Sharp Roll-off Characteristics Research Articles

Design of FSS Based Radome Wall for Airborne Radar Application

In this paper, a broad band A-sandwich radome wall structure based on band-pass FSS (frequency selective surface) is proposed for an airborne radar applications. The FSS structure having two square conducting rings, which are embedded on either side of core layer. The conventional and proposed FSS based radome wall is analyzed with different incidence angles (0°, 10°, 20° and 30°) for both TE and TM polarization. The radome wall structure consist of a low density Nomex honeycomb core layer sandwiched between two high density Quartz skin layers. The structure shows the percentage impedance bandwidth of 40.8 % in the frequency range from 7.8GHz to 11.8GHz with sharp roll-off characteristics. The proposed novel approach involves high frequency unit cell simulation, which is carried out using EM Simulation Tool. To understand the practical behavior of the proposed structure for radome application the conformal analysis has been also carried out, with respect to different radius. The superior EM performance of the proposed broadband novel radome wall structure makes it suitable for the design of airborne radome.

Reconfigurable Low-Pass Filter With Sharp Roll-Off and Wide Tuning Range

A miniaturized reconfigurable low-pass filter (LPF) with a sharp roll-off, wide tuning range, and extended stopband is presented in this letter. The proposed LPF consists of two fixed low-pass (LP) cells and a tunable bandstop (BS) cell loaded with two pairs of varactor diodes. The BS cell with tunable stopband edges is employed to achieve the reconfigurable cutoff frequency and sharp roll-off characteristics in the whole LPF. The fixed LP cells are utilized to suppress the high passband of the BS cell, which obtain the tunable LP filtering response and wide stopband. For experimental demonstration purposes, a microstrip prototype of the proposed reconfigurable LPF with a wide fractional tuning range of 78.8% and roll-off rate over 103 dB/GHz is simulated, fabricated, and measured. The wide stopband is extended up to 10 GHz with a rejection level better than 15 dB, and the overall dimension is $0.078\lambda _{\mathrm {g}} \times 0.08\lambda _{\mathrm {g}}$ . This physical size is comparable to more compact, prior art reconfigurable LPFs while featuring among the sharpest roll-off rate ever reported.

Dual-Band Frequency Selective Surface Based on Shunted SIW Cavity Technology

The design of a hybrid frequency selective surface (FSS) is presented based on the substrate integrated waveguide cavity (SIWC) technology. The intended design combines two FSS slots (multiapertures) based on the SIWC by sharing the adjacent vias of the unit cell to exhibit unique features in terms of their cavity designs and performance. The design consists of a circular slot with a circular cavity (named as Cavity-A) and a cross slot with a shared cavity with an adjacent unit cell (named as Cavity-B). As a result, the structure shows the dual-bandpass response with sharp roll-off performance characteristics. One band possesses narrowband characteristics at 8.12 GHz. Whereas, the next band with wide bandpass characteristics from 9.5 to 11.5 GHz. Further, the structure has shown a very low insertion loss (IL) of better than 0.15 dB in its operating bands. For proving the concept, a physical prototype has been fabricated, and its functionality verified. A good agreement has been found between the estimated and experimental results.

Design of a hybrid A-sandwich radome using a strongly coupled frequency selective surface element

AbstractThe airborne radomes have to cater superior electromagnetic (EM) performance with bandpass characteristics of stealth application. In this regard, a hybrid A-sandwich radome is proposed in this paper. The proposed radome consists of a novel strongly coupled frequency selective surface (FSS) core sandwiched between two dielectric layers (acts as skin) to form an A-sandwich structure. The dielectric layers are cascaded in such a way that the middle layer has less dielectric parameters than the skin dielectric. The core layer comprises a modified FSS array using strongly coupled FSS layers through a series of metallic vias. This strongly-coupled FSS element will have the advantage of eliminating inter-element interference and improves the EM performance characteristics of the structure. The structure exhibits very good band-pass characteristics (>90%) at a normal impinging angle with sharp roll-off characteristics. To show the efficacy of the proposed structure, the transmission loss has been compared with that of conventional A-sandwich radomes at 0°, 50° incidence angle for both TE and TM polarization. Conformal analysis of the unit cell has been carried out, and sector-wise thickness optimization was performed to analyze the structure for the conformal shaped radome application. Finally, a physical prototype has been fabricated and measured its scattering parameters, radiation characteristics in a fully shielded anechoic chamber. The results are encouraging and prove its suitability for radome application.

