Search

One of the challenges of antenna development for wireless communication systems is to create an antenna that casn be operated in wide frequency so that a single antenna can be used in various wireless communication technologies. This paper discussed the wideband antenna with Telkom University Logo-shaped patch, using Fr-4 (?r = 4.3) substrate with 1.6 mm thickness. The antenna can be operated in the frequency range of 760 MHz – 13.75 GHz. The gain performance at the working frequency is still above 0 dBi. Hence, the antenna design to work properly for wireless communication systems which require relatively long distances. The Defected Ground Substrate (DGS) method is applied to achieve that bandwidth. Measurement shows the logo-shaped patch antenna achieves 12.994 GHz bandwidth with 1.33 VSWR and gain 2.85 at 921.5 MHz frequency.

This paper deals with an experimental approach for investigating characteristics of an electromagnetic (EM) wave absorber made of artificial magnetic conductor (AMC) structure. An array of ring resonators in symmetrical shape used as the basis of AMC structure is designed to absorb the incoming EM waves at a certain operating frequency. The proposed design of wave absorber made of ring resonator-based AMC structure is deployed on a Flame Retardant (FR) 4 Epoxy dielectric substrate with the thickness of 1.6 mm. The shape and dimension of ring resonator are optimized to work at the certain operating frequency using a unit cell with proper boundary conditions. To investigate the absorptivity rate of proposed wave absorber, resistive elements are incorporated into the ring resonator. Here, the experimental measurement aims to verify the realized wave absorber with the proposed design and to measure the absorptivity characteristics of realized wave absorber. The measured results for the realized wave absorber which takes the dimension of 220 mm × 220 mm have the absorptivity rate, in terms of reflection coefficient (S 11 ), of –16.65 dB and –25.72 dB for the wave absorber without and with resistors, respectively. These results are comparable to the simulated ones with the S 11 values of –18.01 dB and –23.41 dB for the design without and with resistors, respectively.

This paper presents an implementation of a dual-band wearable reflector composed of an artificial magnetic conductor (AMC) structure and its characterization through experimental measurement. The proposed wearable reflector, which is meant for wireless communications, comprises 3x3 AMC unit cells. Each unit cell comprises a square patch and a square ring patch with gaps placed in a concentrically organized pattern. An RT/Duroid® RO3003 dielectric substrate with a thickness of 0.5 mm is employed for the design and implementation. Meanwhile, a printed dipole antenna as an inseparable part of the wearable reflector is also deployed on the same dielectric substrate. This configuration, i.e., a printed dipole antenna and a wearable reflector, is expectable to operate at two different frequency bands or dual-band, covering the required frequencies of wireless communications while maintaining its compact size and simple configuration. Experimental characterization is applied to validate the proposed design, in which the results demonstrate the ability of configuration to work at two frequency responses, namely 2.45 GHz band, and 3.35 GHz band.

This paper aims to produce a high data capacity and miniaturized flexible chipless RFID tag based on the frequency signature using the Modified Complementary Split Ring Resonator (MCSRR). The proposed 19 bits chipless RFID tag using the frequency shifting technique consists of five slotted overlaying MCSRR with Different Width (MCSRR with DW) structures and the dimension of 48 mm $\times48$ mm. The structure is designed by using a flexible (Polyethylene Terephthalate ) PET substrate with permittivity of 0.2. The operating frequency is between 0.9 GHz and 2.7 GHz. The advancement of slotted overlaying MCSRR with DW structures has successfully miniaturized the chipless RFID tag structure to about $107~{\mathrm {mm}}^{2}$ / bit, $0.02\lambda _{mid}^{2}/\mathrm {bit}$ and 0.09 GHz/bit by maximizing the number of resonators in a limited space and minimizing the frequency separation between the resonators. The omnidirectional tag antenna is incorporated with the proposed MCSRR structure using the retransmission measurement method. The log-periodic antenna with a gain of 5–7 dBi is used for this measurement to improve the range distance between tag and reader system. Based on the retransmission measurement involving the antenna tag, the 19 bits chipless RFID tag which consists of five MCSRR with DW structures can be detected with a maximum range distance of 30 cm and a power transmitted level of 30 dBm.

