering response is obtained by implementing five metallic layers FSS formed by two layers of parallel LC resonators with an inductive impedance inverter layer in between them. The proposed design offers a very thin profile and an insensitive frequency response to the polarization of the incident electromagnetic wave. A design procedure is developed for the proposed FSS structure based on an equivalent circuit model analysis. Using this model, a prototype of MEFSS with the second-order bandpass response at 3.34 GHz and a fractional bandwidth of 3.7% is designed, realized, and characterized experimentally. The measurement results of the FSS verify the effectiveness of the FSS design procedure and the stability of its frequency response up to 60° oblique incidence angles.

Analysis and Design of Filtering Series-Feed Omni-Directional Antenna for V2X Application

In general, the vehicle-to-everything (V2X) series-feed antenna excites the spurious mode radiation in the adjacent bands and thus causes the strong mutual coupling between the vehicle antennas. To solve this problem, this article proposes a method to realize a filtering series-feed V2X antenna. This antenna consists of two radiators connected to a double-sided parallel strip line (DSPSL). The DSPSL operates as the series-feed structure and the first resonator. The radiators function as the second resonator. An equivalent filtering network is analyzed and derived. Then, based on the filter synthesis, the initial design parameters are obtained to realize a second-order bandpass response. However, the synthesis method only involves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula> and efficiency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{21}$ </tex-math></inline-formula> ). The radiation performances are not concerned and satisfied. To solve this problem, the antenna currents are manipulated to generate the taper exciting. Thus, the upper sidelobe and the gain are improved. Moreover, to further enhance the out-of-band suppression level, three radiation zeros are generated by manipulating the current distribution on the DSPSL. The fabrication prototype demonstrates that the out-of-band suppression of the proposed antenna is better than 8.8 dB, which significantly reduces the mutual coupling.

A Tri-band Second-order Frequency Selective Surface Designing and Analysis

In this paper, inspired from the technique of patch–aperture–patch, a novel tri-band frequency selective surface with second-order band-pass response in each operation band is presented. The design is implemented by cascading a two-dimensional periodic array of three square loops and an array of wire grids. The proposed structure composed of three metal and two dielectric layers acts as a spatial dual band microwave filter with large band separation. The predicted FSS has the merits of broadband response, excellent stability for different incident angles, and sharp roll-off at X-, Ku- and K-band, respectively. The simulation and measurement are carried out and discussed. The measured results agree well with the simulated ones.

Quasi‐elliptic bandpass filtering power divider with ultra‐wide stopband

In this Letter, a novel filtering power divider with second-order quasi-elliptic bandpass response is proposed, which has two transmission zeros near to the passband for sharp frequency selectivity. In addition, it is featured by ultra-wide stopband owing to specific topology. For demonstration, a filtering power divider example operating at 3.1 GHz is designed, fabricated and measured. Its 3 dB fractional bandwidth is about 11.9%, and the in-band isolation between two output ports exceeds 20 dB. Specifically, more than 21 dB out-of-band suppression is achieved from the upper side of the passband to 4.8f 0, and more than 12 dB suppression is achieved to at least 20f 0. The measurement agrees well with the simulation.

A Highly Selective Rasorber Based on Second-Order Resonance

A novel frequency-selective rasorber with one highly selective passband between two absorption bands is presented. Based on the equivalent circuit analysis, the approach of using a second-order band-pass response in the lossless layer is adopted to improve the selectivity of the passband. A two-layered structure consisting of one lossy and one lossless layer is then used for implementation. The lossy layer is constructed using stub resonators, while an aperture-coupled resonator is used to realize lossless layer and achieve the highly selective passband. Under normal incidence, the operating bandwidth of the proposed rasorber is 110.6%. One passband with sharp roll-off edge and small insertion loss (0.08 dB) is achieved at 4.3 GHz. For demonstration, one prototype was fabricated and measured, and a good agreement is observed accordingly.

Design Method for Low-Profile, Harmonic-Suppressed Filter-Antennas Using Miniaturized-Element Frequency Selective Surfaces

A new technique for designing low-profile filter-antennas with wideband harmonic suppression capability is introduced. A filter-antenna element in a periodic infinite array consists of a radiating patch and an asymmetric frequency selective surface with an inductive wire grid and cascaded capacitive metallic strips. Based on this topology, a filter-antenna element operating at 2.12 GHz was designed with an extremely small thickness of approximately λ/27. A desirable second-order bandpass response and an excellent harmonic suppression of better than 30 dB over 2.4–10.0 GHz were achieved. Using this element, an 8 × 8-element filter-antenna array was designed. A maximum aperture efficiency of 60.3% was obtained within the operating band of the array. The aperture efficiency reduces to nearly zero over the frequency range from 2.3 to 10.0 GHz, which demonstrates the excellent filtering performance of the proposed filter-antenna outside of its band of operation.

