ABSTRACTThis letter presents a filtering Wilkinson power divider (WPD) with good in‐band and out‐of‐band performance based on a filtering impedance inverter (FII). The FII consists of a high‐pass filter (HPF) and a low‐pass filter (LPF). This FII is capable to produce a required value of phase shift at the designed frequency and matched with any impedance value. To validate this, the quarter wavelength lines of conventional WPD having an impedance of 70.7 Ω are replaced by FII. Therefore, the proposed power divider provides bandpass response and power division simultaneously within a small circuit area. The physical area of the proposed power divider occupies only 30% (0.12λg × 0.16λg, where λg is guided wavelength) circuit area of the conventional WPD. Moreover, the in‐band return loss and isolation were better than 30 dB and the out‐of‐band rejection level was better than −25 dB up to 6.5f0 obtained.

In this work, a high degree of miniaturized Gysel power divider (GPD) along with harmonics suppression is presented. Firstly, a GPD consisting of three kinds of quarter wavelength lines (QWLs) is designed based on the conventional technique at 0.9 GHz which serves as the reference GPD. To reduce the circuit area of this reference design, conventional lines are replaced by multiple transmission line techniques like coupled line-based transmission line, dual transmission line and Tshaped transmission line. As a result of this, the overall circuit area of the reference GPD is reduced by 80.4 %. Moreover, 2nd, 3rd, and 4th orders unwanted harmonics are suppressed by a level better than 19 dB, 12 dB, and 11 dB, respectively.

A slow-wave structure based on a pair of an interdigital capacitor and a stepped meander line is demonstrated. The proposed structure provides not only a high slow-wave factor (SWF) but also a sharp transmission zero near passband. SWF of the structure is investigated and compared with the traditional line. SWF of the proposed structure is increased by a minimum of 177

This letter presents a filtering directional coupler (FDC) with enhanced coupling and high directivity simultaneously. The proposed FDC is composed of a pair of coupled lines instead transmission line of a directional coupler. This coupled lines resonator increases the design parameters by which even/odd mode phase velocity can be compensated to improve the directivity and coupling level. The coupling enhancement can be explained by analyzing the even mode and odd mode circuit of the proposed coupler. A prototype of the proposed coupler is designed which provides a high directivity of 44 dB for 6 dB coupling level at 1 GHz frequency. The proposed coupler is designed, fabricated, and tested.

This paper presented a compact Wilkinson power divider (WPD) operating at 0.9GHz with harmonic suppression based on the compact modified hairpin unit (MHPU). First, HPU is designed with low impedance (coupled line) and high impedance section. Further, the structure is modified by folding the low impedance section inside the free space of HPU and analyzed its slow-wave characteristics. The proposed unit provides high slow-wave characteristics compared to the reference line. In addition to this, two transmission zeros (TZs) are obtained by adjusting the impedances and electrical lengths of HPU. The proposed unit is used to design a compact WPD due to the high slow-wave factor (SWF). Therefore, the physical dimension of the proposed WPD occupied only 76% circuit area compared to reference WPD. In addition to this, two transmission zeros are also observed in the frequency response above the operating band, which are properly tuned to suppress 2nd and 3rd order harmonics by more than 40dB.

A multiple band bandpass filter (BPF) is designed using multilayer arrangement. The bandpass filter has three passbands having centre frequencies at 2.45 GHz, 4 GHz and 5 GHz. First a single band BPF is designed which includes a pair of coupled resonator and a split ring resonator in a multilayer arrangement. This geometry of the filter structure is studied and validated by fabrication and measurement. The initial single band filter structure is further improved to provide triple band BPF. All these bands are realized by a stub loaded U-shaped step impedance resonator (SLU-SIR). However, to improve the response of the second and third band a modified split ring resonator and a pair of open stubs are used. Each passband can be controlled individually. A mathematical analysis is done to study the proposed SLU-SIR using transmission line model. The proposed filter provides compactness and low insertion loss. A prototype is measured using vector network analyser (VNA) and shows a good matching with the simulated result.

