Investigation of transformers' turn ratios and design procedure for an aperture coupled slot antenna

L. Liu, Z. Ghassemlooy, A. Sambell, S. Danaher, Q. Lu, E. Korolkiewicz

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


An aperture coupled antenna consists of feed, slot, and a radiation patch. The feed is normally a microstrip line with the slot etched in the ground plane and the radiating patch is located above the ground plane. To obtain maximum power transfer the microstrip line is orientated at right angle to the slot to obtain tight coupling. It is shown by Pozar that the patch and the slot modelled as two transmission lines connected in parallel produces a series impedance on the microstrip line. In the equivalent circuit of this antenna, the coupling between the microstrip line and the slot line is modelled as a transformer by a turn ratio n f. The coupling between the slot and the patch is modelled as a transformer by a turn ratio n p. Initially derived equations for n f for finite lengths of the slot obtained by different researchers are reviewed and shown that they do not agree. To investigate this turn ratio the microstrip line and slot structure is modelled using CST software while the equivalent circuit of this structure is modelled using AWR software. For different lengths of the slots the series impedance Z on the feed line is obtained from the S 21 parameter. The turn ratio in the equivalent circuit is tuned for the lengths of slots to obtain the value of the S 21 parameter. Then the turn ratio of the transformer modelling the coupling between the slot line and the patch is also investigated. The antenna for both models has several interdependent design parameters so that an analytical design process is very difficult to implement. From the investigation carried out a design procedure for the antenna is proposed which is used to design the antenna for a frequency 2 GHz. The designed antenna is modelled using CST and AWR software and a good agreement has been obtained for the return loss of both models.

Original languageEnglish
Title of host publicationProceedings of the Active RF Devices, Circuits and Systems Seminar
Number of pages5
ISBN (Electronic)9781849195409
Publication statusPublished - 24 Sep 2012
Externally publishedYes
EventActive RF Devices, Circuits and Systems Seminar - Belfast, United Kingdom
Duration: 12 Sep 201112 Sep 2011

Publication series

NameIET Seminar Digest


ConferenceActive RF Devices, Circuits and Systems Seminar
Country/TerritoryUnited Kingdom

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