This paper investigates electromagnetics (EM) wave absorber with modified checkerboard surface pattern configured with broadside SRR. There are three proposed absorbers which all were designed on FR-4 substrate with 1.2mm thickness. Each of these absorbers has a single resonant frequency at 8.41 GHz, 9.75 GHz, and 10.65 GHz for absorber A, B, and C, respectively. The three proposed absorbers are used to construct a checkerboard absorber surface pattern with several variations. From the simulation result, we found that a combination of two absorbers with a checkerboard pattern can create dual resonant frequencies. The combination of A and B absorber has a dual resonant frequency at 8.91 GHz and 9.78 GHz of resonant frequencies, the combination of A and C absorber has a dual resonant frequency at 8.9 GHz and 11.08 GHz of resonant frequencies, while the combination of B and C absorber has 9.79 GHz and 10.98 GHz of resonant frequencies. By combining A, B, and C with the proposed combination, the simulation result shows that it can achieve triple resonant frequency at 8.89 GHz, 9.77 GHz, and 10.96 GHz while achieving a minimum return loss of -29.6 dB.

This study presented the development of the bowtie antenna system design as the transmitter in the Ground Penetrating Radar (GPR) system. The Artificial Magnetic Conductor (AMC) reflector was integrated into the antenna system as a ground plane to obtain a high gain, increase bandwidth and produce a low-profile antenna. The antenna is designed to work at a center frequency of 2.1 GHz with a range of 1.6 - 2.6 GHz and has ultrawideband (UWB) characteristics with a fractional bandwidth of ≥ 25%. In addition, the value of late-time ringing must also be reduced to -30 dB to prevent masking effects on the detected object. Antenna modeling and simulation was done to obtain the optimum prototype design. Bowtie antenna realization was carried out using RT Duroid 5880 as a substrate with dielectric constant (εr) = 2.2 and thickness (h) = 1.57 mm. The AMC reflector was fabricated with FR-4 Epoxy substrate with a dielectric constant (εr) = 4.4 and thickness (h) = 1.6 mm. The antenna realization results show that the antenna has bandwidth = 510 MHz, return loss = -15.17 dB and VSWR = 1.15. The AMC integrated bowtie antenna radiation pattern produces a unidirectional pattern with gain = 4.2 dB. However, the ringing level becomes high by -19.18 dB. Further development is needed to achieve ringing level values that meet the GPR antenna system specifications.

The use of artificial magnetic conductor (AMC) on microstrip antenna design allows the dimension of antenna to be more compact so that it is beneficial for the use in portable communication devices. Apart from its small size, the microstrip antenna can generate multiple frequency response which is more cost effective due to its suitability for several applications which have appropriate frequency specifications. In this paper, an AMC-based tunable multi-band microstrip antenna is designed by incorporating external components, namely varactor diode, into the AMC structure. The incorporation of varactor diodes with varied reverse DC bias voltages can affect the capacitance value on the antenna. Two layers of 1.6 mm thick FR4 Epoxy dielectric substrate are used for designing the antenna with the dimension of 51 mm × 51 mm × 3.2 mm. The characterization results show that the proposed microstrip antenna could produce tunable multi-band frequency response in the frequency range of 1.575 GHz to 2.595 GHz along with the reverse DC bias voltage variation. The higher the applied reverse DC bias voltage across the varactor diode, the smaller the capacitance value yielding the higher the resonant frequency.

In absorbent applications, the technology of surface textured is often used to reduce the material thickness thus allowing the realization of thinner materials. In order to obtain high absorption rate of electromagnetics (EM) wave absorber at the desired frequency, a metal patch upon the wave absorber can be made in a specific shape. In this paper, a characterization of EM wave absorber composed of ring resonator structure is carried out by incorporating resistors between the ring resonator structures on two types of boundary condition, namely perfect electric conductor (PEC) and perfect magnetic conductor (PMC) to represent an infinite double periodic arrangement, and the radiation boundary to analyze the performance of proposed EM wave absorber in an actual condition. By using an FR4 epoxy dielectric substrate with the thickness of 1.6 mm, the proposed EM wave absorber is constructed by two-dimensional array of unit cells. Meanwhile, each unit cell has the dimension of 22 mm × 22 mm and is composed of a couple of ring resonator structures in a symmetrical configuration. Based on parametric studies, the resistor value required to be incorporated into the structure is in the range of 1 kΩ to 6 kΩ. The characterization result shows that the absorption rate of proposed EM wave absorber is −23.41 dB on the PEC and PMC boundaries with the resistor value of 6 kΩ, and −18.3 dB on the radiation boundary with the resistor value of 5.6 kΩ at the frequency of 2.45 GHz.