Design of a Microstrip Diplexer-Integrated Filtering Power Divider

This study proposed a new method and structure for designing a diplexer-integrated filtering power divider. A filtering function with equal power division was integrated with a diplexer. The multifunctional diplexer comprised eight coupled resonators and two 50-Ω resistors with a distributed coupling structure. Moreover, a connected coupling technique provided improved flexibility and freedom to construct the diplexer. High isolation was obtained using the proposed coupling configuration through the introduction of out-of-phase cancellation between multiple coupling routes. Moreover, because the distributed coupling structure was employed as an input, no complex matching network was required; this significantly reduced the size and simplified the design of the diplexer. Moreover, each channel passband was individually designed. For demonstration, a multifunctional diplexer operating at 1 and 1.15 GHz with a second-order Chebyshev bandpass response and equal power splitting was designed and fabricated using microstrip technology, and the simulation results were consistent with the measured results.

Dual-band bandpass filters with multiple transmission zeros using λ/4 stepped-impedance resonators

Two novel dual-band microstrip bandpass filters (BPFs) with multiple transmission zeros are proposed in this article. The dual-band BPFs with second-order bandpass responses are due to two λ/4 stepped-impedance resonators (SIRs). Two passbands (center frequency ratio f s/f0 is 2.36) are realized based on the asymmetric SIRs. The transmission zeros near the passbands can be adjusted conveniently using the stopband transmission characteristic of the open/shorted coupled lines. Two planar microstrip dual-band BPFs (ε r = 2.65, h = 0.5 mm) with four and six transmission zeros are designed and fabricated. High selectivity and good in-band performances can be achieved in the proposed filters.

Lightweight and Compact High-Gain Filtering Aperture Antenna Fabricated by Three-Dimensional Printing Technology

In this letter, a novel high-gain filtering aperture antenna is proposed. It consists of five resonators, four of which have radiation apertures in the end and are coupled to the fifth one in the center by dislocation. Such a mechanism gets rid of conventional irises and, hence, saves volume to some extent. The proposed antenna is characterized by a second-order Chebyshev bandpass response. Simultaneously, high gain is achieved through four radiation apertures. In order to minimize its size and weight, three-dimensional printing technology is adopted for fabrication. Finally, an antenna prototype with a center frequency of 34 GHz is designed, fabricated, and measured. The measured results show that the fractional bandwidth is 2.94% covering from 33.5 to 34.5 GHz, with the gain of 12.51 dBi. Besides, it only weighs 2.63 g for the adopted polymer material.

Compact microstrip eight‐channel multiplexer with independently switchable passbands

A compact eight-channel multiplexer with independently switchable passbands has been presented and investigated. The use of the dual-mode stub-loaded resonators can lead to significant size reduction for the multiplexer, this is because the required resonator number is reduced. In addition, the multiplexer is designed based on the distributed coupling technique, so that each passband can be designed individually due to the loading effect is small. Moreover, the complicated nine-port matching network at the input is not required. Besides, since the p-i-n diodes are connected to the output resonators for each channel, all passbands of the multiplexer can be independently switched on and off when the diode is in the reverse-biased and forward-biased states, respectively. Therefore, the proposed multiplexer can arbitrarily transfer to a single-band bandpass filter, a diplexer, a triplexer, a quadruplexer, a quinqueplexer, a sexaplexer, a septiplexer, and an octoplexer. For a demonstration, an eight-channel multiplexer with the second-order bandpass response have been designed and fabricated with microstrip in printed circuit board. The measured results are in good agreement with the full-wave simulation results.

A novel miniaturized-element frequency selective surface with a second-order bandpass response

A novel miniaturized-element frequency selective surface with a second-order bandpass response

A New DVCC+ Based Second-Order Current-Mode Universal Filter Consisting of Only Grounded Capacitors

In this paper, a new second-order current-mode universal filter using only two plus-type differential voltage current conveyors, three resistors and two grounded capacitors is proposed. The proposed circuit with two identical inputs and three outputs can simultaneously provide second-order high output impedance low-pass, band-pass and notch filter responses. Also, it can realize high-pass and all-pass filter responses with interconnection of relevant output currents. It can be easily tuned electronically. It can be operated properly at high frequencies. A number of simulations based on SPICE program and an experimental test are achieved in order to demonstrate the performance of the proposed filter.

A Low-profile Miniaturized Second-Order Bandpass Frequency Selective Surface

High-order bandpass frequency selective surfaces (FSSs) (N ≥ 1) can achieve high performance with a flat in-band frequency response and fast roll-off. One particular practical issue of designing bandpass FSSs using resonant surfaces is that the thickness of the substrate would be around a quarter of a wavelength. On the other hand, the size of a nonresonant FSS array element is usually large. A new miniaturized FSS capable of exhibiting a second-order bandpass response is proposed in this letter. Two miniaturized resonant surfaces coupled by a nonresonant inductive layer are used to build the proposed FSSs. An FSS operating at around 3.8 GHz is designed to verify the method. The element size is smaller than 0.076λ × 0.076λ for the proposed structure. This is significantly smaller than the element size of second-order FSSs designed using conventional approaches. The overall thickness is less than λ/24, where λ is the free-space wavelength at the resonant frequency. The method could be particularly useful for the design of FSSs at lower frequencies with longer wavelengths.