This letter presents novel composite dual-transmission lines. The proposed line consists of one direct series line and two identical transmission lines connected by a series lumped capacitor. The line is analyzed with an even-odd mode analysis method to have simple closed-form design equations. From the design equations, it is also observed that one can maintain a more realizable value of the impedance of the lines and achieve a good amount of miniaturization by adjusting only the lumped capacitor. To verify this technique, a 74.6% miniaturized Gysel power divider (GPD) is designed at 0.95 GHz compared to reference GPD. The physical size of the proposed GPD is 60mm x 32mm (equivalently 0.25 lambda(g) x 0.13 lambda(g), lambda(g) is guided wavelength line). Moreover, two transmission zeros (TZs) are obtained near passband which improve the out-of-band performance.

A novel design of a compact penta-band frequency selective surface (FSS) is presented in this letter. The FSS unit cell consists of five metallic structures, two at the top surface and three at the bottom surface of the dielectric, which provide five stopbands in PCS, WiFi, CBRS, lower WLAN, and X-band downlink satellite communication frequency ranges. The mechanisms of stop-band generations are elaborated with current distribution patterns and equivalent circuit modeling. The structure is polarization-insensitive and shows a stable response under oblique incidence up to ±54°. The FSS unit cell is compact with dimensions 0.1λ × 0.1λ, where λ signifies the free-space wavelength corresponding to the lowest resonant frequency. A prototype of the proposed FSS is fabricated, and the measured results are in accord with the simulated results.

This paper presents a compact transmission line based on the coupled line section to reduce the circuit size of Gysel power divider (GPD). The line is composed of one direct line and one coupled line section. The coupled line section consists of two series lines and one coupled line. The proposed line is symmetrical and analyzed with even-odd mode analysis to derive design equations. The line not only reduces circuit size but also improves the out-off band performance. To validate the properties of the line, a GPD is designed at 1 GHz. The physical size of this GPD occupies only 38% (0.32 lambda(g)x 0.16 lambda(g), lambda(g) is the guided wavelength) circuit area compared to reference GPD. Furthermore, the proposed design includes 2nd order harmonic suppression with attenuation level better than -20 dB. The proposed GPD is designed and fabricated on an Arlon substrate of relative dielectric constant of 2.2, thickness of 0.787 mm, and loss tangent 0.0009.

This paper presents a compact design of a hybrid branch line coupler (BLC) operating at 1.8 GHz frequency for the global system for mobile communication (GSM) applications. The miniaturization is achieved by using two short circuited stubs and one series transmission line (TL) instead of series quarter wavelength line of conventional BLC. The characteristic impedance of the shunt quarter wavelength section is optimized to improve the overall performances. Therefore, the proposed technique is 59% compact in size is compared to conventional BLC. The outputs at two ports (|S21| = |S31|) are 3.5 ± 0.3 dB with return loss (|S11|) and isolation (|S41|) is better than 20 dB. The prototype coupler is simulated using ANSYS HFSS EM simulator and fabricated on a substrate of dielectric constant (εr) = 2.2, thickness (h) = 0.787 mm and loss tangent of 0.0009 and tested. The measured result is completely compiled with the simulated one.

In this paper hairpin unit based compact quarter wavelength line is proposed in order to miniaturize the Wilkinson power divider (WPD) and hybrid branch line coupler (HBLC). The proposed line consists of two series lines and a hairpin unit (HPU) in between them. The proposed line provides significant size reduction due to high slow-wave factor. The electrical lengths and impedances of the HPU are adjusted to produce two transmission zeros (TZ5) above the operating frequency. These TZs are tuned to get good selectivity as well as suppress the harmonics. The proposed line is further utilized to design a compact WPD and HBLC operating at 1.5 GHz. The dimensions of those are 0.06 lambda(g) x 0.184 lambda g and 0.06 lambda(g) x 0.25 lambda(g), respectively, where lambda(g) is the guided wavelength. A significant size reduction of 55% and 70% are obtained for WPD and HBLC, respectively, as compared to reference one at 1.5 GHz. The proposed designs (WPD and HBLC) are analyzed, fabricated and tested. (C) 2019 Elsevier GmbH. All rights reserved.