The reflector has a role in enhancing the return loss of antenna becoming a selective frequency. In this paper, an artificial magnetic conductor (AMC) based reflector composed of slotted square rings is proposed and characterized using a printed dipole antenna. The used of AMC layer which has high surface impedance is expected to reduce the distance between the antenna and the reflector yielding a compact device. The configuration of AMC reflector and printed dipole antenna is designed each on an RO3003 dielectric substrate with the relative permittivity of 3.0 and the thickness of 0.5 mm. The configuration is intended to be used for wireless communication at the Industrial, Scientific, and Medical (ISM) band frequency of 2.4 GHz. The proposed reflector is constructed by a 3×3 unit cell of AMC structure where each unit cell is composed of slotted square rings configured concentrically. Meanwhile, the characterization is carried out by varying the parameters of AMC reflector and printed dipole antenna. The result shows the configuration with the distance between the antenna and the reflector of λ/23, or around 5 mm, could produce a significant value of reflection coefficient (S 11 ) among others. This configuration could achieve the S 11 value up to –24 dB at the frequency of 1.98 GHz.

In this paper, the absorption characteristics of tunable electromagnetics (EM) wave absorber developed using artificial magnetic conductor (AMC) is investigated by incorporating varactor diode into the structure. The proposed wave absorber configured by 5×5 cells of AMC structure is designed on an FR4 epoxy dielectric substrate with the thickness of 1.6 mm. Each cell which is composed of a square patch has the dimension of 20.8 mm × 20.8 mm, hence the total dimension of AMC-based wave absorber is 104 mm × 104 mm. To gain a tunable frequency response with the optimum absorptivity, a varactor diode with varied DC bias voltage is incorporated midway along the square patch in parallel to the incident wave. The equivalent circuit of varactor diode is used to characterize the performance of proposed tunable AMC-based wave absorber. Prior characterizing the effect of varactor diode incorporation, parametric studies upon the characteristic of AMC-based wave absorber is investigated by incorporating some passive elements such as resistor and capacitor. The characterization results show that the frequency response of tunable AMC-based wave absorber can be tuned from the frequency of 1.55 GHz to 2.51 GHz which corresponds to the DC bias voltages variation of varactor diode from 10V to 0V.

In this paper, design and realization of tunable multi-band microstrip antenna based on artificial magnetic conductor (AMC) is presented. The involvement of AMC structure on the design of microstrip antenna makes the dimension of antenna to be smaller, hence it is easy to use for portable communication devices. The tunable frequency response of proposed microstrip antenna can be achieved by incorporating external elements, namely varactor diode. Here, the varactor diodes of STMD3001 type are used with the reverse DC bias voltage of 0V, 3V, and 10V. The proposed multi-band microstrip antenna is design using two layers of 1.6mm thick FR4 epoxy dielectric substrate. There is a square patch on the top side of the first layer and 4 identical square patches arranged in a 2×2 array on the top side of the second layer. The results show that the proposed AMC-based microstrip antenna could produce the tunable frequency response in the frequency range of 1.575GHz to 2.75GHz along with the variation of reverse DC bias voltage.

This paper deals with the experimental characterization of thin tunable absorber developed based on artificial magnetic conductor (AMC). To produce the tunable frequency response, the varactor diodes with varied reverse DC bias voltage are incorporated into the AMC structure of proposed absorber. By using an equivalent circuit of varactor diode, the performance of AMC-based thin tunable absorber is characterized through a simulation software. To improve the absorptivity, a resistor with the value of 470Ω is also incorporated into the AMC structure in parallel to each varactor diode. A 1.6mm thick FR4 epoxy dielectric substrate with the dimension of 104mm × 104mm is used for deploying the design as well as for the realization. The experimental characterization which is performed using a horn antenna shows that the realized absorber has a tunable frequency response from the frequency of 2.26GHz with the reflection coefficient (S 11 ) value of -21.5dB at the reverse DC bias voltage of 0V to the frequency of 3.01GHz with the S 11 value of -19.75dB at the reverse DC bias voltage of 10V. This performance is comparable to the simulation result for the proposed absorber with the varactor diode and 470Ω resistor incorporation.

