Wide Passband Research Articles

Miniaturization of a Fully Metallic Bandpass Frequency Selective Surface for Millimeter-Wave Band Applications

This article presents a miniaturized all-metallic bandpass frequency selective surface (FSS) for millimeter-wave (mmWave) applications. The designed FSS is realized as a slot-type element that can be easily incorporated into all-metallic device architectures. The miniaturization is achieved by a convoluted or meander slot structure, i.e., a miniaturization technique borrowed from conventional substrate-based FSS design. It is demonstrated that the proposed FSS element provides a stable and wide bandpass performance from 24.9 to 31.4 GHz for both the transverse electric (TE) and the transverse magnetic (TM) polarizations at the broadside direction ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta = 0^{\circ }$</tex-math></inline-formula> ). Adequate performance is maintained at oblique incidence angles up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta = \pm \,45^{\circ }$</tex-math></inline-formula> . A 25 × 25-elements FSS array prototype has been manufactured using the cost-effective chemical etching technique and experimentally characterized utilizing a free-space measurement setup. The results demonstrate a remarkably good correlation between simulations and measurements. Hence, the proposed miniaturized FSS represents an excellent potential to realize an all-metallic FSS with low insertion loss, low profile, and wideband performance at low fabrication costs for mmWave applications.

Bandwidth-Controllable Third-Order Band Pass Filter Using Substrate-Integrated Full- and Semi-Circular Cavities

The article presents a novel circular substrate-integrated waveguide (SIW) bandpass filter (BPF) with controllable bandwidth. The proposed BPF was configured using two microstrip feed lines, semi-circular SIW cavities, capacitive slots, and inductive vias. The circular cavity was divided into two halves, and the two copies were cascaded. The resulting bisected and cascaded structures were then connected back-to-back. Finally, by introducing two inductive vias to the circular center cavity, a transmission zero was generated. In order to examine the design concept, a coupling matrix was generated. To demonstrate the theory, a third-order BPF was realized, fabricated, and experimentally validated. The BPF prototype features a wide passband of 8.7%, a low insertion loss of 1.1 dB, and a stopband of 1.5 f0 with a rejection level better than 20 dB, which makes it a potential candidate for microwave sensing and communication industries.

Compact and Wide Stopband Bandpass Filters Based on Dual-Mode Folded Circular Substrate Integrated Waveguide Cavities

This article presents a novel class of compact and wide stopband bandpass filters based on dual-mode folded circular substrate integrated waveguide cavities (FCSIWCs). By employing both TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{020}$</tex-math> </inline-formula> and TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{110}$</tex-math> </inline-formula> modes of the FCSIWC as resonant modes and TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{010}$</tex-math> </inline-formula> mode as nonresonating mode, a doublet with two poles and two transmission zeros (TZs) is implemented. The TZs can be located either both below or both above the passband, or one below and one above. By combining the dual-mode FCSIWC and single-mode folded rectangular substrate integrated waveguide cavities (FRSIWCs), a class of compact and wide stopband four-pole box-section filters is proposed. In addition, a more selective five-pole extended box-section filter is implemented by loading a complementary split-ring resonator (CSRR) on the four-pole filter structure, without occupying any additional area. Two prototypes are fabricated and measured to validate the proposed filters.

Dual-Band and Wideband Bandpass Filters Using Coupled Lines and Tri-Stepped Impedance Stubs.

In this paper, two bandpass filters-one with a dual-band response and the other with a wideband response-were designed, implemented, and experimented with. The filters are based on the novel combination of series coupled lines and tri-stepped impedance stubs. However, coupled lines along with tri-stepped impedance open stubs (TSIOSs) give a third-order dual passband response. The advantage of dual-band filters using coupled lines and TSIOSs is that they have wide passbands that are close together and separated by a single transmission zero. In contrast, the inclusion of tri-stepped impedance short-circuited stubs (TSISSs) instead of TSIOSs provides a fifth-order wide passband response. The advantage of wideband bandpass filters using coupled lines and TSISSs is that they have a very good selectivity factor. Theoretical analysis was carried out to validate both filter configurations. The tested bandpass filter using coupled lines and TSIOS units had two close wide passbands operating at 0.92 and 1.52 GHz center frequencies, respectively. The dual-band bandpass filter was implemented to operate in GSM and GPS applications. The first passband had a 3 dB fractional bandwidth (FBW) of 38.04%, while the second passband had a 3 dB FBW of 22.36%. The experimental result of the wideband bandpass filter (with coupled lines and TSISS units) had a center frequency of 1.51 GHz with a 3 dB fractional bandwidth of 62.91% and a selectivity factor of 0.90. A good congruence was demonstrated between the full-wave simulated and tested results for both filters.

