Open-loop Resonators Research Articles

Design of a pHEMT RF mixer based on compact microstrip diplexer

Abstract This paper presents a new topology for a microwave active mixer using compact microstrip diplexer constituted from two dual-mode open loop resonators. The resonators are tuned to the radio frequency (RF) and local-oscillator (LO) frequencies, respectively, to effectively isolate the two input signals, while the diplexer output port is connected to the gate circuit of a commercial low cost GaAs pHEMT transistor. The drain circuit of the active device is connected to the load via an intermediate-frequency (IF)-modified Chebyshev low-pass filter to remove the unwanted RF and LO signals and reduce other spurious frequencies at the output of the mixer circuit. The circuit has been designed and constructed for an RF of 850 MHz, LO frequency of 1050 MHz, and an IF of 200 MHz. Experimental measurements show that the circuit provides a conversion gain of 18 dB at LO drive power of +2 dBm. It also operates satisfactorily over the RF range from 800 to 900 MHz with good image frequency rejection and stable operation.

Hybrid-coupler-based quasi-reflectionless balanced bandpass filter with all common mode suppression

Hybrid-coupler-based quasi-reflectionless balanced bandpass filter (BPF) is proposed and demonstrated in this paper. The reflectionless balanced BPF is comprised of two hybrid couplers and a filtering crossover. The filtering crossover is composed by a dual-mode ring resonator coupled with four short-circuited open-loop resonators, which is used to replace the traditional two BPFs for reduction of interference. Hybrid couplers are used for absorbing the reflected interference to the input and output ports. In order to achieve common-mode (CM) suppression, a double-layer structure with the same microstrip configuration on the upper and lower surfaces is adopted. The absorption characteristics of the differential mode (DM) and CM signals are optimized by hybrid couplers with improved ground. A third-order quasi-reflectionless balanced BPF with central frequency of 2.3 GHz and fractional bandwidth of 14 % is designed, fabricated, and measured. The final measured results demonstrate great consistency with the simulated ones.

Interference cancellation system of a microwave resonator filter for 4G and 5G applications

This paper aimed at designing a microwave resonator filter for use in 4G and 5G applications. A band resonator filter was designed and implemented using microstrip technology. Poor performance of a microstrip microwave resonator filter is due to spurious harmonics and unwanted frequencies which are always present and cause interferences of signals hindering effective communication. The coupling matrix was first obtained using polynomial functions of transmission and reflection coefficients. A cost function for optimization was developed and particle swarm optimization techniques were used to optimize the coupling matrix. The transversal matrix was developed and converted to the folded matrix for practical filter implementation. A bandpass filter was designed and simulated using high- frequency structure simulator software. Unwanted frequencies are eliminated by employing a novel square open loop resonator structure. The filter was designed to specification and the results show that unwanted frequencies were eliminated corresponding to the frequency of the outer resonator and therefore performs better than comparable filter.

A reconfigurable narrow-band bandpass filter using electrically-coupled open-loop resonators based on liquid crystals

Abstract This paper introduces an electrically reconfigurable narrowband bandpass filter that exploits liquid-crystal technology. The filter uses two electrically-coupled open-loop resonators to produce two transmission zeros, resulting in a more compact structure than a single open-loop resonator. The spacing between resonators contributes to easy manipulation of the fractional bandwidth (FBW) and return loss. Theoretical calculations of the electrical length using multilayer microstrip line equations are presented. Experimental results demonstrate that the center frequency can be tuned from 9.70 GHz to 10.86 GHz with a maximum bias voltage of 30 V, achieving a tuning range of 11.34%. With applied bias, the maximum FBW reaches 8.10% and the maximum return loss attains 15.97 dB in each biased state.

