Miniaturized wide‐band rat‐race coupler

New designs of wide‐band rat‐race couplers are proposed. The wide‐band operation is achieved with the use of the microstrip nonuniform transmission line sections for the branches of the conventional rat‐race coupler. The design formulas are developed using ABCD matrix and the even‐ and odd‐mode analysis. The theoretical analysis has been verified by measurements of the two manufactured wideband rat‐race couplers, one operate within 0.85–1.92 GHz and other within 1.55–3.55 GHz frequency range with the equal normalized characteristic impedance functions. For both fabricated couplers, the isolation parameter is better than 15 dB over a 77% relative bandwidth. Also, it is shown that the designed wide‐band rat‐race coupler can be realized in higher frequency bands with the fixed fractional bandwidth. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 23: 675–681, 2013.     

Ultra‐wideband slot antenna for wireless communication systems

In this article, a new ultra‐wideband rectangular‐slot antenna is proposed and developed for multiband wireless communication systems. The radiating slot is fed by a microstrip line with a microstrip fork‐shaped tuning stub. The frequency characteristic and radiation performance of the proposed antenna are successfully optimized, and a prototype is fabricated and tested. The measured results show that the impedance bandwidth can cover the band from 1.85 to 6.1 GHz with return loss of better than 10 dB, and the corresponding radiation displays omnidirectional patterns across the interested bands. With these frequencies, the proposed structure is especially suitable for applications in wireless communication systems, where a single antenna is needed to operate simultaneously at different bands, such as PCS (1.85–1.99 GHz), UMTS (1.92–2.17 GHz) and all WLAN bands (2.4–2.48 GHz and IEEE802.11a WLAN applications at 5.15–5.35 GHz and 5.725–5.825 GHz). © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Design of X‐band Moreno cross‐guide coupler based on superformula curves

This article deals with the design of Moreno cross‐guide couplers based on supershapes for X‐band applications. Crossed‐waveguide couplers are mainly used due to their compact structures. In these couplers, cross‐aperture structures are usually employed to offer flat coupling and high isolation. In the present article, the possible shapes for apertures and metal inserts that can be derived by the superfomula curves are explored and the effects of variations of superformula parameters are investigated on the performance of Moreno coupler. Finally, the proposed Moreno coupler is validated through fabrication and measurement. The experimental validation shows an excellent agreement with the simulated results. In the frequency range from 8 to 12.5 GHz, the measured coupling value changes from 18.8 to 20.8 dB and the directivity is better than 38 dB and 29 dB from 8 to 11 GHz and 11 to 12.5 GHz, respectively. The results are valuable for the design and evaluation of broadband high directive waveguide couplers.     

A low‐profile quad‐port UWB MIMO antenna using defected ground structure with dual notch‐band behavior

A compact (45 × 45 × 1.6 mm³) ultrawide‐band (UWB), multiple‐input multiple‐output (MIMO) design using microstrip line feeding is presented. The proposed design comprises four elliptical monopoles placed orthogonally on a cost‐effective FR‐4 substrate. In order to improve the impedance bandwidth and lessen the return loss of the MIMO antenna, defects in ground plane are created by etching symmetrical square slots and half‐rings. Moreover, a different method (of unsymmetrical H‐shaped slot with C‐shaped slot) was proposed into the patch to introduce dual‐band rejection performance from UWB at center frequency 5.5 GHz (covering lower WLAN as well as upper WLAN) and 7.5 GHz (X band). In addition, a stub is introduced at the edge of each defected ground structure to obtain isolation >–22 dB covering entire performing band from 2 to 16.8 GHz (where, S₁₁ < –10 dB). The proposed design has miniaturized size, very low envelop correlation coefficient less than 0.1, stable gain (2‐4 dBi except for notch bands). Furthermore, various MIMO performance parameters are within their specifications, such as diversity gain (= 10 dB), total active reflection coefficient (<–5 dB, and channel capacity loss (<0.35 bits/s/Hz). The presented design is optimized using the HFSS software, and fabricated design is tested using vector network analyzer. The experimental results are in good agreement with the simulation results.     

