Stub Loading Research Articles

Knowledge‐Based Methodology of CPW‐Fed Open Stub Loaded C‐Shaped Microstrip Antenna by Surrogate‐Based Modeling

Knowledge‐Based Methodology of CPW‐Fed Open Stub Loaded C‐Shaped Microstrip Antenna by Surrogate‐Based Modeling

Frequency selective surfaces-based miniaturized wideband high-gain monopole antenna for UWB systems

In the suggested manuscript, an antenna functional over an ultrawide band with a small geometrical configuration and simplified structure is given. The recommended antenna is designed for the Roger 6002, having overall measurements of 40 mm × 30 mm × 1.52 mm. The wideband is obtained after loading stubs and etching slots from the basic antenna design. In order to improve the antenna's performance further, an FSS sheet is designed. The sheet of FSS is placed behind the antenna to reflect the antenna's backward radiation and improve antenna gain. In the results, the gain of the antenna improved from 4.5 dBi to 9.5 dBi. The resultant antenna loaded with FSS is capable of operating over UWB ranging from 3.4 to 9.8 GHz with stable gain throughout the functional bandwidth. The hardware model is manufactured and tested to validate the estimated results achieved from HFSS (High Frequency Structure Simulator). Moreover, the recommended work is differentiated in the form of a table with literature. The compact size, wideband, high gain and stable performance of proposed antenna system over-performs the literature work and makes it protentional candidate for the UWB system requiring high gain.

Mutual Coupling Suppression Between Two Closely Placed Patch Antennas Using Higher-Order Modes

This paper presents a novel method for decoupling two patch antennas. Instead of using the TM10 mode of a conventional patch, TM20 mode is utilized as the operation mode of the antenna. By loading stubs at the radiating edge of the patch, the resonance frequency of the TM20 mode is moved down to the same band as the original TM10 mode. Then the mutual coupling between two such patch antennas is suppressed simply by physical placement, even when they are placed extremely close to each other. Without using any extra decoupling elements, isolation is improved by up to 20 dB using this method. Furthermore, this method can also be applied to multi-element multi-input-multi-output (MIMO) array and dual-antenna system with different operating bands. The proposed method is verified with three different application scenarios, including a 2-element MIMO array, a 2-antenna system with adjacent operating bands, and a 4-element MIMO array. Reasonable agreements between simulated and measured results can be observed, showing the advantages of simple structure, low cost, high isolation, and good radiation performance.

High Selectivity Millimeter-Wave On-Chip Band-Pass Filter With Semi-Lumped Dual-Mode Resonator by Using GaAs Technology

In this paper, a high selectivity millimeter-wave on-chip bandpass filter is presented. In contrast with the conventional filter with multi-order resonators, the semi-lumped dual-mode resonator with minimal order can be employed to achieve three transmission zeros (TZs), which can maintain high selectivity and compact size. Furthermore, another two TZs are introduced to improve the attenuation level of the upper stopband by two capacitive loading stubs. A chip sample is fabricated with Gallium Arsenide processing with a size of 0.75×0.43 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measurement results show that the center frequency is 33.5 GHz, the fractional bandwidth is 62.7%, and the insertion loss is 1.06 dB. Good agreements are observed between the simulated and measured S-parameters.

