Abstract
Amplitude and phase balances of two types of microstrip-(MS-) to-coplanar stripline (CPS) baluns have been analyzed through simulations and measurements, and their effects on broadband antenna performance are investigated. The impedance bandwidth of the balun determined by a back-to-back configuration can sometimes overestimate the balun operating bandwidth. With the conventional balun with a 180° phase delay line, it is observed that the balun balance over the operating frequencies becomes much more improved as the CPS length increases to over 0.1 λg. As compared with the conventional balun, the proposed MS-to-CPS balun demonstrated very wideband performance from 5 to over 20 GHz. With the proposed balun, amplitude and phase imbalances are within 1 dB and ±5°, respectively. Effects of the balun imbalance on overall broadband antenna performance are also discussed with a quasi-Yagi antenna and a narrow beamwidth tapered slot antenna (TSA).
Highlights
Planar end-fire antennas have been widely used in microwave/millimeter-wave systems because they exhibit low cost, low weight, low profile, and easy integration with microwave integrated circuits (MICs)
This antenna consists of a microstrip feed, microstrip line (MS)-to-coplanar stripline (CPS) balun, and two dipole-elements: one dipole element is a driver dipole fed by CPS and the second strip is a parasitic director
The impedance bandwidths of the baluns have been obtained through a back-to-back configuration and a single balun terminated with a load
Summary
Planar end-fire antennas have been widely used in microwave/millimeter-wave systems because they exhibit low cost, low weight, low profile, and easy integration with microwave integrated circuits (MICs). A novel ultra-wideband MS-to-CPS transition [10] was reported by the authors’ group This balun did not require bulky resonant circuits, and broad impedance bandwidth was inherently achieved by smooth field transformations and good impedance matching through the transition structures. The transition with a 180degree phase delay line, which generated the odd mode on parallel transmission lines with the truncated ground, often limited the frequency bandwidth To use this transition as a feed for quasi-Yagi antennas in [11,12,13,14,15,16,17,18,19,20], the design of the transition was mostly based on minimizing the insertion loss and maximizing return loss for the operating bandwidth. By connecting baluns to a high gain and narrow beamwidth tapered slot antenna, radiation patterns are compared and the effect of the balun on antenna performances discussed
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