A wideband bandpass filter with wide upper stopband attenuation containing multiple resonators

AbstractA compact wideband bandpass filter with a wide passband and very‐wide out‐of‐band suppression is presented. The filter is constructed from a central rectangular‐ring resonator with two open stubs placed around it symmetrically. In addition, tri‐section stepped‐impedance resonators are symmetrically distributed on both sides of the two open stubs, and two symmetrical funnel‐shaped resonators are included to enhance out‐of‐band suppression. The out‐of‐band performance of filter is very good, with a suppression level greater than 20 dB up to 25.72 GHz. The center frequency of the filter is 5.84 GHz, with a fractional bandwidth of 115.8%. Good agreement between the simulations and measurements validates the design principle.

GaiaData Release 3

GaiaData Release 3 provides novel flux-calibrated low-resolution spectrophotometry for ≃220 million sources in the wavelength range 330 nm ≤λ≤ 1050 nm (XP spectra). Synthetic photometry directly tied to a flux in physical units can be obtained from these spectra for any passband fully enclosed in this wavelength range. We describe how synthetic photometry can be obtained from XP spectra, illustrating the performance that can be achieved under a range of different conditions – for example passband width and wavelength range – as well as the limits and the problems affecting it. Existing top-quality photometry can be reproduced within a few per cent over a wide range of magnitudes and colour, for wide and medium bands, and with up to millimag accuracy when synthetic photometry is standardised with respect to these external sources. Some examples of potential scientific application are presented, including the detection of multiple populations in globular clusters, the estimation of metallicity extended to the very metal-poor regime, and the classification of white dwarfs. A catalogue providing standardised photometry for ≃2.2 × 108sources in several wide bands of widely used photometric systems is provided (GaiaSynthetic Photometry Catalogue; GSPC) as well as a catalogue of ≃105white dwarfs with DA/non-DA classification obtained with a Random Forest algorithm (GaiaSynthetic Photometry Catalogue for White Dwarfs; GSPC-WD).

Wideband Low-Loss Filter With Compact Size and Wide Stopband Based on Folded Planar Waveguide

In this letter, a hybrid, compact doubly slot-loaded folded ridged half-mode substrate-integrated waveguide (FRHMSIW) filter with wide bandwidth and high selectivity is presented and investigated. The low-pass and high-pass cutoff frequencies of the wideband filter can be independently controlled by adjusting the dimensions of the quasi-periodic slots and FRHMSIW sections, respectively. The dispersion curves, surface current distribution, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula> -field vector diagram of the proposed hybrid FRHMSIW bandpass unit are illustrated. Parametric study and loss analysis are also conducted. The footprint of the proposed filter is miniaturized due to the upper-side-slot-loaded FRHSIW transmission structure and meandered middle-layer slots. The stopband is further extended by etching I-shaped patterns on the ground layer. Finally, the filter is designed, simulated, and measured, with a wide passband between 3.86 and 8.3 GHz, a minimum insertion loss of 0.56 dB, a rejection level better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 20 dB from 8.6 to 20.8 GHz, and an electrical size of only 0.21 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{g}^{2}$</tex-math> </inline-formula> at the center frequency.

Filtenna-Filter-Filtenna-Based FSS With Simultaneous Wide Passband and Wide Out-of-Band Rejection Using Multiple-Mode Resonators

A novel Filtenna-Filter-Filtenna (FA-F-FA)-based frequency selective surface (FSS) technique is proposed using multiple-mode resonators (MMRs). Based on this method, a bandpass FSS with simultaneous wide passband and wide out-of-band rejection is validated. The MMR unit cell consists of two back-to-back magneto-electric (ME-) dipole antennas and a filter-embedded GND plane. Four modes are analyzed and used to acquire a wide passband of the FSS. At the same time, wide out-of-band rejections in both lower and upper bands are controlled by the filter-embedded GND plane with four rotationally symmetric quarter-wavelength transmission lines (QWTLs). Moreover, the GND plane plays a crucial role in the impedance matching of the proposed FSS. As a result, four transmission poles (TPs) and three transmission zeros (TZs) of the proposed FSS can be obtained, leading to a fourth-order filtering response and wide out-of-band rejection. An equivalent circuit model, current distributions, and electric field distributions are introduced to illustrate the working mechanism of the FSS. Finally, the proposed FA-F-FA-based FSS with a 50.2% 3-dB fractional bandwidth ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FBW</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3dB</sub> ) in the passband, 53.5% and 119.2% of the 20-dB fractional bandwidth ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FBW</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20dB</sub> ) respectively in the lower and upper rejection bands is achieved. The S-parameters are stable under an oblique incident angle of 50 degrees. The measured and simulated results are in good agreement. In addition, the proposed FSS has the advantages of low profile, assembly free, and dual-polarization application, which verify the versatility of the FA-F-FA-based MMR FSS.