Compact CPW-fed Antenna with Controllable WLAN Band-rejection for Microwave Imaging

This work presents the design and experimental validation of a compact frequency reconfigurable coplanar waveguide (CPW)-fed ultra-wideband (UWB) antenna with a capability to on-demand reject WLAN frequencies within the range of 5.15 GHz to 5.85 GHz, specifically tailored for applications in microwave imaging. The design and experimental results are presented and discussed. The bandwidth enhancement is obtained by using T-shaped slots between the feedline and the ground plane of the antenna, and the WLAN band is rejected by using an open loop resonator (OLR) placed on the antenna backside. Switching between UWB with and without WLAN band-notched modes is performed using a PIN diode and a bias circuit. The simulation results corroborate well with the experimental data and clearly showed an interesting frequency reconfigurable behavior for use in microwave imaging applications. An antenna performance simulation and analysis model is presented for breast tumor detection, and the tumor effect has been noticed for both operating modes of the antenna.

A diplexer antenna with extremely high isolation for co-site duplex applications

Co-site full-duplex communication system is facing self-interference (SI) issues caused by tremendous gap between Tx power and Rx sensitivity. SI suppression in the propagation domain is addressed by a co-polarized diplexer antenna with high port isolation in this paper. It shares a dual-band microstrip antenna with a small frequency ratio, at 1.5 and 2.0 GHz as an example. A shorting pin directly connects the antenna and diplexer, avoiding 50-Ω interface and impedance matching circuit. The diplexer is composed of open-loop resonators (OLRs) and step-impedance resonators (SIRs). Compact channel filters are constituted by OLRs, and SIRs are adopted to improve the filtering response of the diplexer. General guidelines of the diplexer are given through rigorous analysis. The fractional bandwidths of the lower and higher channels of the diplexer are 4% and 3%, and the fractional bandwidths of the diplexer antenna are 1.5% and 1%, respectively. The port isolation is greater than 53 dB for both channels. Size of the diplexer antenna is 0.65 λ×0.60 λ×0.016 λ, where λ is the free-space wavelength at the lowest operation frequency. Potential advantages of the proposed antenna in suppressing SI are validated using Software-Defined Radio, which is potentially useful in full-duplex communications.

Low insertion loss open-loop resonator–based microstrip diplexer with high selective for wireless applications

This paper presents a low-insertion-loss open-loop resonator (OLR)-based microstrip diplexer with high-selective for wireless applications. We used two series capacitive gaps in the microstrip transmission line, loaded with rectangular-shaped half-wavelength OLRs, to create a high-selectivity bandpass filter (BPF). The planned BPFs are linked through a T-junction combiner, precisely tuned to align with both filters and the antenna port in order to produce the proposed diplexer. The system is implemented on a rogers TMM4 substrate with a loss tangent of 0.002, a dielectric constant of 4.7, and a thickness of 1.52 mm. The suggested diplexer has dimensions of (90×70) mm². It achieves a modest frequency space ratio of R=0.1646 in both transmit and receive modes by having two resonance frequencies of ft=2.191 GHz and fr=2.584 GHz, respectively. The simulated structure displays good insertion losses of approximately 1.2 dB and 1.79 dB for the two channels, respectively, at fractional bandwidths of 1.24% at 2.191 GHz and 0.636% at 2.584 GHz. The simulated isolation values for 2.191 GHz and 2.584 GHz are 53.3 dB and 66.5 dB, respectively.

Pretty small low-cost bandpass filter using a single square open-loop resonator with a centered stub for WLAN/Bluetooth/ZigBee/RFID and ISM band applications

Pretty small low-cost bandpass filter using a single square open-loop resonator with a centered stub for WLAN/Bluetooth/ZigBee/RFID and ISM band applications

Design and optimization of a compact microstrip BPF for wireless communication systems based on open-loop rectangular resonators

In a wireless communication chain, filters play a critical role in ensuring the efficiency, reliability, and overall performance of the system. In fact, filters are essential for selecting specific frequency bands. They can narrow or widen the bandwidth, depending on the requirements of the communication protocol. Appropriate bandwidth management is crucial for optimizing data transmission rates and accommodating multiple channels within the available spectrum. This article describes the design of a compact bandpass filter with two identical rectangular open-loop resonators. The proposed filter frequency response covers the 3.5 GHz global interoperability for microwave access (WiMAX) and fifth generation (5G) applications. The structure of this filter uses the Rogers RO6010 substrate, which has a dielectric constant of 10.2, thickness of 1.27 mm, and tangent loss of 0.0023. The proposed device is intended for wireless communication systems operating at 3.5 GHz. The filter offers a wide bandwidth of 1.21 GHz with a small size of (5.72 × 12.34) mm2, and a low insertion loss of −0.16 dB. The suggested filter offers effective utilization across various applications including fifth-generation (5G), sub-6G, and WiMAX. Simulation and optimization of the proposed design are conducted utilizing the HFSS (High Frequency Structure Simulator) software. To corroborate the results from HFSS, the ADS (Advanced Design System) software is employed. The simulation outcomes obtained from both HFSS and ADS simulators demonstrate close resemblance.