Broadband Multiple Input Multiple Output antenna for sub‐6‐GHz 5G communications

SummaryThis paper presents the design of a miniaturized broadband monopole antenna for 5G and Wireless Local Area Network (WLAN) applications in mobile handsets. The proposed monopole evolved from a rectangular geometry of size 12 × 5 mm. The slot and stub loading techniques are used to improve the impedance matching offered by the antenna. Furthermore, bandwidth broadening is achieved using lumped elements loaded onto the aperture of the antenna. The proposed miniaturized antenna exhibits a measured impedance bandwidth of 63.6% (3.0–5.8 GHz) covering the 5G spectrum allocations under sub‐6 GHz and the WLAN services. The antenna elements are replicated along the sides of the mock mobile handset PCB to study the functionality of the eight‐element MIMO antenna. The prototype MIMO antenna fabricated and tested in the laboratory offers a peak gain of 3 dBi and total efficiency greater than 72%. Owing to miniaturization, the spatial distribution of the antenna element provides a low envelope correlation (ECC) of less than 0.2 and good diversity gain (DG) greater than 7.8 dB. In addition, the mean effective gain (MEG), channel capacity loss (CCL), multiplexing efficiency (ME), and total active reflection coefficient (TARC) are evaluated and presented. The estimated MIMO metrics are within the desired range of operation and hence make the antenna suitable for a complex propagation environment. The prototype antenna is developed on a thin microwave laminate with low‐loss characteristics and tested under laboratory conditions. The outcomes indicate that the proposed eight‐element antenna can be applied to 5G MIMO communications.

A miniaturized ultra‐wideband filter with ultra‐wide stopband and high selectivity using a capacitive loading stub in a multimode structure

AbstractIn this paper, a miniaturized ultra‐wideband filter with ultra‐wide stopband and high selectivity using a capacitive loading stub in a multimode structure is proposed. The second, third, and fourth harmonics of the proposed filter are all suppressed on account of using a capacitive loading stub, which makes it have the characteristic of an ultra‐wide stopband. In addition, there are two transmission zeros located at the upper stopband close to the passband, which improves the selectivity of the proposed filter. The proposed filter is fabricated and measured, and the result shows the filter with the center frequency f0 1.185 GHz has 151% 3‐dB fractional bandwidth. Its upper stopband is extended to 9.18 GHz (7.75 f0) and the 20‐dB roll off rate is 212.5 dB/GHz. What's more, the size of the proposed filter is 0.175 λg × 0.18 λg, where λg is the guided wavelength at the center frequency f0.

Compact dual‐band bandpass filter with high selectivity based on spiral‐stub‐loaded dual‐mode QMSIW resonators

AbstractA novel miniaturized dual‐band quarter‐mode substrate integrated waveguide (QMSIW) bandpass filter with high selectivity is proposed in this letter. Two passbands are generated by the fundamental mode and the first higher order mode of the spiral‐stub‐loaded QMSIW resonator, respectively. Miniaturization is achieved by loading stubs and applying quarter‐mode cavities. High selectivity can be realized by introducing two transmission zeros (TZs) between the two passbands. One TZ is generated by adding coplanar waveguide coupling between the two resonators, the other TZ is synthesized by coupling between the modes of the resonator. The proposed dual‐band filter has the characteristics of miniaturization, high selectivity, and low loss, which is suitable for satellite communication related applications.

A Compact Narrow-Width Endfire Leaky Wave Antenna on Coplanar Stripline

This communication presents a compact endfire leaky wave antenna (LWA) presented on the coplanar stripline (CPS) with narrow width property under a new operation mechanism. By periodically loading stubs between two strip lines in parallel, the leaky region of its fundamental mode can be generated in the CPS with forward beam scanning property, and the endfire radiation is realized at the frequency where its normalized phase constant is equal to 1. Since the leaky region of the fundamental mode owns a relatively low cutoff frequency, the proposed antenna generally has the property of small overall size in this region. The endfire operating frequency is first discussed based on the circuit model, and the corresponding radiation property is then analyzed from the antenna array point of view. The leakage constant as well as characteristic impedance of the proposed antenna are further investigated with the full-wave extraction method. Moreover, a modified structure is proposed as the last element of the antenna to leak out the rest of the energy at its end. Finally, a CPS leaky-wave prototype antenna is designed and fabricated, where the measured results show good agreement with the simulated ones and thus validate the predicted performances.

