Wideband quasi-log-periodic microstrip antenna

Abstract

The paper describes a new design method for a wideband array of log-periodically scaled microstrip resonator antennas. The radiating elements are series-fed by a simple coplanar microstrip network. This network consists of an open-circuited feed line with a branch line connected to each radiating element. Both a network and a radiating model for the complete structure are explained. These models predict with good accuracy the input impedance and the radiation pattern as a function of frequency. The results for a 5-element 5-band antenna are presented as an illustrative example. This antenna combines a good impedance match (VSWR < 2.6) with a reasonable power gain in broadside direction (> 5.5 dB) over a 22% bandwidth. This means a tenfold increase in the bandwidth in comparison with a single microstrip resonator antenna. List of principal symbols BW C E,H >nK bandwidth capacitance of resonator electric, magnetic field dielectric constant of substrate absolute permittivity, permeability of free space frequency frequency, angular frequency, free space wavelength at resonance correction factor for surface roughness substrate thickness L, W Q.Q md D D O D P Pcu s t tan 5 x, y, z Z X / 4z m = resonator length, width = expansion factor of log-periodic structure = quality factor, radiation quality factor of resonator md = resonant, copper loss, dielectric loss, radiation resistance of resonator = reflection coefficient magnitude = copper resistivity = specified voltage standing wave ratio (VSWR) = copper thickness = loss tangent of substrate = cartesian co-ordinates = characteristic impedance of quarter-wave transformer line = input impedance of resonator 1

Quasi-log-periodic microstrip antenna with closely coupled elements

“…This may be related to the fact that the antenna structure has become large due to the use of the parasitic elements. Moreover, compared to the results of Type 2 obtained by Pues and colleagues [9], the drop of the gains between respective resonant frequencies has been improved from about 4 dBi to about 3 dBi. This may be due to the fact that the parasitic elements have acted at the frequencies between the resonant frequencies of the elements.…”

“…However, in reality, the feeding can be done by means of a simple feed line. Here, based on the idea of Pues and colleagues [9] we will design an antenna as follows:…”

“…Hall has obtained wide-band characteristics by fabricating a two-layer LPMSA excited by common feed line and electromagnetic coupling [8]. Pues and colleagues reported a one-layer quasi-log-periodic microstrip antenna (QLPMSA) using a coplanar fed MSA [9]. However, those reports mainly consider arrangements in which the elements are located on alternative sides of the common feed line and there are few in which the elements are arranged on one side.…”

Bandwidth Enhancement Techniques

“…In [24][25][26], the idea of log-periodic antennas for providing very wide bandwidths has been applied to microstrip patches. In this technique, the microstrip patches are arranged in a logperiodic formation.…”

Frequency-independent antennas and broad-band derivatives thereof

“…This precludes producing radiation near endfire, even if the appropriate phasing of the patches in the active region were possible. Another feeding technique for an LP array of rectangular patches is to print patch and feeder on the level of the substrate and use a microstrip transformer between the near edge of each patch and a common microstrip feeder [30]. Two possible layouts are shown in Fig.…”