Second-Order Voltage-Mode Universal Filters Using Two DVCCs, Two Grounded Capacitors and Four Resistors

In this paper, two new second-order voltage-mode universal filters are proposed. Both of the proposed filters use only two differential voltage current conveyors (DVCCs), four resistors and two grounded capacitors which are advantageous from integrated circuit technology point of view. They can simultaneously provide second-order low-pass, high-pass, band-pass, notch and all-pass responses. They offer orthogonal control of angular resonance frequency and quality factor. However, they have a single matching condition for only all-pass responses. A number of simulations based on SPICE program are accomplished in order to demonstrate the performance of both filters.

A Dual-Band, Inductively Coupled Miniaturized-Element Frequency Selective Surface With Higher Order Bandpass Response

We present a new approach for designing dual-band miniaturized-element frequency selective surfaces (MEFSSs) with independent control of the frequencies of operation of each band. The proposed device is composed of 2-D periodic arrays of subwavelength inductive wire grids and capacitive patches separated by dielectric substrates. The structure is built on an inductively coupled MEFSS that uses capacitively loaded dielectric spacers as its main resonators. The two operating bands of this MEFSS correspond to the first and second resonant frequencies of its constituting resonators. By judiciously choosing the locations where the resonators are loaded and the load values, the frequencies of the first and second resonances can be controlled individually. In this way, a dual-band MEFSS with independent frequency bands of operation can be obtained. Using the equivalent circuit model of this MEFSS, a synthesis procedure is developed that can be used to synthesize the dual-band MEFSS from its system-level performance indicators. A prototype of the proposed dual-band MEFSS with second-order bandpass response at each band is designed, fabricated, and experimentally characterized. The measurement results of this device show a stable frequency response with respect to the angle of incidence up to ±45° for both the TE and TM polarizations of incidence.

Inductively-Coupled Miniaturized-Element Frequency Selective Surfaces With Narrowband, High-Order Bandpass Responses

We introduce a new technique for designing miniaturized-element frequency selective surfaces (MEFSSs) with narrowband, bandpass responses of order $N\ge2$ . The proposed structure is composed of two-dimensional periodic arrays of subwavelength inductive wire grids separated by dielectric substrates. A simple equivalent circuit model, composed of transmission line resonators coupled together with shunt inductors, is presented for this structure. Using this equivalent circuit model, an analytical synthesis procedure is developed that can be used to synthesize the MEFSS from its desired system-level performance indicators such as the center frequency of operation and bandwidth. Using this synthesis procedure, a prototype of the proposed MEFSS with a second-order bandpass response, center frequency of 21 GHz, and fractional bandwidth of 5% is designed, fabricated, and experimentally characterized. The measurement results confirm the theoretical predictions and the design procedure of the structure and demonstrate that the proposed MEFSS has a stable frequency response with respect to the angle of incidence of the EM wave in the $\pm40^\circ$ range for both TE and TM polarizations of incidence.

X-band Band-pass Frequency Selective Surface for Radome Applications

A low profile multi layer miniaturized unit cell frequency selective surface (FSS) with second-order band-pass response is design. The metallic layers in the form of capacitive patches and inductive grids are separated by dielectric substrates. The non-resonant sub-wavelength unit cells with unit cell dimensions and periodicities on the order of 0.15λ. The overall thickness of approximately 0.03λ is designed which is useful at lower frequencies with long wavelengths. The FSS exhibit a stable frequency response to different angles of incidence and polarizations. The analysis and synthesis of the FSS is done using equivalent circuit method and simulated using CST microwave studio at X-band.

X-band Band-pass Frequency Selective Surface for Radome Applications

A low profile multi layer miniaturized unit cell frequency selective surface (FSS) with second-order band-pass response is design. The metallic layers in the form of capacitive patches and inductive grids are separated by dielectric substrates. The non-resonant sub-wavelength unit cells with unit cell dimensions and periodicities on the order of 0.15λ. The overall thickness of approximately 0.03λ is designed which is useful at lower frequencies with long wavelengths. The FSS exhibit a stable frequency response to different angles of incidence and polarizations. The analysis and synthesis of the FSS is done using equivalent circuit method and simulated using CST microwave studio at X-band.

A novel wideband, low-profile and second-order miniaturized band-pass frequency selective surfaces

A novel wideband, low-profile and second-order miniaturized band-pass frequency selective surface (FSS) made of metallic mesh and its complementary structures with skewed arrays of modified triples is presented in this paper. Compared with traditional second-order bandpass FSSs obtained using λ/4 apart from one another, the novel FSS with an overall thickness of λ/18 is composed of three metallic layers (the outside and middle layers are complementary) separated by two electric thin dielectric substrates. This arrangement can shorten the inter-element spacing and increase the bandwidth, while the up and bottom metallic layers can constitute a symmetric biplanar FSS and thus realize ability of maximally flat second-order bandpass response. The novel FSS has a −3 dB bandwidth about 8.2 GHz (6.9 -15.1 GHz) and a fractional bandwidth exceeds 75%. Moreover, such an FSS has the merits of stable performance for incident angles within 50° and different polarizations. The principles of operation along with guidelines for the design of the proposed FSS, the simulated results by vector modal matching method, and the experimental values of the fabricated prototype are also presented and discussed.