Design of low profile high gain antenna using loop-based wideband artificial magnetic conductor for UWB applications

AbstractIn this work, a low profile ultra-wideband (UWB) antenna is designed and investigated using a novel loop-based wideband artificial magnetic conductor (WB-AMC) for gain enhancement. Initially, a compact loop antenna is designed using stub loading and further optimized for the UWB range by applying curve ground methodology. The average gain of the proposed antenna without WB-AMC is 2.7 dBi. To enhance the gain of the entire UWB range, loop-based WB-AMC in [2 × 2] forms is integrated. WB-AMC is used as a ground plane beneath the antenna. To validate the performance, the UWB antenna and WB-AMC are fabricated and tested. The measured results confirm the entire UWB range. Proposed antenna provides a peak gain of 9.4 dBi and an average gain of 5.8 dBi. Vertical profile reduction of 50% is achieved compared to perfect electric conductor ground. The proposed UWB antenna is a potential candidate for UWB wireless applications due to its attractive features such as low profile, wide bandwidth coverage, omnidirectional pattern, constant high gain, and group delay.

Equiripple design of low‐pass filter using stub‐loaded Z‐shaped coupled‐line section

Design procedure of a novel transmission line low-pass filter is presented. The filter has a flexible rejection response for a prescribed cut-off frequency and an in-band ripple factor. It is compact by using a Z-shaped coupled-line section, which is loaded with open-circuited stubs. All of the transmission line elements are identical in electrical length, and the impedances can be calculated by solving certain specific equations according to prescribed in-band specifications. The simulated results show that the circuit can generate low-pass responses with third-, fifth-, and seventh-order filtering functions. The filter order depends on the number and position of the loading stubs. For verification, two sample filters with cut-off frequency of 0.5/0.3 GHz are fabricated using a three-/five-layer PCB process, which generate seventh-order low-pass filtering responses with good selectivity. The experimental results agree well with the predictions.

Quintuple‐mode wideband bandpass filter based on stub‐loaded circular resonator

In this paper, novel compact wideband filters have been implemented using a stub-loaded microstrip resonator based on a circular open-loop configuration for the first time. To offer an alternative wideband filter configuration, the quadruple−/quintuple-mode wideband bandpass filters (BPFs) using stub-loaded circular microstrip resonator (SLCMR) and parallel-coupled microstrip line (PCML) feed configuration are proposed. They are realized by employing a single open stub and two open stubs, respectively. A half-wavelength λ / 2 circular microstrip resonator (CMR) loaded with two open stubs excites three resonant modes, while the one with a single stub produces two resonant modes. One of the modes is odd-mode generated by a λ / 2 CMR, the others are even-modes excited by the two loading stubs. The PCML with enhanced input/output (I/O) coupling degree excites also two modes in the passband. Two loading stubs not only creates transmission poles in the passband, they also create two transmission zeros in the lower and upper stopbands. The quadruple−/quintuple-mode wideband BPFs with fractional bandwidths FBW of 60% and 62% are successfully realized by using the SLCMR and PCML feed configuration together. Both filters are designed, fabricated, and tested where excellent agreement between simulated and measured results is observed.

Reduction of Mutual Coupling in UWB/MIMO Antenna Using Stub Loading Technique

Abstract The research presents mutual coupling reduction between UWB-MIMO antenna elements using stub loading technique. The proposed 2 × 2 UWB antenna geometry consists of two circular-shaped monopole radiators with a partial ground for perfect impedance matching. Stubs of 20 mm × 0.2 mm are inserted between the two antenna elements in the ground plane to improve the isolation. The decoupling stub leads to a mutual coupling reduction of less than 20 dB. The farfield measurement at a selected frequency of 10 GHz confirms an omnidirectional radiation pattern. Different MIMO antenna metric such as channel capacity loss (CCL), mean effective gain (MEG), total active reflection coefficient (TARC), envelope correlation coefficient (ECC), and surface current are presented. Details of the design considerations and the simulation and measurement results are presented and discussed. The proposed MIMO antenna array can be well suited for UWB applications.