Wideband and Wide-Angle Switchable Spatial Filter/Shielding With Polarization-Independent Response

In this Letter, an active second-order frequency-selective surface (AFSS) that features a switchable wide pass-band is proposed. Compared to other multi-layer feeding structures, only one layer of FSS is elaborately reconfigured in this design, whose full planar symmetry structure is not destroyed, to achieve the desired all-polarized controlled behavior. The presented design provides good responses under different incident angles and polarizations. The fulfilled structure is composed of three FSS layers and is controlled by semiconductor switches. When the switches are in OFF-state, the proposed design acts as a high-transmittance second-order filter with a low ripple level, whose -0.5 dB passband width is over 24.4% and minimum insertion loss is only 0.1 dB. By switching the semiconductors to ON-state, the unit cells of the top FSS layer are short-connected, which leads to an ultra-wideband shielding behavior from 0 to 10 GHz. Moreover, the proposed structure presents consistent responses under 0°-90° rotation polarizations. Both filter and shielding responses can be obtained up to the 60° incidence. Finally, a prototype is fabricated and measured, and the desired wideband, high-efficiency, wide-angle, and polarization-insensitive switchable performances are obtained through equivalent-circuit calculations, numerical simulations, and experimental measurements.

Wideband Millimeter-Wave SPST Switch in 100-nm GaN-on-Si Using Strong Mutual Coupling

This article proposes a wideband millimeter-wave (mm-wave) single-pole single-throw (SPST) switch using strong mutual coupling. For on-chip switches, it is very challenging to realize wide bandpass characteristics, especially in mm-wave bands. To address this issue, a wideband switch topology using strong mutual coupling has been introduced, based on which the fractional bandwidth of SPST switch can be easily expanded to over 80%. In addition, the coupling structure using coupled lines is investigated to realize strong mutual coupling. For demonstration, one 20-44.8 GHz switch with two transmission poles (TPs) is designed and fabricated in 100-nm GaN-on-Si. Low ON-state minimum insertion loss of 0.62 dB, preferable return losses better than -20 dB, and small chip size of 0.165 are realized, respectively.

Wideband second‐order bandpass frequency selective surface with high selectivity

AbstractA wideband second‐order bandpass frequency selective surface (FSS), which is composed of three metallic arrays and two dielectric substrate layers, is proposed in this paper. The proposed design has high selectivity and wide passband properties simultaneously and is insensitive to incident angles and different polarizations. The equivalent circuit method and field distribution are analyzed to explain the mechanism of the proposed design. A prototype is fabricated and measured, demonstrating a well wideband second‐order passband ranging from 4.8 to 8.8 GHz with 58.8% bandwidth (−3 dB), and the insertion loss (IL) in‐band is less than 0.4 dB. Meanwhile, the transitional bands at both sides of the passband are 0.64 GHz (9.4%) and 0.6 GHz (8.8%), respectively. Moreover, the frequency responses of the proposed structure are stable up to 60° for both TE and TM polarizations.

Ultra-low-loss multi-layer 8 × 8 microring optical switch

Microring-based optical switches are promising for wavelength-selective switching with the merits of compact size and low power consumption. However, the large insertion loss, the high fabrication, and the temperature sensitivity hinder the scalability of silicon microring optical switch fabrics. In this paper, we utilize a three-dimensional (3D) microring-based optical switch element (SE) on a multi-layer Si3N4-on-SOI platform to realize high-performance large-scale optical switch fabrics. The 3D microring-based SE consists of a Si/Si3N4 waveguide overpass crossing in the bottom and the top layers, and Si3N4 dual-coupled microring resonators (MRRs) in the middle layer. The switch is calibration-free and has low insertion loss. With the 3D microring-based SEs, we implement an 8×8 crossbar optical switch fabric. As the resonance wavelengths of all SEs are well aligned, only one SE needs to be turned on in each routing path, which greatly reduces the complexity of the switch control. The optical transmission spectra show a box-like shape, with a passband width of ∼69 GHz and an average on-state loss of ∼0.37 dB. The chip has a record-low on-chip insertion loss of 0.52–2.66 dB. We also implement a non-duplicate polarization-diversity optical switch by using the bidirectional transmission characteristics of the crossbar architecture, which is highly favorable for practical applications. 100 Gb/s dual-polarization quadrature-phase-shift-keying (DP-QPSK) signal is transmitted through the switch without significant degradation. To the best of our knowledge, this is the first time that 3D MRRs have been used to build highly scalable polarization-diversity optical switch fabrics.