EM Design and Analysis of Frequency Selective Surface Based on Substrate-Integrated Waveguide Technology for Airborne Radome Application

In this paper, a bandpass frequency selective surface (FSS) based on substrate-integrated waveguide (SIW) technology is presented for airborne radome application. The proposed FSS element consists of a tapered cross-slot on either side of the substrate surrounded by metallic vias. The structure selectively allows the impinging electromagnetic (EM) wave through it in the specified frequency band. The element shows very stable frequency response for oblique incidence and the sharp roll-off performance characteristics at the edges of operating region in the rejection band. The −10 dB relative bandwidth (BW) of the element is 12.8% from 9.5 to 10.8 GHz with a very good insertion loss (IL) of 0.1 dB. Furthermore, the spectacular advantages of the FSS element based on SIW have been used for modeling the airborne radome application. The proposed radome structure is operating at 10 GHz with a relative 10 dB BW of 25.0% (8.20–10.6 GHz) with maximum (IL) better than 0.1 dB in its passband. The behavior of the FSS radome has been analyzed at different conformal sectors and thickness is optimized for optimal performance. The key parameters of radome such as transmission performance, radiation efficiency, and radar cross section (RCS) have been studied. Experimental verifications are carried out to prove the validity of the estimated results. The results show promising performance of the proposed FSS based on SIW technology for airborne radome application.

Novel Metamaterial-Element-Based FSS for Airborne Radome Applications

A novel metamaterial (MTM) element for radome applications is presented in this paper, which shows negative permittivity and permeability characteristics at distinct frequency ranges. The MTM element is composed of tightly coupled Swastika-shaped conductors printed on both sides of the dielectric substrate. The electromagnetic (EM) analysis of the proposed structure is carried out using the full-wave method-based standard software package and then validated with the experimental results. The MTM structure is further modified by introducing shorting strips at its edges to improve bandpass FSS response with flat-top and sharp roll-off characteristics in microwave and millimeter-wave frequency regimes. In view of airborne radome application of MTM-FSS structure, a multilayered hemispherical radome is designed by embedding it in the mid-plane of the radome wall. The EM performance of the antenna–radome system is analyzed using 3-D ray tracing geometrical optics in conjunction with aperture integration method, incorporating the transmission characteristics of MTM-FSS-based radome wall using CST Microwave Studio. The MTM-FSS-based radome exhibits superior EM performance characteristics as compared to the conventional optimized monolithic radome over the frequency range of 8.5–10.3 GHz, with high transmission efficiency (~0.30) and minimal boresight error (~4 mrad) for the entire beam steering range.

Novel angular‐independent higher order band‐stop frequency selective surface for X‐band applications

A higher order miniaturised band-stop frequency selective surface (FSS) with angular stability performance for X-band applications is presented in this study. The miniaturisation has been achieved by incurving the arms of conventional cross dipole shape inside. The unit cell size of FSS is diminished up to 75% compared to cross dipole FSS operating at the same resonant frequencies. Moreover, the presented FSS is designed to exhibit stable angular performance for incident angles up to about 60° for TE- and TM-polarised waves. The maximum relative frequency deviation is 1.28% with respect to different angles of incidence. Although the designed FSS consists of two layers, higher order and sharp roll-off filter characteristics have been obtained. The simulation of the proposed FSS is performed with the CST MWS. To verify the simulation results, the presented FSS is measured and a good match between the experimental and simulation results are obtained.

Exploiting nonlinearities of micro-machined resonators for filtering applications

We demonstrate the exploitation of the nonlinear behavior of two electrically coupled microbeam resonators to realize a band-pass filter. More specifically, we combine their nonlinear hardening and softening responses to realize a near flat pass band filter with sharp roll-off characteristics. The device is composed of two near identical doubly clamped and electrostatically actuated microbeams made of silicon. One of the resonators is buckled via thermal loading to produce a softening frequency response. It is then further tuned to create the desired overlap with the second resonator response of hardening behavior. This overlapping improves the pass band flatness. Also, the sudden jumps due to the softening and hardening behaviors create sharp roll-off characteristics. This approach can be promising for the future generation of filters with superior characteristics.

Compact dual‐passband LTCC filter exploiting eighth‐mode SIW and SIW hybrid with coplanar waveguide

A compact dual-passband low-temperature ceramic con-fired (LTCC) filter is proposed. Its electrical size is reduced by exploiting an eighth-mode substrate integrated waveguide (SIW) and a conventional SIW hybrid with a coplanar waveguide (CPW). The filter is fabricated on multilayer ceramic, which makes the filter even more compact. The filter was fabricated and measured. The measured results show that the filter has dual-passband, the first passband is centred at 8.0 GHz with 0.95 GHz 3 dB bandwidth, and the second passband is centred at 11.1 GHz with 0.41 GHz 3 dB bandwidth. The filter has low passband insertion and sharp roll-off characteristics at the transition band. The volume of the filter is only 9.6 × 9.6 × 1.4 mm3.