Electronic bandgap miniaturized UWB antenna for near-field microwave investigation of skin

Near-field microwave investigation and tomography has many practical applications, especially where the trend of fields and signals in different environments is vital. This article shows an elliptical patch ultra-wideband antenna fed by a transmission line for the near-field characterization of cancerous cells in the skin. The antenna comprises an elliptical patch, stub loading to shift the band to lower bands, and an electronic bandgap structure on the ground side. Even though the antenna has a low profile of 15 × 15 mm2, the proposed antenna has more promising results than recent studies. Furthermore, both simulated near-field and far-field results show a broad bandwidth of 3.9–30 GHz and a resonance at 2.4 GHz applicable for industrial, scientific, and medical band applications. The proposed antenna also illustrates a peak gain of 6.48 dBi and a peak directivity of 7.09 dBi. Free space and skin (on a layer of breast fat and a tumor with a diameter of 4 mm at the boundary of skin and breast) are used as test environments during the simulation and measurement of near-field and far-field investigations while considering a phantom breast shape. Both far-field and near-field microwave investigations are performed in Computer Simulation Technology studio, and results are then compared with the measured data. The simulated and measured results are in good agreement, and the focused energy around the tumor is completely reconstructed. Therefore, the proposed antenna can be an adequate candidate for the differentiation of breast skin and tumor to reconstruct the tumor’s image.

A Broadband Ultra-Thin Polarization Rotator Using Periodically Loaded Parallel Strip-Lines

A polarization rotator based on loaded parallel strip-lines is theoretically and experimentally investigated. The unit cells are short-stub loaded parallel strip-lines. The arrays on the front and back layers are rotated by 90° to each other. By loading the stubs, good coupling between the two layers is obtained. Such a structural rotation along with the loading stubs allow the $y$ -polarized wave to be converted to $x$ -polarized wave through field coupling. A broad transmission bandwidth of 30% (86-116 GHz) by using the proposed structure has been reached. In addition, the PTFE substrate is only 0.25 mm thick, which is less than $0.1\lambda $ at 86 GHz. Such a thickness allows the polarization rotator to be easily mounted on antenna radomes. The fabricated prototype demonstrates good agreement between simulation and measurement results.

Design and Characterization of Miniaturized Printed Antenna for UWB Communication Systems

An electrically small ultra-wideband antenna for modern compact devices is presented in this paper. The antenna is constructed using a low-cost FR4 substrate, where etching slot and stub loading techniques are utilized to achieve miniaturization. The antenna comprises of simple geometrical structure with an overall size of 0.13 λo × 0.19 λo × 0.02 λo (λo is the free-space wavelength at 3.5 GHz). A sample prototype was fabricated and tested to validate various performance parameters of the antenna. The antenna has measured 10 dB impedance bandwidth ranging from 3.55–12.16 GHz with a stable gain having a maximum value of 4.52 dBi. The performance comparison with state-of-the-art works shows that the proposed antenna offers the advantages of miniaturized size, simple geometry along with competitive bandwidth and stable radiation characteristics.

Binomial stub loaded compact Vivaldi antenna for superwideband applications

AbstractA compact antipodal Vivaldi antenna with superwideband characteristics is presented in this paper. For improved matching of input impedance at lower frequency region, techniques like binomial tapering of outer edges, binomial slit loaded outer edge, and protruded binomial tapered stub loading have been adopted. The antenna operates in a wide frequency range from 2 to 20 GHz. Experimental results show, stable radiation pattern with peak realized gain of more than 8 dBi, group delay within 1 ns, 164% fractional bandwidth, radiation efficiency of more than 90%, which are in good agreement with the simulated results. The compact size of the proposed antenna (1.14λ0 × 1.21λ0) with wide frequency bandwidth and directional radiation characteristics make it suitable for through-wall radar and medical imaging applications.