A CPW‐fed band notched wideband circularly polarized ZOR antenna based on CRLH‐TL approach

This article presents design and analysis of three wide band zeroth‐order resonance antennas (antennas I, II, and III) using composite right and left‐handed transmission line (CRLH‐TL) approach. Coplanar waveguide technology, single layer via‐less structures are used to have the design flexibility. The bandwidth characteristics are analyzed by using lumped parameters of CRLH‐TL. By introducing a simple slot in the ground plane of antenna I both bandwidth enhancement and circularly polarization characteristics are achieved in antenna II. Another quarter wave L‐shaped slot has been introduced in the ground plane of antenna II to introduce a notch band in the frequency response of antenna III. Achieved measured 10 dB return loss bandwidth of antenna I and antenna II are 960 (3.3‐4.26 GHz) and 2890 MHz (2.77‐5.66 GHz), respectively. Antenna III offers measured 10 dB return loss bandwidth of 3220 MHz (2.32‐5.54 GHz) with a band notch from 2.39 to 2.99 GHz that isolates the 2.4 GHz WLAN and 3.5 GHz WiMAX band. Antenna II and antenna III have circular polarization property with measured axial ratio bandwidth of 440 MHz. The measured peak realized gain of antennas II and III is around 1.53‐2.9 dBi.     

A dual‐band eight‐antenna multi‐input multi‐output array for 5G metal‐framed smartphones

A dual‐band eight‐antenna array operating in the long‐term evolution (LTE) band 41 (2.496‐2.69 GHz) and 3.5‐GHz band (3.3‐3.7 GHz) for fifth‐generation (5G) metal‐framed smartphone is presented. The proposed dual‐band antenna array is composed of four identical dual‐antenna building blocks (DABBs). Each DABB consists of two identical antenna elements with a neutralization line between them. The antenna array is simulated, fabricated, and measured. The isolations are better than 10.5 dB and 11.0 dB in the low band (LB; LTE band 41) and high band (HB; 3.5‐GHz band). The total efficiencies are 41% to 54% and 46% to 64% in the two operation bands, respectively. In addition, the measured envelope correlation coefficients are less than 0.11 and 0.06, the calculated channel capacities are better than 34.5 and 36.3 bps/Hz in the LB and HB, respectively. Furthermore, four hand‐grip scenarios are investigated, and results show that proposed antenna array can maintain excellent multiple‐input multiple‐output performances in all scenarios.     

Uniplanar ACS fed multiband high‐gain antenna with extended rectangular strips for portable system applications

In this article, a compact uniplanar asymmetric coplanar strip (ACS)‐fed multiband antenna with extended rectangular strips is proposed for portable system applications. It is composed of a modified mouse and rectangular‐shaped radiating strip for generating three resonance frequency bands simultaneously. The proposed antenna has a compact size of 16 × 26 × 1.6 mm³. Antenna has |S₁₁| ≤ ?10 dB at three independent controlled bandwidths from 2.2 to 2.4 GHz, 3.5 to 3.7 GHz, and 4.85 to 6.85 GHz. The proposed ACS‐fed antenna is suitable for LTE 2300, WiBro 2300 GHz, 5.2/5.8‐GHz WLAN, 3.5/5.5‐GHz WiMAX, 4.9‐GHz US public safety band, and 5.9‐GHz WAVE applications. The antenna has omnidirectional radiation characteristics in the desired frequency bands in both E‐plane and H‐plane. It has better gain value performance compared with other antenna designs discussed in the literature.     

Compact planar frequency reconfigurable multiple‐input‐multiple‐output antenna with pattern and polarization diversity characteristics for WiFi and WiMAX standards

A compact planar frequency reconfigurable dual‐band multiple‐input‐multiple‐output (MIMO) antenna with high isolation and pattern/polarization diversity characteristics is presented in this article for WiFi and WiMAX standards. The MIMO configuration incorporates two symmetrically placed identical antenna elements and covers overall size of 24 mm × 24 mm × 0.762 mm. Reconfiguration of each antenna element is achieved by using a PIN diode which allows antennas to switch from state‐1 (2.3‐2.4 GHz and 4.6‐5.5 GHz) to state‐2 (3.3‐3.5 GHz and 4.6‐5.5 GHz). In state‐1, the configuration offers isolation ≥18 dB and 20 dB in lower band (LB) and upper band (UB) respectively; whereas, in state‐2, isolation ≥21 dB and 20 dB in LB and UB respectively is achieved. The same decoupling circuit provides high isolation in dual‐band of two states, which makes overall size of the proposed design further compact. The antennas are characterized in terms of envelope correlation coefficient, radiation pattern, gain, and efficiency. From measured and simulated results, it is verified that the proposed frequency reconfigurable dual‐band multi‐standard MIMO antenna design shows desirable performance in both operating bands of each state and compact size of the design makes it suitable for small form factor devices used in future wireless communication systems.     

