CM suppression enhancement for balanced band‐notched UWB closed‐aperture antenna

Abstract

A strategy for enhancing the common-mode (CM) suppression of a band-notched UWB closed-aperture antenna is proposed. The antenna circuit consists of a differentially coplanar-waveguide-fed hexagonal-aperture antenna and a pair of wave-trapping slotline resonators for producing a 5.5 GHz notch band. The enhancement of the CM suppression was achieved by setting the dimension of the aperture along the longitudinal direction (i.e. the direction parallel to the feedlines) small enough, so that the first resonant mode of the CM half-circuit of the aperture antenna can be pushed beyond the differential-mode (DM) UWB passband. A fabricated balanced bandnotched UWB antenna was measured to have a 10 dB DM passband of 3-11.2 GHz with a notch band of 5.1-6.1 GHz. Good measured CM suppression was observed with a maximum return loss of 2.9 dB in the DM UWB passband.

Three‐layered balanced circularly polarized slot antenna with high common‐mode suppression

“…Comparison of CM performance with other balanced antennas that have adopted a CM‐suppression strategy or filter is summarized in Table . Although the comparison may not be fair since those to be compared with are cited from linearly polarized antennas, this table can still give us a hint on how well the CM performance of our proposed CP antenna is, especially when we recognize that the only CM‐suppression structure employed in our proposed design is a simple 180° delay line. Note that the CM‐to‐DM (or DM‐to‐CM) conversion data, that is, (or ), are not shown in the table.…”

“…This might be attributed to the fact that conventional single‐ended antennas are still useful even if the front‐end circuits are balanced as the latter can be connected to the former with a three‐port balanced‐to‐unbalanced (balun) transformer inserted in between . Although that is the case, balanced antennas, if successfully designed, can be connected directly to the balanced frond‐end circuits . Among these balanced antennas, the very important common‐mode (CM) suppression property was not addressed at all in refs.…”

“…Hence, whether these two slots are joined or separated will not affect the DM operation. In fact, this idea has been implemented in other balanced slot antennas, where the two slots have been joined as a bigger one. Besides being placed end‐to‐end, two mirror‐imaged single‐ended antennas can also be placed side‐by‐side to form a balanced antenna .…”

“…The abovementioned balanced antennas are all linearly polarized (LP), whereas balanced circularly polarized (CP) antennas have not been found yet in the literature, to the best of the authors’ knowledge. Those CP antennas available so far are all single‐ended ones with many of which being slot‐type antennas .…”

Differentially fed CP antenna with quasi‐self‐complementary semicircular‐ring structure

“…Like many other differential devices, antennas can also be designed in differentially fed configuration for easy integration with differential microwave/RF circuits. However, up to the present, most differentially fed antennas published in the literature are linearly polarized ones, with the radiating element being slots, metal lines or patches, and so on.…”