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Device Performance Criteria
Published in Jerry C. Whitaker, Power Vacuum Tubes, 2017
When a feedline is terminated by an impedance equal to the feedline characteristic impedance, the feedline impedance at any point is equal to the feedline characteristic impedance. When the feedline is terminated by an impedance not equal to the feedline characteristic impedance, the feedline input impedance will vary with changes in feedline length. The greater the impedance mismatch at the load, the wider the feedline input impedance variation with changes in line length. The largest feedline impedance change occurs with the worst mismatches: open circuit or short circuit.
Design and Developments of UWB Antennas
Published in Chinmoy Saha, Jawad Y. Siddiqui, Yahia M.M. Antar, Multifunctional Ultrawideband Antennas, 2019
Chinmoy Saha, Jawad Y. Siddiqui, Yahia M.M. Antar
Input impedance of an antenna is the most important figure of merit as it determines the amount of power that is accepted by an antenna from a signal source through its feedline. A good impedance matching between the feedline and input impedance ensures that almost the entire amount of incoming power is coupled to an antenna with much less reflected back toward the source. Input impedance is defined as the impedance presented by an antenna at its terminals and normally is determined by taking the ratio of the appropriate components of electric and magnetic field.
Miniaturised band notched printed LPDA design with meander fractal dipole for UWB communication
Published in International Journal of Electronics, 2021
Manas Ranjan Jena, Sanjana Sahoo, Guru Prasad Mishra, Biswa Binayak Mangaraj
Band notch on operational frequency can be achieved using a sub-sectional taper. In fact, the tapering disturbs the original size of the dipole. This disturbance creates a mismatch in the design. Due to this mismatch, band notches are observed. In LPDA design, the length, the diameter, and the position of the dipole cannot be changed. The dimensions of these three parameters are as mentioned in equations 6, 8, 9, and 10. Keeping the length and the diameter remains the same, only the shape and size of dipole elements can be changed using any fractal geometry. The fractal geometry considered in our proposed design is the meander line. The average characteristic impedance of dipole elements is taken as 50 ohms, as discussed in the design methodology section. The feed line also has a characteristic impedance of 50 ohms. Because of proper impedance matching between the feed line and dipole strip, the reflection coefficient of design is found to be less than −10 dB. However, if the shape and size of the dipole element are disturbed, the matching is also disturbed. This mismatch results in notches in the UWB.
Triple-step feed line-based compact ultra-wideband antenna with quadruple band-notch characteristics
Published in International Journal of Electronics, 2022
The evolutionary stages of the proposed planar monopole trapezoidal basic UWB (B-UWB) antenna are illustrated in Figure 1. At the initial stage, the antenna was designed using a basic rectangular monopole geometry with W × L of 20 mm × 29 mm, which consists of a microstrip patch size of 15.5 mm × 19 mm, 20 mm × 12 mm ground size and probe feed dimensions of 3.31 mm × 12.5 mm. The patch geometry and 50 Ω feed line were designed on the top plane with a partial ground on the bottom plane, as shown in Figure 1(a). Between both these layers, flame-retardant (FR–4) dielectric substrate was used. The feed line performs an important role in transferring maximum power from the source to the antenna, which projects radiation into free space. It has a width and length of 3.31 and 4.5 mm, respectively. This configuration creates a resonance at a single frequency of 4.7 GHz (3.9–5.5 GHz) with good impedance matching, as shown in Figure 2(a). In the second stage, the lower contour of a rectangular patch was bevelled (Figure 1(b)) to create two resonances close to each other at 4 and 5.9 GHz, which enhances the bandwidth from 3.2 to 7 GHz, as shown in Figure 2. In the third stage, a triple–step slit was inserted on the ground plane to implement a DGS. This modifies the distance and causes a capacitive coupling between the ground plane and the lower edge of the patch. It results in a variation of two resonances at 4.5 and 11.5 GHz with wider impedance bandwidth to obtain the UWB characteristics. In the fourth stage, the upper side of the feed line was changed to triple steps. Consequently, it increases impedance matching to achieve UWB response ranging from 3.3-12 GHz.