A microstrip line fed planar monopole patch antenna is designed to provide impedance bandwidth (| S 11 | ≤ -10 dB) of 2.56-12.25 GHz, thus exhibiting ultra-wideband (UWB) characteristic. Two metallic strips are branched symmetrically from the patch radiator to generate resonant frequencies at 0.9 and 1.9 GHz, corresponding to GSM operating frequencies. A filtering element based on electromagnetic bandgap (EBG) unit cell is placed near the feedline of the antenna to introduce two notches at 5.17 and 7.97 GHz thereby mitigating any interference from lower WLAN and X-band satellite uplink frequencies respectively. The proposed structure has satisfactory gain at the GSM frequencies and fairly constant gain with a variation of <;2 dB in its UWB operating region except at the notch bands. The radiation patterns are stable and symmetric with low cross polarisation. In order to comprehend the novelty of the proposed structure, it is compared with similar structures found in literature in terms of notch generation, achieving extra resonance outside UWB range, compactness, thickness of the substrate, and maintaining consistent gain in UWB region. A prototype of the proposed structure is fabricated and the measured results are in good agreement with the simulated results.

In this article, a broadband metamaterial microwave absorber on a low-cost FR-4 Epoxy substrate is proposed. The unit cell of the absorber consists of a staircase shape metallic patch placed on the top of the metal-backed ultrathin dielectric substrate having a thickness of 1.9 mm (0.07 lambda(0)). The absorption of more than 90% is achieved with this proposed low profile single-layer microwave absorber throughout the operation band from 8.86 to 15.5 GHz. The performance is analyzed for different values of incident angle, polarization angle, substrate height, and dielectric constant. The surface current and the power loss density at the top and bottom planes at the two absorption peaks of 9.46 and 13.90 GHz are also analyzed to elaborate the absorption mechanism of the structure. Experimental result closely follows the simulated one. The broadband characteristics of the design with relative absorption bandwidth (RAB) of 54.51% at both TE and TM polarizations of incident wave for a wide incident angles makes it versatile for applications in the X and Ku bands of microwave frequencies. The proposed work is very compact (unit cell size: 0.22 lambda(0)) with ultrathin substrate height (0.07 lambda(0)) and giving RAB performance of 54.51% comparable with that of others. Thus with this single-layer low-cost substrate material a broadband absorber is achieved.

Here in this paper a compact wideband bandpass filter (BPF) is presented. The size of the end coupled dual- resonator bandpass filter is reduced with a reasonably wide spacing between resonators. The broadside coupling provided by multi-layered structure is used to produce controllable transmission pole. The first unwanted harmonic is removed by introducing quarter wave resonators. For validation of the design a BPF centred at 2.49 GHz with a 3dB fractional bandwidth of 24% is designed, fabricated and measured. There is good agreement between simulated and measured results. The overall cut out size of the filter is 16x3mm(2).

In this work, a polarization insensitive compact X-band microwave absorber with miniaturized electric field coupled (ELC) resonator is presented. The ELC resonator is integrated with interdigital capacitor for synthesis of miniaturized unit cell area. The structure is also loaded with lumped resistances to achieve wideband absorption. The absorption band with more than 90% absorption covers mostly X-band frequencies from 8.16 GHz to 12.16 GHz with relative absorption bandwidth (RAB) of 39%. The size of the unit cell is 0.16 λL × 0.16 λL and overall thickness of the structure is only 3 mm (0.08 λL, with respect to lowest resonance frequency). The simulated absorption performances of the proposed miniaturized absorber are analyzed for different incident and polarization angles and found to be insensitive and hence can be well suited for Radome application.