This paper deals with the characterization of electromagnetics (EM) wave absorber configured by axially symmetrical C-shaped planar structure. The proposed absorber which is intended to work at C-band frequency with the center frequency of 5.8GHz is designed on a 0.8mm thick FR4 epoxy dielectric substrate. A unit cell of axially symmetrical C-shaped structure is configured with proper boundary conditions to form a double periodic array planar structure of absorber in infinite extent Some physical parameters of unit cell are investigated to evaluate the performance of proposed EM wave absorber in terms of bandwidth characteristic and frequency response. The characterization results show that the resonator length of axially symmetrical C-shaped planar structure affects significantly the frequency response of the absorber with the widest bandwidth achievement of 80MHz.

Electromagnetic wave absorber is a material that can reduce the energy available in electromagnetic waves. Electromagnetic wave absorber can be used to reduce interference in wireless communication devices so as not to quickly suffer damage, as a layer in the room free of reflection and to reduce radar cross section of an object detected in radar tracking applications. In this paper, a discussion about the use of the broadside form using the Split Ring Resonator (SRR) method as an absorber of electromagnetic waves and its characteristics in C-Band. Broadside shape is obtained from the initial form of a square which is developed into a square resonator and then given a gap at the end of the resonator. The results show that the SRR broadside form can be used as an absorbent of electromagnetic waves on the C-Band, precisely the frequency of 6.41 GHz with absorption rates reaching 99.99% and bandwidth of 0.077 GHz with dimensions of 7 mm. From the experimental results, it can also be seen that the change in the gap length variable in the SRR broadside shape is the most influential in changing the resonant frequency value and the amount of bandwidth produced.

Siaran TV digital umumnya menggunakan antena tipe Yagi dan Kubikal yang berukuran besar sehingga tidak fleksibel digunakan di dalam ruangan. Penelitian ini merancang dan merealisasikan antena mikrostrip miniaturisasi fraktal Köch agar dimensi antena lebih kecil dan bandwidth lebih besar sehingga cocok digunakan di dalam ruangan. Miniaturisasi antena berupa fraktal Köch iterasi-1 pada patch dan teknik slot iterasi-2 pada ground plane menggunakan pencatuan mikrostrip proximity coupled feed pada alokasi frekuensi TV digital Indonesia 478 – 694 MHz dengan bandwidth 216 MHz. Antena dirancang pada software perancang antena, direalisasikan, diukur, dan diaplikasikan pada TV digital. Hasil simulasi antena menunjukkan bandwidth yang lebih besar dari spesifikasi yaitu 245,99 MHz pada rentang frekuensi 477,81 – 723,8 MHz. Return loss dan gain untuk direalisasikan sebesar -16,67 dB dan 3,085 dB pada frekuensi tengah 586 MHz. Pola radiasi berbentuk bidirectional dan polarisasi berbentuk linier. Panjang dan lebar antena hasil realisasi 17,33 cm X 17,33 cm. Kata Kunci: TV digital, antena, mikrostrip, Fraktal, Köch ABSTRAC Digital TV broadcasting generally uses large Yagi and Cubical type antennas, so it is not flexible to be used indoor. This study designs and applies miniaturization of Köch fractal microstrip antennas to obtain smaller dimensions and larger bandwidth. The miniaturization of antenna are Köch fractal iteration-1 on patch and iteration-2 slot technique on ground plane using proximity coupled feed at frequency allocation 478 – 694 MHz and the bandwidth is 216 MHz. The antenna was designed in software and developed, measured, and applied to digital TV. Antenna simulation results show a greater bandwidth than specification, 245.99 MHz, at the frequency range of 477.81 – 723.8 MHz. Return loss and gain simulation results that meet the specifications to be applied to digital TV antennas are -16.67 and 3.085 dB at 586 MHz center frequency. The radiation pattern is bidirectional and polarization is linear. The length and width dimensions of the antenna is 17.33 cm × 17.33 cm. Keywords: TV digital, antenna, microstrip, Fractal, Köch

Beside the sub-6 GHz the fifth telecommunication generation (5G) New Radio (NR) also utilize millimeter wave (mmWave) band, which is sensitive to the environments. This paper proposes 5G Indonesia channel model under the humidity effect and their performance evaluations. This paper proposes evaluates 5G NR technology performances based on Orthogonal Frequency Division Multiplexing (OFDM) Numerology μ = 1, at operating frequency of 3.3 GHz and bandwidth of 99 MHz. We also provide outage performances of 5G channel models validated using bit-error rate (BER) and frame error rate (FER) performances of 5G complex-binary phase shift keying (C-BPSK) and Convolutional codes. The results show that 5G channel model is affected by humidity. These results are expected to be useful references for 5G real-field experiments and implementation of Indonesia 5G networks in Indonesia.