Compact reconfigurable triple‐mode triple‐band substrate integrated waveguide bandpass filter

In this study, a reconfigurable triple‐band triple‐mode substrate integrated waveguide filter is designed and fabricated in the C‐band spectrum. A novel and simplified design procedure based on analytical equations is proposed. The filter design also benefits from a reconfigurable structure, using metallic via holes as perturbation, allowing wide‐band selectivity of the C‐band spectrum (from 4.4 to 6.9 GHz). Moreover, the filter benefits from a magnetic coupling solution between the resonators, which only couples the first three modes and rejects the next resonating modes. Therefore, a large bandgap in the spectrum is achieved. The proposed structure is fabricated and measured, and a high similarity between the simulation and fabrication is observed. The measured results show that the first band can be tuned in the frequency range of 4.4 to 7, the second band can be tuned in the range 5.8 to 7.7 GHz, and the third band from 5.8 to 7.7 GHz. The insertion loss 1.5 to 2.5 dB, 2 to 3 dB, and 2.5 to 3.5 dB for the first, second, and third bands, respectively.     

Compact nine‐band antenna for 4G/5G smartphones

This article presents a nine‐band antenna whose size is 70 mm × 7 mm × 5.8 mm for 4G/5G smartphones. The proposed antenna consists of a T‐shape coupled line and two ground branches. The T‐shape coupled line is used to produce the resonances at about 925 and 2900 MHz respectively. One ground branch along with the T‐shape coupled line is used to cover the lower band (698‐960 MHz), and the other ground branch is used to cover the 3.6 GHz band (3400‐3800 MHz). By using the higher order modes of the T‐shape coupled line and the ground branches, the higher band (1710‐2690 MHz) is covered. The advantage of the proposed antenna is that a nine‐band antenna can be realized with an only 7 mm ground clearance and without using any lumped element. A prototype is manufactured and measured. According to the measured results, at the bands of 0.693‐0.98 GHz, 1.69‐2.94 GHz, and 3.05‐4 GHz, the S11 are smaller than ?6 dB. The ?6 dB impedance operating frequency band of the proposed antenna can cover the LTE700, GSM850, GSM900, DCS, PCS, UMTS, LTE2300, LTE2500, and 3.6 GHz bands. The simulated and measured results of the radiation performance also are presented.     

Broadband magic‐Ts with the use of coupled‐line directional couplers and left‐handed transmission line sections

The problem of broadband magic‐T realization with the use of coupled‐line directional couplers and left‐handed (LH) transmission‐line sections has been comprehensively investigated. Broadband amplitude characteristics of the proposed networks are ensured with the use of coupled‐line couplers, whereas the required phase characteristics have been achieved by the appropriate selection of right‐ and left‐handed transmission line sections. To analyze the properties of the proposed networks, a model of an ideal left‐handed transmission line has been utilized. The presented concept has been verified by two designs of broadband magic‐Ts operating in 2.5–3.5 GHz and 0.8–2.3 GHz, respectively. The obtained results proved that the proposed magic‐T networks allows one to obtain broadband amplitude and phase responses together with its compact structure. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:513–521, 2014.     

Performance comparison of a single and multiband power amplifiers using IHP 0.25 μm SIGe HBT technology

In this work, a single‐band power amplifier (PA) with a fixed‐frequency/band output matching network and multiband PA with a switch‐tuned output matching network is designed, using IHP (Innovations for High Performance), 0.25 μm‐SiGe HBT process. The behavior of the amplifiers has been optimized for 2.4 GHz (WLAN), 3.6 GHz (UWB‐WiMAX), and 5.4 GHz (WLAN) frequency bands for a higher 1‐dB compression point and efficiency. Multiband characteristics of the amplifier were obtained by using a MOS‐based switching network. Two MOS switches were used for tuning the band of the output matching network. Postlayout simulations of the multiband‐PA provided the following performance parameters: 1‐dB compression point of 25.2 dBm, gain value of 36 dB, efficiency value of 12.8% operation and maximum output power of 26.8 dBm for the 2.4 GHz WLAN band, 1‐dB compression point of 25.5 dBm, gain value of 32 dB, efficiency value of 13.3% and maximum output power of 26.6 dBm for the 3.6 GHz UWB‐WiMAX band and 1‐dB compression point of 24.8 dBm, gain value of 23 dB, efficiency value of 12.5% and maximum output power of 26.3 dBm for the 5.4 GHz WLAN band. For the fixed‐band, at 3.6 GHz, the postlayout simulations resulted the following parameters: 1‐dB compression point of 25.5 dBm, gain value of 32 dB, efficiency value of 18% and maximum output power value of 26.8 dBm. Measurement results of the single‐band PA provided the following performance parameters: 1‐dB compression point of 20.5 dBm, gain value of 23 dB and efficiency value of 7% operation for the 2.4 GHz band; 1‐dB compression point of 25.5 dBm, gain value of 31.5 dB and efficiency value of 17.5% for the 3.6 GHz band; 1‐dB compression point of 22.4 dBm, gain value of 24.4 dB and efficiency value of 9.5% for the 5.4 GHz band. Measurement results show that using multistage topologies and implementing each parasitic as part of the matching network component has provided a wider‐band operation with higher output power levels, above 25 dBm, with SiGe:C process. These results proved that the PA, with switching/tunable output matching network, provides compatible performance parameters, when compared with the fixed‐band PA. The ability of being capable of operation in different frequency bands with compatible performance parameters, when compared with fixed‐band PA, multiband PA can be realized with additional less parasitics, area, and cost advantages. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