A Planar Bandpass Filter Implemented With a Hybrid Structure of Substrate Integrated Waveguide and Coplanar Waveguide

In this paper, a novel planar bandpass filter is proposed, designed, and implemented with a hybrid structure of substrate integrated waveguide (SIW) and coplanar waveguide (CPW), which has the advantages of good passband and stopband performance inherited from SIW and miniaturized size accompanying with the CPW. Additional design flexibility is introduced by the hybrid structure for efficiently controlling the mixed electric and magnetic coupling, and then planar bandpass filters with controllable transmission zeros and quasi-elliptic response can be achieved. Several prototypes with single and dual SIW cavities are fabricated. The measured results verified the performance of the proposed planar bandpass filters, such as low passband insertion loss, sharp roll-off characteristics at transition band, etc.

Ultra-wideband bandpass filter with a notch band using multi-mode stub loaded resonator

New ultra wideband (UWB) bandpass filter (BPF) with a notch band at 5.8 GHz using multi-mode stub-loaded resonator (SLR) is presented. The very sharp roll-off UWB characteristics of the proposed filter can be easily obtained by using the SLR. The multi-mode stub-loaded resonator consists of two propagation paths with λ/4 open-circuited stubs for providing the two transmission zeros at lower and upper passband edge. The notch band at 5.8 GHz can be well determined by tuning the structural parameters of the asymmetric interdigital coupled input/output (I/O) lines. This study mainly provides a simple method to design the high passband selectivity UWB filter with notch band for Federal Communications Commission (FCC-defined) indoor UWB specification. Experimental verification is provided and good agreement has been found between simulation and measurement.

Steeply Sloped UWB Bandpass Filter Based on Stub-Loaded Resonator

This letter introduces an ultrawideband (UWB) bandpass filter (BPF) with very sharp roll-off characteristics in stripline structure for the U.S. band (3.1-10.6 GHz). The UWB characteristic is basically obtained from capacitive coupling between a main line and a λ/2-length stub-loaded resonator. The stub-loaded resonator consists of λ/8 short-circuited and open-circuited stubs at the center of the λ/2 line. The two stubs provide two attenuation poles at lower and upper cutoff frequencies. For input and output lines, two λ/4 identical capacitively coupled lines have been installed to suppress the unwanted signals in the lower and upper stopbands. The filter has been designed with two transmission zeros at 2.4 and 11.1 GHz to provide 81- and 86-dB/GHz slopes in the lower and upper transition bands, respectively, and realized with low-temperature co-fired ceramic (LTCC) green tape that has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results. Insertion loss less than 1.1 dB and return loss better than 14 dB in the whole passband have been measured. The group delay at the center frequency is 0.26 ns, and the group delay variation within the passband is less than 0.5 ns. The size of the filter is 6 × 18 × 0.6 mm3.