Triband Circularly Polarized Antenna Using a Single Patch

A single-feed single-patch triband antenna with different senses of circular polarization in different operating bands is presented in this letter. The first three pairs of the orthogonal modes of a single patch, TM10/TM01, TM20/TM02, and TM30/TM03 modes, are excited to serve the triband circularly polarized operation, by loading stubs and etching slots in both x - and y - directions. Benefited from the asymmetrical radiating patch and aperture coupling on the diagonal line, the orthogonal modes can be well excited and controlled to realize the different senses of circular polarization in different operation bands by tuning the stubs and slots. A patch antenna prototype has been designed and fabricated for experimental validation. The measured 3 dB axial ratios (ARs) of the three bands are 2.439–2.452 GHz, 3.343–3.365 GHz, and 4.342–4.378 GHz, respectively, and the corresponding polarizations are left-hand circularly polarized (LHCP), right-hand circularly polarized (RHCP), and RHCP, respectively.

Directional‐coupler‐basedmicrowave sensors for differentialangular‐displacementmeasurement

The novel application of microwave directional couplers to develop angular-displacement microwave sensors is reported. The proposed sensor approach employs as stator a branch-line-type coupler arranged in transversal mode by loading its direct and coupled ports with two distinct-length open-ended stubs. Thus, by taking the isolated port of the coupler as the stator output node, a bandpass filtering transfer function with transmission zeros (TZs) is created. Then, a rotor made up of an angularly-moveable open-ended stub is attached to a curved section of the longest loading stub of the stator through physical contact, so that their interconnection point varies with the angular-displacement of the rotor. In this manner, the sensor transfer function is altered with the stub rotation through TZ reallocation, angular-displacement sensing capabilities are achieved. The theoretical operational foundations of the conceived branch-line-coupler-based microwave angular-displacement sensor, which features single/multi-band sensing properties in terms of inter-TZ spacing and stop band attenuation levels, along with design examples and curves are provided. The extrapolation of this sensor principle to other classes of power-distribution circuits, such as the rat-race-type directional coupler, is also demonstrated. Finally, for experimental-validation purposes, two 920 MHz microstrip prototypes of the conceived branch-line-coupler-based angular-displacement microwave-sensor approach are built and measured.

Omnidirectional WLAN Antenna With Common-Mode Current Suppression

An omnidirectional wireless local area network (WLAN) loop-slot antenna with common-mode current (CMC) suppression is proposed in this communication. First, based on the analysis of the equivalent model of odd-even mode, the feeding coaxial line is led out at the voltage-zero point of the loop-slot element, which suppresses the CMC over the full band. Second, through the theory of array, three loop-slot elements form an array to obtain omnidirectional radiation. Finally, the physical size is reduced by loading Stubs T in the slot. The roundness of the radiation pattern is modified by the Stubs T and the chamfering edge of the antenna. A prototype of the proposed antenna was fabricated and measured. The measured results show that the antenna achieves |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -10 dB in bands of 2.15-2.65 and 4.85-5.92 GHz. In addition, the roundness is 0.95 dB at 2.4 GHz, 1.84 dB at 5.2 GHz, and 2.43 dB at 5.8 GHz. The antenna effectively suppresses the CMC to keep a favorable roundness over a wide band, showing its potential in WLAN communication systems.

Geometrically progressive stub loading scheme for miniaturization of transmission line‐based components

This paper presents a novel slow wave structure (SWS) using geometrically progressive loaded shunt stubs for miniaturization of microstrip lines. It is observed that, compared to the conventional periodically stub loaded SWS, the proposed technique renders further miniaturization of around 20%, theoretically. Apart from that, this technique also helps in suppression of higher pass bands inherently present in SWSs. A detailed analysis of this technique has been carried out with corresponding design scheme. For proof of concept, this miniaturization scheme is applied to a rat-race coupler designed at 2 GHz, where 75% reduction in overall footprint is observed. The simulated and measured results are found to be in good agreement with the proposed theory.