A Multiband antenna using plus‐shaped fractal‐like elements and stepped ground plane

A multiband planar symmetrical plus‐shaped fractal monopole antenna with stepped ground plane is presented in this study. Measured results show that the proposed antenna operates with 10 dB return loss bandwidths from 1.630 to 1.88 GHz and from 4.5 to 8.5 GHz covering The Global System for Mobile Communications (GSM) 1800 MHz 2G spectrum band, 4400 to 4900 MHz 5G spectrum band adopted by Japan and China for future 5G communication in sub‐6 GHz band, 5.15 to 5.925 GHz LTE band 46, WLAN IEEE 802.11 y/a/h/j/n/P bands, and 5.8 to 7.707 GHz military band. The antenna gain varies between 1.73 and 1.97 dB in lower band and 3.6 to 5.05 dBi in upper band with radiation efficiencies more than 90% in lower band and more than 80% in upper band. The antenna has more than 64 and 28 dB isolations between the copolar and cross‐polar radiation patterns in the lower and upper bands, respectively.     

Novel compact dual‐narrow/wideband branch‐line couplers using T‐Shaped stepped‐impedance‐stub lines

This article presents a compact model to reduce the physical size and increase the frequency ratio between the second and first resonance frequencies of a dual‐function stepped‐impedance‐stub (SIS) line, which was subsequently employed in the realization of dual‐band branch‐line couplers. The proposed model comprises of a loaded spiral T‐shaped SIS that reduces the size of a conventional SIS line as well as improving its frequency ratio. The proposed model behaves exactly similar to the recently developed dual‐band resonators with the advantage of size reduction of ～35% as well as having a wide range of realizable frequency ratios between 1.4 and 3.7 compared to 1.7–2.7 and 1.8–2.3 for the conventional SIS and T‐shaped transmission‐lines, respectively. Dual‐narrowband and wideband branch‐line couplers were developed based on the spiral T‐shaped SIS lines. The dual‐wideband device's bandwidth was enhanced by 2.7% accompanied by a size reduction of 58.6% in comparison with the conventional dual‐wideband couplers operating at the same frequencies. The theoretical results were verified by measurement. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Design and development of enhanced bandwidth multi‐frequency slotted antenna for 4G‐LTE/WiMAX/WLAN and S/C/X‐band applications

A multi‐frequency rectangular slot antenna for 4G‐LTE/WiMAX/WLAN and S/C/X‐bands applications is presented. The proposed antenna is comprised of rectangular slot, a pair of E‐shaped stubs, and an inverted T‐shaped stub and excited using staircase feed line. These employed structures help to achieve multiband resonance at four different frequency bands. The proposed multiband slot antenna is simulated, fabricated and tested experimentally. The experimental results show that the antenna resonates at 2.24, 4.2, 5.25, and 9.3 GHz with impedance bandwidth of 640 MHz (2.17‐2.82 GHz) covering WiMAX (802.16e), Space to Earth communications, 4G‐LTE, IEEE 802.11b/g WLAN systems defined for S‐band applications. Also the proposed antenna exhibits bandwidth of 280 MHz (4.1‐4.38 GHz) for Aeronautical and Radio navigation applications, 80 MHz (4.2‐4.28 GHz) for uncoordinated indoor systems,1060 MHz (5.04‐6.1 GHz) for the IEEE 802.11a WLAN system defined for C‐band applications and 2380 MHz (7.9‐10.28 GHz) defined for X‐band applications. Further, the radiation patterns for the designed antenna are measured in anechoic chamber and are found to agree well with simulated results.     