"+"자 공진기와 용량성 결합을 이용한 초광대역 대역 통과 여파기

본 논문에서는 급격한 감쇄율 특성을 갖는 독창적인 초광대역(UWB: Ultra Wideband) 스트립라인 대역 통과 여파기(BPF)를 소개한다. 초광대역의 특성은 기본적으로 "+"자 공진기와 주 전송 선로간의 용량성 결합으로부터 얻어진다. "+" 자 공진기는 <TEX>${\lambda}/2$</TEX>의 전송 선로의 중심에 두 개의 스터브를 병렬 연결된 구조를 가진다. 하나는 <TEX>${\lambda}/8$</TEX> 단락 회로 스터브로 <TEX>${\lambda}/2$</TEX> 전송 선로의 상측에 연결되고, 다른 하나는 <TEX>${\lambda}/8$</TEX> 개방 회로 스터브로 <TEX>${\lambda}/2$</TEX> 전송 선로의 하측에 연결된다. 이 두 개의 스터브들은 통과 대역의 하단과 상단의 차단주파수에서 두 개의 감쇄극을 제공한다. "+" 자 공진기 상측에 위치하여 용량성 결합을 이루는 주 전송 선로는 입력과 출력 선로에 또 한 번의 <TEX>${\lambda}/4$</TEX> 길이의 용량성 결합을 하여 통과 대역 하부과 상부의 저지 대역에서 원하지 않는 신호를 억압하기 위해 구성하였다. 본 여파기는 미국에서 허가한 초광대역(3.1~10.6 GHz)의 대역에서 선택도가 우수한 대역 통과 특성을 얻기 위해 2.4 GHz와 11.1 GHz에서 81 dB/GHz와 86 dB/GHz의 기울기를 제공하는 두 개의 전송 영점(감쇄극)을 갖도록 설계되었다. 본 여파기는 유전상수 7.8을 갖는 저온 동시 소성 세라믹(LTCC) 그린테이프로 제작되었다. 측정 결과는 HFSS 해석 결과와 거의 일치하였다. 통과 대역에서 0.7 dB 이하의 삽입 손실과 14 dB 이상의 반사 손실이 측정되었다. 중심 주파수 군 위상 지연은 0.27 ns이고, 통과 대역에서 군 위상 지연의 변화량은 0.5 ns 이하이다. 본 여파기의 크기는 <TEX>$6{\times}18{\times}0.6\;mm^3$</TEX>이다. This article introduces a novel ultra wideband(UWB) bandpass filter(BPF) with sharp roll-off characteristics in stripline structure. The UWB characteristic is basically obtained from capacitive coupled cross resonator. The resonator has <TEX>${\lambda}/2$</TEX> length. And at the center of the resonator, two stubs are loaded, one is a <TEX>${\lambda}/8$</TEX> short-circuited stub and the other is a <TEX>${\lambda}/8$</TEX> open-circuited stub. The two stubs provide two attenuation poles at lower and upper cutoff frequencies. For input and output lines, two identical capacitively coupled lines have been installed to suppress the unwanted signals in the lower and upper stopbands. The filter has been designed for the U.S. UWB band(3.1~10.6 GHz) with two transmission zeros at 2.4 and 11.1 GHz. The filter has been realized with Low Temperature Core-fired Ceramic(LTCC) green tape which has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results. Insertion loss less than 0.7 dB and return loss better than 14 dB in the pass band have been measured. The group delay in the center frequency is 0.27 ns and the group delay variation within pass band is less than 0.5 ns. The size of the filter is <TEX>$6{\times}18{\times}0.6\;mm^3$</TEX>.

New Elliptic Function Type UWB BPF Based on Capacitively Coupled $\lambda/4$ Open T Resonator

This paper introduces two new circuit structures for European and U.S. ultra-wideband (UWB) bandpass filters (BPFs) with sharp roll-off characteristics. The circuit structures consist of capacitively coupled three parts in stripline structure, a λ/4 open T resonator, a λ/4 short-circuited line, and input and output lines. We show first that ultra wide bandpass property is basically obtained from the T resonator with a capacitively coupled λ/4 short-circuited line, which provides two attenuation poles at lower and upper cutoff frequencies. Two identical capacitively coupled input/output lines, which can be λ/4 length open ends or λ/2 length short ends, with the T resonator are adopted to suppress lower and higher frequency components outside of the passband. There is coupling between the input and output lines providing two additional transmission zeros in the lower and upper transition bands of the filter. Since the coupling between the T resonator with the λ/4 short-circuited line and the input/output lines limits the bandwidth of the filter to the European UWB band, both the λ/4 short-circuited line and the input/output lines are inserted between the two stacked T resonators for the U.S. UWB band. The filter structures are simulated with ADS and HFSS and realized with low-temperature co-fired ceramic (LTCC) green tape which has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results.

New UWB BPF with Steep Selectivity Based on T-Resonator and Capacitively Coupled λ/4 and λ/2 Line Sections

In this paper, two new circuit structures for European and U.S. ultra-wide band(UWB) bandpass filters(BPFs) with sharp roll-off characteristics are introduced. We show first that the ultra-wide bandpass property is obtained from a λ/4 open T resonator with a capacitively coupled λ/4 short-circuited line, which provides two attenuation poles at lower and upper cutoff frequencies. Then, two identical capacitively coupled input/output lines, which can be λ/4-length open ends or λ/2-length short ends, with the T-resonator, are adopted to suppress lower and higher frequency components outside of the pass band. There is coupling between the input and output lines providing two additional transmission zeros in the lower and upper transition bands of the filter. Since the coupling between the T-resonator with the λ/4 short-circuited line and the input/output lines limits the bandwidth of the filter to the European UWB band, both the λ/4 short-circuited line and the input/output lines are inserted between the two stacked T-resonators for the U.S. UWB band. The filter structures are simulated with ADS and HFSS and realized with low-temperature co-fired ceramic(LTCC) green tape which has the dielectric constant of 7.8. Measurement results agree well with HFSS simulation results.

A compact thin-film-based all-pass device for the compensation of the in-band dispersion in FBG filters

Fiber Bragg grating (FBG)-based bandpass filters, while possessing close to ideal sharp rolloff characteristics, can suffer from a significant amount of in-band dispersion. Results concerning the compensation of the in-band dispersion of a typical 100-GHz FBG using two thin-film all-pass filters, each composed of two coupled-cavities packaged in a compact configuration, are presented. The total peak insertion loss of the compensation package is less than 2.5 dB.