Implementation of highly isolation OLR: based microstrip full-duplex Tx/Rx antenna systems with low insertion loss for contemporary wireless system applications

This paper presents a Highly Isolation open-loop resonators (OLR)—based microstrip full-duplex Tx/Rx antenna systems with low insertion loss for contemporary wireless system applications. Through a T-junction combiner, the proposed diplexer is accomplished by combining two OLR—based band-pass filters tuned at two distinct frequencies. The system is implemented on a Rogers TMM4 substrate with a loss tangent of 0.002, a dielectric constant of 4.7, and a thickness of 1.52 mm. The suggested full duplex has dimensions of (90 × 70) mm2. It achieves a modest frequency space ratio of R = 0.1646 in both transmit and receive modes by having two resonance frequencies of {f}_{t} = 2.191 GHz and {f}_{r} = 2.584 GHz, respectively. The simulated structure displays good insertion losses (IL) of approximately 1.2 dB and 1.79 dB for the two channels, respectively, at fractional bandwidths of 1.24% at 2.191 GHz and 0.636% at 2.584 GHz. The simulated isolation values for 2.191 GHz and 2.584 GHz are 53.3 dB and 66.5 dB, respectively.

The development of a 10.7-MHz fully balanced current-tunable bandpass filter with Caprio technique

Bandpass filters are integral in modern communication systems for selecting specific frequency ranges to ensure interference-free signal transmission and reception. This paper explores various bandpass filter designs, including those using active inductors, transmission-line unit-cells, microstrip open-loop resonators, and dual-port dual-frequency integration antennas. The focus is on the 10.7-MHz bandpass filter, widely used in FM radio and television systems. The study evaluates current-controlled and balanced designs, analyzing their performance, advantages, and drawbacks. Unique trade-offs in terms of linearity, distortion, temperature sensitivity, and component variations are discussed. Additionally, advancements in filter technology and diverse design options are presented. The paper introduces a novel current-balanced, frequency-adjusted bandpass filter to address odd-order noise issues. This filter aims to achieve high linearity, harmonic distortion attenuation, and the elimination of even-order harmonics. Through synthesis, analysis, simulation, and comparison with traditional filters, the proposed design enhances signal quality and efficiency. The fully-balanced current-tunable bandpass filter with the Caprio technique at 10.7 MHz is developed, exhibiting symmetrical characteristics with lower total harmonic distortion. The circuit’s structure is simple and adaptable for integration, validated through consistent simulation results. The study concludes by emphasizing the constant sensitivity of transistor differential amplifier circuits to the center frequency and the linear relationship between center frequency and adjustable bias current. The suggested transistor and capacitor selection criteria contribute to optimizing the circuit’s performance, aligning with the Caprio technique’s recommendations. Overall, this research presents a promising solution for achieving high-quality signal transmission in contemporary communication systems

Novel flexible chipless RFID tags based on five state resonators

In this paper, novel chipless radio frequency identification (RFID) tags are designed by using asymmetrical triple mode resonators constructed by an open loop resonator with two open stubs in different lengths. Three transmission zeros (bits) can be obtained by coupling a proposed resonator to a straight feeding line that connects input/output ports. Five frequency codes can be achieved with respect to the existence of the open stubs and the open loop resonator. By coupling eight asymmetrical triple mode resonators to the feeding line, a multi-resonant circuit is developed on a flexible substrate of Rogers 5870. Totally 24 bit frequencies can be achieved and it is possible to identify 58 different items. For the chipless RFID tags, two monopole wideband antennas in vertical/horizontal polarizations are integrated instead of the input/output ports. Two tags have been fabricated and tested to demonstrate the identification of different codes under smoothed and curved positions successfully.