Design of an ultra‐wideband power divider with harmonics suppression

The design of an ultrawideband (UWB) power divider with harmonics suppression is presented. With the proposed approach, the size of the quarter‐wavelength transmission line can be reduced and the high order harmonics can be suppressed. The design equations are deduced by transmission line theory. A prototype power divider operated at UWB band is designed and fabricated. Experimental results show good performance of the proposed design. In addition, a stop‐band with rejection level more than 20 dB is from 17.3 to 24.5 GHz. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:299–304, 2015.     

A novel dual‐band ring coupler based on dual‐band phase inverter

A novel dual‐band ring coupler based on dual‐band phase inverter is proposed. And two types of dual‐band phase inverters (Type I and Type II) are designed in this article. The design method of dual‐band ring coupler is simpler than the traditional ways like replace the single‐band λ/4 transmission line with dual‐band λ/4 transmission line. Its main idea is replacing the wide‐band phase inverter with dual‐band phase inverter. Two dual‐band ring couplers (0.9/2.88 and 0.9/2.43 GHz) using the two types of dual‐band phase inverter, respectively, are simulated and measured. The measured results validate the proposed method.     

A novel symmetrical Wilkinson power divider for dual‐band application

A symmetrical two‐way Wilkinson power divider with shifted output ports, much wide bandwidth and large frequency‐ratio is proposed for dual‐band application. The corresponding transcendental design equations are derived by using the even‐ and odd‐mode analysis. Moreover, the closed‐form scattering parameter expressions are derived. Transcendental design equations are solved and accurate numerical design parameters along with different frequency ratios are obtained. Finally, the proposed structure and design method are validated by simulated and experimental results of typical microstrip planar power dividers, the performance is clearly observed for the input and output matching, isolation and transmission characteristic very well at the two band frequencies. More specifically, the measured transmission characteristics of the divider are 3.11 dB/3.58 dB at the 1.0 GHz/3.5 GHz, respectively. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:102–108, 2014.     

Dual‐band circularly polarized aperture‐coupled stack antenna with fractal patch for WLAN and WiMAX applications

This article presents a novel circular polarized (CP) aperture coupled stack antenna for wireless local area network and worldwide interoperability for microwave access dual‐band systems. The compact stack antenna consisted of square fractal patch, aperture couple, feed line and the perturbation. The square patch is constructed with the complementary Minkowski‐island‐based fractal geometry. By way of adjusting the relevant parameters, we can obtain the dual‐band responses at 3.5 and 5.25 GHz respectively. The CP of each band are presented. The measured 10 dB return loss impedance bandwidth are 270 MHz (7.5%) for 3.5 GHz band and 450 MHz (8.6%) for 5.25 GHz band. The 3 dB axial ratio bandwidths for each bands are 1.4 and 0.76%, the polarization of radiation patterns are both left‐hand CP, and the antenna power gain are 2.84–3.1 and 0.16–2.2, dBic respectively. The proposed antenna is successfully simulated and measured with frequency responses, radiation patterns and current distributions. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:130–138, 2014.     

A metamaterial hepta‐band antenna for wireless applications with specific absorption rate reduction

Present article embodies the design and analysis of slotted circular shape metamaterial loaded multiband antenna for wireless applications with declination of SAR. The electrical dimension is 0.260 λ × 0.253 λ × 0.0059 λ (35 × 34 × 0.8 mm³) of proposed design, at lower frequency of 2.23 GHz. The antenna consists of circular shape rectangular slot as the radiation element loaded with metamaterial split ring resonator (SRR) and two parallel rectangular stubs, etched rectangular single complementary split‐ring resonator (CSRR) and reclined T‐shaped slot as ground plane. Antenna achieves hepta bands for wireless standards WLAN (2.4/5.0/5.8 GHz), WiMAX (3.5 GHz), radio frequency identification (RFID) services (3.0 GHz), Upper X band (11.8 GHz—for space communication) and Lower K_U band (13.1 GHz—for satellite communication systems operating band). Stable radiation patterns are observed for the operating bands with low cross polarization. The SRR is responsible for creating an additional resonating mode for wireless application as well as provide the declination in SAR about 13.3%. Experimental characteristic of antenna shows close agreement with those obtained by simulation of the proposed antenna.