This paper presents the characterization of rectangular s-ring resonator as an electromagnetic wave absorber for C band. The structure consists of copper s-ring patch in the top layer, FR-4 dielectric substrate, and the back is fully copper laminated. The initial dimension has 7 mm × 7 mm with the thickness of FR4 is 1 mm. The characterization observes the changes of each variable from the initial design that affect the shift in resonant frequency and bandwidth. Maximum bandwidth can be achieved at S-Ring length 4.4 mm for 0.0941 GHz.

The Federal Communications Commission (FCC) sets the frequency for an Ultra Wideband (UWB) medical imaging must have bandwidth contained between 3.1 GHz and 10.6 GHz. In medical imaging, antenna plays major role as a transmitter and receiver. To support the UWB system in medical imaging, antenna must be planar, compact, with high radiation efficiency and relatively stable in the operating band frequency. Therefore, in this paper the design of UWB antenna for brain cancer detection with circular modification patch microstrip antenna with slotted patch, partial groundplane and reflector. The substrat material of the antenna is Rogers Duroid RT5880 with dielectric constant 2.2 and thickness 1.575 mm. The simulation result show that the antenna had bandwidth ranging from 3.1 to 10.6 GHz and the radiation pattern is unidirectional.

Most of electromagnetics (EM) wave absorbers have been realized on some hard substrates. Therefore the use was limited only in the field of planar surfaces, while absorbing EM waves are required with various forms of field. In this paper, based on a principle of artificial magnetic conductor (AMC) used as a metasurface, a thin EM wave absorber composed of octagonal patch array is designed on a dielectric substrate of silicon with the relative permittivity of 5.7 and the thickness of 0.3 mm. The use of thin substrate for the absorber is necessary to have possibility and flexibility in surface of field with a non planar shape. To obtain high absorption rate of proposed wave absorber, resistive elements are incorporated into the patches and connecting to the adjacent patches. The characterization result shows that the reflection coefficient was up to 29.15 dB at the resonant frequency of 2.5 GHz for the value of resistive elements of $2100\ \Omega$ , in which this is much higher than the result without resistive elements.

Wearable communication systems required high performance, compact and flexible antenna devices. In this paper, a flexible artificial magnetic conductor (AMC) reflector is designed using square patch array for wearable antenna application at the Industrial, Scientific and Medical (ISM) frequency of 2.45 GHz. The proposed AMC reflector is composed of 3 × 3 squares patches with concentric slots to gain the wide bandwidth response. A flexible dielectric material of RO3003@ from Rogers Corporation with the relative permittivity of 3.0 and the thickness of 0.5 mm is used as a dielectric substrate for the reflector deployment as well as for the wearable antenna. The characterization results show that the integration of flexible AMC reflector with a wearable antenna has improved radiation characteristic and gain of the antenna. The results indicate that the proposed flexible AMC reflector has the feasibility for performance enhancement of wearable antenna especially in wireless body area network (WBAN) communications.

The information of textile properties is one of important things in the design of wearable absorber. In this paper, the experimental study of textile properties focused on its relative permittivity is presented based on the cavity reflection transmission-perturbation method. The technique that utilizes a rectangular waveguide is expected to produce high accuracy of property measurement since it combines the reflection-transmission method and cavity perturbation method. Prior to the textile relative permittivity measurement, the proposed method is numerically analyzed and then experimentally examined for some known dielectric materials. From the characterization, the measurement result of relative permittivity for some textiles has some differences which depend on the raw material of each textile. It shows that the proposed method is suitable for the measurement of textile properties which are useful in the design of wearable absorber.