Dual-Band and Triple-Band Filtering Power Dividers Using Coupled Lines

In this brief, new dual-band and triple-band filtering power dividers (FPDs) with sharp frequency selectivity are proposed. Firstly, the dual-band FPD is developed and mainly composed of a quarter-wavelength three-line parallel coupled line structure, five transmission lines, and a pair of short-ended parallel coupled lines. Based on this specific structure, with two extra transmission lines imported, a triple-band FPD is further attained. Multiple transmission zeros are generated successfully in the above two designs, thus leading to a sharp skirt selectivity. For the above FPD designs, only a single isolated resistor is arranged between the two side lines of three-line parallel coupled line for nice port-to-port isolation within wide passbands. For demonstration, a prototype dual-band FPD operating at 2.38 and 3.80 GHz with a size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.67{\lambda }\text{g}\,\,{\times }\,\,0.68{\lambda }\text{g}$ </tex-math></inline-formula> , and a triple-band FPD operating at 2.38 GHz, 3.42 GHz, and 3.91 GHz with a size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.66{\lambda }\text{g}\,\,{\times }\,\,0.68{\lambda }\text{g}$ </tex-math></inline-formula> are designed, fabricated, and tested, respectively.

Dual-Band Power Divider With Wide Passbands and Wide Harmonic Suppression Utilizing Multi-Mode T-Stub Loaded Slotline Resonators

This brief proposes a novel dual-wideband slotline power divider (DWSPD) with ultrawide stopband, which is suitable for the multi-band wireless communication system application. The proposed DWSPD is mainly constructed with two multi-mode T-stub loaded slotline resonators (MTSRs), four folded slotline structures (FSSs), four microstrip-slotline transitions and two isolation resistors. The MTSR can generate four transmission poles (TPs), which forms two wide passbands. Furthermore, the FSS contributes to four additional transmission zeros (TZs), which enhances the harmonic suppression. The fabricated DWSPD demonstrates the 3-dB fractional bandwidths of 45.3% @2.25 GHz and 47.1% @4.37 GHz and the stopband with a suppression more than 18 dB @ up to 40 GHz ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$17.8~f_{01}$ </tex-math></inline-formula> ). To the best of the author’s knowledge, the 3-dB FBWs and stopband achieve the best among the existing dual-band filtering power dividers (DBFPDs).

A large-step stick-slip rotary piezoelectric actuator with high velocity under low frequency and small backward motion

Stick-slip rotary piezoelectric actuators (SRPAs) are commonly used nowadays. However, most of them achieve high velocity by high exciting frequency, which causes the problems of wide power-source passband requirement and the wear of actuators. Moreover, their further applications are limited, due to the poor motion stability caused by the backward motion. To solve the problems, the stick-slip process is analyzed with kinematics, indicating that the large step contributes greatly to SRPAs for achieving high velocity under low operating frequency and backward motion elimination. Then a large-step SRPA is proposed, fabricated, and tested. The experiments show that under the sawtooth signal with 100 V and 400 Hz, the prototype can reach a maximum velocity of 1.854 rad s−1, benefiting from the large step (above 4.636 mrad). While other works require the exciting frequency of several kilohertz to reach the same level of velocity. Additionally, by increasing the step, the backward ratio decreases from 14.43% to 8.89% at the frequency of 1 Hz, and the minimum no-backward frequency decreases from 120 Hz to 60 Hz. The results indicate the effectiveness of the large step for solving the problems, which is significant for the design of SRPA.

High-Q cascaded single-passband microwave photonic filter based on an optical-electrical feedback loop.

A cascaded microwave photonic filter refers to a microwave photonic filter (MPF) with higher performance obtained by cascading a MPF with two different structures. A high-Q cascaded single-passband MPF is proposed experimentally based on stimulated Brillouin scattering (SBS) and an optical-electrical feedback loop (OEFL). In this experiment, the pump light of SBS is provided by a tunable laser. The Brillouin gain spectrum generated by the pump light is used to amplify the phase modulation sideband, and the narrow linewidth OEFL is subsequently used to compress the passband width of the MPF. By carefully adjusting the pump wavelength and tuning the tunable optical delay line, stable tuning can be achieved for a cascaded single-passband MPF with a high-Q value. The results have demonstrated that the MPF has characteristics of high-frequency selectivity and a wide frequency tuning range. Meanwhile, the filtering bandwidth is up to 300kHz, the out-of-band suppression is more than 20dB, the maximum Q-value is 5.333×104, and the center frequency tuning range is 1-17GHz. The cascaded MPF proposed not only achieves a higher Q-value, but also has the advantages of tunability, a high out-of-band rejection ratio, and strong cascaded ability.