Design of Compact Parallel-Connected Chained Function Filters

The design of compact parallel-connected chained function filters is presented in this paper. The proposed filters will offer reduced sensitivity to manufacturing tolerance within the specified bandwidth in comparison to conventional Chebyshev filters for C-band applications. A new filtering function according to a chained configuration is derived for fourth-order filters, and the synthesis procedures are presented. To demonstrate the feasibility of this approach, the circuit simulation based on parallel-connected topology is performed in an advanced design system, while the design and simulation of a fourth-order filter in dielectric technology are carried out in high-frequency simulation software. The prototype of fourth-order microstrip topology is fabricated using open-loop resonators. The overall circuit size of the filter is 2.5 cm × 4 cm. The achieved simulation and measured insertion/return loss are 0.409 dB/20 dB and 2.674 dB/18.074 dB, respectively. Extensive sensitivity analysis is conducted to prove the fabrication tolerance of the filter. The reduced sensitivity of the proposed filter to manufacturing tolerance is fully demonstrated using an open-loop microstrip technology, and its reliability is proven by theoretical analysis. The prototype results in this research are validated and agree with the theoretical results. In terms of implementation, this design technique will be a very useful mathematical tool for any filter design engineer.

High-Capacity Double-Sided Square-Mesh-Type Chipless RFID Tags

This paper presents a novel methodology for designing high-capacity frequency domain chipless RFID tags based on the backscattering principle. The tag consists of multiple square open-loop resonators loaded with a varying number of square metallic patches to form a mesh structure. Thus, in contrast to conventional designs, the overall physical size of each resonator remains fixed and does not change with respect to its operating resonant frequency. The RCS response of the proposed tag can be easily manipulated by varying the loading factor of each resonator. The tag size is further miniaturized by placing resonators on both sides of the substrate used. The tag configuration with resonators arranged in the form of a single row (4 × 1) printed on both sides of the substrate is finally chosen for maximum robustness and efficiency. The frequency shift coding (FSC) technique is used to encode more than one bit per resonator by using segments within sub-bands. The proposed tag encodes 16-bit data in a frequency band from 5.9 to 10.5 GHz and has a very high code density of 23.51 bits/cm2 and a spectral efficiency of 3.47 bits/GHz. The design methodology is novel and leads to a very efficient chipless RFID tag that can be used in a variety of high-data-capacity applications.

Application of Compact Folded-Arms Square Open-Loop Resonator to Bandpass Filter Design

Folded-arms square open-loop resonator (FASOLR) is a variant of the conventional microstrip square open-loop resonator (SOLR) that facilitates further device size miniaturization by having the two arms of the conventional SOLR folded inwards. This paper highlights the benefits of this brand of compact SOLR by implementing a five-pole Chebyshev bandpass filter (BPF) using compact FASOLR. The test BPF is presented, with centre frequency of 2.2 GHz, fractional bandwidth of 10%, passband ripple of 0.04321 dB, and return loss of 20 dB. The design is implemented on a Rogers RT/Duroid 6010LM substrate with a dielectric constant of 10.7 and thickness of 1.27 mm. The filter device is manufactured and characterised, with the experimentation results being used to justify the simulation results. The presented measurement and electromagnetic (EM) simulation results demonstrate a good match. The EM simulation responses achieve a minimum insertion loss of 0.8 dB and a very good channel return loss of 22.6 dB. The measurement results, on the other hand, show a minimum insertion loss of 0.9 dB and a return loss of better than 19.2 dB. The filter component has a footprint of 36.08 mm by 6.74 mm (that is, 0.26 λg × 0.05 λg), with λg indicating the guided wavelength for the 50 Ohm microstrip line impedance at the centre frequency of the proposed fifth-order bandpass filter.

