Circularly polarized log-periodic dipole antenna for EMI measurements

Abstract

Two types of broad-band antennas are widely used for electromagnetic interference (EMI) measurements in the frequency range from 30 to 1000 MHz. Log-periodic dipole antennas (LPDA) are mainly used for the range above 300 MHz and biconical antennas for the range less than 300 MHz. These two antennas have linear polarization. However, EMI measurements can sometimes be more conveniently made with an antenna having circular polarization and so we propose an improved LPDA, which has circular polarization. This LPDA has a second array of dipoles so arranged that each dipole of the second array has a quarter-wavelength phase difference from that of the corresponding dipole of the standard LPDA array for the given radiation field. For this reason, we named it a crosselement LPDA. The cross-element LPDA does not need a broadband 90 hybrid junction to produce circular polarization. We calculated the height pattern and the frequency characteristics of the classical site attenuation (CSA) for the cross-element LPDA when used for both transmitting and receiving, as well as the antenna factor. Moreover, we calculated the normalized site attenuation (NSA) when the cross-element LPDA is used for receiving or for both transmitting and receiving.

Gauribidanur Low-Frequency Solar Spectrograph

“…Our idea was to design an LPDA that can work in the frequency range 40 -440 MHz with a gain of ≈ 7 dB (which is nearly the same as that of most of the commercial LPDAs), broad response/radiation pattern (beam) so that the Sun can be observed for a longer period of time without mechanically or electrically steering the antenna, and a VSWR 2 so that there is a good impedance match and the incident signal on the antenna is maximally transmitted to the subsequent stages of the receiver system. We designed and fabricated the LPDAs at the Gauribidanur Radio Observatory following the standard procedure mentioned in the literature (Carrell, 1961b;Wakabayashi et al, 1999;Balanis, 2005;Kraus, Marhefka, and Khan, 2006;Sasikumar Raja et al, 2013). Figure 1 shows the VSWR of the LPDAs used in the GLOSS.…”

“…The total bandwidth of the F and H components, peak frequencies of F L and H L and F U and H U have a ratio of ≈ 1:2. The intensity of the harmonic component is higher than that of the fundamental component (Wild, Murray, and Rowe, 1954;Roberts, 1959). The event was associated with a C 6.0 class soft X-ray flare (07:16 -07:30 UT) with peak at ≈ 07:27 UT and an SF-class Hα flare (07:19 -07:29 UT) with a peak at ≈ 07:22 UT from AR 11346 located at S19 E08.…”

Polarization Independent Unidirectional Scattering With Turnstile Nanoantennas

“…The presence of the PEC surface reflects one-half of the emission into the opposite direction, thus achieving a unidirectional radiation pattern. Newly, different research group have demonstrated that the RF turnstile structure can be combined with different reflectors such as planar metallic, cavity-backed, and artificial magnetic conductor surfaces, to reach broad-band and one-side emission [7][8][9].…”

Planar endfire circularly polarized antenna using concentric annular sector complementary dipoles

“…By introducing a cross‐dipole element, both endfire and CP characteristics can be realized . In these two cases, endfire CP radiation beams can be obtained by using electrically large turnstile or three‐dimensional (3D), periodical structures . Many attempts have been taken to simplify the configuration and to reduce the size of the endfire CP antennas.…”