The experimental characterization in exploiting the property of microwave devices is an essential complement to theoretical and/or simulation works. Thus, the need of instrument for the characterization is becoming unavoidable thing to be established. This paper reports the development of test-fixture in form of a parallel plate waveguide (PPW) to characterize the reflectivity and/or transmittivity of microwave device whereby the property of reflection and/or transmission can be achieved under normal incidence. Since the PPW is excited using a rectangular waveguide, a transition section which connects the rectangular waveguide and the PPW needs to be investigated to have an optimum performance required for microwave devices characterization. The tapering effect of transition section is examined and analyzed numerically in yielding the influences to the test-fixture performance. Here, a WR248 type rectangular waveguide which has working frequency of 2.60GHz to 3.95GHz for TE10 mode is used as coaxial-to-waveguide transducer for exciting the PPW. The result shows that the linear-tapered transition has better performance in term of bandwidth compared to the step-tapered one. In addition, the discussions of taper length and number of step-tapered transition related to the performance of test-fixture as well as the experimental characterization for linear-tapered transition are also presented.

Recently 15 GHz has been a frequency candidate for fifth generation (5G) mobile communication technology. Minimum bandwidth has to provide for 5G application is 1 GHz. In this paper we proposed antenna design to fullfill those requirement. We use microstrip patch antenna which has narrow bandwidth. To improve the bandwidth, we use proximity couple and observe the hexagonal patch antenna frequency response. We design a 4×4 MIMO antenna with less than -15 dB return loss and -20 dB mutual coupling to each ports. From the realization we have maximum bandwidth 1.34 GHz with lower frequency 14.42 GHz and upper frequency 15.76 GHz.

Pada penelitian ini dirancang sebuah microstrip passive phase shifter berbentuk meander coupled- line yang dapat di implementasikan untuk menggeser fasa sejauh 90⁰ sehingga dapat memudahkan dalam sistem pengarahan antena. Antena dirancang di atas substrat FR-4 dengan nilai permitivitas relatif 4.6 pada frekuensi S-Band (3 GHz), yaitu frekuensi yang digunakan pada Airport Surveillance Radar yang berfungsi untuk memantau pergerakan pesawat saat masuk, keluar atau hanya melintasi wilayah bandara tertentu. Metode yang digunakan adalah Schiffman’s phase shift er sebagai acuan perancangan. Pada jurnal ini, direalisasikan microstrip passive phase shifter dengan return loss untuk sebesar -14.7 dB dan pada sebesar -14.6 dB. Sedangkan nilai fasanya senilai 97.22⁰ untuk dan 92.56⁰ untuk .

In this paper, the development of thin electromagnetic (EM) wave absorber and its characteristic measurement are presented. The absorber is developed based on a textured surface structure of octagonal patch array which is loaded with surface resistor. The octagonal patch is employed as a unit cell which is intended to operate whereby at the resonance frequency of resistively textured surface. Each unit cell which has the substrate width of 14.4mm consists of an octagonal shape of patch with the width of 5.178mm. Here, the surface resistor are incorporated midway in between the adjacent patches to reduce the amount of backscatter from the absorber. The textured surface structure of octagonal patch array is deployed on a single-sided 3.2mm thick FR4 Epoxy dielectric substrate. From the result of experimental characterization, it shows that the reflection characteristic of absorber with 453Ω of surface resistor loading upon the incident wave is up to 34dB at frequency of 2.78GHz where this is 10dB better than the absorber without surface resistor loading.

An investigation of bandwidth improvement for artificial magnetic conductor (AMC) structure based on square patch array by using multiple slots technique is presented. The technique is proposed in overcoming the nature characteristic of square patch as a unit cell of AMC structure which has narrowband bandwidth response. The structure which is designed to work at center frequency around 2.7GHz is constructed of a 2D array of unit cells in which each unit cell is built from a 10.5mm × 10.5mm square patch placed on a grounded dielectric substrate. Each unit cell of AMC structure has the dimension of 12.5mm × 12.5mm and is deployed on a 2.54mm thick Taconic CER-10TM dielectric substrate with the relative permittivity of 10. Meanwhile, the number of slots on the square patch is varied to investigate its effect to the bandwidth response of structure as well as the width of slot and the separation between slots. From the characterization result, although the resonant frequency is shifted as the presence of slots, it shows that the bandwidth response can be enhanced up to 13% as the increase of number of slot. The similar trends also appear for the wider slot width and the larger separation between slots.