In this work, a dual-band microwave absorber is proposed with a periodic array of unit cells which has dual-split ring geometry on the top of a metal-backed dielectric substrate. The dual-split ring resonator on the top plane is electrically excited by the co-polarized component of incident EM wave and gives two absorption peaks at Wi-MAX (3.5 GHz) and WLAN (5.8 GHz) band due to two resonance modes. These two-resonance modes are named as mode 1 and mode 2 for low and high frequency peaks, respectively. The surface current distributions on the top and bottom planes are studied to gain insight into dual-mode resonance for dual-band absorption of the structure. Some parametric studies are also performed on key design parameters, i.e., split gap, stub length, and split angle for further analysis of the design. The measured results are verified with the simulated ones to test their performance and found to be similar.

This paper presents a compact Wilkinson power divider (WPD) operating at 0.7 GHz (LTE band) with higher order harmonics suppression based on step impedance shunt stubs (SISSs) and defected ground structure (DGS). The quarter wavelength lines of conventional WPD are replaced by a host line loaded with a DGS and a pair of SISSs. The DGS and SISS of the proposed line serve as a high series inductance and shunt capacitance, respectively. Therefore, a compact quarter wavelength line is designed compared to conventional one. A prototype of the proposed power divider is designed based on the proposed line, which provides a size reduction of 71% as compared to conventional WPD (CWPD) at 0.7 GHz. In addition, upper edge selectivity is found to be 40 dB/GHz along with higher order harmonics suppression up to the 10th order (7 GHz) by a level better than 20 dB. The proposed power divider is experimentally verified with the simulated one and found to be same.

This paper presents an ultra-thin microwave absorber with a transmission window on a low-cost substrate material. The unit cell of the proposed absorber consists of metallic cross dipole patch on top plane and a ring slot at the conductive bottom plane. The substrate height is 0.8 mm, which is ultrathin. The low profile ultra-thin planar structure makes it valuable for electromagnetic interference (EMI) reduction at 5.9 GHz which is industrial, scientific and medical (ISM) frequency band and a transparent window at 4 GHz (C-band). The surface current distributions on the top and bottom planes are studied to elaborate the absorption and transmission mechanism of the structure. The orthogonal symmetry of the structure makes it polarization insensitive and hence suitable for realization in real time environment. The measured results are verified with the simulated ones to test its performance and found to be similar.

This paper presents a design mechanism of miniaturized wideband branch line coupler (BLC) with loose coupling of 10 dB. Dual transmission lines are used as a feed network which provides a size reduction of 32% with a fractional bandwidth (FBW) of 60% for 10 +/- 0.5 dB coupling but return loss performance is found to be poor in the operating band. For further improvement of return loss performance as well as for size reduction of the BLC, a T-shape transmission lines are used instead of series quarter wavelength transmission lines, and hence the overall size reduction of around 44% with FBW of 50.4% is achieved. The return loss and isolation performance is found to be < 15 dB in the entire operating band (2.5-4.1 GHz) with respect to design frequency 3G Hz. The proposed BLC is analyzed, fabricated and tested.

This paper presents a design of compact dualband Wilkinson power divider (WPD). The cascaded πshape and dual transmission lines are used instead of conventional transmission line sections of the reference WPD in order to miniaturize the circuit area. Therefore, 62% size reduction has been achieved without much affecting the performance of power divider. The insertion-loss of the output ports is within (3.4 ± 0.3) dB, for the reflection coefficient better than –15 dB and isolation better than 18 dB at the lower frequency band of 1.1 GHz. Similarly the insertion-loss is within (3.4 ± 0.3) dB, for the reflection coefficient better than –18 dB and isolation better than 24 dB at the upper frequency band of 2.55 GHz. The proposed WPD is analyzed, fabricated and tested. It is found that the measurement results are in good agreement with the simulated one.