Ku-Band SIW Filter with High Fractional Bandwidth Optimized Using Feed Forward Back Propagation ANN

An Artificial Neural Network (ANN) based Substrate Integrated Waveguide Band Pass Filter (SIW BPF) is proposed in this paper. A Feed Forward Back Propagation Neural Network (FF-BP NN) is utilized to optimize the filter dimensions. The Gradient Descent with Momentum and Adaptive Learning Rate algorithm is used to train the network at a learning rate of 0.01. The high pass characteristics of the SIW is converted into band pass by incorporating U slots on its top plane. Defected Ground Structure (DGS) is utilized in the bottom plane to improve the impedance matching. To validate, the prototype is fabricated using RT/Duroid 5880 and tested. The proposed filter has a center frequency at 14.68 GHz with a wide pass band from 12.92 to 16.43 GHz with a 3-dB Fractional Bandwidth (FBW) of 24%, return loss more than 20 dB and insertion loss of about 1.9 dB within the pass band. The filter has a small dimension of about 0.63 λ g 2 , where λ g is the guided wavelength at the center frequency. This filter offers wide passband, smaller size, low insertion loss, good return loss and it is useful in Ku-band satellite communication applications.

Wideband bandpass filters with suppressed harmonics using vertically installed planar structures

AbstractThis article presents a closed‐form synthesis method for wideband bandpass filters with suppressed harmonics, where stepped‐impedance resonators (SIRs), scaled lines, and vertically installed planar (VIP) structures are introduced to improve the in‐band and out‐of‐band performances. By combining SIRs and scaled lines, the rejection level of the filter is greatly improved and a more compact size is achieved. And the VIP structures help to bring wide passband as well as suppressed harmonics. Then, a 3rd‐order filter is designed to verify the validity of the proposed method and topology. The simulated and measured results demonstrate that the proposed design has a wide passband (FBW = 52.9%), low insertion loss (&lt;0.4 dB), and suppressed harmonics with the level of 20 dB up to 7.1f0.

Highly Efficient Filtering Power Amplifier Using Impedance Area-Based Optimization

This paper presents an optimization method of wideband filtering power amplifier (PA) with high efficiency. In order to achieve the expected high efficiency in the wide passband and reduce design difficulty, a high-performance area-based impedance target for computer-aided automatic optimization is proposed, which avoids the unexpected efficiency degradation caused by the conventional impedance target. In the meanwhile, the out-of-band optimization target described by impedance is also proposed to obtain bandpass filtering characteristic. The in-band and out-of-band optimization targets are utilized to design the output matching network to realize fundamental and harmonic impedance matching precisely, as well as the filtering response. For demonstration, a filtering PA operating in 3.3-3.8 GHz is implemented and measured. The measured small-signal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameter exhibits flat gain in passband and good bandpass filtering response. The measured power-added efficiency (PAE) is larger than 62% within the entire working band and the highest PAE is 71.7%.

Miniaturized frequency selective rasorber with absorption in S–C band and transmission in X band

A miniaturized frequency selective rasorber (FSR) that has a wide absorption band in the S–C band and a wide transmission band based on X-band is presented in this paper. The FSR consists of a lossy layer loaded with lumped resistors and a bandpass layer with a three-screen cascade structure, which has the advantages of low insertion loss, wide passband bandwidth, and stable structural performance in the operating band. The rectangular spiral resonant (RSR) is loaded in the middle of the four arms of the cross to form a lossy layer. The aggregate resistance is loaded between the units to form a closed loop, which will absorb the detection signal and thus greatly reduce the radar cross section (RCS). The bandpass layer is divided into three layers, with two identical square patches coupled with a layer of complementary cross grids to form a multi-order bandpass filter. Furthermore, the operating mechanism of low absorption and high transmission is analyzed and verified based on equivalent circuit theory and impedance matching theory. The simulation results show that the 1 dB transmission band of the FSR is 8.0–12.5 GHz and the 10 dB absorption band is 2.8–6.6 GHz. The highest transmittance reaches over 97% at 10.0–11.5 GHz and the lowest insertion loss is 0.012 dB. It has important theoretical reference value and great application in the field of the new stealthy radome.