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Wireless Building Blocks Using SiGe HBTs
Published in John D. Cressler, Circuits and Applications Using Silicon Heterostructure Devices, 2018
Multifilament transformers can also be constructed on-chip. These devices are used to implement power dividers or combiners and baluns. A balun is a device, which couples a balanced circuit to an unbalanced one. There are many structures used to implement baluns at RF and microwave frequencies, although a differential amplifier is the most commonly used circuit for unbalanced to balanced signal conversion on-chip. Microwave balun structures such as the Lange, rat-race, and branch line coupler require physical dimensions on the order of the signal wavelength and so these devices consume too much chip area when operating below approximately 15 GHz. The transformer shown in Figure 9.9 can also implement a balun by grounding one of the windings at the electrical center, or center tap. The electrical and physical centers of an asymmetric winding differ, which is a disadvantage of asymmetric layouts.
Antenna Parameters, Various Generic Antennas and Feed Systems, and Available Software
Published in Lal Chand Godara, Handbook of Antennas in Wireless Communications, 2018
Jennifer Bernhard, Eric Michielssen
Usually the radio module and the antenna for a wireless communication device are designed for a standard characteristic impedance, such as 50 Ω, so that no impedance matching network is necessary. However, if an antenna impedance does not match with the input impedance of the radio module, an impedance-matching network is required. In the case of resonant antennas, an impedance match can be established using quarter-wavelength transformers, transmission line stubs, or lumped elements. These solutions provide matches over relatively narrow bandwidths, but usually meet system requirements given the narrow bandwidths of resonant antennas themselves. Cascading multiple quarter-wavelength transformers or using tapered transmission lines can provide more broad impedance bandwidths with prescribed frequency responses.6 Baluns can also be used to achieve impedance transitions from unbalanced transmission lines to balanced antennas.
Wearable Printed Antennas for Wireless Communication Systems
Published in Albert Sabban, Novel Wearable Antennas for Communication and Medical Systems, 2017
The diameter of a printed loop antenna is around half a wavelength. A loop antenna is dual to a half wavelength dipole. Several loop antennas were designed for medical systems at a frequency range between 400 MHz and 500 MHz. In Figure 5.14a a printed loop antenna is presented. A photo of a printed loop antenna with a BALUN transformer is presented in Figure 5.14b. A BALUN transformer is a transformer from a balance transmission line to an unbalanced transmission line. The loop may be attached to a human body or inserted inside a wearable belt. The antenna was printed on FR4 with 0.5 mm thickness. The loop diameter is 45 mm. The loop antenna VSWR is around 4:1. The printed loop antenna radiation pattern at 435 MHz is shown in Figure 5.15. The loop antenna gain is around 1.8 dBi. The antenna with a tuning capacitor is shown in Figure 5.16. The loop antenna VSWR without the tuning capacitor was 4:1. This loop antenna may be tuned by adding a capacitor or varactor as shown in Figure 5.17. Matching stubs are employed to tune the antenna to the resonant frequency. Tuning the antenna allows us to work in a wider bandwidth as shown in Figure 5.18. Loop antennas are used as receiving antennas in medical systems. The loop antenna radiation pattern on the human body is shown in Figure 5.19.
Development of a fully planar logarithmic spiral antenna with integrated balun in UWB GPR systems for landmines detection
Published in Electromagnetics, 2022
Narek Grigoor-Feghi, Reza Masoumi, Robab Kazemi
Antenna is a key element of any GPR system. Currently, the antennas, which have been used in GPR systems include horn (Ahmed et al. 2015), bow-tie (Serhir and Lesselier 2018), logarithmic spiral (He and Akizuki 2010; Kazemi 2018; Richardson et al. 2020), slot spiral (Patnaik, Arunachalam, and Krishnamurthy 2016), conical spiral (Yao, Liu, and Georgakopoulos 2017), and Vivaldi (Takach et al. 2016) antennas. In general, it has been shown that logarithmic spiral antenna is often a good candidate for detection systems due to its planar structure and frequency-independent performance. Furthermore, the spiral antenna radiates circularly polarized waves, which is a major advantage over linearly polarized antennas. However, the high input characteristic impedance and the need for balanced feeding structure are the challenges in practical implementation of spiral antennas. A balun is required to transform the signals from an unbalanced feed line (e.g., coaxial cable) to a balanced spiral arm. In recent years, a number of wideband baluns, such as a tapered microstrip to a parallel strip line (Chen et al. 2020; Chen, Zhang, and Xu 2020; Jastram and Filipovic 2018; Sakomura et al. 2018; Singh and Deshpande 2017), coplanar waveguide to coplanar stripline balun (Thaysen, Jakobsen, and Appel Hansen 2000; Tilley, Wu, and Chang 1994), and Vivaldi-shaped balun (Yoo et al. 2019) have been reported. However, most of the configurations are vertically connected to the antenna, which makes the antenna bulky and frail or have limited bandwidth.
A compact, wideband branch-line balun with small magnitude and phase imbalances
Published in Electromagnetics, 2019
Baidenger Agyekum Twumasi, Jia-Lin Li
Many kinds of planar baluns have been studied, including coupled-line baluns, branch-line baluns, Wilkinson power-based baluns and low-temperature co-fired ceramic (LTCC) based baluns, and so on. Baluns with coupled striplines are designed to realize one or two passbands with good electrical performance (Geng et al. 2016; Wu et al. 2016; Zhu and Abbosh 2016). However, the circuit is bulky (Wu et al. 2016), or complex by using multilayers (Zhu and Abbosh 2016) or patterned slots on the ground plane (Geng et al. 2016). The branch-line balun is another important type (Barik, Kumar, and Karthikeyan 2016; Li, Qu, and Xue 2007; Park and Lee 2007; Sun et al. 2018), but in general, compact design is further required (Barik, Kumar, and Karthikeyan 2016; Park and Lee 2007; Sun et al. 2018). For the Wilkinson power-based baluns, they are composed of Wilkinson power divider and phase shift transmission lines (Antoniades and Eleftheriades 2005; Zhang et al. 2005). In (Zhang et al. 2005), the structure with 180° phase shifter achieves a broad bandwidth at the cost of circuit size. In (Antoniades and Eleftheriades 2005), the right/left-handed transmission line was used to realize the phase shift, where the circuit was complex as a result of lumped components. The baluns with LTCC technology can exhibit compact size, small magnitude and phase imbalances (Tsai, Chen, and Wu 2014), but the multilayer generally yields high cost.
Broadband branch-line balun with good isolation and impedance matching
Published in Electromagnetics, 2018
Cheng-Guang Sun, Jia-Lin Li, Si-Yu Yin, Shan-Shan Gao
In microwave engineering, baluns are typical three-port networks that function as the transformation between unbalanced and balanced signals. They found many applications such as the balanced mixers, power amplifiers, antenna feeding networks (Jia et al. 2015; Tsai et al. 2013; Wang and Chen 2016; Wang et al. 2016; Wu, Lu, and Cao 2017; Zhang et al. 2016), and so on. As a three-port network, the Marchand balun could be a basic and classic type. For this kind of balun, two sections of secondary transmission lines are coupled to a main transmission line, where the near ends of the two-section lines are further composed of the outputs with out-of-phase, while the two far-ends are short-circuited. For such a structure, tight coupling is generally required to minimize the transformation loss. The tight coupling can be achieved by using slot-coupled lines, re-entrant coupled-lines, or coupled synthesized coplanar waveguide (Ma, Wang, and Lai 2011; Shie et al. 2010; Tseng and Hsiao 2010).