A Novel Design Methodology to Realize a Single Byte Chipless RFID Tag by Loading a Square Open-Loop Resonator With Micro-Metallic Cells

In this paper, a unique structural design methodology for chipless radio-frequency identification (RFID) tags in frequency domain is presented. The tag geometry is developed by loading an open-loop resonator with micro-metallic-cells (MMC). The realization give rise to a checkerboard resonator type with electromagnetic signatures in its radar cross section that are extremely efficient to manipulate. The resonators layout is distributed on either side of a Rogers substrate to double its coding density. The proposed chipless RFID tag has a memory of 8-bits in total. The operating band of the tag is 6.5-10.5 GHz. The tag has a high bit coding density of 10.94 bits/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and spectral efficiency of 2 bits/GHz. The tag has a very compact size of 17.4 × 4.2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The simple structuring methodology and efficient resonators layout will give RFID system designers the flexibility to apply the proposed tag in a wide range of modern applications.

Bandpass/bandstop switching with tunable pass band operation based on split ring and open loop resonators

In this work, a bandpass filter (BPF) using a split ring and open-loop resonators for wireless applications is discussed. The split-ring resonator (SRR) is the main part of the band stop filter (BSF) as a preliminary design for obtaining a band stop behavior. The proposed filter is printed on a RO4003 substrate with a 3.55 dielectric constant and a total size of 30 × 30 × 0.813 mm3. First, the SRR BSF is presented to operate at a center frequency of 5 GHz then an open loop resonator is added between input/output ports to achieve an extra band stop region to generate a bandpass behaviour between the two stopbands at 3.5 GHz. The PIN diodes are used to switch between the bandstop and bandpass operation. Then, two varactor diodes are embedded in the open-loop resonator to control the bandpass and bandstop regions of the suggested filter. The experimental results validate the simulated ones confirming the suitability of the suggested filter for proper operations in different wireless applications.

Sharp roll‐off triband microstrip bandpass filter with wide stopband for multiband wireless communication systems

Design of a novel triband bandpass filter is presented for wireless communications systems. The filter is based on inter-coupled stepped impedance resonators and inter-digitally coupled to the input/output ports. The configuration of the filter circuit consists of open-loop resonators that are electromagnetically coupled to each other using inverted T-shaped open stubs. The intrinsic characteristics of filter structure generates five transmission zeros that results in triband bandpass response exhibiting sharp selectivity, high inter-band isolation and a wide out of band rejection. Unlike other triband filters reported recently in literature the proposed single layer filter does not require any short-circuited plated through hole which can introduce fabrication complexity and therefore production costs. Moreover, the triband structure can be configured to provide passbands with identical 3-dB fractional bandwidth and whose center frequency can be equally spaced. In the proposed prototype design presented here the passband frequencies are set to 3.6, 4.6, and 5.6 GHz that corresponds to WiMAX, 5G, and WLAN applications. The consequence of employing open-circuited transmission lines in the design results in a relatively large structure, which can be overcome by employing higher dielectric constant substrate. The proposed triband filter was designed to achieve identical 3-dB fractional bandwidth of 11.9%. Measured results confirm inter-band isolation better than 30-dB. The theoretical model is consistent with the measured results.

Implementation of a Highly Selective Microstrip Diplexer with Low Insertion Loss Using Square Open-Loop Resonators and a T-Junction Combiner

Implementation of a Highly Selective Microstrip Diplexer with Low Insertion Loss Using Square Open-Loop Resonators and a T-Junction Combiner

Improvement of microwave detection sensitivity with atoms based on cavity enhancement effect

A high-precision microwave detection technology using atoms is an essential foundation in future communication technologies. In this study, improvement of microwave detection sensitivity by atoms is realized. First, an open-loop resonator is designed based on finite element simulation and subsequently fabricated; then, the microwave electric field intensity is measured with and without the resonator, based on the electromagnetically induced transparency Autler–Townes effect. The microwave electric field with different input power is measured, and the improvement achieved with the resonator is verified. The optimal detection sensitivity is improved from 2.14(5) to 0.73(4)V m−1, and the sensitivity is improved by a factor of approximately 2.9. These results provide a practical reference for the application of high-precision detection of microwave electric fields with atoms and atomic microwave communication in the future.